Control Methods for Major Diseases of Tea Plant Young Shoots and Stems

To effectively control tea plant pests and diseases, reduce pesticide residues in tea, and improve tea quality, the major diseases of tea plants and their control are described below.

I. Damage Symptoms

1. Tea bud blight: After the tea plant is infected, the growth of buds and shoots is obviously inhibited, affecting the yield and quality of spring tea. It mainly damages the first 1 to 3 leaves of the spring tea flush, first producing pale yellow or yellow-brown lesions at the leaf tip or leaf margin, which after expansion become irregular in shape, with the boundary between diseased and healthy tissue distinct or indistinct; the bud tip is damaged and becomes dark brown and scorched, shriveled and unable to extend; later, small black dots are scattered on the surface of the diseased part, with the black dots on the leaves mostly on the upper side. Infected leaves are easily broken and twisted.

2. Tea white star disease: After this disease damages young shoots, buds and leaves, it causes the tea to taste extremely bitter. Small round lesions form on young leaves, sunken in the center, initially red-brown with a purple-brown margin, and later gray with scattered small black dots. The lesions are 0.5 to 2 mm in diameter; when numerous, the lesions may merge with each other into larger lesions and cause the leaves to become twisted and deformed. Lesions on the petiole and young stems are dark brown, later turning gray-white; when numerous, they can cause leaf drop and death of young shoots.

3. Tea seedling damping-off: This disease mainly damages the base of the stem of tea seedlings, and also damages new shoots. The lesions are initially dark brown, oval or irregular in shape; later they become gray-white, slightly sunken, with many small black dots on them, and finally the leaves wither and drop, and the whole plant dies.

4. Tea seedling stem blight: This disease mostly damages short-cuttage nursery beds, and in severe cases can cause death in patches. The stem base near the ground of the affected tea seedlings is initially brown, later dark brown, with the cortex rotting, and the seedlings die after 2 to 3 months.

II. Pathogens

The pathogen of tea bud blight is a fungus of the genus Phyllosticta in the Deuteromycotina, and the small black dots on the diseased part are pycnidia, spherical to flat-spherical, brown. The conidia are located inside the pycnidia, oval or ovoid, colorless, single-celled, with a size of 1 6 to 4 microns x 2.3 to 6 microns. The pathogen of tea white star disease is a fungus of the genus Phyllosticta in the Deuteromycotina; the small black dots on the lesions are pycnidia, and the conidia are located inside them, colorless, single-celled, oval, with a size of 3 to 5 microns x 2 to 3 microns.

III. Occurrence Patterns

The pathogen of tea bud blight overwinters as mycelium or pycnidia on diseased leaves or overwintering buds and leaves. During the sprouting period of spring tea the following year, it produces conidia that spread with wind and rain, infecting young buds and leaves, and new lesions form after 2 to 3 days. During the spring tea period, when the amino acid content of tea leaves is high, the disease is severe. After mid-June, the development of the disease is inhibited. During the disease period, repeated infection can occur continuously, causing serious losses to spring tea, and varieties that sprout early are more severely infected. The pathogen of tea white star disease overwinters as mycelium or pycnidia in the tissues of the diseased part. In early spring of the following year, when temperature and humidity are suitable, it produces conidia that spread by wind and rain, infecting young shoots, buds and leaves, and new lesions form after 2 to 5 days, which then produce conidia for repeated infection. When the environment is suitable, it can easily cause an epidemic of the disease, with the most severe occurrence in April and May each year. Damp, cloudy and foggy weather and poor cultivation management both favor the occurrence of this disease. When the average temperature of a ten-day period is higher than 25°C, it is unfavorable to the occurrence of the disease. Tea seedling damping-off mainly spreads by wind and rain, mostly beginning to occur in early April, with the rainy season from August to October being the peak period of occurrence; high temperature and high humidity conditions favor the occurrence of this disease. Tea seedling stem blight occurs more in the rainy season of April to May and in autumn. The pathogen spreads with rainwater or flowing water, and can also spread through intertillage and weeding or agricultural activities. The pathogen can still retain infective ability after 1 to 2 years in the soil, and nurseries with extensive management have more severe occurrence.

IV. Control Measures

1. Strengthen cultivation management: Strengthen tree cultivation, increase the application of organic fertilizer as well as phosphorus and potassium fertilizers, select disease-resistant varieties according to local conditions, and improve the stress resistance of tea plants. Pick in time and frequently, strengthen tea garden cleanup to reduce sources of pathogen infection, immediately pull out diseased plants and take them out of the nursery to burn, and strengthen quarantine when transporting seedlings. For damping-off, also pay attention to drainage and waterlogging prevention, and for stem blight, pay attention to disinfecting the soil or seedbed.

2. Apply pesticide control in time: For tea bud blight, spray 2 to 3 times at the budding stage of the tea plant and the disease? stage, and the pesticides may be 70% thiophanate-methyl 1500-fold solution or 50% carbendazim 1000-fold solution; for tea white star disease, apply pesticide control from the budding stage to the fish-leaf unfolding stage, and 80% zineb 800-fold solution, 50% carbendazim 1000-fold solution, or 70% thiophanate-methyl 1000- to 1500-fold solution may be used; for tea gardens with severe occurrence, spray once more after 7 to 10 days, and control 2 to 3 times as appropriate; for tea seedling damping-off, at the early stage of occurrence, use 70% thiophanate-methyl 1000-fold solution, 75% chlorothalonil 800-fold solution, and 65% zineb 600-fold solution for spray control; for tea seedling stem blight, spray cycloheximide for control during the disease periods in April and August, or apply 25 kg of 40% quintozene powder per mu between tea seedling rows, then loosen the soil and water, and apply the pesticide again after 15 days.