Sclerotinia sclerotiorum mainly infects ginseng roots for more than three years, and seedlings are rarely harmed. Although the disease is not common, it will also cause losses once it occurs.

(1) Sclerotinia sclerotiorum only infects underground roots and rhizomes. Root infection is soft rot. At first, there was a small amount of white hyphae on the surface, and then irregular black granular sclerotia of rat feces was formed. In the end, the internal organization corruption disappeared, leaving only skins. The disease develops rapidly and it is difficult to identify it early. The early stage is almost a healthy plant. When it was found withered, the ginseng root had already festered. Once the disease occurs, it spreads very fast (Figure 36). (2) The cause of the disease Sclerotinia sclerotiorum overwinters on the diseased remains and in the soil, and begins to infect when the ground temperature is 2℃ in early spring. The disease is easy to occur in early spring and late autumn when the soil is low temperature and humid, and generally occurs after thawing in April-June and before emergence, and basically stops spreading after June. When the soil temperature is above 2℃, the disease begins, when the soil temperature is between 6℃ and 8℃, the disease is serious, and when the soil temperature exceeds 15℃, the disease is mild or stops spreading. When the soil temperature is above 20℃ and the humidity is too high, the roots of diseased ginseng will rot quickly. The peak of the disease is from soil thawing to seedling emergence. High soil moisture, low ground temperature, poor drainage, poor air permeability or excessive nitrogen application are all prone to this disease. Too much precipitation before soil freezing, and then cooling and freezing, bed soil moisture is also prone to diseases. (3) Prevention and control methods ① Strengthen field management and dig drainage ditches to prevent excessive water from flowing into ginseng beds after the snow and ice melt in early spring, so as to avoid the soil from being too wet and hardened. Pay attention to protect seedlings when transplanting, prevent seedlings from freezing injury, reduce disease resistance, and remove cold-proof materials as soon as possible when crossing wetlands. Diligently loosen soil, increase soil permeability and raise soil temperature.

Pay attention to prevent slow sun freezing injury in spring and autumn. If a diseased plant is found in the field, it should be pulled out immediately and the surrounding soil should be disinfected to control the spread of the disease. ② Chemical control: After planting cold-proof soil, disinfect the bed surface, bed ditch, walkway and ginseng ground with 1% copper sulfate solution. One week before transplanting American ginseng, 20 grams of 50% carbendazim wettable powder was evenly mixed in every square meter of ginseng land, which had good control effect on American ginseng Sclerotinia sclerotiorum.

Fig. 36 Symptoms of Sclerotinia sclerotiorum