How to control tobacco red spot disease?

How to control tobacco red spot disease? Tobacco brown spot is a serious disease that widely occurs in tobacco areas of the world. It is estimated that the incidence area of tobacco red spot accounts for about 30% of the tobacco planting area in China every year. Red spot disease not only makes tobacco leaves incomplete, but also continues to expand the disease spot in the curing process, resulting in uneven color, uneven thickness and grade of flue-cured leaves, but also reduces the industrial use value because of the inherent quality disharmony. First, symptoms. Tobacco brown spot mainly occurs when the tobacco leaves are nearly mature and develops gradually from the bottom to the top of the lower leaves of the tobacco plant. The main harmful parts are leaves, stems, pedicels and capsules. The disease spot initially appeared on the leaves with small yellowish-brown round spots, and later turned brown. Generally speaking, the spot is less than 0.1cm at first, and then it expands gradually, and the diameter of the spot can reach 1-2cm. The disease spot is round or irregular round, brown, the disease spot produces obvious concentric wheel lines, the edge of the disease spot is obvious, and there is a yellowish halo on the periphery. Second, the condition of the disease. The main conditions affecting the occurrence and epidemic of tobacco brown spot are disease resistance, growth stage and environmental conditions. 1. Resistance of varieties. The disease resistance of tobacco varieties has a great influence on the occurrence of diseases. 2. Different growth stages of tobacco plants. Tobacco brown spot is a disease in the mature stage of tobacco leaves, which is resistant to disease in the seedling stage. With the maturity of tobacco leaves, the disease resistance weakens and occurs from the bottom up. It spreads horizontally at the initial stage and then vertically. 3. The influence of climatic factors. Temperature mainly affects the occurrence of red spot disease sooner or later and the duration of incubation period, while humidity mainly affects the degree of disease. 4. The influence of planting density. The planting density is too high, resulting in poor ventilation and light transmission in the field, which is conducive to the reproduction of Alternaria alternata, and red star disease often occurs seriously. 5. The effect of fertilization. The incidence and disease index of red spot disease decreased with the increase of the amount of potassium fertilizer. Therefore, the disease can be alleviated by proper proportion of nitrogen, phosphorus and potassium, properly increasing phosphorus and potassium fertilizer and controlling the amount of nitrogen fertilizer. Third, prevention and control. According to the occurrence law of red spot disease, the comprehensive control measures should be adopted by planting disease-resistant varieties, chemical control and reasonable cultivation measures. 1. plant disease-resistant or disease-tolerant varieties. 2. Chemical control. Use 40% sclerotia net wettable powder, use concentration 400-500 times (50-60kg per mu), spray according to the size of tobacco plant, generally spray evenly and thoughtfully, if you want to spray in case of rain, its efficacy is more than 75%, which is a good agent for the prevention and control of red spot at present. 10% Polaroid wettable powder, generally used 600 to 800 times (60kg per mu), its control effect is similar to that of sclerotia net, which can reach more than 70%. 3. Improve the cultivation measures. (1) planting early at the right time. The occurrence of Alternaria alternata mainly occurs in the late growth stage of tobacco. Spring tobacco can be planted early and harvested early, so that the leaf maturity can avoid the epidemic period, which is an effective measure to control the occurrence of Alternaria alternata. (2) reasonable density. The planting density is too high and the light is insufficient, and the leaves shade each other, which is conducive to the reproduction of pathogens and lead to serious diseases. Therefore, it is necessary to make reasonable close planting according to the characteristics of varieties and soil fertility conditions, and the density should be about 1100-1200 plants. (3) rational fertilization. Appropriate application of phosphorus and potassium fertilizer should be applied in tobacco fields. The suitable ratio of nitrogen, phosphorus and potassium is 1:1-2:3, or on the basis of 1:1:1 of nitrogen, phosphorus and potassium, the effect of spraying 1% potassium dihydrogen phosphate three times in rosette stage, prosperous stage and flat top stage is also better. Leave leaves reasonably to avoid the appearance of big and small leaves of tobacco plants. (4) do a good job in field hygiene to reduce the source of infection. (5) implement crop rotation. Red rotation can reduce the content of bacteria in the soil and reduce the harm of red spot disease. Click to get more tobacco planting techniques click to get more flower planting techniques