Effect of Pod Removal, Foliar Fungicides, and Cultivar on Green Stem Disorder of Soybean

Green stem disorder (GSD) is a type of delayed maturity of soybean [ Glycine max (L.) Merr.] when stems remain green and fleshy aft er pods reach physiological maturity and are ready to harvest. Although GSD has not been shown to directly impact yield, the immature green stems may lead to harvest issues. The objectives were to determine how GSD is affected by (i) cultivars and levels of pod removal, (ii) foliar fungicide applications, and (iii) a combination of pod removal and foliar fungicides. A source-sink imbalance caused by abiotic and biotic sources (e.g., drought or pathogen infection) may be a contributing factor to the development of GSD. To simulate a sink-limiting stress and induce GSD, pods were removed from soybean plants, at magnitudes typically not seen in normal field conditions. Experiments were completed during 2014 and 2015 in Iowa. Higher levels of GSD were observed in 2015 across most locations. Cultivars varied in their response to pod removal within specific levels. Combining pod removal and fungicide application indicated that certain quinone outside inhibitors (QoI)-containing fungicides may result in more GSD with and without pod removal under specific conditions. However, this result was inconsistent, especially with no soybean pods removed. Soybean farmers should be aware that prophylactic applications of foliar fungicides might increase GSD incidence, especially in cases that plants experience a sink-limiting stress.