Scallion is a relatively profitable economic crop, but due to serious diseases, it is difficult to cure after the onset of disease, so many farmers did not dare to plant. The main diseases of green onions are purple spot, downy mildew and gray mold. It is necessary to find the cause of the disease and then apply the medicine to the disease.
Purple onion spot, also known as black spot disease, is mainly harmful to leaves and pedicels, but also harm the stem. Lesions begin from the tip of the leaf or middle of the pedicel and quickly spread. In the early stages, the lesions were small, gray to dark brown and slightly purple in the middle, and soon expanded into elliptic type with black coal smears on the upper body. The lesions spread to the whole leaves, causing the leaves and pedicels to be dismantled, causing large dead leaves of the outer leaves. The pathogenic bacteria latent in the host and on the seedlings or conidia attached to the sick body overwintering, the new mycelium in the following year to generate new spores, spread by the wind, rain, high fever and easy to disease. Plants are either less fertilized or more affected by wind damage.
Downy mildew is an important disease of welsh onion, leaf and pedicel disease, lesions are larger oval, yellow-white or milky white, above the emergence of white downy mildew, high temperature grayish purple. Above the onset of disease withered, stem atrophy, distorted blade distortion, pale green. The pathogens are mainly oosspore on the remains in the remaining soil and attached to the seeds for winter. See germination, invasion from plant stomata, spread by wind, rain and insects. It's easy to get sick during the night.
Botrytis cinerea, also known as white spot disease, is only affected by leaves. At the beginning of the disease, the leaves developed white spots, developed from the tip of the leaves, and gradually formed into pieces, causing the onion leaves to die. The pathogens thrive in winter with mycelium or sclerotia, and high temperature and humidity spread through wind and rain.
Drug control: Purple spot spraying 75% chlorothalonil wettable powder 600 times, or 70% mancozeb zinc wettable powder 500 times, or 58% metalaxyl manganese zinc wettable powder 500 times, 7 times Spraying once a day, even spraying three times, the effect will be very good; in the early stage of downy mildew, spraying 40% EB aluminum wettable powder 200 times, or 50% chlorothalonil wettable powder 500 times, or 25% A Shuangling 800 ~ 1000 times liquid, spray once every 7 days, even spray 2 ~ 3 times; early gray mold spraying 50% carbendazim WP 1500 ~ 2000 times, or 50% puhain Wettable powder 1000 ~ 1500 times, or 50% fast-king 1500 ~ 2000 times liquid, spray once every 10 days, and even spray 2 ~ 3 times.
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