Cultural Control
D. N. Ferro
Department of Entomology
University of Massachusetts
Amherst, MA 01003
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Cultural Control
Definition: "Cultural practices" refers to that broad set of management techniques or options which may be manipulated by agricultural producers to achieve their crop production goals (Kennedy et al. 1975), or "the manipulation of the environment to improve crop production." "Cultural control" on the other hand, is the deliberate alteration of the production system, either the cropping system itself or specific crop production practices, to reduce pest populations or avoid pest injury to crops (Ashdown, 1977). From M. Kogan 1986
Functional Mechanisms
1) impediments to pest colonization of the crop
2) the creation of adverse biotic conditions that reduce survival of individuals or populations of the pest
3) modifications of the crop in such a way that pest infestation results in reduced injury to the crop
4) enhancement of natural enemies by manipulating the environment
Destruction or provision of breeding or overwintering refugia
Many natural enemy species require food sources in the form of pollen, nectar, or
innocuous arthropods that are not present in particular crop habitats. These food
requirements may be provided to support natural enemy populations by encouraging or
deliberate development of certain wild vegetation habitats near plantings of the crop
(Altieri and Whitcomb 1979, review).
Sometimes a second species of prey may be essential for a natural enemy to survive in a
region from year to year. One of the better documented examples is based on research by
Doutt and Nakata (1965) with Anagrus epos (Hymen.), an egg parasite of the
grape leafhopper, Erythroneura elegantula. The grape leafhopper is the major
pest of grapes in the San Joaquin Valley of California. This wasp overwinters in the egg
stage and the grape leafhopper overwinters as adults.
The wasp overwinters in the eggs of the blackberry leafhopper, Dikrella californica,
a noneconomic species whose eggs are present throughout the year on wild blackberries (Rubus ursinus and R. procerus). Overwintering wasp populations tend to be
largest in blackberries along rivers that have an overstory of sheltering trees. When the
blackberries produce new foliage in February, heavy oviposition by Dikrella leafhoppers is stimulated. The parasite population increases enormously on the eggs so
that by late March and early April there is widespread dispersal of newly-produced Anagrus wasps. Doutt et al. (1966) reported that vineyards located within 5.6 km of an established
blackberry refuge will benefit immediately from the immigrant parasites. Vineyards beyond
this distance rarely were colonized by wasps until mid-season.
It was presumed that all one needed to do was to establish a blackberry planting
adjacent to the vineyard to support non-pest populations of leafhoppers and wasps.
However, because of the lack of sheltering trees, as occurs in natural blackberry systems
along rivers and streams, populations of never became permanently
established. These blackberries were being irrigated on the same regime as the vineyard
and blackberry plants require more moisture than the grapes. This resulted in the Dikrella populations dying-out. R. ursinus, California blackberry, is a native
species which grows best in shady, moist conditions, while R. procerus,
Himalaya blackberry, is endemic to Europe and grows well in both the shade and sun. When
these plants were grown under shade with high moisture they produced a sufficient
population of Dikrella for maintaining Anagrus populations.
Kido et al. (1983) presented data showing a correlation between adult Anagrus dispersion in early spring from French prune orchards and parasitism of grape leafhopper
in nearby vineyards. Anagrus epos was parasitizing another leafhopper species, Edwardsiana
prunicola which feeds on prune. Both blackberry and French prune provide alternate
hosts for the wasp, and effectively are nurseries for producing Anagrus wasps.
Most aphid species in the temperate areas of North America overwinter as eggs on their
primary woody host. The green peach aphid (GPA), Myzus persicae, overwinters on
peach and wild cherry and a number of other Prunus spp. Green peach aphid vectors
maize dwarf mosaic virus of sweet corn. Because GPA does not migrate into horticultural
crops until early July, it is primarily the later plantings of sweet corn that show
symptoms and yield reductions. We recommend to our growers to plant the early plantings of
sweet corn near to peach trees, so that the later plantings can escape heavy probing by
these vectors as they move from their primary host plants. A similar situation exists with
GPA as a vector of cucumber mosaic virus of green pepper. Again, either the destruction of Prunus spp. or planting away from these primary hosts can reduce losses to these
viruses.
Destruction or provision of alternate hosts or volunteer plants
The black cutworm, Agrotis ipsilon, is a major pest of corn seedlings in the
corn belt states, especially in a no-till system. Young larvae feed on seedling corn
leaves until fourth instar when they cause serious damage by cutting or drilling the
plants. However, if the seedlings can reach the four leaf stage before being infested, no
significant yield reductions occur, creating a "the two-edged sword." However,
if the grower waits until the corn reaches the four leaf stage before cultivating or using
herbicides to control the weeds, yield reductions occur due to weed competition. So, the
best management tactic is to time preplant herbicides at least 14 days before planting to
minimize ovipositional sites and early instar food sources (Engelken et al. 1990).
