Cowpea rust mainly occurs on the leaves, and can also damage the petiole and seed pods when severe. At the beginning of the leaf back, there was a pale yellow small mottled, which was mutated brown, arched into a small pustule shape, and then expanded into a summer spore heap. The epidermis broke and the reddish brown powder was released. In the later stage, the black spore heap is formed, which causes the blade to deform early and fall.
Sometimes the urediospores or teliospores also occur on the veins and seed pods. The seed pod is sick and cannot be eaten. In addition, the front side of the leaf is sometimes visible with a slightly raised chestnut brown grain point, that is, the nature of the pathogen; the yellow-white thick velvet is the ruster on the reverse side of the leaf.
Causes
Cowpea rust is caused by Phytophthora sol and Phytophthora solani. It is a single-hosted rust fungus that can produce spores, rust spores, urediospores, teliospores and basi spores. It is an obligate parasite that only harms cowpea. In northern China, winter spores mainly overwinter on sick bodies. The average daily temperature of Hunchun is 21--28 °C. Under the conditions of water-wet and scattered light, the spores are sprouted by 3-5d teliospores, which are conveyed by airflow, and germ cells are formed, which invade the leaves of cowpea, and spores and rust spores occur simultaneously. .
After the rust spores mature, they are invaded and attacked on the cowpea leaves, and then form the urediospores, and the urediospores occur. After the maturation of the summer spores, they are conveyed by the airflow, and repeated repeated infections are carried out until the autumn, or when the conditions of the late growth of the plants are uncomfortable, the teliospores are formed, and the winter spores are overwintered. However, the southern pathogens mainly use summer spores for wintering and summering. The average daily temperature is 23 ° C, the relative humidity is 90%, and the incubation period is 8-9 days. It is simple and popular when the daily average temperature is stable at 24 ° C and continuous rain.
Control method:
At the beginning of the disease, spray 15% triazolone wettable powder 1000--1500 times solution, or 40% Fuxing emulsifiable oil 8000 times solution, or 50% rust emulsified concentrate 800 times solution, or 50% sulfur suspension agent 200 times solution, or 30% solid stone sulphur mixture 150 times solution, or 25% enemy de-emulsion 3,000 times solution, or 65% of daisen zinc WP 500 times solution, or 50% carbendazim WP 800-1000 times solution , or 25% of the enemy de-emulsion 4000 times liquid plus 15% triazolone wettable powder 2000 times liquid, every 10-15 times once, 2 - 3 times.
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