Germination and Emergence (VE)

      The radicle is first to begin elongation from the swollen kernel, followed by the coleoptile with the enclosed plumule (embryonic plant), and then the three to four lateral seminal roots (seminal root system). VE (emergence) is  attained by rapid mesocotyl elongation which pushes the growing coleoptile to the soil surface. Under warm, moist conditions, plant emergence will occur within 4 to 5 days after planting, but under cool or dry conditions, 2 weeks or longer may be required.

    Upon emergence and exposure of the coleoptile tip to sunlight, coleoptile and mesocotyl elongation stops.  The rapidly developing embryonic leaves then grow through the coleoptile tip and development of the above-ground plant follows. Growth of  radicle and lateral seminal roots slows soon after VE and is virtually non-existent by the V3 stage.

     The nodal root system is initiated at about VE, and the first set (whorl) of nodal roots begins
elongation from the first node during V1. From V1 to about R3 (after which there is very limited root growth), a set of nodal roots begins development at each progressively higher node on the stalk, up to 7 to 10 nodes total. The nodal root system becomes the major supplier of water and nutrients to the plant by the V6 stage.

V3 Stage
    Root hairs are growing from the nodal roots by this time, and growth of the seminal root
system has virtually ceased. All leaves and ear shoots that the plant will eventually produce are being initiated (formed) now. At about V5, leaf and ear shoot initiation will be complete and a microscopically small tassel is initiated in the stem apex tip. The stem apex at tassel initiation is just under or at the soil surface, although total above-ground plant height is about 20 cm (figure)

V6 Stage
  At V6, the growing point and tassel are above the soil surface and the stalk is beginning a period of greatly increased elongation (figure). Below ground, the nodal root system is now the major
functioning root system. Some ear shoots or tillers, which initially look very similar, are visible at this time. Tillers (also termed suckers) will generally form at nodes originating below the soil surface. Loss of the two lowest leaves may have already occurred by the V8 stage.
 
 
 
 

V9 Stage
Ear shoots (potential ears) are visible upon dissection of a V9 plant. An ear shoot will develop from every above-ground node, except the last six to eight nodes below the tassel. Only one or two ear shoots  develop into a harvestable ear. The tassel develops rapidly and the stalk rapidly elongates (figure). Stalk elongation occurs through elongation of its internodes. By V10, the time between the appearance of new leaf stages will shorten, generally occurring every two to three days.
 
 

V12 Stage
    Although the ear shoots (potential ears) were formed just before tassel formation (V5), the number of ovules (potential kernels) on each ear and the size of the ear are determined at the V12 stage (figure left). The number of rows of kernels per ear (figure right) has already been established, but the determination of the number of kernels per row will not be complete until about one week from silking or about V17.
 
 

V15 Stage
 The V15 maize plant (figure) is approximately 10-12 days from the R1 (silking) stage. This  stage is the beginning of the most crucial period of plant development in terms of grain yield determination. Upper ear shoot development by V15 has surpassed that of the lower ear shoots, and a new leaf stage is now occurring every 1-2 days. Silks are just beginning to grow from the upper ears at this time. By V17 the upper ear shoots may have grown enough that their tips are visible at the top of the leaf sheaths that surround them. The tip of the tassel may also be visible at V17.
 
 

V18 Stage
     In a V18 maize plant (figure left) silks from the basal ear ovules are first and silks (figure center) from the ear tip ovules are last to elongate. Brace roots (also termed aerial nodal roots, figure right) are now growing from the nodes above the soil surface. They help support the plant and obtain  water and nutrients during the reproductive stages.

VT Stage
    The VT stage (figure left) is initiated when the last branch of the tassel (figure right) is completely visible and the silks have not  yet  emerged. VT begins approximately 2-3 days before silk emergence, during which time the corn plant will almost attain its full height and pollen shed begins. The time between VT and R1 can fluctuate considerably depending on the hybrid and environmental conditions. Under field conditions, pollen shed (also termed pollen drop) usually occurs in the late mornings and early evenings.

R1 Stage - Silking
    R1 begins when any silks are visible outside the husks (figure). Pollination occurs when these new moist silks catch the falling pollen grains. A captured pollen grain takes about 24 hours to grow down the silk to the ovule where fertilization occurs and the ovule becomes a kernel. Generally 2-3 days are required for all silks on a single ear to be exposed and pollinated. Silks grow 2.5-3.8 cm (1-1.5 inches) each day and continue to elongate until fertilized.     The R1 ovule or kernel is almost completely engulfed in the surrounding cob materials (technically termed the glumes, lemmas and paleas) and is white in color on the outside. The inner material of the R1 kernel is clear and has very little fluid present. The embryo or germ is not yet visible when dissected. The shank and husks attain full size between the R1 and R2 stages. The figure reveals the presence of silk hairs, which help catch the pollen.

R2 Stage - Blister (10-14 days after silking)
    R2 kernels are white on the outside (figure) and resemble a blister in shape. The endosperm
and its now abundant inner fluid is clear in color and the tiny embryo can now be seen upon careful dissection.  Within the developing embryo is a developing miniature corn plant. The silks having completed their flowering function are now darkening in color and beginning to dry.
 

R3  Stage - Milk (18-22 days after silking)
    The R3 kernel displays yellow color on the outside, and the inner fluid is now milky white due to accumulating starch. The embryo is growing rapidly now and is easily seen upon dissection. Most of the R3 kernel has grown out from the surrounding cob materials and the silks at this time are brown and dry or becoming dry.

R4 Stage - Dough (24-28 days after silking)
    Continued starch accumulation in the endosperm has now caused the milky inner fluid to thicken to a pasty consistency. The R4 embryo has greatly increased in size from the R3 stage. The shelled cob is a light red to pink color due to beginning color changes of the surrounding materials (lemmas and paleas). The reduced fluid and increased solids within the kernel at this time produce a doughy consistency. Just prior to R5 kernels along the length of the ear begin to dent or dry on top.

R5 Stage - Dent (35-42 days after silking)
At R5 (figure) all or nearly all kernels are dented or denting and the shelled cob is dark red in color. The kernels are drying down now beginning at the top where a small hard white layer of starch is forming. This starch layer appears shortly after denting.
 
 

R6 Stage - Physiological Maturity (55-65 days after silking)
    All kernels on the ear have attained their maximum dry weight or maximum dry matter accumulation. The hard starch layer has advanced completely to the cob and a black or  brown abscission layer has formed. The husks (figure left)  and many leaves are no longer green although the stalk may be. The figure at right shows an R6 kernel (left) on the side opposite the embryo and slices laterally cut from the top, middle and bottom of the kernel.
 
 

Description, Biology and Plant Damage Caused by Maize Insects

   Insects attack all parts of the maize plant and attack the plant through all stages of plant growth. Numerous insect species attack maize in North America but the economic importance of the various species differs by region. The insects discussed in this section are grouped according to the plant parts that they feed on. (1) Seed, Root  and Lower Stem Feeders; (2) Stalk Borers; (3) Leaf Feeders; and (4) Ear Feeders.
 
 

        Seed, Root  and Lower Stem Feeders

   A failure in emergence expressed in skips along the rows indicates a potential problem with seed attacking insects. The most common insect pests attacking the maize seed are the seedcorn maggots, wireworms, and seedcorn beetles. Wireworms and  white grubs attack the maize root system throughout the growing season and may be found in the soil at any time of the year. Rootworms feed on the plant roots from  mid season to late mid season. Billbugs, chinch bugs and black cutworms feed on the lower portion of the stem.
 

1. Seed Corn Maggot

Description

    Seedcorn maggots, Hylemya platura (Meigen), are larvae of small flies that are attracted to germinating seeds, especially in situations having decaying organic matter. Since the seed maggots are larvae of flies, they have no legs and are similar to fly maggots in a manure pile. The seedcorn maggot is a yellowish-white larva that reaches a length of 7 mm (see figure). The has a
rounded tail that tapers to a sharply pointed head, giving it a spindle shape. It has black hook-like mandibles.  After the maggot stage, it changes into a brown capsule-like puparium, then matures into an adult fly. The gray, blacklegged fly resembles a house fly, but is only half as large (5 mm) and folds its wings over the body when at rest. Eggs are small, white and elongated.

Biology and Life Cycle

    The seedcorn maggot passes the winter as a pupa in the soil. Adults emerge from the overwintering pupae in the late spring or early summer  to lay eggs in soils high in decaying organic matter (muck soils or fields with abundant weeds, stubble or manure that have been plowed down).  Adults deposit their eggs near the seed. The seed furrow may have some turned under vegetation that attracts the egg laying females. The longer the seed takes to germinate, the longer it is susceptible to attack by the seedcorn maggot. As a result, cold wet soils tend to have more problems with the seedcorn maggot than other soils. The maggots hatch in 2 - 4 days and the maggots  readily burrow into germinating maize. These maggots mature into puparia after about two weeks. Adults emerge from puparia in about 2 weeks. There are 4 - 5 generations per year, but only the first generation is a significant problem on maize.

Damage

    A failure in the emergence of seedlings that is evident as missing plants along the rows indicates a potential problem with seed attacking insects.  Seedcorn maggot damage is obvious because the maggots will be present and boring into the seeds. Seedcorn maggots  damage both sprouting seeds (see figure)  in  the soil and seedlings. Seedcorn maggots feed on the seed contents (often leaving only the empty shells) causing seed death or poor germination. Problems due to seedcorn maggot problems are generally worse on soils with decaying organic matter or when germination is delayed, such as during cool, wet springs. Unlike the spotty nature of wireworm or white grub damage, seedcorn maggot damage may cover most of the field.
 

2. Seedcorn Beetles

Description

    Seedcorn beetles are small ground beetles about 6 -8 mm in length that feed on maize. Two species of seedcorn beetles occur in the field. The seedcorn beetle, Agonoderus lecontei Chaud. (left figure) is oblong and dark with two dark  stripes on its wing covers and the slender seedcorn beetle, Clivinia impressifrons LeConte (right figure) is  a uniform chestnut brown (or shiny  reddish-brown)  and spiny front legs.

Biology and Life cycle

   Seedcorn beetles are distributed throughout the USA and into Canada. The slender  seedcorn beetle is common in the Corn Belt states. Seedcorn beetles are assumed to overwinter in the pupal or adult stage. Adult activity fluctuates throughout growing season due to the fact that these beetles pass through a number of generations per year. Adults are attracted to lights where they may be abundant on  warm spring evenings. The larvae are predacious on other insects and regarded as beneficial.

Damage

     The damaging stage of the seedcorn beetle is the adult. They attack germinating maize seed and destroy the germ. Holes into or hollowed out seeds (see figure)  with dead or stunted sprouts can be seen. Missing plants are a sign of damage. Adults can be seen inside the damaged seed, or in the surrounding soil. They also feed on the mesocotyl of seedling plants causing stunting. These plants will usually recover after reaching the  3 or 4-leaf stage. Seedcorn beetles are most likely to be found under the same conditions and in the same areas that are infested with wireworms or seedcorn maggots. Probability  of damage by seedcorn beetles is increased by poor or slow  germination and cool, wet weather following planting.
 

3. Wireworms

Description

  Wireworms (several species of the order Coleoptera, family Elateridae)  are larvae of a group of beetles commonly called click beetles. Wireworm larvae are hard (heavily chitinized), wire-like and buff to reddish brown (left figure). Although the several species that attack maize are similar in appearance, they can vary greatly in size from 13 to 38 mm long when fully grown.  They have three pairs of legs just behind the head. The dark adult (right figure) is referred to as a "click beetle" because, when placed on its back, it flips into the air making an audible click when righting itself.

 Biology and Life cycle

    The larval stage of wireworms requires from two to five years or more to complete development. The variation in time required varies between species. Larvae spend the winter deep in the soil, moving up  to feed or pupate as soil temperatures warm.  In contrast to the long period of larval development, the pupae and adult stage require only a few months. Larvae pupate in earthen cells and adults emerge in the spring or in late summer, depending on the species. Adults lay eggs in grassy areas. Eggs hatch in about 2 weeks. The tiny larvae that hatch from these eggs feed on the roots of grasses and other weeds until fall when they burrow deeper into the soil for hibernation. Because some species can take 4 - 6 years to complete a generation, wireworm damage can occur in a particular field for several years.

