Lagerstroemia indica tender leaf disease

Tea tree is a shrub or small tree belonging to Theaceae and Camellia, and likes warm and humid climate. When the average temperature is above 10℃, the buds begin to germinate, and the optimum temperature for growth is 20-25℃. The annual precipitation should be above 1000 mm. It has been cultivated in China for more than 6000 years, mainly distributed in Anhui, Fujian, Guizhou, Sichuan, Jiangxi, Hunan, Yunnan and other provinces.

Tea refers to the leaves and buds of the tea tree, which originated in China and later spread all over the world in Du Dong, Jian Zhen. It has become one of the most important varieties in the world beverage market. China is the hometown of tea, with 6 kinds of tea such as green tea and black tea, 20 tea-producing provinces and 80 million tea farmers. The national planting area and output rank first in the world, and it is a veritable tea-producing country.

With the steady growth of market demand at home and abroad, the potential of China's tea industry is increasing, the planting area and output of tea are increasing, and there are more and more diseases in tea-producing areas (especially tea gardens with high mountains and fog), among which the most common disease is that tea leaves, especially young leaves, are infected with brown spot or white spot, which leads to the reduction of tea production 10%-50%, or even no harvest. The quality of tea is poor, bitter, dark and fragrant, which seriously affects the commodity value of tea and the economic income of farmers.

At present, the commonly used control methods in tea gardens are basically chemical fungicides, which not only have certain toxicity, increase the risk of pesticide residues, pollute the environment, and are prone to drug resistance, but also can only play a preventive role and can do nothing for tea gardens with diseases. Some organic tea gardens, which have high requirements for chemical pesticides, can only be treated in destructive ways such as pruning and burning. Today, we will elaborate on the pathogens, symptoms, epidemic transmission laws and prevention methods of tea brown spot and white spot in detail, hoping to help you effectively and safely prevent and control tea brown spot and white spot.

First, the causes of tea scab and white scab

1, the cause of tea brown spot disease

Brown spot of tea tree is caused by fungi, and its pathogen is Cercospora obliqua, which is a colorless conidia cell with 4-6 partitions and a whip-like colorless or gray conidia.

2. The causes of white star disease in tea trees.

Like scab, the pathogen causing scab is Hemiptera, but it belongs to pholiota adiposa (Figure 2). Conidia are dark brown, spherical to oblate, with a * *-shaped hole at the top, which was initially buried and then exposed through the epidermis. Colorless unicellular conidia, oval to ovoid.

The pathogens of brown spot disease and white spot disease overwinter in diseased leaves, diseased branches and deciduous tissues of tea trees with mycelium and conidia, and a large number of conidia are released in conidia when tea buds first bloom in the following spring, which spread through wind and rain and invade young leaves and new shoots when humidity is appropriate. After an incubation period of 2-5 days, new disease spots will appear, conidia will be produced on the disease spots, and the disease will continue to spread after repeated infection. If the external conditions are suitable, it will easily lead to epidemic.

Second, the symptoms of tea scab and white scab

1, symptoms of brown spot disease

Tea brown spot disease mostly occurs on young leaves and adult leaves of tea trees, and occasionally old leaves also occur. At the initial stage of infection, reddish-brown spots appeared on the leaves, and then gradually expanded into circular spots, with a concave center and grayish white color, dark brown to purplish brown ribs on the edges, with a diameter of 0.8-3.5 mm, scattered black spots in the center, and obvious boundaries between diseased parts. When the humidity is high in the later stage, black spots and gray mold layers can be produced in the center of the lesion. When the condition is serious, petiole and tender tip will also get sick.

2. Symptoms of White Star Disease

Tea white star disease mainly harms young leaves, buds and stems of tea trees. At the early stage of tender leaves, light brown wet spots are produced on the leaves, which gradually expand into gray-white round spots with a diameter of 0.5-2 mm. The spots are sunken, with dark brown to purple brown edges, and the boundaries with healthy parts are obvious. The lesion can be several irregular large spots, and small black spots can be produced on the lesion in wet environment.

After tea plant infection, the new shoots grow poorly, the internodes are short, the bud weight is reduced and the leaves are easy to fall off. Dry tea made of diseased bud leaves is covered with small spots after brewing, and the tea soup tastes extremely bitter, which has a feeling of stomach discomfort after drinking, which has a great influence on the quality of finished tea.

