Keeping Soybeans Green: Benefit or Bane?

Dan Davidson, Agronomist PhD, CPAg, CCA

Is it good for yields or a challenge for harvest when crops have stay-green characteristics?

One of the things growers have learned about high-yield corn production is that keeping foliage greener for longer improves overall plant health, stalk integrity and yield, while preventing rots and molds from infecting the plant and ear. Growers achieve stay-green by selecting the right hybrids, applying fungicides and minimizing stress. The benefits include higher yield, better standability and less ear drop. However, the downside of these characteristics is that stalks resist insect wounding and disease, and decomposition is tougher, leading to residue management challenges.

Will soybeans experience the same benefits and disadvantages?

Green Foliage: Planning and managing for plant health are good yield strategies. Yield is based on photosynthesis and biomass and its longevity. To get yield, you need to keep the foliage as green and healthy for as long as possible. In soybeans, the two main tactics include selecting varieties that have resistance to local diseases and applying a fungicide or insecticide at R3 to protect foliage at the beginning of pod fill.

One of the new lines of products coming to market are what I call stress alleviators that enable the plant to better handle stress. Companies such as Plant Impact and Crop Microclimate Management market Fortalis® and Photon, respectively, that help soybean plants resist later season stress that tends to shut down the plant and leads to pod abortion or premature foliage loss. Some growers have tried applying nitrogen, potassium or micronutrient applications at R3 to reduce stress and keep the plant from prematurely moving nutrients from leaves, stems and roots to the seed. Foliar micronutrients, biostimulants or other biologicals have been touted as stress relievers and yield enhancers.

Green Stem: One of the concerns with soybeans staying green too long is green stem syndrome (GSS). This refers to soybean plants that have green stems (and even green foliage) after pods have matured. These plants create problems at harvest since they slow down the threshing process through the combine and can damage bean seeds. Green stem syndrome results from several possible causes, including viral infections, insect feeding and certain environmental stresses. There is also a physiology link that suggests when a soybean plant produces more carbohydrates than the seed growth demands, the resulting pool of carbohydrates in reserve may cause the plant to stay green longer.

To answer the original question, green stem doesn’t appear to increase soybean yield. However, it can put yield at risk at harvest. Extra care should be taken to make sure the threshing process does not lose any additional beans by using a draper head, cutting at a slight angle to the row and making sure the threshing unit is in good shape and properly adjusted. You can also wait until hard frost kills the stems and they dry down. But by then the pods will be so dry that shattering is a real possibility.

Green stem is what it is, and seems related more to environment than genetics. Improvements in management that lead to better plant health and hopefully higher yield, however, can moderate this risk in some years.

Dan Davidson is a PhD agronomist, part-time farmer and soybean expert from Nebraska who consults with soybean checkoff and industry on crop production, marketing, and product development projects.


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