Control of scab of sweet potato

Sweet potato scab, also known as black spot.

(pathogen) Alternaria bataticola Ikata.

(host crop) sweet potato.

(disease diagnosis) damaged leaves, petioles and stem vines. Leaf disease, at the beginning of the emergence of waterlogged brown spots, after the expansion of the disease spot round, oval, the size of 3-5 mm, brown. In the later stage, the center of the lesion is grayish brown, the surrounding brown, and then the outer layer is light brown, and the junction with the whole body is dark brown, forming a thick and light alternating concentric pattern. When the disease is serious, the disease spots converge, causing the leaves to turn yellow and even fall off. The disease spot on petiole and stem is fusiform, oval, brown to dark brown, slightly sunken. When severe, the disease spot surrounds the petiole, causing the connected leaves to turn yellow and dry. When the humidity is high, there is a light black mildew on the lesion. The pathogen is Alternaria sweetpotato. Conidiophores solitary or 2-3 fascicles, brown, uniform color, basal cells slightly larger, unbranched, upright or slightly curved, no geniculate nodes, with 1-4 septum. Conidia solitary, obclavate, light brown, with 5-12 diaphragms, 0-3 mediastinum, constriction at the septum, beak slightly long to long, unbranched, light-colored, with 0-3 septum.

The pathogen overwintered mainly as mycelium on the disease residue, or the conidia attached to the seed potato overwintered in the cellar. Raising seedlings with bacteria can cause the disease of seedlings, and the diseased seedlings can be transmitted over a long distance. After the disease occurred in the field, the disease produced conidia and spread by wind and rain. The incubation period of the disease is 3-7 days, the re-infection is frequent, and the disease develops rapidly under suitable temperature and humidity conditions. The disease preferred warm and humid conditions, the optimum temperature was 24 ~ 25 ℃, and the disease was serious with heavy rain, heavy fog and dew. The soil is barren, the ploughing layer is shallow, and the condition is serious when the fertilizer and water are insufficient.

(control measures) (1) seed potato disinfection, can be soaked in 50% carbendazim 1000 times solution for 5 minutes. (2) ploughing the soil and applying enough manure. Timely topdressing and irrigation make the plant grow exuberantly. (3) pay attention to the field hygiene, remove the initial diseased leaves at the initial stage of the disease, thoroughly remove the disease and residue in the field after harvest, and turn the soil deeply. (4) Pesticide control. Spray 64% alum wettable powder 500 times liquid, or 70% mancozeb wettable powder 500 times liquid, or 80% Dasheng wettable powder 600 times liquid, or 80% spray gram wettable powder 800 times liquid, or 77% can kill wettable particle powder 500 times liquid, or 1buzzer 200 Bordeaux solution.