Soybean Pod and Seed Rots

• Excessively wet and warm conditions following maturity can negatively affect seed quality and yield in soybeans by causing pod shattering, seed sprouting in the pods, and growth of fungal diseases.
• Conditions favoring pod and seed rots in mature soybeans can result from extended periods of above-average rainfall and temperatures or from extreme rainfall events often associated with hurricanes or tropical storms.
• There a few common fungal pathogens that infect soybean pods and seeds causing reductions in yield and seed quality.

Cercospora Leaf Blight and Purple Seed Stain

• Caused by the fungal pathogen Cercospora kikuchii, which attacks both the leaves and the seeds of soybeans.
• Seeds are infected through their attachment to the pod, the hilum. Infected seeds may show a pink to pale or dark purple discoloration, which varies in size from specks to blotches to the entire seed coat.
• Sporulation occurs under conditions of high humidity and temperatures of 75ºF or higher. Sporulation increases as temperatures rise above 80ºF.
• Spores carried by wind and water infect leaves and stems. Infection may remain latent until favorable conditions develop during soybean pod-fill stages.
• Cercospora diminishes seed appearance and quality, but usually does not decrease yields significantly.

Anthracnose

• Anthracnose in soybean is primarily caused by the fungal species Colletotrichum truncatum in the Midwestern U.S.
• Anthracnose can infect stems, leaves, and pods of soybean.
• Infected pods may be completely filled with mycelium and can have no seeds or fewer/smaller seeds form. Seeds that do form may be discolored, shriveled, and moldy.

Opportunistic Fungi and Bacteria

• Opportunistic pathogens are those that are normally associated with degradation of crop residue.
• Once the plant tissue is dead, it can no longer defend itself against these pathogens and is susceptible to infection.
• Soybean plants that remain in the field for extended periods following maturity can be degraded by opportunistic pathogens when conditions are favorable for diseases.

• Fungal pathogens that commonly infect soybean pods and seed overwinter in crop residue, so are present in essentially all soybean fields at some level.
• The severity of infection that actually occurs is largely determined by the favorability of weather conditions.
• Soybean seed quality problems are often the result of an unusual confluence of weather conditions that both delay harvest and provide a uniquely favorable environment for fungal diseases.

• Soybean seed quality issues associated with abnormally warm and wet conditions after maturity inpacted a large area during the 2018 growing season.
• In general, seed quality issues tended to be more prevalent in earlier-planted soybeans.
• Problems did not appear to be associated with any particular soybean maturity groups or varieties. It is likely that the interaction between maturity timing and weather conditions was the primary determinant of seed quality problems in a given field.
  • Soybean plants that are mature and weathering in the field under conditions favorable for disease are highly prone to infection.
  • The longer the soybeans remain in the field before harvest, the more time diseases have to work.
  • Soybeans easily take up water, which can cause seed swelling and pod splitting and increase susceptibility to diseases.
  • Warmer temperatures drive faster fungal growth.
• Effects of foliar fungicide applications varied in terms of preventing yield loss from pod and seed diseases in 2018.
  • In many cases it appears there was no effect. An application made around the typical timing (R3 stage) would not have any activity left to control pathogens invading the mature plant late in the season.
  • In areas with heavy frogeye leaf spot pressure, more consistent yield benefits were observed, particularly on soybean varieties with lower genetic resistance. 

• Affected fields should be harvested as soon as feasible to prevent further loss of yield and quality.
• If soybean plants have retained green foliage due to wet conditions, a desiccant may be needed.
• Soybeans should be dried down to 11% moisture to inhibit fungal growth, aerated, and delivered as soon as possible.
• Soybeans should be dried at temperatures between 100 and 130ºF. Higher temperatures can cause damage to the seed.
• Damaged soybeans can be blended with good quality soybeans, if possible.
• Growers should open a claim with their crop insurance provider if there is a concern over soybean quality and yield.

• Seed quality problems are often the result of a highly unusual set of weather conditions that favor disease growth and delay harvest, so there are often no simple management changes that could have prevented problems or that will prevent problems in the future.
• In general, anything growers can do to reduce the amount of time mature soybeans remain in the field before harvest will help reduce the potential for seed quality issues.