Matthew E. Baur, Louisiana State University Agriculture Center, 402 Life Sciences Bldg, Department of Entomology, Baton Rouge, LA 70803
Insect defoliaton causes yield losses, especially when it occurs during reproductive stages susceptible to this type of stress. This fact is well documented with full season soybean varieties and these varieties have historically been the most susceptible to insect defoliation in the Southeastern US. Determination of levels of defoliation caused by insect defoliators and the effect of defoliation on yield was necessary information in the determination of economic injury levels for insect defoliators. However, production practices have shifted to shorter season varieties, planted earlier, and grown in narrow rows in much of the US where soybeans are susceptible to insect defoliation. These changes have altered the affect insect defoliators have on soybean production. The critical element in the study of insect defoliation is how defoliation affects light interception. Recent work has demonstrated that any factor (defoliation, competition, drought) that affects light interception will affect yield similarly. Therefore, the entire question of insect defoliation can be shifted to studies on the effect of light interception on yield, and in this way the results are much more broadly applicable across different production practices and stress factors. While studying light interception is conceptually much more appealing, its application is more problematic. For instance, how does one scout light interception? How does one develop recommendations (concerning insect control, row width, variety, water managment, weed management, disease management, etc.) based on light levels? Although data in this area are limited, we will discuss several hypothetical solutions to these questions.