Colorado potato beetle, Leptinotarsa decemlineata (Say), overwinters as adults
in fields of origin or in the undisturbed habitats adjacent to fields. The beetle emerges
in the spring and it must regenerate its flight muscles before it migrates. If a host
plant is not within walking distance of the beetle, hence no food source, it can fly
several kilometers in search of a host. However, if it emerges into a host habitat, such
as a potato field, it will feed and oviposit, and after about a week the beetle will fly
from the field to colonize another host habitat. If volunteer plants are allowed to grow
in the previous years field, the emerging beetles will colonize these plants, feed and
oviposit before migrating, hence, delaying the colonization process of adjacent fields.
Crop rotation or maintenance of a host-free season
Crop rotation interrupts normal life cycle of insect pests by placing the insects in a
non-host habitat. Rotation is generally most successful against arthropod pest species
with long generation cycles and with limited dispersal capabilities.
White fringed weevil complex,Graphognathus leucoloma (Boheman) and G.
peregrinus (Buchanan), adults lay many eggs when fed on soybean and cause heavy damage
to this crop. However, the grass crops, including corn, are in some way nutritionally
deficient to support feeding, and do not suffer damage from this pest. So, a soybean/corn
rotation is effective and economical.
Crop rotation interrupts the life cycle of the northern (Diabrotica longicornis)
and western (D. virgifera) corn rootworms, and both species can be effectively
controlled by rotation throughout the corn belt of the U.S. This tactic has been
compromised in some areas where the rootworms diapause for more than one year.
Overwintered Colorado potato beetle (CPB) can disperse to colonize new fields; however, after they emerge from the soil they need to regenerate their flight muscles and they will not oviposit until they have fed on a nutritionally acceptable host plant. So, between the colonization process and physiological development, a rotated field that was rotated as little as 200m from last years field can be colonized 1-2 weeks later and generally at lower population densities than a non-rotated field. This saves 1-2 sprays for first generation larvae. And, often pushes most emergence of summer adults after August 1 (diapause switch). Those beetles that emerge after diapause induction do not produce flight muscles or a reproductive system. When rotated with corn (sweet or field) where large populations of Coleomegilla maculata (CMAC) buildup feeding on pollen and aphids, CMAC move into the potato fields in late spring or early summer to feed on CPB eggs.
Tillage
Tillage operations used to produce a crop include soil turning and residue-burying
practices, seedbed preparation, and cultivation. Some forms of tillage can reduce pest
populations indirectly by destroying wild vegetation (weeds) and volunteer crop plants in
and around crop-production habitats.
Overwintering populations of Heliothis zea may be greatly reduced by either fall
or spring plowing operations.
Overwintering survival of the soybean stem borer Dectes texanus is inversely
related to depth of burial of soybean crop residue following harvest.
The stalk borer, Papaipema nebris, has become a major pest of corn in the
midwest where farmers use conservation tillage. That is, serious infestations have
occurred throughout entire fields where no-till is practiced. Using a fall moldboard plow
and a spring disk reduced borer damage when compared to no till. However, other studies
suggest that stalk borers would be better managed by controlling grassy weeds within
fields in the late summer and early fall to prevent oviposition rather than relying on
tillage or weed control practices to reduce populations of eggs and larvae after
oviposition has already taken place.
Timing of planting or harvest
Alterations in planting date and harvest date can frequently result in plants escaping from damaging pest infestations.
Delayed planting
Late planted potatoes (>June 15 emergence) in Massachusetts in non-rotated fields
suffer less damage than conventional planting dates (plant emergence prior to June 15).
Overwintered beetles remain in the field for about 5-7 days after emerging from the soil,
and if no host plants are present, they leave the field by flight. 90% of the overwintered
population emerges by early June, and a late planted field is only colonized by a small
proportion of this population. Because oviposition occurs late, first generation adults do
not emerge until after the induction of diapause (August 1), resulting in only one
generation of larvae to control.
Buntin et al. (1990) showed that by delaying the planting date of wheat in the fall
wheat seedlings were not present for oviposition by the Hessian fly, Mayetiola destructor (Say). Infestations of fall and winter wheat by this pest, declined without enhancing
spring infestations or reducing wheat yields.
Early harvest date
Pink bollworm, Pectinophora gossypiela, overwinters as last instar larvae and
diapause is controlled by short days (<13 hours of light). By harvesting early (before
diapause induction) the number of overwintering larvae is reduced to low levels.
Practices: 1) defoliate or desiccate the mature crop to cause all bolls to open at nearly
the same time, expediting machine harvesting; 2) harvest the crop early, shred stalks, and
plow under crop remnants immediately; 3) irrigate prior to planting in desert areas if
water is available to encourage plant growth; 4) delayed planting - plant new crops during
a designated planting period, which allows for maximum suicidal emergence of moths that
emerge during the spring time, that is, moths emerge and die before cotton fruit is
available for oviposition. Short season cultivars are key to this program.
Trap crops
Crop monocultures are often damaged more severely by pests than is the same crop
located in an area with crop diversity. However, there are cases where such diversity can
aggravate pest problems. It is in these situations where trap crops can be important.
