A multi-pronged approach to organic soybean pest management

Annual certified organic soybean production in the U.S. was listed at 125,621 acres in 2011. Organic soybeans grown in Iowa are destined for foreign and domestic tofu and soymilk markets and for organic livestock feed. Food-grade soybeans are bred for a specific seed size and protein requirement. In addition, the market requires a white seed color, which affects aesthetics rather than food quality. The soybean aphid (Aphis glycines) is native to China and Japan, and was observed in Iowa beginning in 2000, reducing yields by direct feeding, and interfering with photosynthesis and growth. Another key pest, the bean leaf beetle (Cerotoma trifurcata), consumes leaves and may open infection sites for seed-staining fungi, in addition to vectoring bean pod mottle virus, which discolors the seed coat. Seed coat staining from Cercospora kikuchii, Fusarium spp., soybean mosaic virus, or bean pod mottle virus can lower the price received for food-grade soybeans. Reducing the extent of soybean staining is therefore of great economic importance to organic producers who rely on the premiums associated with unstained seed. The goal of this project is to find effective organic soybean pest management strategies, including organic-compliant treatments, to help producers maintain the premium price received for unstained organic soybeans. Organic farmers utilize habitat modification (e.g., insectary plants) and delayed planting to encourage beneficial insects and escape early pest emergence. Overall, organic-compliant pest management treatments, including neem, karanja, pyrethrum, and microbials, did not decrease bean leaf beetle levels below that of the control treatment. The most effective method of managing soybean aphid included resistant varieties, but neem-based products also lowered aphid populations. Beneficial insects were not harmed by these treatments, but their population numbers alone were insufficient to maintain low pest levels. A systems approach is warranted for improved eco-functional intensification in organic soybean production.