Symptoms The disease mainly affects the leaves, stems, flower organs, and seed pods. It produces near-radial white patches. The mycelium is born on both sides of the leaves, and the entire surface of the leaves, pedicels, and pupa is often covered with white powder. The powdery mildew conidia and conidia, the incidence of light lesions are not obvious, only a slight deformation of the capsule; disease severity leaves chlorosis and early yellowing, seed thin.
The pathogen Erysiphe cruciferarum (Opiz) Junel1 is known as the powdery fungus of the cruciferous family and belongs to the genus Ascomycete. Synonyms Erysiphe communis (Wallr. & Fr.) Link, Erysiphe martii Lev. The closed capsule shells are clustered to scattered, flat spherical, dark brown, diameter 88-125μm, with 7-39 appendages, attached filaments generally not branched, individual irregularly branched 1 times, often zigzag, long 70-256μm, 1-2 times the length of the closed capsule shell, containing 5-7 ascants in the shell. Ovule ovate to obovate, many stipitate, few sessile or sessile, size 55.9-76.233.0-40.6 (μm), containing 4-6 ascospores. Ascospores oval to oblong, yellow, some with oil droplets, size
16.4-23.812.2-15.4 (μm). The conidia were columnar, size 27.9-43.212.7-17.8 (μm). In addition to infecting rapeseed, this strain can also infect cassia, mustard, cabbage, and cabbage.
Transmission routes and conditions In southern parts of the country where cruciferous vegetables are planted throughout the year, they are mainly propagated by mycelium or conidia on cruciferous vegetables. In the north, the cystic shell overwintered on the diseased body, becoming the primary source of infection in the following year. When the conditions are appropriate, the ascospores are released and spread by wind and rain. After the onset of disease, the diseased part also produces conidia for repeated infections, resulting in epidemic disease. Drought, with low rainfall, is prone to onset, and when it is sunny and rainy, high temperatures and high humidity alter the infection and the disease spread, resulting in severe disease.
Prevention methods (1) Selection of disease-resistant varieties such as New Oil 8th and 9th. (2) Adopt formula fertilization technology, increase phosphorus and potassium fertilizers appropriately, and increase host disease resistance. (3) Spray 2% Wuyimycin (B0-10) water 200 times or 40% polysulfide suspension 600 times, 40% Fuxing Emulsion 8000-10000 times, 15% triadimefon wettable powder 1500-2000 times liquid, 12% green milk copper emulsion 500 times. Some varieties of rape are sensitive to copper preparations and they should be strictly controlled in order to avoid phytotoxicity.
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