Characteristics and control of walnut canker

   1, distribution and occurrence characteristics were distributed in most walnut producing areas. The pathogen was mainly mycelium overwintering in the current year, and began to move when the temperature rose to 11.4 ~ 15.3 ℃ in April of the next year. A large number of conidia formed in late May, spread by wind and rain, and mostly invaded from wounds (frostbite, burn, mechanical injury or insect injury, etc.), and the incidence reached the peak. The disease basically stopped spreading in late June. When the temperature and humidity were suitable in autumn, the disease developed again, but it was not as serious as in spring. The incubation period of the disease is 15-60 days. The disease is common and serious in areas with poor soil, heavy clay, poor drainage, high groundwater level and poor tree growth.

   2, pathogen and damage symptom is a kind of fungal disease, which mainly harms the trunk, twig and fruit of young walnut trees, which can cause early fruit drop, reduce fruit quality and yield, and cause plant growth weakness, withered branches or whole plant death in serious cases.

   is harmful to the main and lateral branches of walnut seedlings and trees, and often occurs at the base of the trunk. Within 5 minutes 1. 0 meters. The initial lesion is brown and black with a diameter of 0. 5%. 1cm to 2cm, some expanding into wilt-shaped or long-striped spots. On the young and smooth bark, the disease spot is waterlogged or obvious blisters, brown mucus flows out after rupture, and the air becomes dark brown, and then many small black spots are scattered in the disease part. in severe cases, the disease spot is connected in the shape of a diamond or long strip, infiltrating around, so that the whole disease spot is watery, dark brown in the center, light brown all around, and no obvious edge. In the later stage, the disease spot is withered and sunken, with a small crack in the center, and many small black spots are scattered on it, which is the germ meristem. The phloem and endodermis of diseased trees are rotten and necrotic, brown or dark brown, sometimes as deep as xylem. After the fruit was damaged, it showed brown round spots of different sizes, which fell early, shrunk or became black and rotten.

   3. Prevention and control methods

  ① can prevent drought and waterlogging, open ditches and drain water, and lower the groundwater level.

  ② should avoid mixed planting with susceptible maple poplar, black locust or poplar to avoid cross-infection.

  ③ trunks are painted white. Whitening agent formula: quicklime 5 kg, salt 2 kg, oil 0. 5 kg. 1 kg, 20 liters of water.

  ④ chemical control. From April to May and August, the branches were sprayed with 50% methyl topiramate wettable powder 200 times or antibiotic 402 EC 200 times once. Scrape or cut the diseased skin with a knife, reaching to the xylem, and then apply 3-5 Baumetolite sulfur mixture or 2% copper sulfate solution, 10% alkali water (sodium carbonate), 10% carbendazim 50 times solution and so on.