Damage

    Since grasses are the primary host plant of various wireworm species, wireworm problems affecting maize are most likely to occur when infested pastures or alfalfa sod are plowed under and planted to maize. Because of their extended life cycles, wireworm damage may persist 2-3 years after a sod is tilled. The most significant damage occurs to germinating seeds and seedling plants during cold, wet springs. Like seedcorn maggots, they also leave behind empty seed hulls as well as snipped-off roots. Wireworm injury is often associated with a small feeding hole at the base of the plant, which may kill the growing point and stunt plant growth.
 

4. White Grubs

Description

    The larvae of scarab beetles  are commonly called white grubs and consist of species in the Phyllophaga, Cyclocephala and Popillia genera.  White grubs have brown heads, three pairs of legs just behind the head, and  white, thick, soft bodies that curl into a C-shape when disturbed (figure).  These C-shaped larvae range in size from 18 mm to more than 38 mm in length if straightened out. The tip of the abdomen is shiny and transparent and body contents are seen through the skin. They move very sluggishly. The common white grubs, the Phyllophaga species can be distinguished  by 2 parallel rows of spines, which are located in the center of the underside of the last abdominal segment. The annual white grubs, Cyclocephala spp. have a uniform distribution of setae (hairs) on the underside of the last abdominal segment while the larvae of the Japanese beetle, Popillia japonica have 2 rows of spines in an inverted "V"-pattern. Adult stages of the common white grubs, Phyllophaga spp. are called May or June beetles. Adult May or June beetles are reddish-brown (left figure) or black (right figure) in color.  If grubs are found in abundance and the larvae are all less than an 25 mm in length, the grubs are probably larvae of the Japanese beetle, Popillia japonica Newman.

Biology and Life cycle

      The life cycle of the common white grubs may be 2,  3, or 4 years, but a 3-year life cycle is most  common.  Adults deposit eggs on the soil surface of  grass sod during late spring. Following a few weeks in the egg stage, the eggs hatch into larvae that feed on plant roots or decaying vegetation near the soil surface. When cool autumn temperatures arrive, larvae tunnel downward in the soil to about 46 cm, to overwinter. Most white grub damage is caused during the second year when these larger larvae return to the surface in the spring  to feed voraciously on plant roots. The larvae or grubs continue to feed until they pupate  in the late summer and emerge as adults. Some species have a longer life cycle and will feed for a third year before changing into adult beetles.

    Annual white grubs and Japanese beetles have 1-year life cycles. Eggs are laid in the soil in June and July. The grubs feed on decaying organic matter or on grass roots until October, when they burrow down  further into the soil. They move upward in the spring and resume feeding on roots. The grubs pupate in May and emerge as adults in a few weeks.

Damage

    White grub damage is usually patchy, resulting in plant stunting or death. Grub damage results in a general pruning of the root system. Plants with severely pruned roots may grow no more than 0.5 m tall and can be easily lifted from the ground. Lodging and stand reduction occurs in heavy infestations. Damage is usually spotty, rather than being uniform throughout the field. Small areas may be entirely destroyed while other areas are not affected. This may be due to variations in soil texture, which affect egg laying by the beetles.
 

5. Billbugs

Description

    There are several species of billbugs that damage maize in North America. Three  species present in the Midwest are the maize billbug Sphenophorus maidis Chittenden, southern corn billbug S. callosus (Olivier), and clay-colored billbug S. aequalis Gyllenhal. The maize billbug (figure at left) is 8 mm long and is the most common of the three species. The southern corn billbug (figure  below, left) and the clay-colored billbug (figure below, right) are much larger, up to 20 mm. All three species are characterized by a very hard body and a long, downward curved beak. Adults are often so covered with dirt that they resemble a small clod. They are often found attached upside down to seedling cornstalks near the ground line. The cream colored, kidney-shaped egg is about 3 mm long and 1 mm in diameter.

The grub is cream colored, legless and with a distinct reddish-brown head (figure, left).   Billbug larvae range from 2 to 15 mm long. The pupa is cream colored to reddish-black, or reddish-brown, depending on its age.

Biology and Life Cycle

    Billbugs are found throughout the most of the maize growing regions of the United States (figure below). The overwintering adults rarely fly but may walk 1/4-mile in search of food. They emerge during April and May from litter in fields, ditches and hedgerows. Each female feeds, mates and lays about 200 eggs, usually at night. They are laid in holes chewed out by the female in the basal area of the host plant. In 4 to 15 days, tiny legless, grublike larvae hatch, migrate down the outside of root crowns, and feed in roots and lower stalks. There is usually only one larva per cornstalk though as many as five have been known to attack the same stalk. The larvae develop in 40 to 70 days and pupate in the soil around the excavated taproot or in a cell in the taproot. Most pupae occur from July to September. Adults develop in 7 to 10 days and either remain within pupal cells or emerge to feed before hibernation. There is only one generation per year. When startled, billbugs often act as though they are dead by falling to the  ground and not moving for several minutes. This behavior, plus the fact that they are usually dusted with soil, makes them difficult to find.

 

Damage

  Billbugs are early-season seedling  pests that seldom cause economic damage. But billbugs can kill seedling plants and significantly reduce stands if their populations are large. Both billbug adults and larvae injure maize. The adult weevils feed on the lower stems of maize seedlings up to the 6-leaf stage, especially on plants along field edges.  They chew small holes into the stalk (figure left) where they eat the tender leaves in the center. When the leaves emerge, they often wilt and are riddled with transverse rows of circular or linear holes.   A  single beetle may kill a seedling plant. Less injured plants may only exhibit small holes in the leaves as they expand. The perforated leaves often fall or curl so as  to interfere with the growth of the following leaves (figure right). Plants may be killed.Those that live are stunted and deformed,   often with twisted leaves and numerous tillers or suckers around the base of the stalk. Billbug larvae tunnel in the base of the stalk, causing further stunting of the plant. Extensive damage is generally restricted to non-rotated maize fields or to areas adjacent to the previous year's maize. Injury may occur most frequently in fields recently put into production, especially in low, wet areas.
 

6. Chinch Bug

Description

    The adult chinch bug, Blissus leucopterus (Say), is about 5 mm long and black with  red to reddish yellow legs (figure below).  The opaque wings may be as long as the body or 1/3 to 1/2 the length of the body. In either case, each wing bears a distinctive, triangular, black mark. The cylindrical yellowish eggs are approximately 0.84 x 0.30 mm, and flattened at one end which bears three to five nipple-like projections. Eggs are laid behind leaf sheaths on the lower leaves. The egg gradually changes in color from pale yellow to red before hatching. The wingless nymph is smaller than, but similar in shape, to the adult. The head and thorax are brown; the eyes are dark red; and the abdomen is pale yellow or light red with a black tip and a  band of white on the back just behind the wing pads (figure, right). Nymphs become dark-colored with a small white patch between the wing pads, as they grow older.

Biology and Life Cycle

   The chinch bug is found throughout the United States, southern Canada, and Mexico (figure, below). The blue areas in the map indicate historical outbreak locations. Chinch bugs overwinter as adults in various protected areas, particularly among weeds and grasses near fields. Up to 5,000  bugs may be found in a square foot area in preferred hibernating places. Adults emerge in the spring when temperatures pass 70^o F. for several hours  during which the sun is shining. Adults deposit eggs singly behind the leaf sheath or in the soil at the base of the plant. They lay a few eggs each day for up to a month for a total of about  200 eggs per female. In a few days, the eggs hatch and the nymphs begin feeding on all parts of the host plant from the roots to the uppermost leaves. The nymphs undergo six developmental stages, the last being the adult stage. Development to the adult stage takes about a month. Two to three generations occur per year, the later generations migrating to maize and sorghum when small grain crops become dry.

Damage

    Chinch bugs attack a wide range of plant species including  forage, lawn, wild grasses  and crop plants. The principal crop plants damaged are maize, spring barley, wheat, sorghum, Sudan grass, rye, and timothy. The chinch bug is found from the East Coast into the western plains of Nebraska, Kansas, Oklahoma, and Texas. Most injury is caused by the nymphal stage. Chinch bugs injure maize by sucking juices from maize leaves, stalks, and leaf sheaths. Infested plants first exhibit wilted, white lower leaves (figure, left). Feeding prevents normal growth and results in dwarfing, lodging, and yield reduction.  In heavy infestations, entire plants may turn white and wilt. The injury resembles severe frost  injury. Heavy infestations frequently destroy the outer rows that border small grain fields.
 

7. Black Cutworm

Description
    The color of the black cutworm, Agrotis ipsilon (Hufnagel) larva (figure below, left) varies from light gray to black in color, often appearing greasy. The skin is granulated (as seen under a
hand lens), the granules resembling rounded, flattened pebbles.  Above the spiracles, the larva is basically one color, varying from light gray to nearly black. There is an  indistinct pale stripe on the back. The spiracles are distinctly black.  There are six instars ranging from 4 to 46 mm in length. When disturbed, the larva curls up. The brown pupa is about 17 to 22 mm long, with distinct mouthparts and antennae. Pupae taper posteriorly and are blunt at the head end.  The nocturnal moth (figure, right) is characterized by long, narrow, usually dark forewings that are pale near the tips. There are three black dashes on each forewing. Hind wings are white with dark veins and broad, dark, indefinite margins. The wingspan varies from 38 to 51 mm. The egg is white, round, and about 0.5 mm in diameter.

Biology and Life Cycle

    Cutworms that attack maize in Nebraska can be divided into two general categories based on seasonal life cycles. Black cutworms do not overwinter in  Nebraska. Dingy, claybacked, darksided, sandhills, pale western, and other species overwinter as partially grown larvae in the soil.

    The black cutworm is a widespread species that can be found from southern Canada throughout the United States, Mexico, and South America. Northern regions of the United States must be recolonized each year by migrating moths from southern regions.  Since black cutworms do not overwinter in the northern regions, they are dependent on spring weather conditions, primarily southeasterly winds, to bring them into the region. Devastation of maize by the black cutworm is most often reported in the region east of the Mississippi River and in the contiguous states west of  this boundary.

    The black cutworm feeds on a wide range of field and garden crops. Other known hosts include asparagus, bean, beet, cabbage, castor bean, cotton, grape, lettuce, peanut, pepper, potato, radish, spinach, squash, strawberry tobacco and tomato.
    Eggs are laid on grasses and weeds before maize  is planted. When weeds are destroyed by cultivation or herbicides, the black cutworm larvae migrate to newly emerged maize.

 In the south, where the black cutworm overwinters, there are several generations annually. In Tennessee there are four generations. Moths of the first or overwintering generation emerge between the middle of March and the first of May. They mature about the middle of May. Second generation moths emerge from the latter part of May to the middle of July. Third generation moths emerge between the middle of  July and the last of August. Fourth generation moths make their appearance near the first of September and continue to emerge into December; they produce the overwintering generation.

    Between 5 and 11 days after emergence, each female begins to deposit about 1,300 eggs in clusters of 1 to 30. Most eggs are laid on low, densely growing plants like chickweed, curly dock, and mustard; maize is among the least attractive of the oviposition hosts. The egg stage lasts 3 to 16 days, depending upon the temperature. These cutworms prefer moist soil where they are usually found in tunnels 8 to 10 cm beneath the surface. The destructive larval stage varies in duration from 3 weeks. The pupal stage lasts about 2 weeks for early summer generation; later generations require as much as 8 or 9 weeks.

Damage
    It is extremely rare to experience cutworm problems in continuous maize because maize stubble is not a preferred egg laying site. Potential problems in continuous maize may be the result of planting in  no-till or weedy maize fields, planting maize following soybeans that had an abundance of  winter annual or perennial weeds, planting maize in poorly drained areas, or an interseeding of a fall cover crop such as rye. These cultural practices result in the attraction of egg laying moths to the maize field.
    Black cutworms are among the most destructive of all cutworms. Leaf feeding (figure, left) by  cutworms usually occurs before  cutting is observed . The larvae sever plants (figure, right) near the soil   line. After cutting a seedling, the black cutworm commonly pulls it into the entrance of its burrow and feeds on it during the day.  Some larvae move from plant to plant on successive nights, while others stay to feed on the roots and underground stems of  cut plants. Although there is more than one generation per year, the first is the only one that causes significant damage to maize.

