Powdery mildew is more prevalent in cooler than normal seasons. While this disease is uncommon, when it does show up in fields, there can be noticeable yield loss. The most common and characteristic sign of powdery mildew is white, powdery fungal growth that can cover all aboveground plant parts, particularly the upper surface of leaves. Powdery mildew usually does not appear until mid- to late reproductive stages. Initially, small fungal colonies form and grow together as they enlarge. Eventually, entire surfaces of infected plant parts are covered with white fungal growth. Advanced symptoms include yellowing of plant tissues and premature defoliation. The fungus survives in infested crop residue. Favorable conditions include cool, cloudy weather and low humidity. Powdery mildew is frequently more severe in late-planted soybeans.
The best time to scout for this disease is R3 through R6. This disease is more prevalent in late-planted fields.
Variety selection: Most commercial varieties are resistant
Fungicides: Fungicides effectively manage powdery mildew; however, there are limited situations where fungicide use will be profitable.
Photo by Daren Mueller