How to control "white rust" of asparagus

Due to the high temperature and rain after the beginning of summer, asparagus is prone to white rust. Once the disease occurs, it not only reduces the yield, but also affects the quality. 1. At the beginning of the onset of the symptoms, the disease spot appears yellowish to yellow on the front of the leaf, and then gradually turns brown, the disease spot is larger, and the back of the leaf produces white protuberant blister spots, which are nearly round or oval to irregular shape, and sometimes heal into larger blister spots. In the later stage, the blister spot ruptured and scattered white sporangia. When the leaves are seriously damaged, the disease spots are dense, the diseased leaves are deformed, and the leaves fall off. Second, prevention and control methods 1, the implementation of crop rotation. Fields growing asparagus should be rotated with other vegetable varieties. 2. Select disease-free seeds. The seeds were treated. The newly purchased seeds were soaked in 50 ℃ warm water for 25 minutes and then sowed after cooling. Before sowing, the seeds were evenly mixed and sterilized according to the proportion of 100 kg seeds with 300 grams of metalaxyl and 25% metalaxyl. 3. Strengthen the field management. Choose fields with high topography, fertile soil, good drainage and irrigation and ventilation. Rational fertilization, increase the application of organic fertilizer and phosphorus and potassium fertilizer, scientific management of water. If diseased plants are found, remove them in time and bury them deeply. After harvest, clear the garden thoroughly, remove the diseased branches and residues, and turn deeply to reduce the source of bacteria. 4. Chemical control. Spray control at the initial stage of the disease, the medicament can be selected as follows: 25% metalaxyl wettable powder 800 / 1000 times, 75% chlorothalonil wettable powder 800 / 1000 times, 65% Dysen zinc wettable powder 800 / 1000 times, once every 7 to 10 days, 3 times in a row.