Topic: Green stem syndrome is a condition where soybean pods and seeds mature while stems remain green, which may cause challenges during harvest.
Effect: Green stems are difficult to cut and are known to plug up combines.
Action: Waiting for a killing frost or using an approved herbicide might help aid in the drying of soybean stems.
As normal soybean plants mature and near harvest, leaves drop and stems lose their green color. In some fields, stems retain their green color although pods and seeds are mature. This phenomenon is known as green stem syndrome.
An exact cause for green stem syndrome is not known. Factors that may influence green stem syndrome include environmental conditions, viruses, insects (i.e. spider mites, soybean aphids, thrips, stink bugs), and the soybean product.
Under very warm and dry environmental conditions, pods and/or seeds may abort. When pods and/or seeds abort, the plant redistributes sugars and nutrients or photosynthate. This redistribution may increase the concentration of photosynthate in the stem causing it to retain its green color longer.
According to a study conducted by the University of Kentucky, when 25% to 50% of pods were removed from a soybean plant, pod maturation was not delayed, but stem maturation was delayed from as few as four days to a month or longer. Additionally, green stem syndrome was more pronounced when a higher percentage of pods were removed.
Soybean viruses and insect pressure can also result in green stem syndrome. Stress caused by bean pod mottle virus, soybean mosaic virus, tobacco ringspot virus, bean leaf beetle, and green stink bug can increase the occurrence of green stem syndrome. Symptoms may occur in isolated or irregular shaped patches. These viruses may also produce discolored and distorted seed, which can be diagnosed at harvest.
Fall drydown conditions could also be contributing to green stem syndrome. In some regions, low humidity coupled with warm temperatures may speed up grain drydown but not give stems enough time to dry due to a potential increase in photosynthate.
Any number of pod-reducing stresses may be responsible for green stem syndrome at harvest. Highyielding seed products may be more prone to lateseason pod abortion, as these plants would produce a higher number of pods early in the season.
Harvesting soybean plants with symptoms of green stem syndrome may be a challenge. Green stems are difficult to cut and are known to plug up combines. When harvesting soybean plants with green stems, the combine should be in good operating condition, properly adjusted with sharpened cutting knife sections, and operated at slower speeds. Always refer to the manufacturer’s manual before performing any maintenance.
Many of these fields are difficult to harvest because combines must handle dry and wet material at the same time. Seed moisture content from normal plants and plants with green stem syndrome can differ, which can further complicate harvest. At times, combines can plug up from green tissue.
Waiting to harvest until after a killing frost may be necessary, depending on the severity of the greenstem problem and the condition of the seed pods. However, waiting for a frost or for the stems to drydown may increase the risk of yield loss from pods shattering in the field during harvest.
One option growers may want to consider, if waiting on frost is not a viable option, is the use of herbicides that are labeled for harvest aids in soybean. Two important things to take into account if considering using a chemical harvest aid are the cost and variability of maturity in your fields. It is imperative to closely monitor your fields as yield may be diminished if your fields are not as mature as required by label.
Proper timing of harvest operations, management decisions, and making adjustments to combine settings are critical to reduce harvest losses.
1 Casteel, S. 2010. Green soybean stems and dry grain. Soybean Station. Purdue University Cooperative Extension. www.soybeanstation.org.
2 Egli, D.B. and Bruening, W.P. 2006. Depodding causes green-stem syndrome in soybean. Crop Management. www.plantmanagementnetwork.org.
3 Holshouser, D. 2009. Green stem syndrome in soybeans. Virginia Cooperative Extension. 2912-1430. http://www.ext.vt.edu.
4 Sprague, C. 2009. Harvest-aid options in soybean. Michigan State University Extension. http://www.msue.anr.msu.edu.