Main root diseases of growing tea and their control

1. White silk disease of tea seedlings

(1) Distribution and symptoms: White silk disease of tea seedlings is a common root disease in nursery. The distribution is wide and the harm is serious. In addition to tea, it can also harm more than 200 kinds of plants, such as melons, Solanaceae, hemp, tobacco, peanuts and so on. Occurs in the root neck, the disease initially showed brown spots, the surface of the white woolly, after expansion around the root neck, shaped or white silk filamentous membrane, can expand to the soil surface. In the later stage, rapeseed sclerotia was formed in the disease, from white to yellowish brown to dark brown. Due to the pathogenicity of the pathogen, the cortex of the diseased plant rotted, the transport of water and nutrients was blocked, the leaves withered and fell off, and finally the whole plant died.

(2) pathogen: it is a kind of fungus of subphylum basidiomycetes. The mycelium is colorless at first, slightly brownish later, dense, forming sclerotia. The sclerotia is round, smooth, hard and dark brown. Vegetative forms, namely basidiospores and basidiospores, are produced under hot and humid conditions, but they are not common and have little effect on disease transmission.

(3) occurrence regularity: the sclerotia overwintered mainly in the soil or attached to the diseased tissue, and could survive for 5 to 6 years under dry conditions. At the turn of spring and summer in the following year, the hyphae germinated and produced when the temperature and humidity were suitable, which spread along the soil gap or spread with Rain Water, irrigation water, agricultural tools, etc., infecting the root neck of the seedlings. High temperature and high humidity are beneficial to the disease, which occurs most frequently from June to August. Heavy soil viscosity, excessive acidity, low-lying terrain, poor growth of tea seedlings, and the former as a susceptible parasite, the disease is also serious.

(4) Control methods: select wasteland or land of non-susceptible crops as nursery. Pay attention to the drainage of tea garden, improve the soil, promote the construction of seedlings and enhance disease resistance. The susceptible nursery should remove the diseased seedlings and disinfect the soil in time. The medicine uses 50% carbendazim 500 times solution, 0.5% copper sulfate solution or 70% methyl topiramate 500 times solution. The leaves of transplanted tea seedlings can be soaked in 20% lime water for disinfection.

2. Tea root cancer (compared with tea seedling blight)

(1) Distribution and symptoms: it is mainly harmful to tea seedlings, which occurs seriously in some tea areas, resulting in the death of tea seedlings. It is common in the cutting nursery, and both the main and lateral roots can be damaged. The bacteria invaded from the cutting mouth or root wound of the cuttings, producing light brown spherical protuberances at the initial stage, and then gradually enlarged like a tumor, small like millet grains, large like peas, and multiple tumors often healed into irregular large tumors. The tumor is brown, Lignified and hard, and the surface is rough. After the tea seedlings were damaged, the fibrous roots decreased, and the aboveground parts grew poorly or withered.

(2) pathogen: the pathogen of tea root cancer is wild bacillus, which belongs to bacteria. The cell is short rod-shaped, with 1-3 polar flagella. Gray-white round colonies were formed on the common medium. The suitable temperature for development was 25-29 ℃, and the lethal temperature was 51 ℃ (10 minutes). The development is the best in pH7.3.

(3) occurrence regularity: root cancer bacteria overwintered in soil or diseased tissue. When the environment is suitable in the following year, the damage will be caused by water flow, underground insects and agricultural tools. Germs invade from the wound or incision of the seedling, grow and develop in the tissue, stimulate cell division and produce cancer.

(4) Control methods: strict seedling inspection, control of underground pests and reduction of root wounds. If necessary, the seedlings can be soaked in 20% lime water for 10 minutes before transplanting.

3. Root knot nematode disease of tea seedlings

(1) Distribution and symptoms: mainly distributed in warm tea-producing areas. The disease is caused by a very small nematode. When the nematode invades the tea root, it forms a tumor in the root, which is similar to soybeans and rapeseed, and has different sizes, the damaged root has no fibrous root and is deformed, and sometimes the end of the root is thicker than the front end. The aboveground part of the diseased plant grows poorly, the plant is short, the growth is weak, the leaves turn yellow, and the leaves are easy to fall off and die in dry season.

(2) occurrence regularity: root-knot nematode is a kind of aerobic organism that likes high temperature and dryness. When the soil temperature reaches 25030 ℃ and the soil moisture is about 50%, the first generation can be completed in 20-30 days in sandy soil with high topography and loose soil structure, while nematode occurs more frequently in surface soil than in subsoil, and stops when it is below 10 ℃.

(3) Prevention and control methods:

① chose the wasteland as the nursery, but the land where peanuts, melons, legumes, sweet potatoes and other crops had been planted should not be used as the nursery. The soil should be turned deep in summer and turned again after 10 days in the sun to kill nematodes in the soil.

② should apply more phosphate and potassium fertilizer to the diseased seedlings and improve their disease resistance. At the same time, disinfecting with lime or applying 1:20 tea low water to the soil also has a better control effect.

4. Tea purple stripe feather disease

(1) Distribution and symptoms: it is distributed in all tea-producing areas, but it is more common in North and East China. The disease mainly occurs in the seedling stage and adult stage, causing damage to the root or root neck. At first, the fibrous root is rotten, brown or dark brown, and then it spreads to the lateral root. After decay, it is purple-brown, and the surface of the disease spot is covered with purplish-brown filaments. On the surface of the diseased root, there are hemispherical granular wormwood nuclei and centimeters of nitrate, which is often surrounded by purplish red filaments. It is easy to peel off, and the root cortex is also easy to peel off. In severe cases, the aboveground part wilts, the new shoots sprout less, and the diseased plants die.

(2) occurrence regularity: the disease is more serious at the turn of high temperature and rainy spring and summer or between summer and autumn, and it is easy to occur in tea gardens with high groundwater level, poor drainage and over-dry soil. This pathogen can survive in the soil for many years, with agricultural operations; Rain Water, underground pests and root contact and spread, the transfer of infected seedlings and soil can also be transmitted over a long distance, continuous cropping and pre-cropping susceptible crops are also prone to disease.

(3) Prevention and control methods:

Select the aseptic healthy seedlings to dig up and burn the diseased seedlings in time, wash the tools after use, and then soak the rest of the healthy seedlings with 20% lime emulsion for 1 hour, or 50% carbendazim 1000 times diluted solution for half an hour before planting. Tea gardens with poor drainage and high water level should pay attention to drainage and dig drainage ditches before waterlogging. The land that had previously planted sweet potatoes, potatoes and fruit trees and had the disease should be disinfected with 70% pentachloronitrobenzene, disinfected with 2.5kg fine soil per mu, or irrigated with formalin 30 times dilution, and the root neck was watered with potassium permanganate or doinling 1000 times dilution at the initial stage of the disease.