1. Leukoplakia type: The disease occurred on the middle and lower leaves after the period of the tree cluster. There are many small water spots on the front of the leaves. The lesions are generally round, nearly round or irregular, with a diameter of about 1 to 3 mm and then turned brown, and turn grayish to white again within 1 to 2 days. The marginal tissue retreats slightly to yellow, and the lesions often concentrate on both sides of the main vein and lateral veins and on the tip of the vein. Finally, the center of the lesion was necrotic and subsidence, and perforation and shedding were severe. The center of the lesion is opaque with no black spots and black mold.
2. Brown spot type: This disease also occurs in the middle and lower leaves of the group tree period. Symptoms and their evolution are similar to those of the white-spot type, but the lesion no longer turns gray after it has turned brown. The lesions have deeper inner rims and are more pronounced at the junction of disease and health.
3. Ring spot type: lesions often have one or even two to three multi-point discontinuities around the white spot and brown spot, which resembles the symptoms of tobacco ring spot virus disease. It cannot be transmitted by vaccination such as sap rubbing. This ring spot on the same blade can occur simultaneously with the above two types.
4. Dust type: the lesions are extremely small and close to each other, like dust or common plant leaves are harmed by red spiders. The grayish white color at the beginning and the brownish color afterwards occurred mostly on the tips of the young leaves, the margins of the leaves, and on the leaves with slightly poorer growth. The perforation was rarely perforated.
Second, the environmental conditions of the disease
Occurrence of tobacco cicada disease, in addition to disease susceptibility of tobacco varieties, is also affected by the concentration and duration of O3 (pronounced: ozone), the growth period of tobacco plants and the age and maturity of leaves, and the meteorological conditions before and after the occurrence of disease. , the moisture content of tobacco plants, nutrient supply status of fertilizers, and the combined effects of other pollutants and the presence of pathogens (ie, ozone). After the tobacco plant enters the conglomerate, in case of low temperature, more rain, less sunshine, continuous rain on the sunny days, irrigation, high soil moisture content, leaf cell gap filled with water, insufficient supply of nitrogen, phosphorus and potassium fertilizer or imbalance, will lead to the occurrence of disease .
III. Comprehensive prevention and technical measures
1. Selection of resistant varieties: In our province, the promotion of varieties of safflower Dajinyuan is better than anti-tobacco climate speckle disease;
2. Strengthen the cultivation and management: Each tobacco zone should be transplanted in time according to the local climatic conditions, reasonably densely planted, enough base fertilizer should be applied, fertilizer should be applied in time, nitrogen fertilizer should be properly controlled, drainage should be taken care of to prevent water accumulation, reduce the humidity in the field, and timely cultivating and weeding. Increase ventilation and transmittance in the field, promote normal growth of tobacco plants, and increase the ability of tobacco plants to resist O3 (pronounced: ozone);
3. Application of pharmaceutical protection: in the disease-prone tobacco area, before and after the tobacco plant enters the group stage, use a quick solution of Bordeaux fluid with a quicklime: copper sulphate:water ratio of 1:1:180 or 80% 600-times dose of dexamethasone. Foliar spray control.
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