The so called "green stem" disorder was seen in almost every soybean field scouted the first week in October according to Emmanuel Byamukama, SDSU Extension Plant Pathologist.
Byamukama explained that the characteristics of this disorder include delayed senescence of stems and occasionally leaves. Plants with this disorder are randomly dispersed in the whole field without any particular pattern at the field edges or center of the field.
"Both cases of green stems without leaves still attached and green plants with leaves still green can be found in soybean fields around this time of the soybean growing season," he said.
The green stems cause problems at harvest by clogging the thrasher on the combine. Byamukama said that adjusting ground speed and increasing engine power can help in avoiding blockage of the thresher. However, he added that this action increases fuel consumption and harvest time.
"Another strategy of minimizing impact of green stem disorder is delayed harvesting until after hard frost to dry down all plants still green. However, delayed harvesting has its disadvantages including pod shattering and increased seed decay caused by fungal pathogens," he said.
What causes green stem?
Several factors have been thought to be causing this disorder including viruses, stink bugs, bean leaf beetles, fungicides, late herbicides, and late planting/emergence.
"However, recent research data in the region has shown that viruses and insects are not the absolute cause of the green stem disorder because not all plants that had viruses or were fed on by various insects developed green stem disorder. It is possible that insects will be attracted to plants remaining green in the field increasing the chance to transmit viruses. Research on the exact cause of this phenomenon is still on-going.," Byamukama said.
A most recent research study out of Illinois demonstrated that increased incidence of green stem disorder depended on fungicide application, application timing, location, and cultivar used.
Byamukama said growers noticing increased number of plants with the green stem disorder in soybean should take records of cultivar planted and fungicide applied and time of application and change cultivars and timing of fungicide application the following season.