Downy Mildew of Soybean

We have been receiving lots of reports of downy mildew of soybean throughout the state. Downy mildew is common disease of soybean that rarely affects soybean yield in the state. Based on our own observations and comments from growers and consultants, the increased incidence of downy mildew appears to be somewhat variety dependent. Downy mildew is caused by the fungus Peronospora manschurica. Symptoms of downy mildew are typically found on the upper surface of young soybean leaves. Spots of downy mildew are green to light yellow that can enlarge into bright yellow spots. Also, during periods of high humidity, the spots will look slightly gray and fuzzy when looking at them from below. As the lesions age, they may become brown with a yellow border. Depending on soybean variety, there may be a leaf distortion that may look like virus symptoms.