Prevention and cure of radish downy mildew

Symptoms of radish downy mildew: can occur from seedling to seeding. The disease spreads upward from the lower part of the plant, and the leaf surface is irregularly chlorotic yellow spot, and then gradually enlarges into a polygonal yellow-brown lesion with a size of 3-7 mm. When the humidity is high, white mold is formed on both sides of the leaf back or the leaves, that is, the pathogens are propagated, and the severe lesions cause the leaves to dry up. After the stem is infected, dark brown irregular spots appear, and white mold is formed on it. Pathogenicity and pathogenic conditions of downy mildew: The pathogen mainly overwinters with oospores in sick bodies or soil. The oocysts in the next year germinate and produce germ tubes, which invade from the germs of the seedlings; or the mycelium is collected in the roots or storage of the mycelium On the radish overwintering, the mycelium of the leap year spreads upward to the first true leaf, and the sporangia are produced on the young stem and the leaves to form a limited systemic infection; the pathogen can also attach to the seed for wintering, and the seeds of the seeded bacteria directly invade. Dyeing seedlings, causing seedling disease; pathogens can also be wintering in the diseased part of the vegetable, and sporangia are produced after wintering. After the sporangia matures, it will fall off, spread by airflow, produce germ tube on the surface of the host, have pores or invade from the cell gap, and then reproduce the sporangia after 3-5 days of incubation; the disease spreads through the wind and rain, Generally, the cruciferous vegetables are infested first to infect the root vegetables; such a variety of infestation sources, until the conditions in the late autumn and early winter are bad, the ovarian spores are overwintered in the host tissue, and after 2-3 months of dormancy It can also germinate and become the source of infection at the beginning of next year. The infection conditions of downy mildew are basically the same everywhere. The average temperature is around 16 °C, the relative humidity is higher than 70%, and there are five consecutive days of rainy weather for one or more times. There are susceptible varieties or bacterial sources. Can spread quickly. According to its onset conditions, downy mildew mostly occurs from mid-August to mid-September. Downy mildew prevention and treatment methods: (1) Selection of downy mildew resistant varieties, such as: Ludai No.1, Selected Sanjibai, Hongfeng No.2, etc.; (2) Removing the diseased leaves after harvesting, and timely turning over; (3) timely sowing, not suitable for early sowing; (4) selective seed and seed disinfection, seedless plant retention, or seed dressing with 0.3% of the weight of the seed before the sowing of 25% metalaxyl WP; (5) Chemical control: Spray 72% manganese zinc·cream urea wettable powder 600 times liquid, 70% manganese zinc·ethyl aluminum wettable powder 500 times liquid, 25% enestrox emulsifiable concentrate 1000 times liquid, 70 after spraying the diseased plants. % propyl zinc wettable powder 700 times solution, 69% manganese zinc enoyl (an yttrium manganese zinc) wettable powder 600 times liquid or 55% fu enoyl (cream) WP 700 times liquid. Spray 60 grams of good liquid per acre, spray the leaves evenly, do not re-spray or leak spray, spray once every 7-10 days, even spray 2-3 times, the control effect is very good.

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