What are the key technical points for late-stage cotton management?

As autumn begins, cotton growth enters the late reproductive stage, dominated by boll opening and the completion of autumn boll development. This period centers on nourishing the roots and preserving the leaves, using scientific management methods to promote vigorous cotton plant growth, prevent premature senescence as well as excessive vegetative growth with late maturity and rotten bolls, and strive for a bumper cotton harvest. The specific management methods are as follows.

1. Drought resistance and waterlogging prevention After the Beginning of Autumn, drought is often severe. From mid-August to mid-September, the soil moisture content at 0-40 cm must be maintained above 55% of field capacity. Only under sufficient moisture conditions can cotton grow and develop normally and carry out all physiological functions properly. No water means no fertilizer, and the amount of ethylene produced by cotton plants increases greatly, leading to massive shedding of flowers and bolls and premature senescence. Therefore, if the level falls below this target, water lightly or irrigate in alternate rows. Never use flood irrigation or soaking. Irrigate and drain as you go, keeping the cotton field drainage unobstructed; avoiding standing water is especially critical so as not to affect root vigor. At the same time, pay attention to waterlogging damage to cotton from heavy rain and excessive autumn rain, and do a good job of clearing ditches and draining water to protect the root system and reduce rotten bolls.

2. Intertillage and soil loosening In cotton fields after rain or irrigation, the soil surface becomes compacted, permeability is poor, and root vigor declines. Shallow intertillage with animal power or manual hoeing can be used (loosening the soil should be shallow rather than deep) to break up soil compaction, improve soil permeability, and also raise soil temperature and promote cotton root growth. At the same time, in conjunction with loosening the soil, earth up around the roots, which can effectively enhance the cotton's resistance to lodging.

3. Foliar topdressing Make full use of the absorption function of leaves to carry out foliar spraying of fertilizer, so as to make up for the insufficiency of nutrients absorbed by the roots, improve the photosynthetic capacity of leaves, and increase the boll-setting rate, yield and quality. Apply flower and boll fertilizer heavily to meet the nutrient needs of cotton during heavy flowering and boll setting; supplement boll fertilizer. Because insect-resistant cotton has a high boll-setting rate, an early peak demand for fertilizer, and a high demand for potassium fertilizer, it has already consumed a large amount of nutrients, and many cotton fields show signs of fertilizer deficiency and premature senescence. If nutrients are not supplemented in time, it is difficult to achieve a full top canopy of autumn bolls. Spray fertilizer at the right time to prevent premature senescence. From August to early September, spray a 1% urea aqueous solution every 5-6 days, about 100 kg per 667 sq m. Focus the spray on the back of the middle and upper leaves. On sunny days, spray after 4 p.m.; on cloudy days, it can be done all day. Never spray when the temperature is high and sunlight is strong, so as to avoid excessive evaporation of water after spraying, which causes a sudden increase in concentration and leaf burn.

4. Timely topping and pruning When cotton enters the squaring stage, appropriately remove 4-5 early squares on the first and second fruiting branches to encourage the cotton to build a high-yielding framework early and set bolls in a concentrated way; removing the terminal bud before the Beginning of Autumn can effectively inhibit ineffective upper growth of cotton, improve field ventilation and light penetration, promote normal boll setting of upper young squares, and increase the number of autumn bolls. After topping, promptly remove superfluous buds. Prune in time to promote the conversion of nutrients toward reproductive growth, achieving the goal of preserving young bolls and increasing boll weight. Remove ineffective old leaves at the bottom of the cotton, take waste branches and leaves covered with pests out of the cotton field, dig pits and bury them deeply, to reduce the number of pests in the cotton field.

5. Preventing excessive vegetative growth and late maturity In the late growth stage of cotton, due to an overly large population and excessive or too-late nitrogen application, overly vigorous cotton plant growth can easily lead to excessive vegetative growth and late maturity, with many late autumn bolls, and cotton bolls cannot open normally, affecting cotton quality. At this time, ethephon spraying should be used for ripening. When applying ethephon, it should be controlled from around "Cold Dew" to "Frost's Descent," when the average temperature is above 20°C for 3 consecutive days and more than 80% of cotton bolls have reached a boll period of more than 40 days. Use 100-150 g of 40% ethephon per 667 sq m, add 50 kg of water, and spray.

6. Scientific pest control and disease prevention All localities should, according to the forecasts of the plant protection station, focus on the prevention and control of Verticillium wilt, cotton bollworm, red spider mite and other pests and diseases. Pests such as cotton aphids and cotton bollworms all have strong pesticide resistance; when controlling them, pay attention to mixed and rotated use of pesticides. Because yellow-leaf wilt disease is a physiological disease caused by malnutrition, mainly potassium deficiency, the main causes of this disease are generally a lack of organic fertilizer in cotton fields, poor and thin soil, and drought. Therefore, when controlling it, methods such as supplementing potassium fertilizer and foliar spraying of fertilizer can be used.