Soybean Yield Decisions: Interactions of Variety, Planting, and Foliar Protection.

Increasing soybean yield is based on many agronomic management decisions including variety selection, planting date, and foliar protection from diseases and insects. Twelve treatments (2 x 2 x 3 factorial: planting dates, varieties and foliar products, respectively) were arranged in a randomized complete block design with 6 replications. Varieties AG3402 (untreated seed) and AG3539 (Acceleron-treated seed) were planted late April and late May in 76-cm rows in Lafayette IN, Urbana IL, and Seymour IL in 2010. Headline® (pyraclostrobin), Headline® + Respect® (dimethylcyclopropane carboxylate) and untreated control (UTC) were applied at R3 growth stage across the variety and planting date combinations, which were mid July for the April planting and late July for the May planting. Data collection included plant stand (~V2, harvest), disease ratings 0, 28, and 42 days after application, pod counts at R8, stay green (1-9), lodge (1-5), test weight, grain moisture, yield, protein, oil, and seed mass. Insect pressures were minimal throughout the season with some Japanese beetles, stink bug, and bean leaf beetles. Thus, insecticide applications did not add yield protection in 2010. Disease ratings provided a basis for yield differences among variety and foliar combinations. The severity of Septoria brown spot was moderately high and thus, yield protection was observed with Headline® applications in 2010. Adding foliar protection for diseases and insects, regardless of pest thresholds, did not raise the yields of the late-planted soybean varieties to the same level as the April-planted soybean varieties without foliar treatments.