Green stem is a disorder of soybean in which stems remain green and moist well past the point when pods and seeds are fully ripe and dry. Various names are used to describe the problem including green soybean syndrome and greening effect. Green stem disorder complicates harvesting by significantly increasing the difficulty in cutting and threshing affected plants during harvest. As a result, combine operators often must reduce ground speed and increase engine power, resulting in poor fuel efficiency and increased harvest time. Harvest delays also increase the chances of lodging, shattering, and seed decay that can reduce grain yield and/or quality.
The cause of green stem disorder is uncertain but it can be the result of several different potential factors. Specific causes of green stem syndrome vary from year to year and location to location, but are frequently associated with plant stress during pod and seed development (Holshouser, 2009). A common characteristic of plants exhibiting green stem disorder is that they have significantly fewer pods. Research at the University of Kentucky clearly established this relationship of increasing green stem disorder with a reduction in pod number. When a pod-aborting or seed-aborting stress is brief and most leaves remain intact, the inability of the crop to use any excess photosynthates can lead to green stem disorder. Therefore, a brief but significant period of stress during the reproductive stages can greatly alter the source:sink ratio in soybean and lead to green stem syndrome.
Previous experiments explored the impact of different depodding levels; however, there have been no attempts to identify the most sensitive period for green stem disorder expression. A better understanding of the effect of stress timing on the expression of this disorder would be useful to predict the occurrence and severity before its expression at harvest maturity. This would be helpful for harvest logistics and efficiency. The question we want to answer is: Can we connect stress timing with green stem disorder incidence and severity? Additionally, since the ultimate cause of green stem syndrome is thought to be reduced pod and/or seed-set, the ultimate goal of this research is to attempt to correct or minimize these yield-reducing factors to increase yields while reducing green stem syndrome.