うどんこ病
Powdery mildew of soybeans is an important pathogen and tends to cause epidemics about every 10–15 years in Wisconsin. In 1975 the first epidemic there was observed and several have occurred since. Powdery mildew affects the soybean plants. When 82% of the soybean leaf area is covered by "M. diffusa", photosynthetic and transpiration rates are less than half of normal soybeans, thus affecting soybean yield. Different studies have found different amounts of yield reduction due to the powdery mildew. In Illinois, measured yield losses ranged up to 14 percent. From Iowa studies, measured yield losses were estimated up to 10 bushels per acre. In Wisconsin, the yield loss was up to 5 bushels per acre. And it's important to note that yield loss due to powdery mildew will be greater for soybeans planted late for a region compared to early-planted soybeans.