大豆霜霉病分布于全国各大产区,尤以气温冷凉地区发生普遍,多雨年份病情加重。一般减产6%~15%,种子被害率10%左右,严重的达50%以上。叶部发病可造成叶片提早脱落或凋萎,种子霉烂,千粒重下降,发芽率降低。一、发病症状危害幼苗、叶片、豆荚及籽粒。最明显的症状是在叶反面有霉状物。在带病种子的病菌经系统侵染引起幼苗发病,但子叶不表现症状。大豆不同时期和部位霜霉病 Soybean Downy mildew distributed in the major producing areas in the country, especially in cold and cold areas occur generally, rainy years aggravating. The general reduction of 6% to 15%, the rate of seed damage is about 10%, severe up to 50%. Leaf disease can cause leaves fall off or withered earlier, mildew seeds, grain weight decreased, the germination rate decreased. First, the onset symptoms of seedlings, leaves, pods and grains. The most obvious symptom is a mildew on the opposite side of the leaf. Sick seeds in the disease caused by systemic infection of seedlings, but the cotyledons do not show symptoms. Soybean different parts and downy mildew