I. Identification of Cotton Verticillium Wilt
Verticillium dahliae can infect during the entire growth of cotton. Verticillium wilt is generally diseased after one month of sowing. Due to the resistance of cotton varieties, pathogenicity of pathogens and environmental conditions, Verticillium wilt shows different types of symptoms.
1. Seedling period. First, the edge of diseased leaves was soft and green, showing water loss. Irregular pale yellow lesions appeared between the veins. The lesions gradually expanded, became brown and dry, and the vascular bundles were obviously discolored. The second is that some strains are not obvious at the seedling stage and their appearance looks normal, but the cross section of the cotton is cut, and some xylem and vascular bundles have turned dark brown.
2. Adult stage. Verticillium wilt gradually developed after the budding period. Generally, in late June, Verticillium wilt strains gradually increased and reached the highest peak in flowering and ringing season in July and August. In recent years, the symptoms have been diversified. Common symptoms include: 1 The diseased plant gradually develops upward from the lower leaves, irregular yellowish patches develop between the veins, and the veins remain green near the veins. The edge of the diseased leaf curls upward. Sometimes there are purplish red dehydration wilting irregular lesions between leaves and veins, the lesions gradually expand, become brown spots, or even the entire leaf coke, fall off into light stalks; 3 sometimes leaves on the trunk or on the lateral branches of a large number of shedding After scorching, a large number of axillary buds and leaves may grow in the stems of the diseased plants or in the defoliated leafhoppers. 4 In July and August, during the cotton boll season, some plants were found in the fields in the middle of drought and heavy rainfall in summer. Some symptoms of acute Verticillium wilt often occur. First the cotton leaves are water-like, followed by sudden wilting, gradually falling off into light stalks; 5 Some yellowing of Verticillium wilt but the plants are not dwarfed and have little bells; Some Verticillium wilt strains change Be short, hardly bell, and even die.
Second, the pathogenesis, transmission and disease conditions of Verticillium wilt
1. The route of transmission. Verticillium dahliae is a disease that damages cotton vascular bundles. (1) The spread of cotton seeds has been confirmed in production practice; (2) Dissemination of diseased plant residues: diseased plants, diseased leaves, and diseased plant residues in cotton fields can be directly dropped into the ground or used to compost compost. It is an important way to cause the re-circulation of Verticillium wilt to spread. Some defoliants in the year will infect the new cotton plants and healthy cotton plants of the year. 3 Flowing water and agricultural operations can also cause the disease to spread. 4 spread by soil with bacteria, Verticillium dahliae in the soil, can live on humus or dormant in diseased plant residues, can survive in the soil for as long as 20 to 25 years, continuous accumulation of bacteria in cotton soil, serious illness . Once the cotton field is introduced into Verticillium dahliae, if measures are not taken in time, it will spread rapidly (especially after rain).
2. Incidence conditions. 1 The optimum temperature for the onset of Verticillium wilt is 22°C to 25°C, which is higher than 30°C. The onset is slow. When the temperature is 35°C or above, the symptoms are temporarily concealed. In June, when four or five true leaves of cotton seedlings began to develop, there were sporadic diseased plants in the fields; budding stage entered the appropriate stage of disease development and the disease developed rapidly; in July and August, the flowering and boll stage reached its peak. 2 Different cotton varieties have different resistance to Verticillium wilt. 3 The growth period of cotton is different, and the disease resistance is also different. When cotton grows from vegetative growth to reproductive growth, the disease resistance begins to decline, and the occurrence of verticillium wilt gradually increases. 4 Different cultivation conditions, the incidence of Verticillium wilt also vary. In the continuous cropping of cotton fields, the more bacteria accumulate in the soil, the heavier the disease; the larger the water, the faster the disease spreads; and the malnutrition is also the incentive for the host to become sick. Nitrogen and phosphorus are indispensable nutrients for cotton, but partial or heavy application. Nitrogen fertilizers can help promote the occurrence of Verticillium wilt.
Third, the comprehensive control measures of Verticillium wilt
1. Choose resistant varieties. This is the most economical and effective measure to control Verticillium wilt and increase cotton production.
2. The rotation is down. Crops grown in cotton fields for 3 to 5 years or plots with more diseased plants take rotation. Crops that have been grown for many years are replaced by crops.
3. Strengthen cotton field management. Clean cotton fields, reduce soil bacteria sources, drain gutters in time, and reduce moisture in cotton fields, which is not conducive to breeding and infestation of pathogens. Balanced fertilization, reasonable use of nitrogen, phosphorus, and potassium, should not use excessive nitrogen fertilizer, re-applied organic fertilizer, focusing on nitrogen and potassium fertilizer, in order to facilitate the robust growth of cotton plants, and enhance their own resistance to stress. Spraying potassium fulvic acid 3 to 4 times throughout the growing season can reduce the incidence of Verticillium wilt.
4. Drug treatment. 1 Soil disinfection before cotton planting: Use soil disinfectants such as quintozene, Qingwu or Libenjing, together with fertilizer to apply deep plowing to the soil. 2 The management of cotton seedlings should adopt the measures of “prevention as the main and treatment as the supplementâ€. Spray 70% mancozeb 500 to 600 times solution, 100% allicin or 1000 times solution. Seedlings are young and easy to absorb. The pesticides are sprayed 2 or 3 times at the seedling stage to reduce the risk of disease. It is easy to achieve the expected effect of prevention. 3 flower bell period. It is a period when Verticillium wilt is easy to occur. According to the obvious feature of Verticillium wilt, this method can be used to reduce costs. In the cotton field where the disease occurs lightly, the healthy cotton plants around the diseased plants and diseased plants are sprayed uniformly with 1000 times solution of ethyl allicin or 1000 times solution of chlorine-free nitrobenzene, and at the same time, 0.25-0.5 for each strain is used. Kilograms of liquid irrigation; for the more serious diseased plants, repeated spray irrigation 2 to 3 times, the diseased plants can be controlled in time; seriously remove the cotton field diseased plants, together with litter, concentrated for fuel use or timely burned in the field, remove Irrigate the root of the diseased plant at the same time to prevent the infection cycle of the year or the second year.
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