Field Validation of Speed Scouting for Soybean Aphid

Agricultural professionals are spending increasing amounts of time making treatment decisions for soybean aphid, Aphis glycines Matsumura. In an effort to reduce the time required to make treatment decisions, a binomial sequential sampling plan called "Speed Scouting" was developed for soybean aphid. In 2005, we validated Speed Scouting using commercial fields in Minnesota and replicated small plot trials in four states in the North Central Region of the USA (Iowa, Michigan, Minnesota, and Wisconsin). In commercial fields, yield (bu/acre ± S.E.) was significantly higher in areas of the fields where treatment was applied based on Speed Scouting (50.7 ± 1.7) compared to untreated controls (46.9 ± 1.6). When comparing treatment decisions based on Speed Scouting and whole-plant counts, the same decision was reached 79% of the time. Results from 5 of the 6 small plot trials showed no significant yield difference when aphid control decisions were made using Speed Scouting compared to whole-plant counts using an economic threshold of 250 aphids per plant. Speed Scouting is a conservative sampling plan, and consistently recommended treatment before populations reached the economic threshold using whole-plant counts. Using either sampling method, soybean aphid management should rely on multiple samples over time to accurately assess population growth rates to avoid unnecessary foliar applications.