8. Corn Root Aphid

Description
    The corn root aphid, Anuraphis maidiradicis (Forbes) adult is  typically wingless,  spherical,  pale green or blue-green, and has a black head and black or reddish eyes. There are 4 different forms in the adult stage: the male,  the egg-laying female,  and the winged and wingless females that give birth to living young. The female in the egg- laying period has a gray body with a pink abdomen and a white, powdery coating.  Length varies from 0.3 mm for small nymphs to 2.0 mm for mature adults. The dark green, oval-elongate egg is less than 1 mm long. The pale green nymph has red eyes, resembles the adult in shape.

Biology and Life Cycle

    Although generally distributed, the corn root aphid is most prevalent throughout the maize- and cotton-growing areas east of the Rocky Mountains (figure below). Maize, cotton, and smartweed roots seem to be the most common hosts of the corn root aphid. Other hosts include broomcorn, crabgrass, dock, foxtail, knotweed, mustard, pigweed, plantain, purslane, ragweed, sorghum, sorrel, squash, and wheat.

    Throughout their life cycle, corn root aphids are highly dependent upon ants, especially cornfield ants. In most areas, at least in the northern areas,  the aphids overwinter as eggs deep within the ant nest. In spring, ants carry newly hatched nymphs to the roots of maize or weeds, particularly dock and smartweed. If maize seedlings are available, aphids are transferred to them either from the over-wintering nest or from weeds. Later the ants feed on the honeydew produced by the aphids. First-generation aphid nymphs feed on roots for 2 to 3 weeks before developing into wingless female adults. By-passing the egg-laying stage, these mature aphids soon give birth to 40-50 live nymphs. As summer approaches and temperatures increase, nymphs may mature in as
few as 8 days. After several generations, winged female aphids often appear and fly to nearby fields, especially maize or cotton. After landing on anthills, they are carried to the roots by ants. Here the aphids continue to feed and reproduce as before until the approach of cold weather. In the fall, wingless male and female forms develop, mate, and are responsible for the production of  overwintering eggs. These eggs are protected from the cold by the ants which carry them deep into their nests. The number of annual aphid generations varies greatly with latitude and environmental conditions. In no-till maize, 10 to 22 generations per year may occur.

Damage

    Successive crops of maize, availability of spring host plants and a favorable environment for the cornfield ant are key  factors determining the populations of the corn root aphid. Maize infested by the corn root aphid germinates normally, and plants reach a height of  4  to 10 inches, when growth becomes retarded, especially during dry years. Clinging to the maize roots are many bluish-green aphids about the size of  pinheads when full grown. The corn root aphid pierces roots with its needle- like mouth parts and extracts sap. As a result of aphids' feeding, the foliage develops a characteristic yellowish to reddish tinge before the maize is knee-high. Heavily infested seedlings  rarely grow taller than 25 cm (10 inches). In addition to these symptoms, infested fields are likely to harbor many anthills around the maize plants. The presence of anthills, however,  does not necessarily imply infestation by the corn root aphid.
 

9. Western Corn Rootworm

Description

    Three kinds of rootworms attack corn in the Corn Belt -- the western, the northern, and the southern. The western (Diabrotica virgifera virgifera LeConte),  and the northern (Diabrotica barberi Smith & Lawrence), are the most damaging.  The southern, Diabrotica undecimpunctata howardi Barber is less damaging and annually migrates from the south in the spring. It does not overwinter in the northern portion of the Corn Belt.
   Adults of the western corn rootworm are yellow with a dark stripe on the outside edge and center of each wing cover (figure  left). Males and females differ somewhat in  their markings. On the males, nearly the entire posterior half of each wing cover is black, whereas in the female, the  dark stripes are more pronounced. They are about 4 to 6 mm long. Larvae are a creamy-white color with reddish-brown heads (figure right).

Biology and Life Cycle

    The western corn rootworm, D. virgifera virgifera was once restricted to Colorado, Nebraska, and Kansas but in the early 1960's it spread throughout  most of the Corn Belt (figure below). The western corn rootworm has one generation per year. Adults emerge from pupae in the soil and feed on silks and pollen. The female beetles lay 300 to 400 eggs in the upper 5 to 20 cm of soil among the roots of maize during later summer and early fall. Eggs are usually deposited in the same fields where the adults feed. Western corn rootworm eggs pass the winter in the soil and hatch the next Spring in late May and early June. The start of hatching depends to some extent on soil temperatures and continues for several weeks.

    Some of the western corn rootworm eggs may not hatch until the second spring due to "extended diapause", a resting period during which the insect does not develop. After hatching late in the spring, the larvae first feed on young roots of maize or other grass hosts.  After the larvae finish feeding, they change to the pupal stage in pupal cells in which they change into the adult, or beetle stage. The pupal stage requires 5 to 10 days before transformation to the adult stage. After emergence, the adults feed for about 2 weeks before the females start laying eggs. Depending on climatic soil conditions, the period from egg hatch to adult emergence requires 4 to 6 weeks. Western corn rootworm beetles usually begin to emerge from the soil in late June, and continue to emerge until September. They are active in fields until frost.

Damage

    With a few exceptions corn rootworms are only damaging in continuous maize. In some instances, however, economic corn rootworm injury has occurred on maize  following small grains (primarily oats), or weedy soybeans, in northeastern Nebraska. Only in rare instances has damage followed in a maize rotation with the other major crops grown in Nebraska.  However, in the last few years, the western corn rootworm has altered its behavior to lay eggs in soybean fields in east central Illinois, Indiana, western Ohio, southern Michigan and northeastern Iowa. This behavioral change has reduced the effectiveness of crop rotation for control in these locations. Now it appears that adult western corn rootworms may have further changed their behavior to feed on soybean leaves as well as maize.

    The preferred food of the adults (beetles) is maize silks (figure below) and pollen. However, early emerging western corn rootworm beetles may feed on maize leaves, producing a
parchment-like appearance if pollen isn't present. If adults are numerous during the pollination period and silks are chewed into the husks, poorly filled ears may result due to lack of pollination.  Depending upon growing conditions, 10-20 beetles per silk mass are usually required to seriously affect pollination. Late planted maize is more likely to be damaged by adults. Most fields are pollinated before sufficient beetles are present to reduce fertilization. When pollination is complete, silks are wilted or turning brown, and then silk feeding is no longer of concern.

     Larvae feed on roots and can cause direct grain losses by reducing both plant stand and vigor. Root pruning (figure below, left) can also cause plant lodging, which may further reduce yields due to harvest losses. Usually, peak rootworm feeding occurs from late June to mid-July, when all maize roots may be destroyed (compare undamaged and damaged plant in figure on right). The resulting loss of grain may vary widely depending upon the number of larvae per plant, time of planting, available moisture, soil fertility, wind, and general climatic conditions during and immediately following peak injury.
 
 
 

10. Northern Corn Rootworm

Description

    Adults of the northern corn rootworm, Diabrotica barberi are green beetles without any spots or stripes (figure below, left). Adults that have just emerged are very light colored - almost beige. Larvae are creamy-white with a reddish-brown head (figure below, right).

Biology and Life Cycle

     The northern corn rootworm was first reported from Colorado. It is now a predominant pest  in the Central States (see figure), but  is also present in the eastern and southern states. Damage is negligible south of latitude 30^o N. The biology and life cycle is similar to that of the western corn rootworm. Female northern rootworm beetles lay up to 400 eggs in the upper 2 to 8 inches of soil during later summer and early fall. Eggs are usually deposited in fields where the adults feed. The eggs hatch the next spring in late May and early June. Some (as many as 30-40%) of the northern corn rootworm eggs may not hatch until the second spring due to an extended diapause. Extended diapause is associated with northern corn rootworms where eggs remain in the soil for two winters rather than hatching in the spring following the first winter. This phenomenon has been identified in Iowa, Minnesota, and South Dakota where corn/soybean rotation has been used for several years. Some of the northern corn rootworm population has adjusted to every-other-year maize planting in those areas.

    After hatching, rootworms feed on the underground root systems of  maize plants, causing varying degrees of damage ranging from none to complete root destruction. After larvae finish feeding, they change to the pupal stage in which the larva changes into the adult, or beetle stage.  They may be active in fields until frost.

Damage

    Feeding damage by the larvae is similar to that described for the western corn rootworm. However, the northern corn rootworm adult feeds more on the silk than the western corn rootworm. Also, the northern corn rootworm rarely feeds on the leaves, whereas the western corn rootworm does.
 

11. Southern Corn Rootworm

 Description

    Adults of the southern corn rootworm,  Diabrotica undecimpunctata howardi, also known as the spotted cucumber beetle, have 12 dark spots on their yellow or yellowish-green wing covers (see figure). The head and antennae are black. The adults are slightly larger than either the western or northern corn rootworms, being about 6 mm long. The young larvae are slender, white to yellowish, turning to a greenish-yellow color as they mature. The larvae and pupae resemble those of the western and northern corn rootworm. The full grown larva is about 12 mm long and has a brownish head and brown dorsal shield on the ninth abdominal segment.
 

Biology and Life Cycle

    The southern corn rootworm is distributed in states east of the Rocky Mountains, in southern Canada and in Mexico. Adults probably do not overwinter in the northern states but migrate  from the south each year and deposit eggs in maize fields in the spring. The southern corn rootworm does enter diapause during the fall in Nebraska. However, overwintering survival is probably minimal and would be most likely to occur in southeast Nebraska. More than one generation of southern corn rootworms occurs each year.

    In the southern part of its range, the southern corn rootworm passes the winter in the adult stage. Beetles hibernate in most any type of shelter but prefer the bases of plants that are not killed by frost. They become active early in the spring and migrate northward. The females deposit eggs in the soil around maize plants. Larvae upon hatching bore into the roots of maize plants and the underground parts of the stem. They have two generations per year in the southern states and at least a partial second generation in the North.

Damage

    The southern corn rootworm larvae will feed on the roots of many plant species, including maize, soybeans, sorghum, wheat, cucumbers, and other vegetables, and many legumes, but the feeding damage is not serious on maize, except in the southeastern states and southern Texas. Symptoms of larval feeding are holes through the base of small plants, and tillering that follows growing point injury and root injury, similar to that described for the western and northern corn rootworms. On older maize, larval feeding occurs in the base of the stalk, on the young brace roots, and on the lower leaf sheaths. Southern corn rootworm adult feeding is similar to that of the western corn rootworm adults in that they also feed on both the silks and on the leaves.
 

                                    Stalk Borers

    Insects feeding in the stalks of maize may also feed on the leaf, ear or other plant parts some time in their life cycle.  The insects covered in this section are primarily known for the damage that they do when boring in the stalk. These are the European corn borer, southwestern corn borer, southern cornstalk borer, stalk  borer and the lesser cornstalk borer.
 

12. European Corn Borer

Description

    The sexes of the European corn borer, Ostrinia nubilalis Hübner adults differ in color and size (figure below). The female moths (left) are larger and are a pale yellowish-brown color, with irregular darker bands in wavy lines across the wings. The male moth (right) is smaller, more slender, and darker than the female. The outer third of its wings is usually crossed by two zigzag streaks of pale yellow, and often there are pale yellow areas on the forewings. The male moth is darker, with distinct pale yellow bands on the wings (right). The adults have a wingspan of 20 to 30 mm. At rest, the tip of the male abdomen protrudes from the  folded wings. Eggs are laid in masses of 20 to 30 eggs that are covered with a shining waxy substance. Within the egg mass, the eggs overlap each other like fish scales. Each white egg is about half the size of a pinhead. Eggs change to pale yellow and darken just before hatching, as the brown head of the borer inside becomes visible.

   The newly hatched larva, about 1.5 mm long, has a black head, five pairs of prolegs, and a pale yellow body bearing several rows of small black or brown spots. It develops through 5 or 6  instars to become a fully grown larva about 25 mm long. When fully grown, the larva has a reddish tinge or is pinkish in color (figure left). The larval head capsule is dark brown and, on top of each abdominal segment, there are several small dark brown or black spots. The  reddish-brown to dark-brown pupa is 13 to 15 mm long with a smooth capsule-like body.