The difference between tea brown spot disease and white spot disease is that brown spot disease mainly harms adult leaves and young leaves, while white spot disease mainly harms young leaves and new shoots. The red star lesion is larger, with a diameter of 0.8-3.5 cm, while the white star lesion is smaller, with a diameter of only 0.5-2 cm. Gray mold layer is produced in the late stage of brown spot disease, and white spot disease is always gray and white, and no mold layer is produced. After these two diseases, tea leaves are easy to fall off, even all new and old leaves fall off.

Iii. characteristics of epidemic situation

Both tea scab and white scab are fungal diseases with low temperature and high humidity, with early onset and long epidemic time. Their occurrence and popularity are closely related to the disease resistance of varieties, environmental temperature and humidity, cultivation and management conditions.

Among them, there are obvious differences in disease resistance among varieties, and Longjing, Eriocheir sinensis and Huangyezao are relatively resistant to disease. Secondly, the tea garden with short sunshine, high humidity and fog caused by extensive management, excessive picking and insufficient fertilizer is more serious. Low-lying and humid tea gardens in the plain and foggy tea areas in mountainous areas are prone to diseases. Tea seedlings with shallow soil layer, weak tea growth and too soft growth are also prone to disease.

Generally speaking, when the average temperature of the month is 20℃ and the relative humidity reaches 80%, the onset is the most favorable. In the season suitable for onset, if it rains continuously for 3-5 days, the disease can often break out. Generally, it begins in late March, and the epidemic period is from early April to early June. Alpine tea gardens are most suitable for occurrence because of fog, high humidity and low temperature.

Fourth, efficient prevention and control technology.

At present, farmers mainly use chemicals to control tea brown spot and white spot. Considering the problem of pesticide residues, it is suggested that agricultural control should be given priority to, supplemented by chemical control in time, and different chemical agents should be used alternately in early spring and early season to improve the control effect, reduce the use of pesticides and reduce farmers' production costs.

1, agricultural control

The pathogens of these two diseases are spread by wind and rain, so the organization, time and prevention in the same area should be unified. First of all, what farmers should do is to adjust measures to local conditions, choose suitable varieties and plant them reasonably and closely; Secondly, increase the application of organic fertilizer, phosphorus and potassium fertilizer, and pick it reasonably. After picking in each season, we must pay attention to supplementary fertilization to promote the recovery of tea trees and improve their disease resistance; Third, picking tea in batches at the right time and picking tender tea early can reduce infection and incidence; In addition, tea gardens should pay attention to ditch drainage in rainy season to reduce relative humidity; Weeds in and around the tea garden should be removed in time. Grass should be spread in the garden in summer to help fight drought and protect trees. In autumn and winter, diseased branches and leaves should be completely removed by pruning to reduce the source of overwintering bacteria. The whole garden should be sprayed with 1 Baume mixture, and the tea garden should be covered with antifreeze.

2. Chemical control

At present, the commonly used chemicals are 65% mancozeb wettable powder, 70% thiophanate-methyl wettable powder, 50% carbendazim wettable powder, 75% chlorothalonil wettable powder, 25% triadimefon wettable powder, 77% kocide, 70% thiophanate-methyl wettable powder, 70% mancozeb wettable powder and so on. For uniform spraying, 0.3% dihydrogen phosphate is used in combination. The results showed that the control effect of 25% carbendazim plus 500 times potassium dihydrogen phosphate (100g/ mu) was 85%.

3, other prevention and control measures

In recent years, the harm of brown spot disease and white spot disease has become more and more serious, seriously endangering the production of famous tea in early spring. It is an urgent problem to find safe and effective methods to control these diseases. There have been studies on biological pesticides, but the control effect is not as good as that of chemical control, and it is still being explored.

The results showed that spraying 100μg/mL chitooligosaccharides on tea trees for three times could activate the plant's own immunity and improve the disease resistance, and the control effect on brown spot was 53%. 100mg/mL camellia saponin can inhibit spore germination, and the control effect on white star disease is 88%.

summary

Brown spot disease and white spot disease of tea trees are very common, and often break out at the same time, which seriously affects the yield and quality of tea. At present, there is no ideal disease-resistant variety, chemical control is easy to produce resistance, and once the disease occurs, it is difficult to control, so everyone must give priority to agricultural control, supplemented by chemical control. According to their own medication habits, different drugs should be used alternately, and prevention should be carried out as soon as possible, and potassium dihydrogen phosphate should be added to improve the prevention and control effect.

Tea garden pruning, as an effective method to prevent and control tea brown spot and white spot disease, is the first one, which not only effectively reduces infected leaves, transmission media and living organisms, but also is a physical measure with simple operation and no pollution to the environment.