The Effects of Three Cultural Variables on the Incidence ofNomuraea rileyi, Phytophagous Lepidoptera, and Their Predators on Soybeans1

Abstract

The effects of soybean planting date, row width and seeding rate on populations of Plathypena scabra , Heliothis zea , Pseudoplusia includens , and their natural enemies Geocoris punctipes , Orius insidiosus , Nabis spp., Araneida and Nomuraea rileyi were monitored in a 3-yr study in North Carolina. Of the cultural variables, seeding rate had the least effect and planting date generally had the greatest effect on all populations except O. insidiosus . Early-planted soybeans in narrow rows at a high seeding rate generally had larger numbers of N. rileyi -killed larvae and a higher percentage of mortality of the total larval population due to N. rileyi . There is strong evidence to support the recommendation of planting soybeans early (before June 5) because yields were higher and parasitism (by N. rileyi ) and predation on the key pests were higher than on late-planted soybeans. When soybeans are planted late as a 2nd crop following small grain, planting in narrow rows at a high seeding rate maximizes the effects of N. rileyi and key predators.