 Biology and Life Cycle

    The European corn borer was introduced into the U.S.A. from Europe in 1909, and has spread west to the Rocky Mountains with the western distribution running from New Mexico in the south to Montana in  the north.  Its range goes north into Canada. It feeds on  more than 200 plant species but maize is a preferred host.

  The number of generations per year varies from the southern to the northern portion of  its range (figure left). There are four generations a year in the southern portion of the range and one generation in the north. The first generation develops from the overwintered fifth instar in stalks, cobs, and plant debris. The larvae change into pupae in the spring and emerge as second generation moths approximately ten to fourteen days later during May and June. Moths aggregate or gather in weedy or grassy areas, normally field margins, to mate and drink water, usually in the form of dew. On warm, calm, humid evenings in June, female moths fly from these protected areas into maize to lay masses of 15 to 25 eggs near the midrib on the underside of the leaves (< 1% of the eggs may be laid elsewhere on the plant).

    Eggs hatch within five to seven days depending on temperature. Eggs that are about to hatch have distinct black centers and are referred to as being in the "blackhead" stage. This is due to the black head of the larva showing through the translucent eggshell. Blackheaded eggs will hatch within twenty-four to forty-eight hours. Newly hatched larvae disperse and soon establish themselves deep in the whorl, feeding on developing leaves during the first two larval instars. As the leaves grow and unroll from the whorl, the "shot-hole" feeding signs (small round holes scattered in the leaf tissue) can be seen. Following a feeding period in the plant whorl (approximately 2 weeks for each larva), third instar larvae leave the whorl, bore into stalks and excavate tunnels (cavities), in which they complete development. Fifth instar larvae of this first generation change into pupae within the plant cavity, from which the summer moths emerge in July and August. Occasionally, larvae will pupate outside the stalk on the maize leaf.

    The moths of the first generation (summer moths) generally emerge in late July and August. Similar to first spring moths, they move to grassy or other dense low vegetation near or inside maize fields to mate. In weed-free maize fields these areas may be fence line bromegrass or adjacent soybean or alfalfa fields. If grassy weeds are present in the maize field, moths may remain in the field and aggregate in weeds or patches of volunteer maize. Summer moths lay over 85 percent of their eggs on the undersides of the ear leaf and the three leaves above and three leaves below. Adult females may lay up to 500 eggs over their lifetime.

    After hatching, second generation larvae feed on the leaves and in leaf axils for a few days (particularly if pollen is available), then move behind leaf sheaths and the leaf collar area, or into ear tips. Some third, but mostly fourth instar larvae, bore into the stalk, ear shank, or ear. These larvae usually overwinter and do not pupate until the following spring. In years of extended growing seasons with greater than average degree-day accumulations in Nebraska, a small proportion of the larvae pupate, and produce moths, giving rise to a third generation of larvae. Third generation larvae are not of economic significance, because the maize plant at this late date is normally well beyond the period of susceptibility.

Damage

   In maize, feeding first occurs in the whorl. Shotholes are visible when the leaf unrolls from the whorl (figure below, left).  Later, the larvae bore down midribs of leaves into the stalk. Frass and silk near entrance holes are evidence of the presence of larvae (figure below, right). Extensive amounts of frass may be seen at the collar (figure below,  left). They also bore into,  feed,  and tunnel within the tassel, ear, ear shank and stalk, forming cavities. Cavities produced by borers (figure below, right) interfere with the translocation of water and nutrients. Cavities also reduce the strength of the stalk and ear shank, thereby predisposing the corn plants to stalk breakage and ear drop, which is aggravated by high winds or other adverse environmental conditions.

  Yield losses due to damage by the larvae are primarily reduced ear and kernel size (physiological losses) as well as broken plants and dropped ears (potential harvest loss). Larvae feeding in the ear (figure below) may cause seed yield loss and/or reduce quality in seedcorn, popcorn, and fresh market sweet corn.

   Yield losses are highly correlated with plant stage, water stress, and the hybrid. Cavity formation by the  first generation borer usually occurs before tassel emergence resulting in approximately 5 percent yield loss per borer per plant. Yield losses (per borer) from second generation larvae vary widely because cavity formation may occur over several weeks, and rapid physiological changes occur as the ear approaches maximum size and physiological maturity. As the ear advances from the blister stage to physiological maturity, the yield reduction per borer rapidly decreases. Average grain weight reductions are 5.9, 5.0, 3.1, and 2.4% per larva per plant  when feeding at the 10-leaf, 16-leaf, blister, and dough stages respectively.
 

13. Southwestern Corn Borer

Description

     The adults of  the southwestern corn borer, Diatraea grandiosella (Dyar),  are a light-straw color with a wing expanse of 1 1/4 inches. The labial palps extend in front of the head like a short beak. Eggs are whitish or yellow, oval in shape, and laid in groups in an overlapping, fish scale-like fashion. Initially eggs are greenish-white, but develop three distinct red transverse lines within 24 to 36 hours. There are two color forms of the larvae. During the growing season, the larva has a white abdomen with conspicuous dark brown or black spots (left figure). During the winter, the southwestern corn borer becomes pale yellow with very faint spots  (right figure). The full grown larva is about 30 mm in length.

Biology and Life Cycle
    The southwestern corn borer is found throughout the southern Corn Belt. It is now widely distributed in Arizona, New Mexico, Texas, Oklahoma, Colorado, Kansas, Nebraska, Arkansas, Missouri, Louisiana, Alabama, Mississippi, Tennessee, and Kentucky. The southwestern corn borer has two or more generations per year, depending on the severity of the previous winter. First generation larvae first appear in  June. For the first two weeks, first generation larvae feed within the whorl of the plant. After feeding in the whorl, larvae move down the stalk and tunnel into the stalk. Larvae may move from one plant to another. Pupation occurs in the stalk.  Adults emerge from the pupae in about a week and soon lay eggs. Upon hatching, the larvae feed on the leaf sheath before boring into the stalk. The second generation occurs during mid- to late summer. In the fall, the larvae migrate to the base of the plant and tunnel. Overwintering occurs as a larva in stalk base below the soil.  In the spring, pupation takes place in the stalk base. Moths emerge from the stubble, mate, and deposit their eggs on the upper and lower surfaces of the leaves. Eggs are laid singly or in groups of 2 to 5.

Damage

    The southwestern corn borer is primarily a pest of maize but also attacks sorghum. Major damage by this pest is due to the girdling of the stalk by the second generation larvae. The first generation attacks whorl-stage corn and is associated with losses to yield by stunting or killing plants. Numerous holes in the emerging leaves and leaf breakage due to midrib tunneling are characteristic. While leaf feeding may not lead to serious yield loss, destruction of the bud in the whorl can result in a "deadheart", and stunting, and complete loss of yield by a plant.
    The second generation larvae first feed in the leaf axils. Then, the larvae bore inside the maize stalks and move down the stalk in a straight line and feed at about three to five inches above the soil surface (figure left) where they girdle the plants (figure right). Larvae girdle the stalk by chewing a complete or partial internal groove around the stalk near the base. This leaves only a thin outer layer of the stalk for support. As a result, plants lodge and yield losses occur.
 

14. Southern Cornstalk Borer

Description

    The southern cornstalk borer, Diatraea crambidoides (Grote), adult is a straw-colored or dull white moth with a wingspan of 15 to 40 mm (females larger than males). Adults have the  distinct, extended labial palps in the form of a beak. The forewings are slightly darker than the hind wings. The flat, elliptical egg, approximately 1.3 mm by 0.8 mm, is creamy white when laid but later develops an orange hue due to the presence of three transverse, orange-red lines. The larva, which reaches a length of 25 mm, is creamy yellow during the winter and white with black spots in the summer (figure).  The pupa is about 22 mm long and the same color as the larva when first formed but later changes to a reddish-brown.

Biology and Life Cycle

     The southern cornstalk borer causes damage primarily in the states from Maryland and Kansas on the north to, and including, the southern and southwestern states. It also occurs in Mexico and in South America. This borer attacks primarily maize but also feeds on grain sorghum, sugarcane, broomcorn, and Johnson grass.

    The biology and life cycle of the southern cornstalk borer is similar to that of the southwestern corn borer. There are usually two generations each year although three generations can occur. Southern cornstalk borers overwinter as larvae below the ground level within cavities in maize taproots. Prior to pupation in March or April, the larvae make a silk-lined exit tunnel to the outside of the stalk through which they later emerge as adults. Approximately 10 days after pupation, moths emerge, mate, and begin laying eggs at night, usually on the underside of lower leaves. The flat eggs are laid either singly or in small clusters of 2 to 25 overlapping one another like shingles. Each female  lays up to 400 eggs. When the eggs hatch 7 to 10 days later, larvae move into the whorl of the plant, feeding on the leaves and spinning a silken thread behind them. Third- or fourth-instars move down the stalks and eventually tunnel inside the stalk at a point near the ground level. They may move from one plant to another, as does the southwestern corn borer. In the summer, southern cornstalk borer larvae live from 20 to 35 days and develop through seven instars. Mature larvae seal off the tunnels with frass and form cells in which to pupate. Summer pupation occurs in the above- ground stalk. The first generation  becomes adults in midsummer and the second generation reaches  maturity in early fall and remain as larvae during  the winter.

Damage

    The southern cornstalk borer is one of the most damaging maize insects  in the southern states. Maize  infested by the borer is twisted and stunted, and the stalk at the surface of the ground may be enlarged. The leaves are ragged, broken, and dangling. They have many holes caused by larval feeding when the leaf was still in the whorl stage.

    Early-season larvae start to feed in the whorl; as the leaves unfold, rows of irregular holes may appear. Larvae also tunnel in the midribs of leaves, and sometimes destroy growing points within leaf whorls. As larvae grow larger they tunnel into stalks. Masses of frass accumulate outside the entrance holes. Tunneling may be extensive in the lower portion of the stalk, primarily just above the soil line and into the taproot. This damage may be very destructive because of reduced nutrient and water uptake. Late-season larvae feed but little on the leaves, but tunnel through the base of the stalk.
 

15. Stalk Borer

Description

    The stalk borer, Papaipema nebris  Guenée, adult is a dull, grayish-brown moth that commonly has several white or silver spots in two rows across the front wings. There is a faint whitish line across the wing near the outer edge. The hind wings are dull brownish-gray. The wingspan ranges from 25 to 40 mm. The longitudinally ribbed egg may be spherical or slightly flattened and measures 0.4 to 0.6 mm in diameter. White when first deposited, it gradually turns brownish-gray or amber before hatching. Young larvae are purple to black and have prominent longitudinal white stripes at the front and rear ends of the body. The stripes are interrupted at mid-body by a solid dark purple to black area on the third thoracic segment and first three abdominal segments. Fully grown larvae are cream colored with faint purple markings. There is a distinct dark band on the side of the  prothoracic segment and the head (figure). Larvae reach a length of  30 to 40 mm prior to pupation. The light brown pupa gradually darkens as it matures and is 16 to 22 mm in length.

Biology and Life Cycle

   The stalk borer occurs in all areas east of the Rocky Mountains from southern Canada to the Gulf of Mexico. This borer tunnels in almost any large- stemmed plant. Their host range encompasses at least 44 families and 176 species of plants. Some cultivated crops subject to infestation include maize, cotton, potato, tomato, alfalfa, rye, barley, pepper, spinach, beet, and sugarbeet. Although many weedy plants are infested, giant ragweed is preferred.  Highest populations are associated with fields and fencerows with large-stemmed weeds. Stalk borers overwinter as eggs. Female stalk borer moths lay their eggs primarily on dry grasses such as smooth brome and giant ragweed in late summer and early fall. The moths tend to lay eggs singly or in groups under sheaths and in folded or rolled leaves. Eggs overwinter and hatch in the spring. In May, the newly emerged larvae feed as leaf miners on broadleaf plants or as stem borers on grasses. Larvae eventually bore into the stem. If they kill or outgrow their host, they will emerge at night and tunnel into new plants, including maize seedlings. The migrating stalk borer larvae can attack maize that is between the two and eight leaf stages. Larvae develop through 7 to 10 instars, in about 10 weeks. Pupation occurs in individual cells that are constructed in the soil beginning in late July. Moths emerge during August, September and early October and deposit eggs singly or in masses between the leaf sheath and stems of weeds. One generation occurs each year.

