Characteristics and control methods of walnut powdery mildew

   1. Distribution and occurrence characteristics is one of the most common and important diseases in walnut production areas in China. The disease seriously affects the yield and quality of walnut in the current year and the tree potential in the following year. The pathogen overwinters on fallen leaves or diseased shoots with a closed capsule. When the temperature rose in the next spring, Rain Water became sick from July to August when the temperature rose, the closed capsule swelled and ruptured, and the ascospores spread to the young bud shoots and leaves with the air flow. After the onset of the disease, conidia were produced many times for re-infection. Small grains are produced on the diseased leaves in autumn, that is, the closed capsule, which overwinters with the fallen leaves. Warm and dry, with more nitrogen fertilizer and less potash fertilizer, it is easy to develop when the branches are not fully developed, and young trees are more vulnerable than big trees.

The picture shows walnut

   2, pathogen and damage symptom is a kind of fungal disease, which is caused by two kinds of pathogens: Streptomyces walnut and Streptomyces walnut. In order to damage leaves, buds and shoots, resulting in early defoliation, and even seedling death. In the early stage of the disease, the leaves faded or caused macula, but in severe cases, the leaves were twisted and wrinkled, fell off early, the buds germinated and could not spread the leaves, and a thin flake-like powdery layer appeared on the front or back of the leaves, and brown or black particles were produced in the white powder in the later stage. or the powder layer disappeared and only black particles were seen, that is, the sexual stage of the pathogen. When the seedlings are damaged, the plant is short, the top dies, and even the whole plant dies.

   3. Prevention and control methods

After   ① harvest, the diseased and residual branches and leaves were removed and burned centrally to reduce the source of infection.

  ② chemical control. 0. 5% can be used at the initial stage of the disease. 2. 0. 3 Pomedo stone sulfur mixture spray wine. In summer, 50% methyl thiophanate wettable powder 800 / 1000 times or 25% trimethoprim 500 / 800 times were sprayed, and the latter had better control effect.