Insect Pest Management for Cotton
Cotton production has historically involved the use of large amounts of pesticides. The eradication of the boll weevil from the Carolinas, Georgia and Florida has provided an opportunity to move pest management on cotton to a more sustainable system. The other major cotton pests such as the bollworm, beet armyworm, thrips and aphids are attacked by a wide variety of natural enemies that with proper management can suppress these pests. These beneficial insects can be of major value to the economic success of cotton and to the transition to more sustainable agriculture.
Three primary approaches to conserving habitats and enhancing the populations of beneficial predators include: reduced tillage, habitat enhancement through refugia strips within the crops fields or around their margins and reduction of pesticide use.
In this project, cotton producers working closely with USDA entomologists developed the following objectives for field trials on their farms.
1.) Identify and quantify the beneficial arthropods found in various conservation-tilled systems as compared to conventional agro-ecosystems.
2.) Evaluate the benefit of planting and maintaining beneficial-insect-enhancing plants, either in refugia strips within the field or as margins around the borders of the field.
3.) Quantify the biological and economic benefits of reduced pesticide use.
Pitfall traps were used in 1994 and 1995 to monitor and compare the seasonal abundance of ground-dwelling arthropods in cotton fields located in the Coastal Plains region of south-central Georgia. In 1994 traps were placed in a 50-acre conservation-tilled crimson clover/cotton field and in an adjacent 50-acre conventionally tilled field in Dooly County. In 1995, traps were also placed in a third field in Tift County planted with cotton and a series of six three-row, non-cultivated refugia strips. A second series of traps was placed in a perpendicular transect across the Tift County field to monitor density and dispersal of beneficial arthropods from the refugia strips into the cotton strips.
Commonly collected arthropods at all three study sites included two species of Collembola, Bourletiella hortensis (Sminthuridae) and Podura aquatica (Poduridae), the striped earwig Labidura riparia, the red imported fire ant, Solenopsis invicta and nearly 20 species of Carabid beetles. Several Staphylinid species and two Cicindelids, Megacephala carolina and Cicindela nr. sexguttata, were also common. Other abundant arthropods included spiders, primarily Wolf spiders (Pardosa) and Clubionids, and one species of centipede, nr. Lithobius forficatus.
Whole plant and sweep samples were also used in the same fields to monitor and compare the seasonal abundance of plant-dwelling beneficial and pest arthropods. Samples were also taken in a perpendicular transect across the Tift County field to monitor density and dispersal of beneficial arthropods from the refugia strips into the cotton strips.
Commonly collected pest arthropods at all three study sites included thrips, aphids, Aphis gossypii, the tarnished plant bug, Lygus lineolaris and four lepidopterous species, including the budworm, Heliothis virescens, bollworm, Helicoverpa zea, cabbage looper, Trichoplusia ni and soybean looper, Pseudoplusia includens.
Beneficials commonly collected included up to 15 species of spiders, the big-eyed bug, Geocoris punctipes, three species of ladybird beetles: Coccinella septempunctata, Hippodamia convergens and Harmonia axyridis, brown and green lacewings and the red imported fire ant, Solenopsis invicta.
All pest management decisions were made by independent consultants employed by the cooperators. Treatment decisions were based on established intervention guidelines.
Early in the season, thrips populations were generally lower in the clover field than in the conventionally treated field. Later in the season, thrips populations were comparable for both fields, but failed to attain economic levels in either field. Tarnished plant bug populations were reduced in the clover field relative to the conventional field.
Square retention counts in both fields remained over 90 percent; therefore, the cotton was not treated for plant bugs.
Eggs of the budworm and the bollworm were less abundant in the clover field than in the conventionally tilled cotton, which was also reflected in the number of heliothine larvae present in the two fields. Five insecticide treatments were required in the conventional field, four of them for bollworm/budworm controls, whereas only two treatments (one for bollworms and budworms) were necessary in the clover field.
In contrast to the researchers’ observations for heliothine eggs, eggs of cabbage and soybean loopers were observed in higher numbers in the clover field than in the conventional field. The number of resultant larvae, however, was reversed, with more larvae occurring in the conventional cotton than in the conservation-tilled field.
They contributed this difference in larval numbers to the increased activity of fire ants in the conservation-tilled fields. Although soybean looper populations became quite high, no insecticides were applied for control since loopers are considered a minor pest because they attack the foliage rather than the bolls.
Cutworms were rarely observed in either field. Aphid populations peaked earlier and attained higher levels in the clover field than in the conventional one. After these populations declined in both fields (due to the entomopathogenic fungus Neozygites fresenii and parasitoids and predators), aphids rebounded more rapidly and to higher levels in the clover field than in the conventional field. Again, the more rapid and extensive growth of aphid populations in the clover field can likely be attributed to the elevated activity of fire ants in the conventionally treated field.
The results indicate that the use of a leguminous cover crop, in conjunction with conservation tillage may provide considerable benefit for managing insect pests. It appears that one of the key components in the pest reductions observed in the clover field was the presence of fire ants. Their presence, however, may have been a function of reduced tillage rather than the use of a particular cover crop. Conventional tillage disrupts fire ant foraging and destroys ant mounds, whereas these disruptions are reduced in conservation-tillage systems.
In regions where the aphid-pathogenic fungus is present, the increased aphid populations occurring in conservation-tilled fields may present little difficulty. In other regions, however, the protected aphid populations may present serious challenges, including possible induction of secondary pests after treatments for aphid control.
Despite its apparent benefits, several agronomic problems were encountered with the crimson clover system. The cotton stand was reduced by nearly 20 percent in the clover field, resulting in a yield loss estimated to be 25 percent (final results are still being tabulated). In the coming season, the producers plan to make adjustments, such as increasing the seeding rates and the width of the tilled planting strips to improve stand and yield.
Two field days were held in 1995. On July 12, the Georgia House of Representatives Agricultural Committee and other invited policy makers visited the field in Dooly County as part of their review of farm usage. On August 21, growers from Arkansas and other southern states stopped at the Dooly County field for exchange of information about advances in sustainable cotton production systems.
A full review of the project complete with results to date were published in the proceedings of the 1995 Beltwide Cotton Conference. Final results are currently in preparation and will be published in the 1996 Proceedings.