Detailed Explanation of the Damage Symptoms, Occurrence Patterns and Control Techniques of Tea Blister Blight in Spring

The important disease of tea plant buds in spring is tea blister blight, which occurs in tea gardens everywhere and causes serious damage. The damage symptoms and control techniques of tea blister blight are described below:

1. Damage symptoms of tea blister blight

On young leaves, the initial infection appears as pale yellow or reddish-brown translucent small spots, which then gradually enlarge and sink into pale yellow-brown or purplish-red round lesions, 2 to 10 mm in diameter; the lesions on the underside of the leaf are blister-like and raised, and bear grayish-white powdery material, and finally the lesions become dark brown and ulcer-like. Occasionally there are also blister-like raised lesions on the upper surface of the leaf, with the underside sunken. After the petiole and young shoots are infected, they swell and twist, and in severe cases the new shoots above the diseased part die. Flower buds and young fruit are occasionally affected.

2. Occurrence patterns of tea blister blight

The pathogen overwinters or oversummers as mycelium in diseased leaves. It is a low-temperature, high-humidity disease. When the temperature is 18 to 20°C and the relative humidity is above 85%, rainy and humid conditions favor the disease, and it generally occurs severely during the spring tea period from March to May and the autumn tea period from September to October. In shaded tea gardens in hilly and flat areas, the disease is severe under rainy conditions; tea gardens with extensive management, overgrown weeds, improper fertilization or shading are severely affected; and tea gardens in foggy high mountains and humid low-lying areas are severely affected.

3. Control techniques for tea blister blight

a. Strengthen seedling quarantine to prevent the tea blister blight pathogen from spreading through the transport of tea seedlings.

b. Remove weeds and dead branches and prune appropriately to promote ventilation and light penetration, which can reduce the disease.

c. Apply more phosphorus and potassium fertilizer to improve the disease resistance of tea plants.

d. At the early stage of the disease, spray 70% thiophanate-methyl wettable powder at 1000 to 1500 times dilution or 75% chlorothalonil wettable powder at 800 to 1000 times dilution, at intervals of 7 to 10 days, for 2 to 3 consecutive sprays.

e. At the early stage of the disease, spray 25% triadimefon at 3500 times dilution; it has a long residual effect, and one spray during the disease period is sufficient.

f. In non-picking tea gardens, 0.6 to 0.7% half-strength Bordeaux mixture, 0.2 to 0.5% copper sulfate solution, or 12% copper abietate emulsifiable concentrate at 600 times dilution may also be sprayed to protect the tea plants.

g. In picking tea gardens, if Bordeaux mixture is sprayed, it can be applied once before spring tea or after each tea-picking season, and picking may be done only 20 days after spraying. (Bordeaux mixture is an inorganic copper fungicide. The chemical composition of its active ingredients is CuSO4·xCu(OH)2·yCa(OH)2·zH2O. In 1882, the Frenchman A. Millardet discovered its fungicidal effect in Bordeaux, hence the name Bordeaux mixture. It is a sky-blue gelatinous suspension prepared from about 500 g of copper sulfate, 500 g of slaked lime and 50 kg of water. The proportions of ingredients may be appropriately increased or decreased as needed. It is generally alkaline and has good adhesion, but its physical properties are destroyed after long standing, so it is best prepared and used fresh or made into dehydrated Bordeaux powder. When used, it is mixed with water.)