Decision Models for Fungicide Applications for Soybean Rust

Abstract

Soybean rust (SBR), caused by Phakopsora pachyrhizi, can be a devastating disease to southeastern U.S. soybean (Glycine max) production. Fungicides can be applied to avoid yield loss, but growers need to know when an application will be most beneficial. To better understand and manage SBR epidemics in the southeastern U.S., fungicide application decision models were developed and validated. Application decision models were developed based on SBR presence and hours of leaf wetness or amount of cumulative rain and compared to non-treated controls and applications based on crop growth stage. The models were evaluated in 2009, 2010, and 2011. High disease pressure and conducive weather conditions in 2009 resulted in significantly greater disease severity and lower yields in non-treated plots compared to treated plots. In 2010 and 2011, low disease pressure and drought conditions resulted in no significant differences in disease severity or yields among most treatments. Results indicate two fungicide applications during early reproductive stage can reduce yield loss due to SBR, but subsequent applications need to be determined based on disease pressure, weather conditions, and crop growth stage. Accepted for publication 1 March 2015. Published 1 May 2015.