From June to August each year, the leeks in the Beijing area enter the summer breeding period. The leek disease is the main disease during the breeding period. The roots, stems, leaves, flowers and other parts of the leek can be affected, especially the pseudostem and bulb. When the roots are damaged, they turn brown and rot, the root hairs are significantly reduced, and the lifespan of the roots is shortened. When the pseudo-stem was damaged, it was light brown in color and soft in water. The leaf sheath was easy to fall off. When the air was wet, a sparse gray and white mold layer was seen. When the bulb was damaged, the root disk was flooded, and light brown to dark brown rotted. The inside of the bulb was light brown and the new leaves were delicate. Leaf and calyx infections mostly start from the lower middle, beginning with dark green water immersed lesions, 0.5-5 cm long. The diseased part collapses after dehydration, resulting in vertical rot to leaves, wilting, and visible thin white molds when humidity is high. .
Pathogens of leeks are Phytophthora fungal pathogens that can infect onions, garlic, eggplants, tomatoes, and other vegetables. They use mycelia or chlamydospores to thrive in the soil with plant debris, and produce sporangia and zoospores when appropriate. After the initial infestation is formed and the humidity increases, sporangia are produced in the diseased department to release spores, which spreads through wind and rain and agricultural operations to form repeated infections. The optimum temperature in the field is 25°C-32°C, and the humidity increases and the incidence increases. In Beijing, the disease usually begins in early July and enters the peak period in late July. In early August, it is the peak period of onset. After the heavy rains, there were more incidence peaks. Continuous cropping, water accumulation in the field, partial application of nitrogen fertilizer, and poor ventilation can cause the disease to occur.
Control measures
1. The plant residues after harvesting are promptly removed to maintain the cleanliness of the pasture; the old yellow leaves and weeds are promptly removed during the rearing period to improve the ventilation and light transmission capabilities. The above-mentioned sundries can be harmlessly treated in a timely manner. Solar ozone agricultural garbage treatment stations, mobile ozone agricultural garbage disposal vehicles, or decontamination treatment can be carried out by deep-seated and high-temperature sealed stacks of waste greenhouse films.
2. Avoid continuous cropping with onion and garlic crops, eggplant, and tomatoes, and implement a 2-3-year crop rotation.
3. Carefully level the land and trim the drainage system in the field before the onset of the rainy season.
4. Pay attention to raising the roots, do not over-harvesting, remove the calyx in time, apply fertilizer after harvesting reasonably, avoid partial nitrogen fertilizer, and control irrigation.
5. Severe disease plots should be removed before the rainy season, the lower yellow leaves, the green leaves together, fluffy banding, so as not to contact the ground loquat leaves, reduce the incidence of disease.
6. In the early stage of disease, available 72% cream urea manganese zinc wettable powder 600-800 times liquid, or 69% magnesium zinc enemethacrylate wettable powder 600-800 times liquid, or 72.2% potassium moldewine hydrochloride salt water 600-800 Double liquid, or 58% metalaxyl MnZn wettable powder 500 times liquid spray, once every 7 days, continuous control 2-3 times. In addition to spray application, it is also possible to fill the roots with liquid medicine at the beginning of the rainy season.
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