Soybean Disease Identification

As soybeans enter the full pod stage (R4), several late-season diseases may start appearing. The big three are sudden death syndrome (SDS), brown stem rot (BSR), and Sclerotinia white mold (SWM). Red crown rot is an additional disease to keep an eye out for this year.

Separation and correct ID of these diseases comes from a split stem and crown evaluation. Once identified, there are no curative measures that can be taken this season; however, noting areas of infection can help drive management for areas of positive ID in the future.

Sclerotinia White Mold 

High organic matter or muck soils, and areas with a history of SWM infection, are locations to scout. SWM is most noticeable from the road as soybeans enter maturity (R7). Infected plants will have brown or graying leaves in the upper canopy that will stick out from unaffected plants. As the development of the soybeans progresses, and leaves begin to drop, the plants impacted by SWM will retain their leaves and petioles, which is the structure that attaches leaves to the stem. The following are the ID characteristics for SWM.

• White, fuzzy fungal bodies on the stem and petiole
• Yellow or brown leaves that stay on the plant through maturity.
• Sclerotia on the outside and inside of the stem; these fungal bodies resemble rodent excrement.