The main diseases of cotton seedlings include anthracnose, blight, brown spot, and red rot, among which anthrax and blight are more common, and the damage to cotton seedlings is also the most serious. First, the main symptoms of each disease and ways of transmission 1, anthrax disease: the leaves and stems of cotton seedlings may be harmful. After the seedling was injured, red-brown nucleus-shaped streak (vertical fissure) appeared on the stem, the lesion became brown after being enlarged, and then blackened and turned rotten, causing the cotton seedlings to fall and die. When the air is wet, orange-red sticky substances are produced on the lesions. A semi-circular brown spot develops on the edges of the leaves when the leaves are infested, and the lesions are red-brown when the air is dry, and when the leaves are severe, the leaves are dead and fall off. The germination temperature of anthracnose spores was 10°C, approximately the same as the initial temperature of germination of cotton seedlings. After germination of the spores, the germ tube invaded from the top of cottonseeds. 2, blight: cotton seedlings in the most vulnerable to disease two weeks after emergence, the base of the stem near the ground from dark brown to dark brown, and gradually sag down rot, so that the site of the disease shrinking shrinkage, severe cotton seedlings fall to death . Rhizoctonia pathogenic bacteria latent in the soil, when appropriate conditions will invade the roots, the next year by wind and rain, harm cotton seedlings, especially buds out of the seed shell to the cotyledon before the most vulnerable. 3. Brown spot: The needle-point purple-red spots began to appear on the leaves of the injured cotton seedlings. The lesions were yellow-brown after the lesions expanded, slightly raised, and scattered small black spots below. The diseased tissue is easily detached and appears perforated, causing severe leaf loss. 4. Red rot: generally harmed before cotyledon excavation, mainly harming rhizome transition zone and cotyledons and true leaves. The radicles were tan-brown after being victimized, gradually rotted, resulting in rotting buds; when the roots were damaged, the color of root tips and lateral roots became yellow, and when they were severe, the whole roots became brown and rot; the cotyledons began to appear yellow water spots, and then gradually appeared irregular Grey red lesions. The pathogenic bacteria of cotton seedlings mainly overwintered on cotton seed, soil and diseased plant residues. In general, low temperature and high humidity are not conducive to the growth of cotton seedlings and are conducive to the infestation of pathogens. The severity of the disease at the seedling stage is related to the seedling age of the cotton seedlings. Generally, the seed coat of the cotton is shedding, and the cotyledon begins to develop disease. When the two cotyledons develop completely, the lateral roots and the true leaves begin to grow. The disease resistance of cotton seedlings will gradually increase, and the disease will gradually ease. Second, the prevention and treatment methods Cotton seedling disease prevention and treatment should be based on prevention, to create favorable conditions for the growth of cotton seedlings unfavorable to bacterial infection, and through the spray chemical agents to control and prevent the occurrence and spread of the disease. 1.Selected cotton seeds: After degreasing seeds, diseased seeds, insects, etc. on the basis of sulfuric acid degreasing (can be selected once after depilation), the emergence rate of cotton seeds can be significantly increased, and cotton seedlings can be enhanced. The resistance to disease. 2, paddy and dry rotation: in the seedling stage more serious and conditional conditions can be rice and cotton rotation. After the cotton field has been planted with rice for 2-3 years and then planted cotton, the disease at the seedling stage can be effectively controlled and generally can be reduced by more than 50%. 3, to strengthen the management of the field: seedbed should pay attention to timely ventilation and hardening seedlings, dry bed temperature, increase potassium fertilizer. Seedbed beds and fields need to be well drained to lower the water table. Strengthen the disease resistance of cotton seedlings by strengthening field management and create environmental conditions that are not conducive to the spread of germs. 4. Seed treatment: Cotton seedlings of coated cotton seedlings have stronger resistance to disease. Uncoated cotton seedlings can be seed-dressed with carbendazim, amizolide, etc. after sulfuric acid degreasing, which can significantly improve the disease resistance of cotton seedlings. . 5. Chemical control: After the onset of cotton seedlings, a 1:1:200 Bordeaux mixture can be used for spray treatment after cotyledon leveling. It can also be sprayed with 25% carbendazim gel suspension 200-300 times, usually once a week. , spray a total of 2-3 times.
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