First, symptoms: fruit lesions are dark brown spots at first, and then expand into round or irregular black spots. There is no obvious edge, and it is surrounded by waterlogging. At the onset, the center of the lesion sank, cracked and turned gray, and the fruit was slightly deformed. When the damage is serious, the whole fruit will turn black and rot quickly, and the fruit will fall early. When the young fruit is sick, because the endocarp has not hardened, bacteria can spread inward and make the nucleolus rot. When the fruit is close to maturity, because the core-shell gradually hardens, the disease is limited to the exocarp, and the harm is less. The lesions on the leaves first appear small black spots along the veins, and then expand into nearly round or polygonal black-brown lesions with translucent halo at the outer edge, mostly in the form of water stains. In the later stage, the center of the lesion is gray or perforated, and in severe cases, the whole leaf turns black, brittle and incomplete. The diseased spots on petioles and twigs are oblong or irregular, dark brown and slightly concave, and the diseased spots surround the branches, causing the twigs to wither and fall leaves.
Second, the incidence law: the bacteria overwinter in diseased branches, ulcer spots, bud scales and diseased fruits. The next spring, infected pollen spread to leaves and fruits through rain or insects, and was reinfected many times. Bacteria invade from wounds, hair holes or stigma. The incubation period of pathogens is generally 10- 15 days. The onset and severity of diseases are closely related to rain. In rainy years and seasons, the onset is early and serious. In Shandong, Henan and other provinces, it generally starts in the middle and late May, and the peak period is in June-July. Walnut has high planting density, dense crown, poor ventilation and light transmission, and serious diseases. Generally speaking, local walnuts are less susceptible to diseases than Xinjiang walnuts, weak trees are heavier than strong trees, and old trees are heavier than young trees.
Control methods: (1) Select disease-resistant varieties, reasonable planting density and reasonable pruning, so as to make the tree structure reasonable, the branches and leaves evenly distributed, and maintain good ventilation and light transmission conditions. (2) Strengthen fertilizer and water management, improve tree vigor and enhance disease resistance; Cut or remove diseased branches, leaves and fruits in time, and burn or bury the peel of walnuts after harvesting to reduce the source of overwintering bacteria. (3) Prevent pests such as walnuts in time, and use sticks as little as possible when picking fruits to avoid damaging branches, reducing wounds and reducing the chance of bacterial infection. (4) In the first half of March before germination, carefully spray sulfur and a mixture of sulfur once. Spraying 70% thiophanate methyl and streptomycin sulfate once every 15 days from May to July after germination and flowering can be used alternately with ethylicin, copper oxalate or 1: 0.5: 200 bordeaux solution to prevent drug resistance.