T. Eugene “Gene” Reagan
Integrated pest management (IPM) has two distinctive components—economic protection from pest damage and a more favorable environmental outcome than would occur in the absence of IPM. Integrated pest management is a dynamic process and involves balance among biological, cultural and chemical measures deemed most appropriate to a particular situation after careful study of all factors involved.
The U.S. Environmental Protection Agency (EPA) has encouraged selection of Best Management Practices (BMPs) for major field crops. The BMP-developed practices for sugarcane entomology are to:
A goal of LSU AgCenter entomology research is to improve IPM in the Louisiana sugarcane industry. Although several insects threaten sugarcane, the larval stage of the sugarcane borer moth causes the greatest amount of injury. It is responsible for 90 percent of crop losses by insects. Because of adoption of pest management practices, the average annual number of insecticide applications for control of the sugarcane borer has decreased dramatically. For example, in 1960, the average number of annual insecticide applications was 12; now it is slightly less than one.
During the last 30 years, borer resistance and environmental concerns with fish and bird kills caused the review and termination of many effective insecticides in the sugarcaneindustry. In 1993, LSU AgCenter researchers began a study of a new class of insecticides called the MACs, or “molting accelerator compounds.” These insecticides affect larval growth. The first phase of the assessment involved a five-replication, 2-acre, summer study on the St. Gabriel Research Station, where fire ant predators are suppressed to allow for high borer infestations.
A follow-up experiment the next year involved a four-replication, 60-acre aerial application trial on a private farm in a heavy borer infestation area. In this test, the impact on secondary pests (such as the yellow sugarcane aphid) was studied along with length of control and yield loss from the sugarcane borer. Another important part of this study was an assessment of beneficial insects and other non-target arthropods like crickets and spiders. Fire ants eat crickets, which also help to sustain high numbers of arthropod predators, including spiders.
From among many insecticides evaluated in 1994 and 1995 (many causing a significant two- to three-fold reduction of beneficial insects), the only chemical not suppressing crickets and spiders was tebufenozide, which was soon labeled as Confirm. In classical biological control studies, borer parasites were exposed to leaves taken immediately from insecticide-treated field plots. Only one material (tebufenozide) did not kill the parasites.
To successfully implement this new environmentally friendly technology into the sugarcane industry, laboratory feeding studies were conducted. This work determined a sensitivity baseline and was used to show consultants that they could not rely on the traditional approach of making live and dead insect counts three days after application. With this new chemistry, the borer quits feeding but may not die for several more days.
LSU AgCenter research has shown that the MAC chemistry provides the first effective insecticide for control of the sugarcane borer with compatibility for parasite releases in classical biological control programs. Experimental field data indicate an enhanced length-of-control period in succeeding applications, because of both a less detrimental insecticide impact on beneficial arthropods and increased effects on other life stages of the borer. In 1998, the EPA presented its Presidential Green Chemistry Challenge Award to the invention and commercialization of this new chemical family of insecticides, represented by Confirm.
The narrow range of activity of tebufenozide is both an asset and a problem because it does not control secondary pests in sugarcane. Other insecticides must be used for other insect pests and potentially for resistance management of the sugarcane borer. As insecticide selection pressure increases in an area, the need to alternate insecticide classes also increases. Several other insecticides are necessary to control other sugarcane insect pests. Recently completed research on borer infestation sampling will also assist with changes in scouting procedures.
Pest management for soil insects in sugarcane has not achieved the environmentally friendly nature of sugarcane borer control. Economic thresholds have been established for wireworms. But when chemical insecticides are needed, their impact has the potential for substantially enhancing sugarcane borer infestations. Recent experiments indicate that the usual rate of a commonly used soil insecticide applied at fall planting can cause at least a 50 percent reduction of crickets and a 30 percent suppression of fire ants. As shown in Table 1, even with approximately two additional applications of insecticide for borer control, boredinternodes averaged 17.8 percent compared to less than 3 percent when soil pesticide was not used. For most varieties, 0.75 percent bored internode injury is comparable to a 1 percent loss in sugar yield.
In addition to hot, dry weather conditions, resistant varieties have the greatest potential for reducing areawide populations of the sugarcane borer. The pest management impact of varieties evaluated in the LSU AgCenter’s sugarcane variety development program involves assessment five to seven years before release to the farmer. To predict the impact of moth populations, both thepercentage of bored internodes (damage and yield loss), and the number of distinctive moth emergence holes are counted. Adult (moth) production on an areawide basis is compared by counting emergence holes from each variety plot. Even though the high-yielding variety LCP 85-384 is susceptible to the sugarcane borer, implementation of the new tebufenozide chemistry in borer management has made the production of this susceptible variety more feasible.
Two New Insects
During the last five years, two new insect pests have invaded the industry. One of these, the “white” sugarcane aphid, is the most damaging aphid on sugarcane worldwide. It is also capable of spreading yellow leaf virus, a disease new to sugarcane in Louisiana. Thus, IPM in sugarcane will need to continue to evolve and become more team interdisciplinary to address the new challenges presented by the ever-changing situations confronted by farmers in Louisiana.
Dale Pollet, LSU AgCenter entomologist, and Bill White, entomologist with the U.S. Department of Agriculture, Houma, La., for assistance and cooperation in this research.
(This article appeared in the fall 2001 edition of Louisiana Agriculture.)