Tobacco brown spot disease is a serious disease that occurs extensively in the world's tobacco districts. It is estimated that the annual incidence of black spot disease accounts for about 30-35% of China's tobacco planting area. Not only does the disease cause the incompleteness of tobacco leaves, the lesions continue to expand during the baking process, which results in uneven coloration of the baking leaves, uneven thickness and grades of the leaves, and an inconsistency in the intrinsic quality, which reduces the industrial use value.
First, the symptoms.
Tobacco brown spot disease mainly begins when the tobacco leaves are nearly mature, and gradually develops from the lower leaf of the tobacco plant from bottom to top. The main hazards are the leaves, stems, pedicels, pods are also endangered. The lesions initially appeared yellow-brown small spots on the leaves and later turned brown. In general, the initial spot is less than 0.1cm, and then gradually expanded, the lesion diameter of up to 1-2cm. The lesions are round or irregularly round, brown, and the lesions produce obvious concentric ring patterns. The edges of the lesions are obvious and there are pale yellow halos around the lesions.
Second, the incidence conditions.
The main conditions affecting the occurrence and prevalence of tobacco blast disease are: disease resistance of the varieties, reproductive stage and environmental conditions.
1, the variety of resistance. Disease resistance of tobacco varieties has a greater impact on the occurrence of diseases. 2, the different growth stages of tobacco plants. Tobacco brown spot disease is a disease of tobacco leaves at maturity, and it is resistant to disease at the seedling stage. With the maturity of tobacco leaves, disease resistance is weakened, and the disease starts from the bottom and spreads horizontally at an early stage and then spreads vertically. 3, the impact of climate factors. The temperature mainly influences the duration of the disease and the duration of the incubation period. Humidity mainly affects the extent of the disease. 4, the impact of planting density. Excessive planting density results in poor ventilation and light transmission in the field, which is conducive to the reproduction of the disease. 5, the impact of fertilization. The incidence and disease index of the disease are decreasing with the increase of potassium fertilizer. Therefore, appropriate proportions of nitrogen, phosphorus, and potassium, appropriate increases in phosphorus and potassium fertilizers, and the use of nitrogen fertilizers can reduce disease.
Third, prevention and control.
According to the law of the occurrence of the disease, prevention and control should adopt comprehensive prevention and control measures combining disease-resistant varieties, chemical control and rational cultivation measures.
1. Plant disease-resistant or disease-resistant varieties.
2, pharmaceutical control. Use 40% sclerotium net wettable powder, using a concentration of 400-500 times (50-60kg per mu of liquid medicine, according to the size of the tobacco plant spray spraying liquid, generally spray uniform and thoughtful, such as rain to make up the spray, its The drug efficacy is stable at more than 75%, and it is currently a good agent for prevention and treatment of disease.10% Polaroid wettable powder, generally 600 to 800 times (60 kg per mu), its control effect and sclerotia net Similar effect, but also up to 70%.
3, improve the cultivation measures. (1) Early planting at a proper time. The occurrence of the disease is mainly in the late growth period of tobacco. The spring tobacco can be planted in due time and matured earlier to avoid the occurrence of the disease during the mature period of leaves. It is an effective measure to control the occurrence of the disease.
(2) reasonable density. Insufficient illumination due to excessive planting density and mutual shading between leaves are conducive to the reproduction of pathogenic bacteria, resulting in severe disease occurrence. Therefore, according to the characteristics of varieties, soil fertility conditions, to do a reasonable dense planting, the density of planting leaves is not suitable for ridges, generally around 1100-1200 strains.
(3) Rational fertilization. Tobacco fields should be appropriately increased phosphorus and potassium fertilizers. The ratio of nitrogen, phosphorus, and potassium is preferably 1:1 to 2:3, or 1% of phosphoric acid is sprayed on the foundation stage, the prosperous period, and the flat top stage on the basis of nitrogen, phosphorus, and potassium 1:1:1. Potassium hydrogen is also effective for three times. Reasonably leave the leaves to avoid the appearance of large and small leaves on the leaves of tobacco plants.
(4) Do a good job in field sanitation to reduce the source of infection.
(5) Implement rotation. The red-rotating crop reduces the amount of bacteria in the soil, which can reduce the risk of disease.
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