Control of Brown spot of seed Sweet Potato

Sweet potato brown spot, also known as corner spot.

(pathogen name) Cercospora batatac Zimm

(host crop) sweet potato, water spinach, morning glory, etc.

(disease diagnosis) mainly damaged leaves. Leaf disease, at the beginning of the emergence of water-like spots, and then the disease spot gradually expanded, due to the limitation of leaf veins, the disease spot is mostly angular, but also irregular. The disease spot is yellowish green at the beginning, and then becomes yellowish brown or dark brown, with a light brown in the middle. When the humidity is high, a light gray sparse mildew is produced on the disease spot. When the disease is serious, the leaves are covered with disease spots, causing the leaves to wither and fall off. The pathogen is sweet potato brown spot. The pathogen conidiophores are produced by stomatal bundles, light brown and terminal conidia. Conidia whip-shaped, colorless to slightly yellowish brown, with 4-6 separations.

The pathogen overwinters with the remnant of the disease in the form of mycelium or conidia. In the following year, the overwintering pathogen produced conidia and spread to the leaves of sweet potato to cause the disease. After the disease, the conidia on the diseased leaves were spread by airflow and re-infected in the field, and the disease spread continuously. The bacteria liked the condition of high temperature and humidity, and the development of bacteria was suitable for 25 ~ 28 ℃. In the high temperature season, when it is cloudy and rainy or the clouds are heavy, the disease often occurs seriously.

(prevention and control measures) (1) Fine soil preparation, ridging cultivation, pay attention to the planting density is not too dense. (2) fully apply mature manure and pay attention to the application of phosphorus and potassium fertilizer. (3) timely and appropriate irrigation. Remove the stagnant water in the field in time after rain and reduce the humidity in the field. (4) 2-year rotation between seriously diseased plots and non-host crops. (5) after the harvest of the diseased land, thoroughly remove the disease and residue in the field and turn the soil deeply. (6) spraying insecticides in the early stage of the disease. The medicament can be selected as 800x solution of 70% methyl thiophanate wettable powder, or 600x solution of 50% mixed sulfur suspension, or 1500 times liquid of 50% carbendazim wettable powder, or 600x liquid of 40% Baishuangjing gel suspension, or 500x liquid of 40% carbendazim wettable powder, or 800x liquid of 80% Dasheng wettable powder.