Symptoms occur in all tea regions in China, and new tea gardens or high mountain tea regions occur more frequently. The main damage to the leaves, petioles, young shoots and other parts. Leaf disease mainly seen in early spring leaves or on the first leaf, the disease part of the primary brown dots, after the expansion of a grayish white lesion in the middle of the depression, the size of 0.8-3.5mm, the edge of a dark brown or purple brown ridge line The central reddish-brown, scattered black spots in the middle of the late lesions, that is, the mycelium block of pathogenic bacteria. When the humidity is high, there is a layer of gray mold, which is the sub-solid layer of pathogenic bacteria, which is different from the white spot disease. Petioles and tender shoots produce similar symptoms.
The pathogen, Cercospora theae (Cav.) Breda, is known as Chaetomium spp. The gray, black, moldy dots in the diseased area are the mycelia of the germ. The conidiophores are clustered on the hyphae under the epidermis. The size of the spores is 29-433-4(um). There are more than ten roots per cluster. The unit cells are colorless, straight or slightly curved at the top, and the top conidia are conidial. . Conidial whip, gradually tapering and curved from base, colorless or gray, separated by 4-6, size 42-1062.5-3.5 (um).
Pathogens and Pathogenic Conditions The pathogenic bacteria are overwintering in the diseased leaves and deciduous leaves of the tea plant with mycelia. The conditions in late spring are suitable for the production of conidia, which spreads through wind and rain, infects young leaves, leaves, and young stems, and is submerged for several days. After the new lesions are formed, conidiospores are formed again, and repeated infections are repeated, so that the disease condition is continuously expanded and the disease is also a high-temperature and low-temperature disease. The relative humidity is higher than 80% and the temperature is 20°C. The onset of the disease occurs in late April and early May, and it often occurs in autumn, especially in low-lying plains, moist tea gardens, and foggy tea areas. Excessive management of tea gardens, lack of fertilizers, and excessive picking have contributed to the declining incidence of tea trees. The difference in disease resistance among varieties is obvious, Longjing tea, hairy crab, yellow leaf early and other disease resistance; Baimao tea, Yuntaishan large leaf species, Phoenix daffodil susceptible to disease.
Prevention and control methods (1) Promote the use of compost made from fermented bacteria, strengthen management of tea garden fertilizers, increase tree vigor, and increase resistance to disease. (2) Select resistant varieties and gradually eliminate susceptible varieties. (3) timely removal of diseased leaves to reduce the initial infestation. (4) In the early spring or early autumn, spraying 50% benomyl wettable powder 1500 times or 36% thiophanate-methyl suspension 600 times, 75% chlorothalonil wettable powder 800-900 times. (5) Non-picked tea gardens may also be sprayed with a 0.7% lime half Bordeaux mixture.
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