Bean Binoculars Incident

Irregularly shaped lesions that are pale-green in color were scouted on R4 (full pod) soybeans in south central Ohio. The lesions were identified as Downy mildew, which is caused by the oomycete Peronospora manshurica. Older lesions will turn brown and may have yellow margins. Another potential foliar symptom of downy mildew is a fuzzy gray growth on the underside of lesions. Infected pods may be covered in a white fungal mass and infected seeds are often smaller with cracks in the seed coat and a dull white color.  

While downy mildew is a relatively common, minor disease, it rarely causes yield loss in soybean. Most foliar fungicides for soybean are not labeled for downy mildew. Burying infected crop residue and crop rotation may reduce pathogen levels.