Comprehensive Control Measures of Cotton Blight
Infected cotton seeds before germination caused bad seeds, which were infested before emergence and finally caused rotting buds. After the cotton seedlings were unearthed, they suffered yellow-brown lesions at the base of the near-early soil surface. The lesions gradually spread around the entire base and contracted. The diseased seedlings wilted and fell to death. Pulling up the diseased seedlings, the cortex below the base of the stem is left in the soil, leaving only the rat tail-like xylem of the tip. After the cotyledon is victimized, irregular brown lesions are often produced in the middle of the cotyledon, often causing perforation. After the disease has occurred, it often leads to the death of cotton seedlings. White thin sparse mycelia are common on the base and surrounding stems of diseased and dead seedlings.
I. Transmission routes and conditions
The pathogens used conidia to overwinter on cottonseed linters, and a few of them were latent on the seed coats of cottonseeds or in the cotyledons between winters. Seed carriers were an important primary infestation source. Then, the disease department produces conidia that are transmitted by wind and rain, insects, and irrigation water. Cotton boll pathogens invade cottonseeds. The diseased leaves, stems, and leaves fall into the soil, causing soil contamination, causing the onset of seedling stage, and infestation of cotton bolls by rainwater splashes, causing morbidity.
Second, the symptoms
Cotton blight occurs in all major cotton areas in China, and can occur every year in the field, killing cotton seedlings, and lack of seedlings in cotton fields. It is one of the world's diseases. The main symptoms are: rotten and rotten buds before seedling emergence. After the seedlings have been unearthed, spots of brown depression appear near the ground at the base of the young stems; afterwards, they develop around, and the color gradually turns dark brown; until the lesions expand and contract, they cut off the supply of water and nutrients and cause the cotyledon to droop. Finally, the seedlings will fall. The diseased cotton seedlings generally do not have spots on the cotyledons, but irregular brown spots are sometimes formed in the middle of the cotyledons, and the lesions break and perforate later. The pathogenic bacteria are propagated by the mycelium, and the mycelium has no color at the initial stage of growth. It is yellowish-brown at the later stage and has multiple septa. This is the most easily identified feature of Rhizoctonia solani. The onset of disease is characterized by low temperature and rainy conditions. The optimum soil temperature for invading cotton seedlings is 17～23°C. The pathogenicity of 23°C or more is gradually reduced. The cotton seedlings are not invaded until 34°C. The higher the humidity, the heavier the incidence. .
Third, control methods
1. Bed soil treatment
(1) Zeson zinc. Use 3 to 4 grams per square meter, mix the right amount of fine soil, and spread it evenly into the soil.
(2) Pentachloronitrobenzene. 6 grams per square meter of the amount of mixed fine soil, made of toxic soil, sprinkled in the soil.
(3) Formalin. 35% to 40% of formalin solution, 50 ml of water per square meter of soil, 6 to 12 liters of water, evenly poured into the soil 7 days before sowing, covered with plastic film and sealed for 3 to 5 days, then sowed after turning .
(4) Carbendazim. Add 50% carbendazim powder 40g per cubic meter soil, mix and cover with plastic film for 2 to 3 days.
2. Agricultural control
(1) timely sowing. With good quality cotton seeds, when the average temperature is above 20°C, sowing is appropriate. The determinant of root disease caused by early sowing is temperature, while the determinant of root disease caused by late sowing is humidity.
(2) Deep plowing winter irrigation, fine soil preparation. Northern cotton fields should be cultivated in autumn, and winter irrigation should be completed before the soil is frozen; in the southern two mature cotton fields, winter irrigation should be deepened in the wheat row, and the loose soil should be used for weeding and clearing before planting, and the cotton fields should be turned twice in winter before being planted. In cotton fields that turned over once, the incidence in the seedling stage was lighter than in the cotton fields that had not been plowed.
(3) Deep ditch sorghum, drainage drainage. There are more spring rains in the southern cotton fields, and the cotton fields are vulnerable to waterlogging, which is an important cause of large numbers of dead seedlings. Deep ditch sorghum in cotton fields can eliminate dark stains in alum, reduce soil moisture, and help prevent disease and protect seedlings.
(4) Rotation prevention and disease prevention. It is best to use rice-cotton rotation for 2 to 3 years, and the effect of disease prevention is above 50%.
(5) soaking in warm soup. When the seeds were immersed in hot water at 55°C for 30 minutes or hot water at 60°C for 20 minutes, the incidence rate was reduced by about 50%.
3. Field spray prevention
(1) Cotton Zeng Ling and carbendazim. The cotton seedlings are sprayed with 0.16% cotton Zeng Ling (berberine hydrochloride brass) 800 times, 50% carbendazim WP 800 times, and 50% thiram WP 800 times. The liquid drip into the soil along the main stem, once every 3 to 5 days, 3 times in a row, the control effect is about 50%.
(2) Bordeaux spray with half amount. 200 times the amount of Bordeaux spray, spray along the main stem of the cotton seedlings, so that the liquid drip along the main stem into the soil, 10 to 15 days once, 2 or 3 times, the prevention effect is good. 200 times the half-Bordeaux liquid configuration method is: copper sulfate: lime: water = 1:0.5:200. The specific preparation method is: dissolving copper sulfate in a large amount of water (tenth of a tenth of the water) and forming a diluted sulfur-coppered copper liquid; dissolving lime in a small amount of water (one tenth of water) to make it into thick lime Milk; then slowly dilute the copper sulphate solution into the milk of concentrated lime and stir it up while stirring (you must not pour lime milk into the copper sulphate solution). In order to guarantee the quality of Bordeaux mixture, several issues must be paid attention to: A. Metal containers must not be used in the preparation; in particular, iron; B should use high-quality quicklime (ie, quick lime), and do not use slaked lime. If slaked lime is used, it must also be fresh. , and the amount to increase about 30%; C copper sulfate is best pure blue, should not be entrapped green or yellow-green impurities; D water temperature should not be too high, generally not exceeding the temperature as degree.
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