First, the factors that affect the shedding of cotton bolls:
1. Physiological disorders: Light is a key factor. In closed cotton fields, the lower parts of the plant receive less sunlight, which reduces photosynthesis and limits the supply of organic nutrients, leading to premature boll drop. Temperature also plays a role—when daily average temperatures fall below 20°C or rise above 32°C, boll shedding increases. Excessive soil moisture can also lead to higher boll loss. Additionally, improper nutrient management, such as insufficient fertilization, incorrect fertilizer ratios, or poor timing of application, can contribute to boll drop.
2. Pests and diseases: Several pests and diseases can interfere with the normal growth of cotton plants. Some directly damage flowers, buds, and bolls, causing significant losses. For example, cotton bollworms and aphids can weaken the plant and cause bolls to fall prematurely. Diseases like fusarium wilt or verticillium wilt can also reduce boll retention by affecting the plant’s vascular system.
3. Mechanical damage: Human activities, animal interference, or machinery operations in the field can cause physical damage to cotton plants, resulting in boll drop. Natural disasters such as strong winds, hail, or heavy rain can also lead to mechanical stress on the plants, increasing the likelihood of boll shedding.
Second, ways to reduce boll shedding:
1. Timely and proper pruning helps improve light penetration and air circulation within the crop. The principle for topping cotton should be "prune when needed and cut branches as required." In dense or overgrown areas, it's important to remove unnecessary branches and thin out old leaves to promote better growth and reduce boll drop.
2. Scientific growth control is essential. For cotton fields that are overly vigorous, moderate control measures should be applied. During dry periods or excessive growth, light control is sufficient, while during rainy seasons or overgrowth, more frequent chemical interventions may be necessary to manage plant development effectively.
3. Proper fertilization and irrigation practices are crucial. For fields with high fertility, focus on controlling growth first before promoting further development. After the boll-setting stage, apply 2–3 kg of urea per acre. For weak or thin seedlings, increase nitrogen application during the bud stage, using 3–5 kg of urea per acre. If the base fertilizer lacks organic matter or potassium, adding 25 kg of cake fertilizer and 5 kg of potassium sulfate or chloride per mu can help. Watering should be done when soil moisture drops to around 17%, or when plants show signs like dark leaves and red stems. The flowering and boll formation stages require the most water and nutrients. For high-fertility fields, top-dressing at full flowering is ideal. For low-fertility fields, early and repeated applications during the early flowering stage can improve yield.
4. Strengthen pest and disease management. To control cotton bollworms, spray 20% methomyl diluted 1000 times during the egg-laying peak, and use 28% emulsifiable concentrate or 25% chlorpyrifos at 1000 times dilution during the larval stage. For aphid control, treat fields showing signs of infestation, such as oily leaves, when the infestation rate reaches 5%. Early application of fungicides is key to preventing disease-related boll loss. By maintaining good field hygiene and monitoring regularly, farmers can significantly reduce boll shedding caused by pests and diseases.
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