Three inducing factors of Red Leaf Stem Blight in Cotton

Cotton red leaf stem blight is a physiological disease caused by potassium deficiency, which occurs in the middle and later stages of cotton growth, especially in dry years. The disease of cotton in the field generally begins to show in the bud stage, and the disease is the most serious in the boll opening stage. The symptoms were mainly on the leaves, and the diseased leaves developed from the top to the bottom and from the outside to the inside. The diseased leaves began to lose green from the edge, first yellow, then red spots, and finally the whole leaf turned red, the mesophyll thickened, wrinkled and brittle, and the veins remained green. When the disease is serious, the leaves of the whole plant turn red and brown after losing green, the leaves scorch and fall off into smooth rods, and the plants die ahead of time. Vascular bundles of diseased plants generally do not change color, which is an important feature different from cotton Verticillium wilt.

First, the cause of the disease. ⑴ soil is lack of organic matter, especially low content of potassium. In Haimen and other places, farmers are used to applying sheep pen ash and human feces to corn and vegetable fields, cotton fields mainly apply urea and other nitrogen fertilizer, rarely topdressing potassium chloride, and the lack of potassium in cotton fields is more serious. High temperature and drought of ⑵ affected potassium uptake. The absorption of nutrients by cotton is related to soil water condition. Drought and water shortage in cotton field for a long time from July to August will accelerate soil potassium fixation, affect plant absorption of potassium fertilizer, resulting in potassium deficiency in cotton plants. Especially in the case of rainstorm or continuous rain after a long drought, a large amount of soil available potassium is lost with water, and the root absorption capacity of cotton plant is weakened, which is more likely to cause the outbreak of red leaf stem blight. ⑶ cotton is sensitive to potassium. In recent years, the planting proportion of insect-resistant cotton in Haimen and other places has reached more than 90%, while insect-resistant cotton needs a large amount of potassium, is more sensitive to potassium, and is prone to red leaf stem blight.

Second, prevention and control countermeasures. ⑴ topdressing fertilizer to supplement potassium. Plant ash, human feces and urine and sheep fold ash were applied in cotton bud and boll stage to increase the available potassium in the soil. Can also be combined with the application of flower and boll fertilizer, 15 kg potassium chloride per mu. Can also be combined with insect control potassium fertilizer, per mu with 400 grams of potassium dihydrogen phosphate plus water spray, focusing on the back of the middle and upper leaves, every 7-10 days, 2-3 times. ⑵ scientific irrigation. In the early stage of the disease, if the soil is dry, we should timely irrigate to fight drought, advocate furrow irrigation and avoid flooding irrigation. Timely drainage and ploughing after rain can enhance soil permeability and improve cotton root activity. Resistant varieties were selected for ⑶. Reasonable selection of cotton varieties, in the year of light occurrence of cotton bollworm, fewer insect-resistant cotton varieties.