Control of scab of seed sweet potato

Sweet potato scab, also known as sweet potato sprout disease, commonly known as "leprosy", "hard stalk disease" and so on.

(pathogen) Sphaceloma batatas Sawada.

(host crop) sweet potato.

(disease diagnosis) mainly for damage to tender shoots, leaves, stems, but also to potato lumps. The disease occurred in many tender leaves, mostly on the back of the leaves, and small brown-red and slightly transparent spots appeared at the beginning of the fine veins, and then the disease spots gradually enlarged, and the surface tissue of the disease spots were corked, rough, protruding, like scabs, grayish white to yellow-white. The veins of the injured leaves are bent and the leaves are wrinkled and curled. Stem vines and petioles occur, forming round or oblong scab-like spots, and even synthetic scars in severe cases. The cortex of the diseased stem is rough, corked, and it loses flexibility, so that the tip of the diseased vine hardens and stiffens and no longer winds its way. Shoot disease, produce dense lavender disease spot, shoot wrinkle can not grow, called shrinkage bud. Potato pieces are infected, buds curl, dark brown to grayish brown spots appear on the surface of potato pieces, and the scabs are easy to fall off and remain rash spots or scars when dry. The diseased potato is small and deformed. The most common pathogen in the field is its asexual generation, which is sweet potato scab spores. Pathogen conidia stem on the spore disk, short, unbranched, cylindrical, tip more pointed and slender, its upper conidia. Conidia unicellular, colorless, long oval.

The pathogen overwintered as mycelium on seed potato or in soil with disease residue. Spawned potatoes and potato seedlings can spread. After the disease occurs in the field, the conidia produced by the disease department can be transmitted by wind and rain, and can also be transmitted by human contact and field insects. Most of the germs invade from lenticels and wounds. The disease re-infected frequently, and the disease developed rapidly in the field under suitable conditions. The disease began to occur when the temperature was above 20 ℃, and the optimum temperature was 25-28 ℃. Rain and dew, especially continuous rainfall and storms, are conducive to the spread and prevalence of diseases. When the vine is turned over in rainy days, the disease spreads faster.

(control measures) (1) select disease-resistant varieties, such as unbearable, Honghong 1, Guangxuan 16, regardless of spring, Xindazi and so on. (2) choose disease-free potato (vine) to raise seedlings. Soak the potato seedlings in 1000-fold solution of 70% methyl topiramate for 5 minutes before planting. (3) rotation of seriously diseased fields and food crops for 4-6 years. (4) adequate application of rotten manure to prevent partial application of nitrogen fertilizer and increase application of phosphorus and potassium fertilizer. Reasonable irrigation. Drainage after rain can reduce the humidity in the field and inhibit the spread of diseases. (5) early detection of diseased plants and timely removal. After harvest, thoroughly remove the sick and residual bodies in the field, and dig deep into the soil. (6) spraying insecticides in the early stage of the disease. The medicament can choose 1000 times liquid of 70% methyl thiophanate wettable powder, or 50% carbendazim wettable powder, or 80% Dysen zinc wettable powder, or 80% Xinwansheng wettable powder, or 30% luyedan wettable powder.