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Cotton sprouts suddenly wilted
Cotton plants suffering from weakened root absorption often show signs of malnutrition. The leaves begin to wilt from the top down and from the outside in, but they don't turn pale green. There are no visible lesions on the roots or cuttings. This condition is typically caused by prolonged drought, insufficient water, or poor soil moisture, which leads to reduced root development and blocked nutrient uptake. Sudden heavy rains or continuous rainfall can worsen the issue. Sandy soils, infertile soils, saline-alkali soils, and fields with low base fertilizer or potassium levels are more prone to this problem. Affected cotton fields may experience premature aging in the mid to late growing stages, resulting in significant yield losses.
In the middle and late growth stages, symptoms may include: (1) the petiole base becoming soft and shriveled, (2) yellowing at the leaf edges with chlorotic tissue but green veins, later turning purple and becoming brittle, (3) dry, shriveled tops with many bolls dropping off, and (4) stunted roots that appear thin and short, often referred to as "chicken roots," with dark brown coloration and rot at the tips.
To address this issue, ensure timely irrigation if the soil is dry, or aerate the soil if it's too wet. If base fertilizers were insufficient, especially in fields lacking potassium, apply potassium and phosphate fertilizers as a top dressing. Foliar sprays such as potassium dihydrogen phosphate, dipotassium phosphate, six-in-one yield enhancer, disease-resistant high-yield factor, high-boron and high-potassium formulas, and diammonium phosphate solution can also be used to help alleviate symptoms.
Another common issue is black root rot. Affected plants show leaf wilting during the day, which may recover later, but eventually lead to complete wilting and blue-dry leaves. When pulled out, the main root’s wood layer appears light brown, with dark brown lesions inside the root, though the stem remains unaffected. This condition is more severe in seedlings than in mature plants.
Key differences between nutrient disorders and black root rot include: (1) stunted seedlings with curled or wilted, blue-dry leaves, (2) purple-black stems and roots that rot over time, with cracked bark and gray mold under high humidity, (3) thinner roots with increased lateral roots, (4) dark and brittle subcutaneous tissues, and (5) swollen root bases and fewer bolls.
The pathogen responsible is a fungus from the Rhizoctonia genus, specifically Lepidium nodosum, which affects various crops like legumes, solanaceae, cucurbits, and mallows. Spores can survive in the soil for years and infect plants through infected residues. Disease occurrence is influenced by temperature, with 15–20°C being ideal for infection. It becomes rare below 15°C or above 27°C, and almost nonexistent above 30°C. Continuous cropping, compacted soil, slightly acidic to alkaline conditions, high organic matter, low-lying areas, and excessive irrigation all favor disease development.
Recommended treatments include applying 50% carbendazim at 600 times dilution, 6-gao-lic acid I-garicin at 1000 times, one-limb at 3000 times, 70% diuresis at 500 times, and 70% hymexazol. Adding regulators like alizarin lactone, DA-6, agroxigenin, sodium nitroprusside, and cytokinin can enhance effectiveness. Spraying twice is usually sufficient. For severely affected plants, applying these solutions directly to the roots can produce better results.
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