Potato Knowledge Base

Potato Scab

Pathogene

Streptomyces scabies (Thaxter) Waks.et Henvici

Symptom

Small brown spots first appear on the surface of potato tubers, and then expand to form brown round or irregular large patches. The surface is rough due to the production of a large number of suberized cells, and in the later stage, the center is slightly sunken or raised as a scab-like hard plaque. The lesions are limited to the skin and do not penetrate deep into the potato, which is different from powdery scab.

Transmission and epidemic factor

The fungus grows saprophytically in the soil or overwinters on diseased potatoes. In the early stages of tuber growth, before the epidermis is corked, the bacteria can invade through lenticels or wounds and become infected. When the tuber surface is corked, it is more difficult to invade. Plants grown from diseased potatoes are very susceptible to the disease, and healthy potatoes can also become sick if they are sown into contaminated soil. The suitable temperature for the occurrence of the disease is 25-30℃. The disease is severe in neutral or slightly alkaline sandy loam soil, and rarely occurs in pH below 5.2. There are differences in disease resistance among varieties. White thin-skinned varieties are susceptible to the disease, while brown thick-skinned varieties are more resistant.

Prevention and control methods

(1) Select disease-free seed potatoes and do not transfer seeds from diseased areas. Soak the seeds in 40% formalin 120 times for 4 minutes before sowing.

(2) Applying more organic fertilizer or green manure can inhibit the disease.

(3) Rotate crops with Cucurbitaceae, Leguminosae, and Liliaceae vegetables for more than 5 years.

(4) Choose vegetable plots with good water retention for planting, and water them in time if there is drought during the potato-bearing period.