Damage

   Damage is sporadic but most commonly associated with the border rows of conventionally planted maize and with no-till plantings. Stalk borer larvae can injure corn plants in June and early July in two ways: 1) by burrowing into the base of the plant and tunneling up through the center of the stalk, or 2) by entering the plant through the whorl and tunneling down.  Plants attacked at earlier growth stages tend to receive more damage. A single stalk borer larva may attack more than one plant if the first plant does not support the larva as it increases in size.

    A damaged plant will show irregular rows of holes through the unfolding leaves (see figure). These irregular rows of holes will be much larger and more ragged than those caused by whorl feeding of first generation European corn borer larvae. If the feeding injury to the central part of the plant is severe, the whorl will appear dead while the outer leaves are green and apparently healthy. In severe cases an infested plant will have a very ragged appearance, with destroyed tassels and  with abnormal growth habits such as twisting, bending over, and/or stunting. Suckers may be  produced. Frass is usually evident around the base of more mature infested plants. Once past the whorl stages, maize is somewhat resistant to the stalk borer and recovers more readily from damage.
 

16. Lesser Cornstalk Borer

Description

    The lesser cornstalk borer, Elasmopalpus lignosellus (Zeller) is a small insect.  The male's front wings are brownish yellow and have grayish margins with several dark spots .The moth has a wingspan of about 25 mm. Wings are wrapped around the body  when at rest. The egg is greenish-white and less than 1 mm in diameter. The larva is a slender, bluish-green, brown-striped caterpillar up to 19 mm long. The pupa is brownish and about 8.5 mm long.

 Biology and Life Cycle

     The lesser cornstalk borer is found throughout the United  States but most severe feeding damage occurs in the southern states, particularly Alabama, Georgia and South Carolina. This insect is also found in Mexico, Central America and South America. The lesser cornstalk borer prefers maize but it also feeds on beans, cowpeas, crabgrass, Johnson grass, peas, peanuts, sorghum, soybeans, and wheat.

    In the southern states, these borers usually hibernate as larvae. The larvae transform into pupae  and the moths emerge early in the spring. The moths lay their eggs on the leaves or stems of the plant upon which they feed. The eggs hatch in about a week. The larvae feed first on the leaves or roots. Later they construct underground silken tubes or burrows from which they bore into plants near the ground line. They become fully grown in 2 to 3 weeks, leave their burrows, and spin silken cocoons under trash on the surface of the ground. In these cocoons, they change to pupae from which moths emerge in 2 to 3 weeks. Two generations occur in most southern states.

Damage

    The larva of this small moth has been sporadically injurious to the seedlings of many plant
species. This larva may be found feeding on leaves or roots of maize but eventually tunnels into the plant's stem usually at or near the soil line.  Injury is caused when the larva bores into the stalk of the host plant, thereby disrupting the growing point. The presence of the larvae in maize is evident by the masses of borings that are pushed out through holes in the stalk. A silken, soil-covered tube is often connected to the plant stem at the entrance hole. Damage can be slight, or it can kill the plant. In older plants the larvae may girdle the stem near the ground level resulting in stalk breakage. Damage is most prevalent during drought conditions in crops grown on sandy soil.
 

                                             Leaf Feeders

    Insects feeding on the leaves of maize remove sap with sucking mouthparts, lacerate the leaves  or  remove  a portion  of the leaves.  Aphids remove plant sap, thrips lacerate the leaves and cutworms, armyworms and beetles remove portions of the leaves. All of these types of feeding remove chlorophyll resulting in reduced photosynthesis.
 

17. Corn leaf aphid

    The wingless corn leaf aphid, Rhopalosiphum maidis (Fitch) adult, is oval and about 2.0 mm long (figure, left). It is usually green to bluish green with black antennae, legs, and cornicles and a dark area at the base of the cornicles. The head is marked with two dark, longitudinal bands, and the abdomen with a row of black spots on each side. The body often seems to have a powdery coating. The winged form is about the same size as the wingless form  and has a dark green and black body and black cornicles (figure, center). The nymph (figure, right) is smaller than but similar to the wingless adult in appearance.

Biology and Life Cycle

    The corn leaf aphid is common wherever small grains and maize are grown in the United States and Canada, being especially abundant in the South. Its range extends throughout the tropical and temperate regions of the world. The corn leaf aphid is commonly found on maize, barley, millet, broomcorn, sorghums, Sudan grass, and many other wild and cultivated grasses. It shows a preference for barley and sorghums. Although this aphid has been reported to attack wheat, oats, and rye, economically significant infestations on these crops are uncommon.

     Little is known about the biology of this pest. Apparently it only overwinters in the southern states as an adult. Infestations in northern areas are believed to result from populations of wingedforms carried  by air currents from the south.  Ovoviviparous (producing living young by the hatching of the ovum while still in the mother) females, both winged and wingless, form the bulk of the population. Males are rarely found, and no eggs have ever been seen. This suggests that the aphid can reproduce parthenogenetically (asexually). The female aphids and  molted skins are found in large clusters on the leaves (figure, left), where the females feed and reproduce. Reproduction slows in winter and summer and is most rapid during cool weather. Therefore, corn leaf aphids tend to be a problem on winter grains in the fall, on warm winter days, and in the spring. The number of generations per year varies from 9 in Illinois to 50 in southern Texas.

Damage

    The corn leaf aphid injures maize by the removal of plant sap and the introduction of diseases. Feeding by colonies of this aphid causes mottling and discoloration of the leaves. Feeding of large colonies in the vascular system causes an accumulation of  carbohydrates and abnormal synthesis of anthocyanin resulting in the reddening of the leaves.  Infested plants become covered with sweet, sticky honeydew secretions. Sooty mold fungi grow on the honeydew causing reduced grain development and interfere with photosynthesis. These aphids also transmit a mosaic diseaseof sweet corn.

   Wingless colonies first are observed on the  emerging leaves and the tip of the tassel. The winged form is observed when colonies on the leaves (see figure) and tassels increase in size at  pollen shedding and silking time. Prior to tassel emergence, the  nymphal infestation occurs on the moist part of the leaves in the whorl where they feed on the phloem. If infestations begin early in the season on mid-whorl maize and increase to large colonies by the time of tassel emergence, anthesis is affected and varying degrees of missing kernels may  occur.
 

18. Spider Mites

Description

    Spider mites are small microsocopic arthropods belonging to the class Araneida, and the order Acarina. They differ from insects in having 8, rather than 6 legs in the adult stage. There are several spider mite species that attack maize in North America. These include the twospotted spider mite Tetranychus urticae Koch, Banks grass mite Oligonychus pratensis (Banks), carmine spider mite, Tetranychus cinnabarinus (Boisduval) and the Pacific spider mite, Tetranychus pacificus McGregor.

    Two species of spider mites, the twospotted spider mite, and the Banks grass mite,  damage maize in Nebraska. They are somewhat similar in appearance but differ in the amount of damage they cause. Proper mite identification  is important since the twospotted spider mite is  much more difficult to control. The most useful characteristic for differentiating between these two species is the pattern of  pigmentation. Generally, in older twospotted spider mite females, pigmentation
appears as a well-defined spot on each side of the body, ending abruptly
just beyond half the length of the body (left figure). The two dark spots on the sides of the abdomen are digested food visible through the mite's translucent body.  Banks grass mite females tend to have blackish-green pigmentation extending the full length of the body (right figure). The twospotted spider mite is about 0.4 mm long. The oval-shaped  female is yellow to  dark green, with two or four dark, dorsal spots; the male is smaller and has a more pointed abdomen. The eggs are spherical, and white to transparent when first laid. Just before hatching, they become a yellowish-green color and average 0.14 mm in diameter. The larvae (first stage after hatching) are slightly larger than the eggs. They are six-legged and colorless except for carmine eyespots. The two nymphal stages are difficult to distinguish. Both are pale green, oval, and eight-legged, sometimes spotted, and slightly smaller than adults.

Biology and Life Cycle

    Twospotted spider mites have been found on over 180 host plants, including at least 100 cultivated species. Spider mites have four stages of development: (1) the spherical, somewhat translucent egg stage;  (2) a six-legged translucent larval stage; (3) an eight-legged nymphal stage; and (4) the eight-legged adult stage. A resting or quiescent stage occurs at the end of the larval and nymphal stages.

   Spider mites usually overwinter as fertilized females resistant to low temperatures. These females are red as opposed to the active summer forms which are yellowish-green. In mild winters, they may continue to feed and lay eggs. In summer, many generations (7 or more) develop. The number of eggs laid is dependent on the temperature.  In warm weather, each female produces up to 19 eggs per day  for a total of about 100 eggs over several days. Eggs are fastened to leaves or to silk spun by the adult mites and hatch in 2 to 4 days. Eggs hatch into six-legged larvae that next develop into eight-legged nymphs. There are two nymphal stages. After the larval, and each nymphal stage, a resting stage occurs.  Adults mate soon after emerging from the last resting nymphal stage.  Development is rapid in hot, dry weather. A generation requires 1 to 4 weeks and  may pass in as few as 5 to 7 days in mid-summer, or in a month during cool periods.

Damage

    Banks grass mites appear earlier in the season and are more likely to remain on lower leaves. Twospotted spider mites appear later in the season and may spread rapidly over the entire plant.
Weather and natural enemies appear to be important determining factors in spider mite abundance. Spider mites are most likely to develop economically damaging populations in fields that are moisture-stressed during June and July, particularly if weather is hot, windy, and dry. Mite build-up can occur even in irrigated fields, especially if irrigation problems exist or if irrigation is delayed during stress periods prior to the blister stage of maize. Other fields likely to develop mite problems are those that have received foliar applications of certain insecticides for European corn borer, western bean cutworm or other pests and fields located  next to grasses, ripening wheat or alfalfa.

    All active stages of spider mites damage maize by piercing plant cells of the leaf with their mouthparts and sucking the juices. Feeding causes premature drying that results in loss of leaf tissue, stalk breakage, and kernel shrinking. Effects on yield are most severe when mites damage leaves at or above the ear level. Evidence of mite feeding, which is visible on the upper surface of the leaf, is a yellowish and stippled area (figures below) where the mites are feeding on the lower leaf surface. Heavily infested leaves turn completely pale and dry up. Both the Banks grass mite and the twospotted spider mite produce webbing on the lower leaf surface in which the various stages of the mites are present. Webbing is initiated near the midribs of the host plant and gradually envelopes the plant as the population increases.  Severe infestations resemble drought stress since damage progresses from  the bottom of the plant up. Spider mites can be a serious problem on maize, particularly silage and sweet corn.
 

19. Thrips

Description

     Thrips attacking maize include the western flower thrips, Frankliniella occidentalis (Pergande) and the corn thrips, Frankliniella williamsi Hood. The western flower thrips adultsare very small, about 1 mm long. Wings are narrow and fringed with long hairs. The female is larger than the male, varies from yellow to dark brown, and has a more rounded abdomen. The male is always pale yellow and has a narrower abdomen. The eggs are yellowish and not visible because they are laid into the plant tissue. Immature thrips are wingless, whitish to yellowish in color (figure left). The larvae develop through two instars. Second instars become whitish prior to molting. Both, the prepupa and pupa, are yellowish, quiescent non-feeding stages.

Biology and Life Cycle

    Thrips metamorphosis is intermediate between simple and complete and consists of five stages: adult, egg, larvae, prepupa, and pupa. There are two larval instars. Both prepupa and pupa are quiescent, non-feeding stages.
    Adults emerge continuously throughout the warm months. Adults and immatures may be found in maize at any time during the growing season. Eggs are deposited in tender plant tissue and hatching occurs in 2 to 14 days, depending on temperature (about 5 days during the summer months). First instar larvae begin feeding soon after hatching. The immature stages take about 5 to 7 days to complete development. Thrips develop through two quiescent, non-feeding pupal stages in the soil, plant litter or in a protected area on the plant. The entire life cycle from oviposition to adult emergence ranges from 12 days in hot weather to 44 days in cool weather

Damage

   Thrips build up on alfalfa, weeds, and other vegetation in spring, and then move to maize from these hosts when they are cut or dry up. Thrips are most commonly found in whorls, tassels, ears, or on the underside of leaves. They  feed by inserting their modified left mandible into the tissue, and sucking the fluids from cells. Thrips are most noticeable and cause most severe damage at two maize growth stages, young seedling plants and at ear formation. Feeding on young seedlings stunts plants. A common sign of a heavy thrips infestation is distorted leaves that turn brownish around the edges and cup upward. Usually the plants will recover. At ear formation, thrips injury provides entry for infection by Fusarium spp. and subsequent Fusarium ear rot diseases. The actual thrips injury does little damage but ear rot diseases can be serious.
 

