How to prevent cotton red leaf stem blight? These integrated measures must be mastered

Cotton red leaf stem blight is a physiological disease. In recent years, it has occurred in large amounts in the cotton region of the Yangtze River Basin in our area. It begins at the early flowering stage, and is more severe and widespread from the full flowering stage to the boll-setting stage. In our area specifically, it occurs sporadically in July and August. It reaches its peak from mid-to-late September to October. Lightly affected plants are yellow and thin, with few and small bolls, short fiber, and poor boll opening; severely affected plants die prematurely, and the bolls cannot mature, greatly affecting yield.

1. Disease symptoms. At the early stage of the disease, red and purple spots appear on the leaves, gradually spreading until the whole leaf turns reddish brown or brown. The leaves drop from bottom to top, leaving bare stems. Sometimes diseased leaves may also be red-yellow, accompanied by plant wilting, ultimately leading to the death of the whole plant. After rain when the sky just clears, the wilting symptoms are especially obvious, and from a distance it looks like cotton Fusarium wilt, but the vascular bundles inside the stem and roots do not turn black.

2. Causes. Through years of investigation, it has been confirmed that cotton red leaf stem blight occurs more severely in fields planted with insect-resistant cotton and with little potassium applied, and occurs more severely in sandy loam fields than in horse-liver soil fields. For example, in 2000, in our area, all 150 mu of cotton in plots 1-4 of the 8th team of Menghu Farm developed cotton red leaf stem blight, and by October 18 all the leaves had fallen off, greatly affecting yield. According to the investigation, all 4 plots were sandy loam, the cotton variety planted was insect-resistant cotton 410, and no potassium fertilizer or phosphorus fertilizer was applied in the flowering and boll fertilizer; only cake fertilizer and urea were applied, at 40 kg per mu and 25 kg of urea respectively, and the disease incidence rate was 58.3% higher than that of the adjacent 7th team of Menghu.

In addition, fields with premature senescence have more severe disease. The main reason is insufficient supply of fertilizer and water during the vigorous reproductive growth period, which causes a poor root growth environment, makes the cotton plants less stress-resistant, and worsens the occurrence of red leaf stem blight; prematurely senescent cotton plants are also more easily infected by other pathogens, inducing other diseases.

3. Control measures

1. Select disease-resistant varieties. Since the cotton bollworm outbreak in the cotton region of the Yangtze River Basin in 1998-1999, the pest disaster caused heavy losses to cotton farmers, and the planting area of insect-resistant cotton has reached more than 98%, which is one of the main reasons for the major outbreak of cotton red leaf stem blight in our area. It is recommended to rationally select cotton varieties and plant an appropriate amount of hybrid cotton to suppress the occurrence of cotton red leaf stem blight.

2. Fertilize rationally and strengthen fertilizer and water management. Increase the application amount of organic fertilizer. Topdressing should be applied in split applications, light first and heavy later, with a reasonable ratio of nitrogen, phosphorus, and potassium fertilizers, and appropriately increase the amount of potassium fertilizer in potassium-deficient fields. Do a good job in drought resistance and drainage, irrigate in a timely manner to resist drought, coordinate the supply of fertilizer and water, and use water to promote fertilizer uptake.

3. Strengthen field management. Carry out timely intertillage. In dry seasons, carry out shallow intertillage in a timely manner to cut off capillary action, reduce water evaporation, preserve soil moisture, and promote root development, which is beneficial to cotton plant growth and increases resistance. In affected fields, apply quick-acting potassium fertilizer in a timely manner to reduce the occurrence of the disease.

4. Carry out timely chemical control. After cotton develops the disease, promptly spray fungicides such as metalaxyl and carbendazim 2-3 times to prevent invasion by other pathogens and alleviate the symptoms. When spraying, 100 g of potassium dihydrogen phosphate per mu can be used as a foliar fertilizer, which can both supplement nutrients and achieve a disease-control effect.

Once cotton red leaf stem blight occurs, effective measures must be taken immediately to control the spread and expansion of the disease and reduce losses.