Characteristics and Control Methods of Cotton Rhizoctonia Damping-Off

Characteristics of cotton damping-off: After the cotton seedlings emerge, they are damaged; in the early stage, yellow-brown lesions appear at the base near the soil surface, and the lesions gradually expand to surround the entire base, showing obvious constriction; the diseased seedlings wilt, lodge, and die. After the cotyledons are damaged, yellow-brown irregular lesions mostly appear in the middle of the cotyledons and often fall off and perforate. After this disease occurs, it often causes cotton seedlings to die in patches. On the stem base of diseased and dead seedlings and around it and on the soil surface, sparse white mycelium is commonly seen.

Control methods:

1. Strengthen field management. After emergence, intertillage should be done early; generally when about 70% have emerged, intertillage and loosening of the soil should be carried out to increase soil temperature, reduce soil moisture, make the soil loose and well ventilated, which is beneficial to the development of the cotton seedling root system and inhibits root disease. Strengthen insect control, thin seedlings in time, and collect diseased and dead seedlings for centralized burning to reduce pathogen transmission in the field.

2. Chemical control. Cotton seedlings are prone to disease under low temperature and rainy conditions, so spray promptly for protection before cold waves and rainy weather; generally when about 80% have emerged, spraying should be carried out, and afterward the number of sprays and the type and concentration of chemicals should be decided according to the condition of the disease. Methods of use: ① Spraying. In the early stage of disease, use 10 ml of 30% metalaxyl-hymexazol or Shimaidan + 5 ml of Shenqi Buxiu or 15 ml of shenqinmycin + 15 ml of 38% oxadixyl-cymoxanil-copper fungicide in one bucket of water (15 kg), spray along the main stem of the cotton seedlings so that the solution drips down the main stem into the soil, spraying 2 to 3 times consecutively with an interval of 10 to 15 days, which has a special effect on controlling cotton damping-off at the seedling stage; ② Root drenching. In the early stage of disease, use 15 ml of shenqinmycin + 15 ml of metalaxyl-hymexazol + 15 ml of 38% oxadixyl-cymoxanil-copper fungicide in one bucket of water for root drenching, drenching 2 to 3 times consecutively with an interval of 5 to 7 days; ③ Brushing. Use 10 ml of Shenqi Buxiu or Shimaidan + 5 ml of aiduoshou or 15 ml of shenqinmycin + 15 ml of 38% oxadixyl-cymoxanil-copper fungicide in 0.5 kg of water, pull away the soil around the cotton plant to expose the lesions, brush with a bristle brush, brushing 2 to 3 times consecutively with an interval of 7 to 10 days.