20. Dingy Cutworm

Description

    The dingy cutworm, Feltia jaculifera (Guenée) larvae are a dull pale gray to reddish brown color with a broad  gray dorsal stripe, subdivided into V-shaped areas on each segment and margined by a narrow dark stripe on each side (figure). The larvae are similar in appearance to those of theblack  cutworm. They, however, differ from the black cutworm larvae in that they have four black tubercles (warts or spots) on each abdominal segment which are equal in diameter, while in the black cutworm, the front pair of tubercles are about half the diameter of the back pair. Larvae are about 32 mm long when full grown. The adult is gray with distinct whitish gray markings on each forewing. The hindwing is grayish brown with a white fringe and a wingspan of 30 to 40 mm. Eggs are white and oval-shaped. The pupa is brown and oblong.

Biology and Life Cycle

    Dingy cutworms are northern species found from southern Canada through the upper two-thirds of the of the United States from southern Utah to southern  Virginia on the south and from the east coast to Idaho and Utah in the west (figure). Dingy cutworms overwinter as larvae.  In early spring, larvae become active and feed in weedy areas of fields. Fourth through sixth instars are present when maize is planted and seedlings develop. Mature larvae undergo summer hibernation (aestivation) from mid-May until July, then pupate just beneath the soil surface from late July through mid-August. Moths emerge during August and September and the females lay eggs on host plants. Eggs are laid singly or in groups of a few.  There is one generation per year.

Damage

   Dingy cutworm larvae have a wide host range feeding on many plant species, including maize, wheat, alfalfa, grasses, and broadleaf weeds. They are most common in fields following legumes or in fields with heavy crop residues and are among the first insects to damage maize in the spring. Dingy cutworms are climbing cutworms that feed almost entirely on leaves (especially the ends) and seldom cut or bore into seedling maize. Thus, they cause less damage than the black cutworms which may feed on the leaves and cut the stems.
 

21. Armyworm

Description

   The true armyworm, Pseudaletia unipuncta (Haworth) moth has pale brown to grayish-brown forewings with a wingspan of about 39 mm. There is a distinct white spot in the center of each forewing. The  hind wings are grayish-white. The egg is greenish-white and globular. The young larva is pale green. Late instar larvae vary in color from green to light brown (see figures).

Longitudinal stripes are as follows: a narrow broken stripe down the  center of the back, bordered by a wide, darker, mottled stripe reaching  halfway to the side; on the side there are 3 stripes of about  equal width; next to the mottled one on the upper side is a pale-orange, white-bordered stripe, next a dark brown stripe just reaching the spiracles; and just below the spiracles, there is a pale-orange stripe edged with white. Each proleg  has a dark band on the outer side and a dark tip on the inner side. A mature armyworm is 30 to 35 mm long.  The head is brown with dark honeycombed markings. The pupa, about 13-mm long is reddish-brown at first, and gradually darkens becoming black.

Biology and Life Cycle

    The armyworm is found in California, New Mexico, Arizona,  and in all states and in Canadian provinces east of the Rocky Mountains. In the southern states, partially grown larvae overwinter in soil near the surface.  The insect does not overwinter in the northern states. The adults migrate to these areas each year from mid to late May. Early in the spring, larvae resume feeding at night, usually on grasses and small grains. During daylight hours, larvae prefer to remain under litter on the ground. The larvae pupate and the adults emerge. First generation adults appear in May or June depending upon climatic conditions. Moths mate soon after emergence and feed on nectar for 7 to 10 days. Within about 21 days after emergence, at night, females  deposit up to 2000 eggs  on the leaf sheaths of grasses and small grains which usually grow near maize fields or around field margins. Eggs are laid in masses or rows of  30 to 75, often with the edge of the leaf folded over them. About 8 days later, larvae emerge and feed for 3 or 4 weeks on the foliage of grains and grasses.  After stripping the grasses, the larvae invade adjacent maize fields. Occasionally, when herbicides fail to control grassy weeds within maize fields, armyworm moths may lay eggs throughout the maize field, resulting in an outbreak.  After feeding, mature larvae drop to the ground and pupate in earthen cells 5 to 8 cm deep within the soil. Moths emerge about 2 to 4 weeks later. True armyworms complete about 3 generations per year in most locations but in extreme southern locations, there are continuous generations.

Damage

     The armyworm is a pest of maize, sorghum and small grains. In maize it is a common early season pest of maize. Damage to maize consists primarily of stripping of the leaves (figure below). Larvae may feed on the ear causing injury similar to that of the corn earworm but damage to the ear is usually slight. Armyworm infestations are noted for their rather sudden appearance in large numbers.

    Armyworms feed on the maize foliage starting with the edge of the leaf. Feeding starts on the lower leaves and progresses up the plant. The whorl leaves are eaten last. Depending on the plant size, armyworms may completely defoliate to the point that only the leaf  midribs remain. In the case of heavy infestations, armyworms may devour plants to the point that only stubble
remains. Because they feed at night, the larvae may inflict much injury before they are detected.Once having exhausted their food supply, larvae migrate  to new host plants. Field borders are typically more severely damaged.
    Armyworms often cause problems in maize when grassy areas of fields are destroyed by cultivation or by herbicides, or when maize is planted no-till into wheat or rye. In some northern states, the second and third generation larvae often are most  injurious to maize, especially in fields that have an abundance of grassy weeds.

    The armyworm  does not overwinter in the upper-Midwest, but reinvades the northern part of its range each spring. Armyworm outbreaks in Texas, Missouri, Oklahoma or Kansas indicate a potential invasion of Nebraska and other states to the north. Damaging infestations, however, may occur despite low numbers of migrating moths. Conversely, large moth flights into the Midwest do not always result in economic infestations. The high reproductive potential of  this insect and complex environmental factors determine the ultimate degree of infestation.
 

22. Grasshoppers

Description

    In the Midwest, four grasshopper species -- the differential, Melanoplus differentialis (Thomas); redlegged, M. femur-rubrum (De Geer);  migratory, M. sanguinipes (F.); and twostriped, M. bivittatus (Say)-- cause about 90 percent of the total damage to cultivated crops. Grasshopper  species are generally similar in appearance. The differential grasshopper (figure, left) is one of the largest of the crop destructive species in North America reaching a length of 45 mm. Adults and nymphs are brownish or olive green with yellow areas on the lower parts and black chevron-like markings on the hind legs. The redlegged grasshopper  is smaller, about  25 mm long, brownish red with the hind tibiae pinkish red with black spines (figure, right).

The migratory  grasshopper is similar in appearance to the red-legged but the hind tibiae is not as bright pink as the red-legged. The twostriped grasshopper is about 35 mm in length. The upper part of the body is olive colored with a yellow stripe on each side, extending from the head to the tip of the wing.  It is distinguished by the dark stripe on the upper half  of the hind leg.
Grasshopper eggs are  laid in masses (egg pods) about 25 m  long consisting of up to 30 elongate eggs cemented together (figure, left).

Biology and Life Cycle

    There are three stages in the grasshopper life cycle -- the egg, nymph, and adult. The number of egg pods deposited by a single female may range from 7 to 30, and the number of eggs per pod may vary from 8 to 30, depending on the species. The eggs are well protected by the insulation of the pods and can survive extremely cold temperatures. Some grasshoppers prefer to lay eggs in soil surrounded by  roots of grasses; other species select open areas in locations with accumulations of surface debris. Grasshoppers in croplands only lay their eggs in untilled soil. Therefore, to infest a crop the grasshoppers have to migrate from field margins or other areas of untilled soil. Most grasshoppers overwinter in the egg stage, but a few species hibernate as nymphs.

    Hatching time is influenced by weather. Hatching time can be predicted by correlating the four developmental stages of eggs (clear, coagulated, eye spot, and segmented) with soil temperatures. Eggs hatch about the middle of May in Nebraska. Most nymphs start feeding within one day after egg hatch, and usually feed on the same plants as the adult.  The nymphal stages require about 6 weeks and adults begin appearing in early July.  Hoppers begin laying eggs one to three weeks after becoming adults, starting in early August. They may live 45 to 50 days.

Damage

     Because many of the grasshopper breeding areas are now under tillage, the potential for devastation, while still serious, is not as great as it was 100 years ago. In the Midwest, croplandgrasshoppers feed primarily on maize, wheat, and alfalfa, but during years of high populations, may feed and seriously damage any crop as well as trees and shrubs.
   Feeding may begin anywhere on the plant but rarely on the bottom leaves. Injury may start at the leaf edge or in the center of the leaf adjacent to the midrib. There is no pattern to the feeding. Very large populations consume all the leaf except for the tougher leaf midrib. Injury is similar to that caused by armyworms, but armyworms start feeding on the bottom leaves and progress up the plant. Defoliation (see figure) is the primary injury to plants, but damage often exceeds the amount of foliage eaten. Grasshoppers may feed on ripening kernels of grain (see figure), causing shattering. They also feed on the green silk, preventing fertilization or filling of  the ear.
 

23. Corn Flea Beetle

Description

    There are a number of flea beetles attacking maize but the corn flea beetle Chaetocnema pulicaria Melsheimer and sweet potato flea beetle C. confinis Crotch are of major importance in North America. Other flea beetle species feeding on maize in the western USA are the western black flea beetle, Phyllotreta pusilla Horn; the potato flea beetle, Epitrix cucumeris (Harris); threespotted flea beetle, Disonycha triangularis Say; and the palestriped flea beetle, Systena blanda Melsheimer.
  The corn flea beetle adult (figure) is oval-shaped, 1.3- to 2.5-mm long, and black colored tinged with bronze or bluish-green and has yellow markings on its legs. The basal segment of each antenna is orange. Flea beetles have enlarged hind legs and jump vigorously like fleas  when disturbed. The white egg is about 0.35 mm long and pointed at one end. Larvae are white, slender, and  cylindrical grubs with a brown head and small legs. Larvae are 3.2 to 8.5 mm long when full grown. The white  pupa resembles the adult in size  and gradually darkens as it matures.

Biology and Life Cycle

   The corn flea beetle occurs in most areas east of the Rocky Mountains. It is a general feeder, but most hosts are grasses.  The corn flea beetle overwinters as an adult beetle in litter and trash around fields. In early spring, the beetles move to weeds and then to maize seedlings. Eggs are scattered on the soil beneath host plants. In about 10 days, the larvae emerge and begin feeding on and tunneling in underground stems, roots, or tubers. They feed for 3 to 4 weeks and develop through three instars before pupating in the soil. In 7 to 10 days, a new generation of  adults emerges. Three or more generations are completed each year.

Damage

    Corn flea beetles attack foliage, leaving small round holes and scraped or striped areas (see figure above). In young plants particularly, the feeding damage can be serious and can result in death. Usually, the direct loss caused by these injuries is relatively insignificant.   These beetles are usually most troublesome after a mild winter followed by a cold spring. Under such conditions, high numbers of beetles survive the winter and attack the slowly growing maize over a prolonged period. Growth is retarded and leaves may wilt. Early maturing varieties in the middle and southern states are most seriously affected.
    Economic damage primarily results from the overwintering beetles which spread  bacterial wilt of maize (Stewart's disease). Stewart's disease of maize is caused by the bacterium Erwinia stewartii that causes a fatal wilt disease in young plants of sweet corn and certain susceptible field maize inbreds. Most common is the appearance of the leaf blight phase, which affects most dent maize inbreds and hybrids after pollination. Stewart's disease symptoms on leaves are long, wavy streaks that are water-soaked, then turn yellow and die.
 