Lygus bugs are a key pest of cotton in the San Joaquin Valley of California. A
major habitat of the bugs is alfalfa fields, which are commonly interspersed with cotton
fields. When the alfalfa is harvested the bugs leave the field in large numbers to infest
cotton fields. By strip cutting the alfalfa field, the number of bugs migrating to cotton
can be minimized (Stern et al. 1967). A twist on this approach is to plant strips of
alfalfa every 400' between cotton fields and then only harvest 1/2 of the alfalfa strip at
any one time. Stern (1969) demonstrated that Lygus bugs concentrate in these
strips, and the need for insecticides was virtually negated. Furthermore, beneficial
parasitoids and predators were extremely abundant in these strips and, as they moved to
and from the adjacent cotton, an added benefit resulted.
A large proportion (>70%) of Colorado potato beetles overwinter in uncultivated
habitats adjacent to potato fields. Movement from these overwintering sites by beetles to
colonize potato fields can be inhibited by using plastic-lined trenches around the
perimeter of the field, or by treating the outer 6 meters of the field with an insecticide
that kills the colonizing beetles. The perimeter plants effectively act as a trap crop, or
barrier. The plastic-lined trench has been shown to be 84% effective at controlling these
beetles, while fields treated with the newly registered insecticide, imidacloprid,
controlled 100% of the beetles. Because the colonizing population has been reduced to low
densities, it is then possible to use the Bacillus thuringiensis tenebrionis-based
insecticides to manage the larvae feeding within the interior of the field.
Sanitation
Destroying culled potatoes by turning them under, so that they decompose is important
in reducing inoculum sources of the late blight fungus, and as an early season host for
aphids and other pests.
Destroying slash in logging operations can reduce the buildup of bark beetles.
Water or nutrient management
Water can be used directly to suffocate insects or indirectly by changing the overall
health of the plant, while fertilizer can influence the injury to a crop primarily through
alterations in crop growth or nutritional value to the pest. Some pest populations are
enhanced by poor crop growth, while others are enhanced by succulent crop growth.
Water
Flooding of cranberry bogs is a valuable tool for controlling several insect pests
(mites and fireworm) and plant pathogens of cranberry. Flood irrigation is frequently used
to reduce populations of wireworms in vegetable and sugarcane crops. Likewise, flooding
can be used to control white grubs in sugarcane, especially under conditions of high
temperature.
Furrow irrigated potato fields in many parts of California tend to crack upon drying,
exposing potato tubers to ovipositing potato tuberworms. In areas where this is a problem,
overhead sprinkler irrigation is recommended to prevent the cracking of soil.
Overhead sprinkler irrigation can enhance dissemination and infectivity of some
entomopathogenic organisms, especially fungal pathogens. Such practices help to promote
epizootics of Nomuraea rileyi in populations of the velvetbean caterpillar in
soybean.
Fertilization
Enhancement of succulent cotton growth through fertilization renders the crop more attractive to populations of the cotton aphid, Aphis gossypii, cotton fleahopper, Pseudatamoscelis seriatus, and the cotton bollworm. Heliothis zea.
Undernourished plants are often more attractive to colonizing aphids because they are
more yellow and reflect more light in 540nm range.
Physical barriers
Floating row covers were used to protect broccoli plants from the imported cabbageworm, Artogeia rapae (L.), flea beetle complex, striped cucumber beetle, Acalymma
vittata (F.) and cabbage maggot, Delia radicum (L.). The row covers were very
effective at protecting the plants from all pests except the cabbage maggot. The cabbage
maggot overwinters as pupae in the soil, so when the row covers were placed over the soil
the flies emerged and became trapped underneath the cover! (Adams et al. 1990)
Floating row covers were placed over potato plants being grown for seed to prevent
aphids from vectoring PLRV (persistent virus) and PVY (non-persistent virus). The covers
were more effective at preventing transmission of PLRV than PVY, mainly because it takes
prolonged feeding by the aphid to vector the persistent virus PLRV, while PVY can be
vectored within 30 seconds (Harrewijn et al. 1991).
Border sprays
This really isn't a cultural control strategy per se. However, the success of
using border sprays is based on knowing how an insect colonizes and moves within a
cropping system.
Chouinard et al. (1992) targeted sprays to the outer row of apple trees to protect the
fruit from the plum curculio, Conotrachelus nenuphar (Herbst). This pest
overwinters outside of the orchard and migrates into the orchard at petal fall. So, an
application at petal fall and another at pink stage reduced the damage at harvest from
this pest from 59% without any sprays (targeted against this pest) to 2.4%.
Cold/Heat treatments
Grain chilling is a non-traditional, non-chemical preservation technology for the
storage of cereal grains. A grain chiller utilizes a refrigeration system to control the
temperature and moisture content in stored grain independent of ambient conditions. Over 1
billion bushels of grain are chilled annually in countries like Argentina, Australia,
Germany, Great Britain, France, Indonesia, Israel and Mexico, but very little within the
U.S. grain industry. It costs about 0.5 to 1 cent per bushel (insecticide costs 0.33 to 1
cent). At temperatures below 65oF, insects and molds cannot survive, or at
least their rate of development is reduced. Cool air from outside is passed over a bank of
refrigeration coils in order to decrease the air temperature, and the air is then reheated
a few degrees to reduce the humidity before it is circulated through the grain.
References
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