Cotton sprouts suddenly wilted

In the middle and late stages, the typical symptoms include: (1) the petiole base becomes soft and shrinks due to water loss. (2) Yellowing of the leaf edges, with chlorosis in the tissue but green veins; later, the leaves turn purple, become shriveled, and brittle. (3) When the leaves fall, the top of the stem appears dry and burnt, with many buds dropping off. (4) Root stunting, with short and thin main roots often resembling "chicken feet." The number of fine roots is greatly reduced, and their color turns dark brown, with the tips showing brown rot.

Suggested measures: If the soil is too dry, water it promptly. If the soil is overly wet, ensure proper drainage. For fields with insufficient base fertilizer, especially those with low potassium levels, apply potassium and phosphate fertilizers as soon as possible to replenish nutrients. In addition, foliar sprays such as potassium dihydrogen phosphate, dipotassium phosphate, six-in-one yield enhancer, disease-resistant high-yield factor, high-boron high-potassium solution, and diammonium phosphate can be used to alleviate symptoms and improve plant health.

Second, cotton black root rot. After infection, the first sign is insufficient leaf supply, with leaves wilting during the day and recovering at night. Eventually, the entire plant wilts, and the leaves turn blue and dry. When pulled out, the main root's wood layer appears light brown, and the cross-section shows dark brown lesions (no lesions on the stem). This differs from conditions caused by malnutrition, drought, or lack of water, where the roots maintain a normal tender color. Black root rot is more severe in seedlings than in older plants.

The key differences between nutrient disorders and black root rot include: (1) Seedlings are slightly stunted, with curled or wilted leaves, and severely affected leaves turn blue and dry. (2) Stems and roots show purple-black discoloration, gradually rotting. When dried, the cortex turns brown, and the epidermis splits longitudinally, peeling off easily. High humidity leads to gray-white mold growth, which is the pathogen’s mycelium and conidia. (3) Infected roots are thinner, with increased lateral roots. The subcutaneous tissues become dark and brittle, and the root base swells. The number of bolls decreases significantly. (4) The peak of the disease occurs during the boll-opening stage, with leaves wilting, drooping, and quickly turning blue and dry without falling immediately.

The pathogen is a semi-known fungus from the Rhizoctonia genus, specifically Lepidium nodosum. It has a wide host range, infecting various crops like legumes, solanaceae, cucurbits, and mallows. The spores can survive in the soil for years and re-infect plants over winter. Disease occurrence is closely linked to temperature, with 15–20°C being ideal for infection and development. Below 15°C or above 27°C, the disease is rare, and above 30°C, it is almost nonexistent. Continuous cropping, clayey soil, slightly acidic to alkaline pH, high organic matter, low-lying areas, flood irrigation, and long-term soil moisture all contribute to disease spread.

Suggested control measures: Once symptoms appear, use a 50% carbendazim solution diluted 600 times, 6-gao-lic acid I-garicin diluted 1000 times, one-limb 3000 times, 70% triadimefon 500 times, and 70% hymexazol. Add alizarin lactone, DA-6, agroxigenin, sodium nitroprusside, cytokinin, or the above-mentioned foliar fertilizers. Spray twice. For severely infected plants, applying the liquid directly to the roots can produce excellent results.

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