Effect of foliar fungicide and insecticide on hail-damaged soybean

Abstract

A fungicide (pyraclostrobin) and an insecticide (alpha-cypermethrin) were applied alone or in combination to hail-injured soybean to determine if yield could be preserved or foliar disease prevented. Pesticides were applied at approximately R3 growth stage and hail injury was simulated with an ice-propelling machine at approximately R1 and R4 growth stages over three years at three Iowa locations. Disease severity was low throughout the study, and included Septoria brown spot, downy mildew, and Cercospora leaf blight. Differences in disease severity among treatments receiving hail and those that did not receive hail were not consistently detected. More importantly, foliar disease severity did not differ among pesticide treatments and untreated controls. Simulated hail caused significant (P = 0.1) yield loss. No difference in yield was observed between untreated and pesticide-treated plots within hail events, except for two site years when hail damage occurred at R1. Seed moisture was generally higher in plots with R1 hail damage. Fungicide and insecticide applied in combination to hail-damaged soybean was more likely to result in a positive economic return than either applied alone. Based on results, R3 fungicide application to soybean injured by hail at R1 or R4 will likely provide little yield-preserving or disease-limiting benefits when foliar disease severity is low.