                                    Ear Feeders

    Several kinds of insects infest the developing ears of maize, and may cause economic damage. These insects can reduce both yield and quality of  maize seed, popcorn, sweet corn and field maize. Insects discussed in this section are the stink bugs, corn earworm, western bean cutworm, fall armyworm, variegated cutworm and sap beetles. The European corn  borer, covered in the Stalk Borer section and the armyworm, covered in the Leaf Feeders section, are also occasional pests on maize ears. Corn rootworm beetles feed on the silks and are covered in the Seed, Root  and Lower Stem Feeders  section
 

24. Stink bugs

Description
     Several species of stink bugs (Hemiptera: Pentatomidae) feed on maize. Among the more common species are the brown stink bug, Euschistus servus (Say) (see  figure), green stink bug, Acrosternum hilare (Say), and the southern green stink bug, Nezara viridula (L.). Brown and green stink bugs have been reported as far north as Quebec. In the United States, however, they are more often injurious in the South. Although the southern green stink bug occurs outside the United States, in this country it occurs only from Texas to the Atlantic coast and northward to Virginia.

   Stink bugs are known for their foul odor. They are shield-shaped insects with five-segmented antennae and a large scutellum (triangle) on the center of the back (see figure). The color patternsvary with the species.

   When first laid, the barrel-shaped eggs of the green stink bug are yellow to green, later turning pink to gray. Eggs of the green stink bug measure 1.4 x 1.2 mm. The white, kettle-shaped eggs of the brown stink bug are slightly smaller than those of the green stink bug. The creamy, cylindrical eggs of the southern green stink bug measure 1.0 by 0.75 mm and develop a pinkish hue before hatching.

   Nymphs resemble adults but are smaller. Green stink bug nymphs are predominantly black when small, but as they mature, they become green with orange and black markings. Nymphs of the brown and southern green species are light green. Southern green stink bug nymphs, however, have two series of white spots along their backs.

    Adults of the various species range in size from about 12 to 19 mm in length. Green and southern green stink bugs are bright green and measure 14.0 to 19.0 mm long. The major body regions of the green stink bug are bordered by a narrow, orange-yellow line. Brown stink bugs are dull brownish-yellow in color and 12.0 to 15.0 mm long.

Biology and Life Cycle

    Stink bugs overwinter as adults and become active in spring. Each female deposits up to several hundred eggs, usually in early summer. These eggs are laid in clusters  primarily on leaves and stems. Nymphs hatch from these eggs and pass through five instars before becoming adults. Approximately 5 weeks elapse between hatching and adult emergence. The number of generations  per year varies in different regions of North America.

Damage

    Stink bugs have a wide host range. On maize, damage is generally most severe in weedy fields. Both the adults and nymphs suck sap. Stink bug feeding causes several types of damage. Feeding early in the early maize growth stages (VE--V5) may kill small seedlings, produce stunted plants,or cause excessive tillering. Stink bugs kill seedling plants by injecting a toxin during feeding. Leaves may be wrinkled with holes of various sizes, scattered randomly or in repeating patterns often with a yellow halo; whorl leaves wrapped tight and failing to expand. Stink bugs pierce the side of the stalk with their beak. Saliva injected into the leaf during feeding creates holes. There is usually a row of oval holes with yellow borders across the unwrapped leaves of damaged plants. This row results from the single feeding puncture that penetrates the wrapped leaves. Holes are up to 25 mm on expanded leaves and are often surrounded by dead, brown tissue and a yellow halo (figure above). Feeding patterns are often repeated across the leaf. Injured leaves are often twisted. The most dramatic symptom is tillering of damaged plants. Tillering is first observed about 10 days after damage occurs. A shoot begins to grow from the base of the plant and may become as large as the original plant.

    Stink bugs also probe through the shuck of a developing ear of corn and suck the juice from individual kernels. This damage may open entrances for other insect pests or fungi to cause extensive damage. Feeding may cause twisted ear shoots with separated husk leaves (figure, left) and with missing grains, mostly on the ear surface away from the stalk. Stylet (feeding) marks can be seen on the inside of green shucks and appear as pin-point bruises . The greatest  damage, however, occurs when stink bugs feed on ears that are less than 20 mm long, beginning about 2 weeks before silking. This damage may result in total ear loss by causing curled ears.
 

 25. Corn earworm

Description

    The moths of the corn earworm, Helicoverpa zea, (Boddie)  are green-eyed, 20 mm long, with a 40 mm wingspan, usually buff-colored, sometimes with shades of pink or green, and with dark forewing markings (figure). Hindwings are light, but have dark margins. Adults range in size from about 12 to 19 mm in length. Eggs, about half the size of a pinhead, are an off-white  to yellowish color, and  dome-shaped with ribs converging on the top. The larvae range in color from light green (light phase) (figure below, left) to almost black (dark phase) (figure below, right). Earworms may vary greatly in color, but all have three or four black stripes running the full length of the body. Basic body coloration may be green, yellow, black, brown or even pink. The head is light brown with faint mottling or spots. Most distinctive are the numerous microspines on the skin which can be seen with a hand lens. Mature larvae are up to 50 mm long.

Biology and Life Cycle

    The corn earworm is native to North America and is found throughout maize growing regions. The earworm probably does not overwinter in the central states, although larvae have been collected as early as April in Nebraska. Instead, the insect reestablishes itself each spring when southern moths fly northward.

    Eggs are placed singly on maize leaves. A red ring appears around the egg after 24 hours and the black larval head capsule is visible in three to four days. Eggs hatch in 10 days or less. There are five or six larval stages.  When feeding is completed, the larvae drop to the ground and enter the soil where they transform into shiny brown pupae. In a few weeks the moths emerge to mate and deposit eggs for the second generation. These locally emerging moths, plus additional migrants from the south, are the parents of the larvae found in maize ears in mid-to-late August. Eggs are laid three or four at a time on the green silks. After eggs hatch, young larvae proceed down the silk channels into the ear tips. Corn earworms are cannibalistic, therefore only one will normally mature in each ear. A larva may move from one ear to another. When ear feeding is completed, the larva leaves the ear through an exit hole made in the husk. The larva then moves down the stalk or drops to the ground where it pupates in a cell about  75 to 125 mm deep in the soil. Moths emerge after a pupation period of about 2 to 3 weeks. In warm climates (south of 40° north latitude), they overwinter as pupae in the soil. There may be 6 generations in the southern states but in the central Corn Belt area there are 1 to 2 generations.

Damage

    The corn earworm  is a common pest of many crops including cotton, tobacco, tomatoes, soybeans, sweet corn, popcorn, and field maize. This pest is distributed throughout North America and is one of the most damaging pests of maize. Early in the season, larvae feed in theterminal of young maize plants damaging the leaves and develop on tassels. These larvae may tunnel into the ears. When fresh silk is available the eggs are laid on the silk, and the larvae first feed on the leaves or bore directly into the silk. Maize ears attacked by the corn earworm have masses of moist castings at the end, and the kernels at the tip of the ear are eaten down to the cob by the larvae (figure, left).
 
 

 26. Western Bean Cutworm

Description

    The western bean cutworm, Loxagrotis albicosta (Smith) adult is a typical cutworm moth about 25 mm long, which flies at night and is attracted to light. The forewings are brown with distinct round and kidney-shaped markings, with a light tan stripe at the leading edge. The hind wings are light grey or white. Eggs are cream-colored and deposited in masses. Small western bean cutworms are similar to young armyworms. These two species are difficult to separate without microscopic examination until they are about one-third grown. At the third instar (roughly 13 mm long), western bean cutworm larvae are not obviously striped, unlike armyworms, and body color  varies from cream to tan. A light area runs lengthwise down the middle of the back. This light area is bordered on each side by an irregular, scalloped, broken dark area that extends to spiracles or breathing holes. On the prothoracic shield, just behind the head, are three white stripes running from front to back (figure).

Biology and Life Cycle

    The western bean cutworm is injurious to maize in several western states and has extended its range eastward into Nebraska and other central states (figure). It overwinters as a prepupa in an earthen cell in the soil. In May and June it transforms into a shiny, reddish brown pupa. In July,the moth emerges from the pupa and pushes its way to the soil surface. Once mated, the females deposit masses of cream-colored eggs in maize whorls. As leaves expand and unfurl out of the whorl, eggs will appear on the upper surfaces. Eggs darken to a purplish color as they develop and hatch in about 7 days, after which young larvae disperse over the maize plants.  Larvae feed on maize for about three to four weeks during which they reach a length of about 40 mm. They then drop to the ground. The larvae then burrow into the soil and form an earthen cell, and enter the prepupal stage which overwinters.

Damage

    The western bean cutworm is primarily a pest of field beans but is occasionally injurious  to maize in several western states. Damaging infestations have been recorded in the Platte River Valley in central Nebraska. Depending on plant growth stage, the larvae may proceed to the unfolding whorl where they feed on parts of the emerging tassel, or move directly to the ear or leaf axil. Once on the ear, they may bore in through the husk (figure below, left) or proceed to the tip, where they feed on green silk and later penetrate the ear through the silk channel and feed on the developing grains (figure below, center).  Late feeding  on dented kernels results in scraping  or removal of whole or partial kernels (figure below, right).

 

27. Fall Armyworm

 Description

   The fall armyworm, Spodoptera frugiperda (J. E. Smith) adult has a wingspan of  about 39 mm. The hind wings are grayish-white; the front wings are dark gray, mottled with lighter and darker splotches. Each forewing has a noticeable whitish spot near the extreme tip. Minute, light gray eggs are laid in clusters and covered with grayish, fuzzy scales from the body of the female moth. The eggs become very dark just before hatching. The general appearance of the fall armyworm larva (figure) is similar to that of the armyworm. The fall armyworm varies in color from light tan to green to black.  Three yellowish lines run down the back from head to tail. These are bordered on either side by a dark stripe and a wide yellow stripe with faint reddish markings
or blotches. On the head is a white, upside down Y-shaped marking that clearly distinguishes it from the armyworm. Larvae have four pairs of fleshy abdominal prolegs in addition to the pair at the end of the body.  On the tail are eight obvious tubercles, or dark colored bumps, each with a strong seta or hair arising from it.  Full grown larvae are about 30 to 40 mm long. The pupa, approximately 13 mm long, is at first reddish-brown but darkens to black as it matures.

Biology

   The fall armyworm is found throughout most of the U.S. It is continuously present in the Gulf States, and the tropics of  Central and South America. The fall armyworm is unable to overwinter at northern latitudes and migrates northward each spring. Annually it migrates as far northward as Montana, Michigan and New Hampshire. In Nebraska, little activity is seen until late July or early August when a few moths begin to show up in blacklight traps.

    The life cycle of the fall armyworm is similar to those of the corn earworm and armyworm. Eggs are laid in masses of about 100,  usually on the leaves of  host plants, such as grasses around field margins. The spherical gray eggs are covered with a coating of moth scales or fine bristles. Larvae hatch in 3 to 5 days, feed on the remains of the egg mass, and move to the whorl. When abundant, the larvae may eat all the available food and then move in  armies to adjoining fields. After feeding for 2 or 3 weeks, the larvae burrow about 20 mm into the ground to pupate. Within 2 weeks, a new swarm of moths emerges, usually flying several miles before laying eggs. There may be 3 to 4 generations per year in the southern portion of its range. They overwinter mostly as pupae in the soil.

Damage

    Maize, sorghum, and other plants of the grass family are the preferred foods, but the fall armyworm also attacks alfalfa, bean, peanut, potato, sweet potato, turnip, spinach, tomato, cabbage, cucumber, cotton, tobacco, all grain crops, and clover. The fall armyworm is one of the more difficult insect pests to control in maize. While fall armyworms can damage maize plants in nearly all stages of development, late planted fields and later maturing hybrids  that have not yet silked are more likely to become infested. Unlike the armyworm, the fall armyworm feeds during the day and night, but is usually most active in the morning or late afternoon. It causes serious leaf feeding damage, feeds on undeveloped tassels of young plants,  causes direct injury to the ear, and the larvae may bore in stalks.  The most common damage is to late pretassel maize. Very early symptoms of fall armyworm resemble European corn borer infestation. Small holes and "window pane" feeding in the leaves emerging from the whorl are common. Late instar fall armyworm larvae consume large amounts of leaf tissue resulting in a ragged appearance to the leaves similar to grasshopper damage (left figure). Larger larvae are usually found deep in the whorl often below a "plug" of yellowish brown frass. Plants often recover from whorl damage without any reduction in yield. Larvae will also move to the ear as plants begin to tassel and young ears become available (right figure). The ear may be partly or totally destroyed. Damage to the ear may be much more important than leaf damage. In Nebraska, the fall armyworm is a more important pest of sweet corn than of field maize.
 

