The late growth stage of cotton, which spans from the beginning of flowering to the end of boll opening, is a critical period for determining both yield and quality. This year, the Huanghuai cotton region has faced adverse weather conditions, leading to a higher proportion of late-maturing (Futao) and early-maturing (Qiutao) cotton. As a result, effective management during this phase is more important than ever. Here are key strategies to ensure optimal results:
Drought and flood control are essential during the late growth stage. Cotton plants often experience slower vegetative growth, reduced stress resistance, and heightened sensitivity to both drought and waterlogging. These conditions can significantly impact yield and fiber quality. Timely irrigation and drainage are crucial to prevent premature aging, encourage early boll formation, increase boll weight, and improve fiber length. In northern China, where dry and rainy conditions typically occur from September to October, proper watering can make a big difference. For example, one irrigation between late August and late September can increase boll weight by 0.13–0.24g, fiber length by 1.2–1.7mm, and yield by 15.3–19.7%. Two irrigations can boost these numbers even further. When soil moisture in the 20–40 cm layer drops below 60% of field capacity, immediate watering is needed. However, avoid overwatering, as it may lead to bud drop or boll shedding after heavy rain. In case of flooding, drain the fields within 24 hours to minimize damage.
Applying top-dressing fertilizer is another vital practice. With the increased prevalence of insect-resistant cotton, premature aging has become more common. To counter this, additional top-dressing should be applied alongside proper irrigation. During the late growth stage, root absorption weakens, making soil fertilization less efficient. Root application, on the other hand, improves nutrient uptake and enhances yield. Spraying 0.3% potassium dihydrogen phosphate or a mixture of 1% urea and 2% calcium superphosphate every seven days can significantly boost boll production and yield. It's best to spray during cloudy or evening hours without strong winds, targeting the middle and upper leaves. Adding 100g of neutral detergent powder to 50kg of solution helps dissolve the mixture better, improving efficiency and also controlling pests like aphids and mites.
Pest and disease control is equally important. As cotton plants become more vulnerable in the late season, especially with uneven weather patterns, the risk of infestation increases. For the fourth generation of cotton bollworms, spraying 4.5% beta-cypermethrin diluted 2000 times or 2.5% cyhalothrin at 1500 times can help manage the infestation. Red spider damage can be controlled using 1.8% avermectin or 20% chlorpyrifos when yellow spots reach 10% of the leaves. Whiteflies on the upper, middle, and lower leaves can be managed with imidacloprid, lesperine, or chlorpyrifos solutions. Yellow sticky traps are effective for aphid monitoring. Removing diseased bolls promptly and drying them in the sun helps reduce losses and prevent disease spread.
Proper ripening measures should be implemented in vigorous cotton fields. Practices such as pruning buds, cutting branches, and removing old leaves can help redirect nutrients, improve ventilation, and promote faster maturity. However, excessive pruning should be avoided in normal fields to prevent premature aging. For late-maturing cotton, using ethephon can accelerate boll opening by 7–10 days, increasing the flowering rate before frost and boosting yield by 6.4–10.2%. The correct timing for ethephon application is when the upper bolls have been open for over 40 days, the average temperature is above 20°C, and there are about 20 days before the first frost. Apply 40% ethephon at 100–150ml per acre, mixed with 20–30kg of water, and spray evenly on the middle and upper bolls. Avoid using it in fields where seed germination is a concern, and do not apply it to normal cotton fields to prevent yield loss.
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