Evaluating foliar fungicides, insecticides
Soybean aphids averaged 320 aphids per plant at the Sutherland location, which exceeded the economic threshold of 250 per plant. Aphids did not reach the threshold at any other location. At Sutherland, the IPM insecticide and insecticide+fungicide treatments were applied at the R4 growth stage on Aug. 3, which was 13 days after the R3 application. IPM treatments were not applied at the other five locations.
Seed moisture ranged from 8 to 11 percent depending on the location, but did not differ more than a few tenths of a percentage amongst treatments within any location.
The results of this experiment illustrate the benefits of foliar fungicide and insecticide applications for the management of foliar diseases and insects. There were very small amounts of foliar disease across the state of Iowa in 2011 due to high heat and low rainfall amounts in July and August. Also, this was a moderate soybean aphid year across much of the state. At the four locations with very low insect populations and disease severity, there were no significant yield responses to either insecticides or fungicides. However, at the Ames location, fungicides reduced frogeye leaf spot in the upper canopy and the largest yield responses to fungicides were at this location.
Also, only one of the six locations (Sutherland) reached the threshold level to spray aphids and this was the only location where all insecticides had significant responses to insecticides. Using foliar fungicides and insecticides is an effective way to prevent yield losses to foliar diseases and insect pests. Also, only applying pesticides when needed can reduce overall production costs and preserve product efficacy for when severe outbreaks do occur.