Recently, due to the heavy rainfall and low temperature in Sichuan, a large number of tea cake disease hazards have occurred in tea gardens. In fact, in the southwest tea area, there are often outbreaks of tea cake disease, which has become an important factor affecting the yield and quality of tea, and in epidemic years, the local disease rate can reach 40%-50%, and in severe cases, it is as high as 90%. Tea cake disease is not only more serious in Sichuan, Guizhou, Yunnan tea gardens, in recent years in Zhejiang, Fujian, Guangxi, Anhui and other provinces have occurred, therefore, the tea cake disease should have a scientific understanding and take effective prevention and control measures.
Tea cake disease can harm the young leaves, young stems, new shoots, flower buds, fruits and petioles of tea trees, etc., mainly harming the young leaves of tea trees, and mature leaves cannot be infected. Tea cake disease infestation of young leaves can be divided into 4 stages. Stage 1, the initial onset of the young leaves is a small yellowish or reddish-brown translucent dot with a spot diameter of 3-6 mm; in stage 2, the disease begins to expand, forming a smooth and shiny leaf front and depression, and the back side is raised in the form of a bun-shaped blister, which has a gray-white or pink or gray powder on it, which is the solid layer formed by the pathogen, which has been attached to the mature basidd spores; Stage 3, the basidispores are formed in large quantities, and the back of the leaves is pure white velvet,which can quickly infect nearby tea tree leaves; Stage 4, The tissue cells within the plaque are depleted of nutrients, the host resistance response is generated, the plaque tissue necrotic, the powder disappears, the bulge is brown dry and ulcerated, and there is a gray-white circle around the edges, and the expansion of the plaque is limited.
When the leaf is severely ill, there are several or dozens of obvious spots on a leaf, the diseased leaves in the middle vein of the leaf are twisted or deformed, and the tea leaves are distorted, folded in half or irregularly rolled. Petioles and young stems are swollen and twisted, and new shoots above the severely diseased parts die or break. Flower buds and young fruits occasionally occur.
Tea cake disease is a fungal disease. The pathogen is Exobasidium vexans Ma-see, a genus of exobasidiums in the order Epidermophytes. The white powder of the bulge on the back of the spot is the solid layer of the pathogen.
Tea cake disease is a low temperature and high humidity type disease, generally in the spring tea period and autumn tea period more severe disease, and in the summer high temperature and dry season mild incidence. Mycelium overwinters and oversells in diseased leaves. In the following spring or autumn, when the average temperature is 15-20 °C and the relative humidity is higher than 85%, the mycelium germinates and forms new spots, and the surface of the spots forms a white powder, that is, a solid layer composed of basidiospores, which becomes the source of the initial infection. After the sadispores formed in this process mature, they spread again with wind and rain, and re-infect more than 10 times in a year, resulting in the epidemic of disease. A mature plaque can produce nearly one million ochonspores within 24 hours, and the pathogen is highly parasitic, and when the diseased tissue dies, the parasitic mycelium dies with it. The lifespan of the oxidium is short, and after 2-3 days, it loses its germination and dies after 0.5-1 hours in direct sunlight.
The duration of the incubation period of the disease is also closely related to temperature, humidity and sunshine. The average daily temperature is 3-4 days when the average daily temperature is 19.7 °C, and 9-18 days when the temperature is 15.5-16.3 °C. Mountain tea plantations are most susceptible to disease in the seasons of moderate temperature and high humidity, little sunshine and continuous rain. The onset of the disease begins in February and April every year in the southwest tea area, enters the peak period from July to November, and gradually stops after November. In East and South China, the onset of the disease is from May to July, and the incidence is at its peak from September to November. Hainan generally enters the peak period from November to February of the following year. As far as the tea garden itself is concerned, the hilly and flat land of the lush tea garden is heavily affected under rainy conditions. Misty mountains, high humidity depressions and tea plantations where dew is not easy to dry have early and heavy diseases. Extensive management, poor ventilation in tea plantations, closed and high humidity are severe. There are certain differences in disease resistance between tea varieties, usually large-leaf species are more severely ill than small-leaf species, and large-leaf varieties with thin leaves, tender and juicy varieties are more susceptible to disease.
1. Agricultural prevention and control
Select disease-resistant tea plant varieties, frequently remove weeds, keep the tea garden ventilated and transparent; pick in batches, and try to leave as few young leaves on the tea trees as possible to reduce the chance of infection.
2. Reasonable fertilization
Strengthen the management of tea plant fertilizer and water, and appropriately increase the application of phosphorus and potassium fertilizer to enhance the tree potential and improve the resistance of the tea plant itself. It is recommended to recommend the "one base and three chases" fertilization technology model, and the tea tree topdressing in February, April-May and August uses 50 kg/mu of pine fertilizer, and the tea tree base fertilizer uses 75-100 kg/mu of pine fertilizer in October-November. It can promote the robustness of tea plants and improve disease resistance.
3. Biological control
During tea picking, it is recommended to use 95% mineral oil 100-200 times liquid spray to prevent tea cake disease, with an interval of 7 days; in the non-production season, spraying 0.3-0.5 Baumedo stone sulfur compound can effectively reduce the base of overwintering diseases and insects.
4. Rational use of chemical agents for prevention and control
Generally, in the early stage of the disease, the spray is timely according to the weather conditions. The agent can be used with Guoguang Biaojian or Guoguang Jiantai or Guoguang triazolidone for foliar spraying to prevent tea cake disease, and the safe interval is 7-10 days.