28. Variegated Cutworm

Description

    The forewings of the variegated cutworm, Peridroma saucia  (Hübner) adult are yellow or brown with pale mottled designs, with a dark brown spot at the upper edge of each forewing. The hind wings are white with brown veins and margins. The wingspan varies from 3.8 to 5.0 cm. The spherical white or pale yellow eggs are ribbed and slightly less than 1 mm in diameter. They are laid in irregular elongate patches and turn brown before hatching. The variegated cutworm larva (figure)  is grey to blackish, with an orange stripe on each side of its cylindrical body. A "W"-shaped black marking is present on the tip of the abdomen, especially in larger specimens. Behind the head is a row of small yellow dots extending along the midline of the back. The mature larva may be as long as 40 mm and curls into a C-shaped ball when disturbed. The pupa is reddish-brown and is 15 to 20 mm long.

Biology and life History

    The range of the variegated cutworm spans most of North America including Canada and Alaska and extends into South America. It is also found in Europe and the Mediterranean area. It is of most importance in the Pacific Northwest and some northeastern states. It is an occasional pest of alfalfa, soybeans and home vegetable and flower gardens.

  Variegated cutworms overwinter as pupae with a high percent mortality occurring during this life stage. The first moths begin to emerge early in May in Nebraska.  Female moths lay over 2,000 eggs during their short life span. Groups of 75 or more eggs are deposited on stems or leaves of low-growing plants. The small white eggs turn dark purplish-grey when nearly ready to hatch, which is about 5 days in the summer.  Larvae feed at night and on cloudy days for about 25 days before burrowing into soil to pupate. The pupal stage lasts two weeks to a month before second generation moths emerge. About 7 weeks are required to complete a life cycle  and variegated cutworms produce two to four generations each year. In Nebraska, there are at least two generations each year, with the second of most concern to maize growers.

Damage

    The variegated cutworm feeds on a variety of garden crops, trees, vines, grasses, field crops, ornamentals, and greenhouse plants. Damaging infestations, however, are sporadic. The variegated cutworm is one of the few cutworm species that climbs plants to feed,  and thus its presence is more noticeable than that of subterranean cutworms. They feed at night and hide in the soil by day. Late larval instars cut off plants at or near the soil surface. Occasionally, when corn is silking, cutworms can be found feeding on the silks at the tip of the ear.
 

29. Sap Beetles

Description

    The two common sap beetle species observed in maize ears in the Midwest are the picnic beetle, Glischrochilus  quadrisignatus (Say) and the dusky sap beetle, Carpophilus lugubris Murray. The wing covers of sap beetles (especially the dusky sap beetle) are relatively short and do not extend to the tip of the abdomen. Antennae have  knobs at the tip (club-shaped) (figure, left). Eggs are laid singly and are milky-white and  slender (sausage-shaped), resembling a house fly egg. The picnic beetle is a small, shiny, black beetle about 6 mm  long with four irregular yellow or reddish spots on the back (figure, left).  Larvae are white to cream colored with brown heads (figure, right).  The dusky sap beetles are brown, drab looking beetles having no distinguishing marks, with short wing covers, and are about 3 mm long.

Biology and Life Cycle

    The sap beetles may overwinter as larvae or as adults in decaying vegetation or fruit buried in the soil. In the spring, they emerge and lay their eggs on rotting vegetation. The sap beetles later lay eggs on the silks of  maize ears. Females lay 5 to 15 eggs per day. Larvae feed until fully grown, then drop to the soil to pupate. The life cycle is about 30 days with apparently 2 or more generations per year, depending on location.

Damage

    Sap beetle adults are scavengers (secondary pests)  and breed in fermenting sap emanating from injuries produced by primary ear invaders, such as the corn earworm, European corn borer or western bean cutworm. Both adults and larvae are found on ears. Because sap beetles lay eggs in silks, the larvae that hatch and feed in  the ear are suspected of being primary pests. Sap beetles may play a role in furthering the spread of rot organisms (molds) which also damage maize ears. On the positive side, there is some evidence that sap beetles may drive European corn borers from their tunnels in stalks. In any case, damage by sap beetles to ears of maize is slight.
 
 

Photo Credits

European corn borer, Ostrinia nubilalis Hübner feeding damage on stalk and leaves:
John van Duyn, Department of Entomology, North Carolina State University, Raleigh, NC.

Southern cornstalk borer larva,  Diatraea crambidoides (Grote), in stem:
Clemson University, Department of Entomology Cooperative Extension Service, Clemson, SC.

Western flower thrips, Frankliniella occidentalis (Pergande) nymph:
Jack Kelly Clark, used with permission of the University of California Statewide IPM Project,
URL= http://www.ipm.ucdavis.edu/PMG/r113300711.html

Geographical insect distribution maps:
Dow AgroSciences, 9330 Zionsville Road, Indianapolis, IN.

Maize growth stages:
Ritchie, S. W., J. J. Hanway, G. 0. Benson and J. C. Herman. 1992. How a Corn Plant Develops, Special Report No. 48. Iowa State University of Science and Technology, Cooperative Extension Service,  Ames, Iowa.
URL= http://www.ag.iastate.edu/departments/agronomy/corngrows.html#
 
 

References

Bessin, R. 1994. Armyworms in corn. Dept. of  Entomology, University of Kentucky, Lexington, KY.
URL= http://www.uky.edu/Agriculture/Entomology/entfacts/fldcrops/ef109.htm

Bessin, R. 1998. Fall armyworm in corn. Dept. of  Entomology, University of Kentucky, Lexington, KY.
URL= http://www.uky.edu/Agriculture/Entomology/entfacts/fldcrops/ef110.htm

Bode, W. M. and D. D. Calvin. 1990. Yield-loss relationships and economic injury levels for the European corn borer (Lepidoptera: Pyralidae)  populations infesting Pennsylvania field corn. J. Econ. Entomol. 83: 1595-1603.

Center for Integrated Pest Management. 1982.  Insect and Related Pests of Field Crops (AG271), Pests of Corn/Sorghum. Armyworm/Corn Root Aphid/Corn Leaf Aphid/Stalk Borers. North Carolina State University. Raleigh, NC.
URL=  http://ipmwww.ncsu.edu/AG271/corn_sorghum/corn_sorghum.html

Center for Integrated Pest Management. Twospotted Spider Mite. North Carolina State University. Raleigh, NC.
URL= http://ipmwww.ncsu.edu/AG295/html/twospotted_spider_mite.htm

Center for Integrated Pest Management,  Variegated Cutworm. North Carolina State University. Raleigh, NC.
URL=http://ipmwww.ncsu.edu/AG295/html/variegated_cutworm.htm

Clemson University. CE Sheets. Corn Insects. Southern cornstalk borer. Department of Entomology, Clemson, S.C.
URL= http://entweb.clemson.edu/cuentres/cesheets/corn

Danielson, S. and F. Baxendale. 1993.  Integrated Crop Management. NebGuide
G93-1153, Corn cutworms. Department of Entomology, University of Nebraska, Lincoln, NE.
URL= http://www.ianr.unl.edu/pubs/insects/g1153.htm

Danielson, S., R. Wright, G. Hein, L Peters and J. Kalisch. 1991. Insects That Attack Seeds and Seedlings of Field Crops. NebGuide 91-1023, Corn root aphids.  Department of Entomology, University of Nebraska, Lincoln, NE.
URL= http://www.ianr.unl.edu/pubs/insects/g1023.htm

Dicke, F. F. 1977. The most important corn insects. In Sprague, G. F (ed.) Corn and Corn  Improvement. American Society of Agronomy, Madison, WI.

Godfrey, L. D., S. D. Wright and M. J. Jimenez. 1999. UC Pest Management Guidelines: Corn. Spider Mites. University of California, Davis, CA.
URL= http://www.ipm.ucdavis.edu/PMG/r113400111.html#DESCRIPTION OF THE PESTS

Godfrey, L. D., S. D. Wright and M. J. Jimenez. 1999. UC Pest Management Guidelines: Corn. Corn Thrips. University of California, Davis, CA.
URL= http://www.ipm.ucdavis.edu/PMG/r113300711.html

Hein, G. and J. B. Campbell. 1997. A Guide to Grasshopper Control in Cropland. NebGuide NF97-328.  Department of Entomology, University of Nebraska, Lincoln, NE.
URL= http://www.ianr.unl.edu/pubs/insects/nf328.htm

Landis, D. and B. Giebink. 1994.  Managing Soil Insects in Corn.  Extension Bulletin E-2267. Department of Entomology and Pesticide Research Center, Michigan State University, Lansing, MI.
URL=  http://www.ent.msu.edu/cgi-bin/ipmfacts.pl?action=article&article=2267.txt

Lyon, W. F. and R. N. Williams.  Sap beetles. Ohio State University Extension Fact Sheet, HYG-2047-97, Columbus, OH.
URL= http://www.ag.ohio-state.edu/~ohioline/hyg-fact/2000/2047.html

National Corn Growers Association. 1999. The World of Corn: Corn Production in the U.S. and Corn Crop Value.
URL=http://www.ncga.com/03world/main/index.html

Ohio Pest Management & Survey Program.  Field Crops Pest Management Circular # 12. Seed Maggots, Seedcorn Beetles,  Wireworms & Grubs.  Ohio State University, Columbus, OH. http://www.ent.iastate.edu/ipm/icm/1997/6-30-1997/recogecb.html
URL= http://www.ag.ohio-state.edu/~ohioline/icm-fact/fc-12.html

Ohio Pest Management & Survey Program.  Field Crops Pest Management Circular # 14.  Armyworms.  Ohio State University,  Columbus, OH.
URL= http://www.ag.ohio-state.edu/~ohioline/icm-fact/fc-14.html

Pierre, W. H., S. R. Aldrich and W. P. Martin. 1967. Advances in Corn Production: Principles and Practices. Iowa State University Press, Ames, Iowa.

Rice, M. 1997. Recognizing European Corn Borer Injury. In Integrated Crop Management/ Insects and Mites. Department of Entomology, Iowa State University, Ames, IA.
URL= http://www.ent.iastate.edu/ipm/icm/1997/6-30-1997/recogecb.html

Ritchie, S. W., J. J. Hanway, G. 0. Benson and J. C. Herman. 1992. How a Corn Plant Develops, Special Report No. 48. Iowa State University of Science and Technology, Cooperative Extension Service,  Ames, IA.
URL= http://www.ag.iastate.edu/departments/agronomy/corngrows.html#

Seymour, R. C., G. L. Hein, R. J. Wright and J. B. Campbell. 1998. Western Bean Cutworm in Corn and Dry Beans. NebGuide G98-1359. Department of Entomology, University of Nebraska, Lincoln, NE.
URL= http://www.ianr.unl.edu/pubs/insects/g1359.htm

Witkowski, J. and S. Danielson. 1988. Stalk Borer in Corn. NebGuide G80-521. Department of Entomology, University of Nebraska.
URL= http://ianrwww.unl.edu/pubs/insects/g521.htm

Witkowski, J. and R. Wright. 1997.  The European Corn Borer: Biology and Management. Department of Entomology, University of Nebraska, Lincoln, NE.
URL= http://ianrwww.unl.edu/ianr/entomol/ecb/ecb1.htm#Item1

Wright, R. 2000. Managing Corn Rootworm Larvae. Department of Entomology, University of Nebraska, Lincoln,  NE.
URL= http://www.ianr.unl.edu/ianr/entomol/pmguides/crwlarv.htm

Wright, R., L. Meinke and K. Jarvi. 1999. Corn Rootworm Management. University of Nebraska Cooperative Extension, EC 99-1563-C. University of Nebraska, Lincoln,  NE.
URL= http://www.ianr.unl.edu/pubs/insects/ec1563.htm

Wright, R., R. Seymour, L. Higley and J. Campbell. 1996. Spider Mite Management in Corn and Soybeans.  Extension NebGuide G93-1167-A. Department of Entomology, University of Nebraska, Lincoln, NE.
URL= http://www.ianr.unl.edu/pubs/insects/g1167.htm

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