Soybean drydown is occurring in rapid fashion, but if you look at fields and note mature brown pods while stems are still green, you may be seeing the effects of an issue known as green stem syndrome. While common in a few plants along field edges or randomly scattered throughout a stand, it can also affect large areas of a farm and make harvest a challenge.

Pinpointing the “absolute” cause of green stem syndrome is difficult. In short, as the plant dries down naturally, nutrients in soybean plant vegetative tissue is shipped to the developing seed. If there isn’t enough developing seed to absorb it all, it remains in stems (and maybe leaves as well), beyond the plant’s “normal” maturity. While not always a yield robber, it can reduce harvest efficiency and potentially contribute to declining seed quality/dockage as well.

Green stem syndrome is often associated with any factor that might result in less grain (sink) tissue than plant (source) tissue. They might include:

Disease: Bean Pod Mottle Virus, transmitted by the bean leaf beetle could reduce seed set.

Insect: stinkbug feeding on pods/seeds can reduce seed load

Genetics: plants predisposed to producing excess pods that might not always produce seed

Fungicide: the delayed senescence sometimes associated with applications might be misidentified as green stem

Weather: If we produce a large plant but weather inhibits pod set or fill, plants may not dry down normally

The best solution for green stem: reduce the stressors contributing to it. Since that’s not always possible, all we can do now is try to understand why it occurred as we plan for next season and be aware that harvest could be slowed if green tissue remains.