Maize Insect Pests in North America

Kathy L. Flanders
Department of Entomology
Auburn University

E.A. "Short" Heinrichs
Department of Entomology
University of Nebraska
Lincoln, Nebraska 68583-0816

J.E. Foster
Department of Entomology
University of Nebraska
Lincoln, Nebraska 68583-0816

Marlin E. Rice
Department of Entomology
Iowa State University
Ames, Iowa  50011

"Grass thus became as milk to the creatures of the animal kingdom, and corn became the milk for mankind." -Frank Waters, Book of the Hopi (1963)

Chapter Contents

Introduction

Description, Biology and Plant Damage Caused by Maize Insects

* all insect pest sections link to separate section pages, with a link at the top to return to this page.

Seed, Root and Lower Stem Feeders

Stalk Borers

Leaf Feeders

Ear Feeders

Photo Credits

References


Introduction

In  the USA, maize is often referred to as "corn" but the word "corn" is a misnomer. "Corn" in  its original sense, meant grain.  The verse in the Bible , "first the blade,  then the ear, after that the full corn in the ear" (Mark 4:28), refers not to maize, but most likely to wheat or barley. The biblical reference to "a corn of wheat" refers to a single grain.

Botanically, maize is a grass of the family Gramineae which includes other common crops such as wheat, oats, barley, rye, rice, sorghum, and sugarcane. Maize is in the tribe, Maydeae, which includes the dent corn (the subject of this chapter), flint corn, sweet corn, and popcorn. Maize was given the scientific name, Zea mays L. by Linnaeus. Zea derives from the Greek word for grain or cereal and mays (eventually the common name maize) stems from the  aboriginal American sound maiz, approximating an inference of that which sustains life.

Origin of Maize

The origin of maize is somewhat controversial. Maize is believed to be a native American plant. One of the first records is dated November 5, 1492 when two sailors of  Christopher Columbus' crew, exploring Cuba, returned with details of  "a grain they call maiz  which was well tasted, bak'd, dry'd and made into flour". Maize was cultivated  by the Indians of North, Central, and South America for centuries prior to Columbus' time. The most advanced systems of maize culture centered in the great  pre-Columbian civilizations-the Incas in Peru, the Aztecs in Mexico, and the Mayas in Yucatán and Guatemala. The spread of maize north and northeast from its native tropical America occurred over many centuries via migrations of Indians.

Maize in the USA

Explorers to the New World in the 1500s found maize  being grown by Indians in most parts of the Americas from Canada to Patagonia of Argentina. The Puritans who landed in New England in 1620, survived  their first dreary winter by eating maize obtained from the Indians, and took lessons in maize culture the following spring. In following years, most everywhere agriculture was practiced in North America, maize was the basic food  plant. Successful colonization of the New World by the Europeans  would have been extremely difficult without maize.

By the late 1830's, the American  "corn belt" centered in Tennessee, Kentucky, and Virginia. The defeat of Black Hawk, chief of the Sac and Fox nations, gave the white man control of the vast maize potential lands of Illinois. Maize farmers moved in and the meat packing industry, dependent on maize-fed animals, followed westward. The Chicago Board of Trade became the leading market for maize and by 1870 Chicago was virtually the food center of the world. By the end of  the 19th century, U. S. (United States) maize production was increasing rapidly  and in 1899 the nationwide crop was 2.7  billion bushels, of which Illinois and Iowa contributed more than 25%.  It wasn't until the 1940's, when 3 billion-bushel crops became common. Hybrid maize was first cultivated on a commercial scale in 1933 and yields thereafter have continued to increase to the present day. In 1998, 9.8 billion bushels were produced   on 72 million acres in the US, for an average yield of 134 bushels  per acre.  Maize accounted for 24% of all crop acres in the United States in 1999 and was valued at US$ 17.93 billion compared to soybeans, at US$ 12.55 billion (http://www.ncga.com/o3world/main/us_corn_crop_value.html).

The value of the U.S. maize crop has significantly increased from 1949 to 1999 (http://www.ncga.com/o3world/main/us_corn_crop_value.html).  The 1949 crop was valued at  only  US$ 4 billion. In 1996 it reached a peak of US$ 25 billion. In 1998 and 1999 the value decreased to US$ 19 and US$ 18 billion respectively. The top producing states in billion bushels in 1999 were Iowa (1.8), Illinois (1.5), Nebraska (1.2), Minnesota (1.0), and  Indiana (0.8) (http://www.ncga.com/03world/main/us_corn_prod_1999.html).

The overall average for the U.S. in 1999 was 133.8 bushels/acre. Average U.S. maize yields by state vary significantly. Highest yields in bushels/acre in 1999 were in Arizona (195), Washington (180), New Mexico (180), and Oregon (175). Lowest yields were in New Jersey (37 bushels/acre). Yields in the top producing states were Minnesota (150)  Iowa (149), Illinois (145), Nebraska (139), and Indiana (132) (http://www.ncga.com/03world/main/us_corn_prod_1999.html).

Maize Growth and Development

The growth stages of maize are described and depicted in the following URL: http://www.ag.iastate.edu/departments/agronomy/corngrows.html#contents.The vegetative and reproductive stages of maize are indicated in the table below.

Vegetative and reproductive stages of a maize plant
Vegetative Stages
VE Emergence
V1 First leaf
V2  Second leaf
V(n)  nth leaf
VT Tasseling
Reproductive Stages
R1 Silking
R2 Blister
R3 Milk
R4 Dough
R5 Dent
R6 Physiological maturity

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.

photo of maize growth and development, V3 stage

V6 Stage

At V6, the growing point and tassel are above the soil surface and the stalk is beginning aperiod of greatly increased elongation. Below ground, the nodal root system is now the majorfunctioning 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.

photo of maize growth and development, V6 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. 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.

photo of maize growth and development, V9 stage

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. The number of rows of kernels per ear 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.

photo of maize growth and development, V12 stage photo of maize growth and developmentv V12 stage showing ear development

V15 Stage

photo of maize growth and development, V15 stage

The V15 maize plant 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, silks from the basal ear ovules are first and silks from the ear tip ovules are last to elongate. Brace roots (also termed aerial nodal roots) are now growing from the nodes above the soil surface. They help support the plant and obtain  water and nutrients during the reproductive stages.

photo of maize growth and development, V18 stage

photo of maize growth and development, V18 stage, root development

photo of maize growth and development, V18 stage, ear development

VT Stage

The VT stage is initiated when the last branch of the tassel 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.

photo of maize growth and development, VT stage

photo of maize growth and development, VT stage, tassel development

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.

photo of maize growth and development, R1 stage

R2 Stage - Blister (10-14 days after silking)

R2 kernels are white on the outside (figure) and resemble a blister in shape. The endospermand 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.

photo of maize growth and development, R2 stage

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.

photo of maize growth and development, R5 stage

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 tothe cob and a black or brown abscission layer has formed. The husks and many leaves are no longer green although the stalk may be. The figure below shows an R6 kernel on the side opposite the embryo and slices laterally cut from the top, middle and bottom of the kernel.

photo of maize growth and development, R6 stage

photo of maize growth and development, R6 stage, kernel development

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.

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