1. Symptoms

The leaves are injured. In the early stage of the disease, light yellow spots with inconspicuous edges appear on both sides of the leaves, and then the lesions appear with white slightly raised vesicles, about 1 to 5 mm in size. After maturation, the epidermis breaks and white powdery substances, namely the spores of the pathogen, are released. bag. When the diseased spots are prolonged, the leaves are withered and yellow. The pedicel of the seed plant is infected, the flower axis is swollen, and it is distorted and deformed.

2. The route of transmission and the law of disease

The disease is caused by the infection of the white rust and white rust fungi of the subphylum Flagella. Pathogens overwinter in seed strains or tissues with mycelium, and can also overwinter and oversummer oospores in the soil. The oospores germinate and grow germ tubes or produce sporangia and zoospores. They invade the host and cause the initial infection, and then the ordinary part. Sporangium and zoospores are also produced, which invade the host and cause the initial infection, which makes the disease spread and expand. In the later stage, the disease produces oospores in the diseased tissue to overwinter.

White rust bacteria can germinate at 0～25℃, and 10℃ is suitable. The disease is more severe in latitudes, high-altitude low-temperature areas, low-temperature years or after rain. many.

3. Control methods

(1) Agricultural control: Rotate crops with non-cruciferous vegetables every other year; after the previous crop is harvested, remove diseased and stubborn plants in the field in time to reduce the source of bacteria.

(2) Chemical prevention and control: spraying in time for prevention and treatment at the initial stage of the disease, use 25% metalaxyl wettable powder 1000 times solution, or use 58% metalaxyl • manganese zinc wettable powder 500 times solution, or use 64% antitoxin alum Wettable powder 500 times liquid, or spray with 40% cream copper wettable powder 600 times liquid. (Reproduced)