Improving Integrated Pest Management in Sweet Corn System

Abstract

Corn earworm (CEW), Helicoverpa zea (Boddie), (Lepidoptera: Noctuidae) is a common insect pest of sweet corn in the United States. The larvae cause chewing damage on corn ears rendering them unmarketable. Traditionally, growers have controlled CEW in sweet corn using multiple applications of insecticides such as pyrethroids during ear development and/or by planting transgenic sweet corn hybrids that produce insecticidal proteins derived from the bacteria Bacillus thuringiensis. However, over the past decade, CEW populations have developed resistance to both the Cry proteins found in many of the Bt sweet corn hybrids and pyrethroid insecticides, which has made management of this pest difficult. In this thesis I investigate strategies that can help improve pest management for this difficult pest in sweet corn. First, I assessed the efficacy of two novel insecticides that could add different modes of action to the insecticide options in sweet corn; these included a product containing a suspension of nucleopolyhedrovirus particles that are specific to CEW and a product that contains insecticidal peptides derived from spider venom. These were tested in conjunction with Bt transgenic corn to enhance their efficacy. Unfortunately, neither of the insecticides provided any effective level of control of CEW. Additionally, I assessed if sweet corn growers could reduce their frequency of insecticide applications by spraying based on a moth capture action threshold compared with standard frequent insecticide applications applied every 2-3 days. I found that a spray program using thresholds as well as more IPM-compatible insecticides provided similar levels of control while reducing the number of sprays needed. In other studies, I assessed the non-target risks of the different insecticides commonly used in sweet corn. I examined the potential for bifenthrin, spinetoram, and chlorantraniliprole to repel bees and other beneficial arthropods after application in sweet corn; repellency could impact their risk of nontarget effects by reducing exposure. I found that there was no significant effect on the number of times honey bees visited the corn tassels or the number of other beneficial arthropods found. Lastly, I examined the residual toxicity of bifenthrin, spinetoram, chlorantraniliprole, and isocycloseram on lady beetles (Coleoptera: Coccinellidae) after 2, 4, and 6 days in the field. I found there was higher mortality in the bifenthrin and isocycloseram treatments across all three application dates than spinetoram, chlorantroniliprole and untreated control.