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What are the three main causes of cotton red leaf stem blight?

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Cotton red leaf stem blight is a physiological disease caused by potassium deficiency. It occurs in the middle and late stages of cotton growth, and in dry years the occurrence and severity of damage are more serious. In the field, cotton generally begins to show symptoms at the bud stage, and the disease is most severe during the boll-setting and boll-opening stages. Symptoms mainly appear on the leaves. Diseased leaves develop from top to bottom and from the outside inward. Diseased leaves begin to lose green color from the edges, first turning yellow, then producing red spots, and finally the whole leaf turns red, the mesophyll thickens, wrinkles and becomes brittle, while the veins remain green. In severe cases, the leaves of the whole plant lose green color, then turn red and brown, the leaves scorch and fall off, leaving bare stems, and the plant

Cotton red leaf stem blight is a physiological disease caused by potassium deficiency. It occurs in the middle and late stages of cotton growth, and in dry years the occurrence and severity of damage are more serious. In the field, cotton generally begins to show symptoms at the bud stage, and the disease is most severe during the boll-setting and boll-opening stages. Symptoms mainly appear on the leaves. Diseased leaves develop from top to bottom and from the outside inward. Diseased leaves begin to lose green color from the edges, first turning yellow, then producing red spots, and finally the whole leaf turns red, the mesophyll thickens, wrinkles and becomes brittle, while the veins remain green. In severe cases, the leaves of the whole plant lose green color, then turn red and brown, the leaves scorch and fall off, leaving bare stems, and the plant dies prematurely. The vascular bundles of diseased plants generally do not discolor, which is an important characteristic distinguishing it from cotton Fusarium wilt and Verticillium wilt.

I. Causes of the disease. (1) The soil lacks organic matter, especially low soil potassium content. In Haimen and other places, farmers habitually apply sheep pen ash and human feces and urine to corn and vegetable fields, while cotton fields are mainly fertilized with nitrogen fertilizers such as urea, and potassium chloride is rarely applied as a topdressing, so potassium deficiency in cotton fields is relatively serious. (2) High temperature and drought affect potassium uptake. Cotton's absorption of nutrients is related to soil moisture conditions. From July to August, prolonged drought and water shortage in cotton fields will accelerate the fixation of soil potassium, affect the plant's absorption of potassium fertilizer, and cause potassium deficiency in the cotton plant. In particular, after a long drought, when heavy rain or continuous rainy weather occurs, large amounts of available potassium in the soil are lost with water, and the absorption capacity of the cotton root system weakens, making it more likely to cause an outbreak of red leaf stem blight. (3) Bt cotton is sensitive to potassium. In recent years, the proportion of Bt cotton planted in Haimen and other places has reached more than 90%, and Bt cotton has a relatively high potassium requirement and is sensitive to potassium, making it prone to red leaf stem blight.

II. Control measures. (1) Topdressing to supplement potassium. During the bud and boll stages of cotton, open furrows and apply plant ash, human feces and urine, and sheep pen ash to increase the available potassium in the soil. It can also be combined with the application of flower and boll fertilizer, applying 15 kg of potassium chloride per mu in furrows. It can also be combined with pest control by spraying potassium fertilizer, using 400 g of potassium dihydrogen phosphate per mu diluted with water for spraying, focusing on the underside of the middle and upper leaves, spraying once every 7-10 days, for 2-3 consecutive sprays. (2) Scientific irrigation. If the soil is relatively dry at the early stage of the disease, irrigate promptly to combat drought. Furrow irrigation is recommended, and flooding irrigation should be avoided. After rain, drain water and cultivate in time to enhance soil permeability and improve the vitality of the cotton root system. (3) Select disease-resistant varieties. Reasonably select cotton varieties, and plant fewer Bt cotton varieties in years when cotton bollworm occurs lightly.

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