This year due to the impact of warm winter weather, onion purple spot disease occurs more seriously, in our county's main onion production areas have emerged in the trend of serious damage to the field, the onion leaves have died. In order to help everyone identify the disease, master control methods, and effectively control the spread of the disease, we will now introduce the symptoms of purple spot disease, the causes of the disease, and the prevention and treatment methods for reference.
I. Symptoms: Purple spot mainly harms onions, green onions, and also infests garlic and leek. On the onion mainly damage leaves, pedicels, bulbs. Lesions begin from the tips of the leaves, or form in the wounds that are damaged by the thrips. The lesions are small at the beginning, gray to light brown, and the center is slightly purple, with black and grey molds. The lesion quickly expanded into an elliptical or spindle-like shape, with a concave, dark purple, concentric ring pattern, and yellow halos around it. When the humidity is high, the lesion expands to the whole leaf, often causing the onion leaves to turn yellow from the bottom up and die or break, seriously affecting the yield and quality of fresh onions.
Second, pathogenic bacteria and disease conditions: The pathogen of purple spot is a sub-genus of the fungus Submycotic fungi, with hyphae attached to the sick in the soil in the winter. Or in the onion plants on the twists and turns, the spread of air, rain, from the pores, wounds or penetrate directly into the epidermis. In the warm and humid conditions, the disease is easy to occur, bulbs are susceptible to disease during the expansion period, sandy soil, dry land, early seedlings, old seedlings, lack of fertilizer, onion growth weakness, heavy field damage caused by thrips is heavy. The local red skin onion is light, yellow onion is very sick, the incidence of transplanting early is heavy, drainage in deep trenches is fast, soil permeability is good, and the disease is lighter. The water that has been poured into the water will become heavier in the near future.
Third, the prevention and control methods: (1) clean the garden, remove the body of the disease and other sources of infection. (2) Strengthen management, apply more base fertilizer and top dressing, make onion grow stronger, and increase resistance to disease. After the onset of disease, irrigation should be controlled to reduce the soil moisture and prevent the trachea from being damaged as soon as possible. (3) Chemical control: Seeds are soaked with 30% formaldehyde 300 times for 3 hours, and washed immediately after leaching. At the beginning of the onset, spray 75% chlorothalonil wettable powder 600 times, or 64% antivirus WP 500 times, 70% mancozeb 500 times, 40% Fudan 500 times, or 50% 1500 times liquid, copper ammonium mixture 500 times, 2% multi-resistance 30ppm, 50% fast-king 30-50 grams, onion garlic net and other agents spray, one of the above agents can be, various agents Should be used alternately, once every 7-10 days, continuous control 3-4 times, add 5-10 grams of neutral laundry detergent in each 10kg liquid, can increase the adhesiveness of the liquid.
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