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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

Adams, R. G., R. A. Ashley and M. J. Brennan. 1990. Row covers for excluding insect pests from broccoli and summer squash plantings. J. Econ. Entomol. 83: 948-954.

Armbrust, E. J. and G. G. Gyrisco. 1975. Forage crops insect pest management. pp. 445-470. In R. L. Metcalf and W. H. Luckmann, Introduction to Insect Pest Management. John Wiley and Sons, New York.

Buntin, G. D. , P. L. Bruckner and J. W. Johnson. 1990. Management of Hessian fly (Diptera: Cecidomyiidae) in Georgia by delayed planting of winter wheat. J. Econ. Entomol. 83: 1025-1033.

Engelken, L. K., W. B. Showers and S. E. Taylor. 1990. Weed management to minimize black cutworm (Lepidoptera: Noctuidae) damage in no-till corn. J. Econ. Entomol. 83: 1058-1063.

Ferro, D. N. 1987. Insect pest outbreaks in agroecosystems. pp. 195-215. In P. Barbosa and J. C. Schultz (eds.), Insect Outbreaks. Academic Press, New York.

Flaherty, D. L., L. T. Wilson, V. M. Stern and H. Kido. 1985. Biological Control in San Joaquin Valley Vineyards. pp. 501-520. In Biological Control in Agricultural IPM Systems, M. A. Hoy and D. C. Herzog (eds.), Academic Press, NY.

Harrewijn, P., H. den Ouden and P. G. M. Piron. 1991. Polymer webs to prevent virus transmission by aphids in seed potatoes. Entomol. Exp. Appl. 58: 101-107.

Herzog, D. C. and J. E. Funderburk. 1986. Plant resistance and cultural practice interactions with biological control. pp. 67-88. In M.A. Hoy and D. C. Herzog (eds.), Biological Control in Agricultural IPM Systems. Academic Press, New York.

Herzog, D. C. and J. E. Funderburk. 1986. Ecological bases for habitat management and pest cultural control. pp. 217-250. In M. Kogan (ed.), Ecological Theory and Integrated Pest Management Practice. John Wiley and Sons, New York.

Mack, T. P. and C. B. Backman. 1990. Effects of two planting dates and three tillage systems on the abundance of lesser cornstalk borer (Lepidoptera: Pyralidae), other selected insects, and yield in peanut fields. J. Econ. Entomol. 83: 1034-1041.

Reynolds, H. T., P. L. Adkisson and R. F. Smith. 1975. Cotton insect pest management. pp. 379-444. In R. L. Metcalf and W. H. Luckmann (eds.), Introduction to Insect Pest Management. John Wiley and Sons, New York.

Risch, S. J. 1987. Agricultural Ecology and Insect Outbreaks. pp. 217-238. In P. Barbosa and J. C. Schultz (eds.), Insect Outbreaks. Academic Press, New York.

Voss, R. H. and D. N. Ferro. 1990. Ecology of migrating Colorado potato beetles (Coleoptera: Chrysomelidae) in western Massachusetts. Environ. Entomol. 19: 123-129.

Voss, R. H., D. N. Ferro and J. A. Logan. 1988. Role of reproductive diapause in the population dynamics of the Colorado potato beetle (Coleoptera: Chrysomelidae) in western Massachusetts. Environ. Entomol. 17: 863-871.