Control Methods for Premature Senescence in the Late Growth Stage of Cotton

The internal cause of late-stage premature senescence in cotton is that after cotton growth enters August, intense competition for nutrients arises among the roots, stems, leaves, and bolls, leading to an imbalance between nutrient supply and demand; the external causes are insufficient water and fertilizer in the cotton field during the late stage, such as phosphorus or potassium deficiency; in some cotton fields, it is also because of too many pesticide sprayings in the late stage, or excessive pesticide concentration, which causes serious damage to cotton leaves.

It should be pointed out that the fundamental measure to prevent premature senescence in cotton is to start with strengthening the basic construction of the cotton field, that is, deep plowing and fine harrowing of the cotton field, increasing the application of organic fertilizers, and maintaining a balance of various soil elements. Once cotton enters the late reproductive stage, only the following remedial measures can be taken:

1. Fertilizer and water management: Heavy application of flowering and boll fertilizer should be carried out according to seedling conditions, climate, and soil conditions. If the flowering and boll fertilizer is insufficient, then supplement with a topping fertilizer. After mid-August, if the maximum field water holding capacity is below 60%, and in early September is below 55%, timely irrigation should be carried out to promote fertilizer uptake with water and ensure that fertilizer efficiency is exerted in a timely manner. If premature senescence of cotton is caused by soil potassium deficiency, 5-10 kg of potassium sulfate or potassium chloride should be applied as a supplement during the seedling and bud stages along with the base fertilizer. When applying fertilizer, it is essential to plow deeper than 20 cm, apply the fertilizer at the bottom of the furrow, ensure deep fertilizer placement, promote downward root growth, reduce fertilizer loss, and improve fertilizer use efficiency. During the flowering and boll-setting stage, if drought occurs, irrigate lightly, carefully clean the ditches and beds, and prevent waterlogging damage again; if waterlogging occurs, drain promptly.

2. Rational chemical regulation: To prevent premature senescence caused by early plant development, the timing of chemical regulation and the dosage of mepiquat chloride should be comprehensively considered in combination with climate, soil fertility, and plant appearance. Generally, at the 8-leaf stage, bud stage, early flowering stage, full flowering stage, and after topping, small amounts of regulators such as mepiquat chloride should be sprayed multiple times to achieve reasonable regulation.

3. Foliar topdressing: After August, for cotton fields deficient in phosphorus and potassium, a 300-500 times dilution of monopotassium phosphate solution can be sprayed once every 10-15 days, with 60-80 kg sprayed per 667 sq m (1 mu). For cotton fields deficient in nitrogen, a 200 times dilution of urea solution can be sprayed. For foliar topdressing, it can be sprayed all day on cloudy days, but on sunny days it should be sprayed in the evening to avoid burning the leaves.

4. Breaking up soil compaction: After rain, for cotton fields that have not yet closed their rows, especially in hilly areas, the soil should be loosened in a timely manner to break up compaction. Loosening the soil should not be too deep, so as not to damage the root system or destroy the hilled soil. A soil conditioner, "Mian Shen Geng," can also be sprayed. Spraying "Mian Shen Geng" can break up compaction, loosen the soil, and improve soil structure; it can fully exert fertilizer efficiency, promote normal root growth, and improve root absorption capacity. Method for spraying "Mian Shen Geng": use 200 ml per 667 sq m diluted in 50 kg of water, and spray evenly on the hilled rows.

5. Topping and pruning: First, timely and careful pruning should be carried out, removing ineffective flower buds. All flower buds after the Start of Autumn or flowers after White Dew should be completely removed to reduce consumption. Second, fewer fruiting nodes should be retained on the lower fruiting branches: retain 1 node on the first and second fruiting branches, and 2 nodes on the third and fourth fruiting branches. Once sufficient node length is reached, the branch tips should be tipped early. This method can save organic nutrients and prevent premature senescence in the late stage of cotton.

6. Pest control and leaf protection: The functional period of normal leaves is generally about 8 weeks, but due to pests such as cotton bollworm, mirids, and red spiders, as well as diseases such as Fusarium wilt, Verticillium wilt, and red leaf stem blight, leaves become damaged or fall off, reducing leaf function and accelerating premature senescence. Therefore, pest control must be carried out well, diseases must be reduced, and leaf function must be prolonged. In the early stage of Verticillium wilt occurrence, 40% carbendazim 1000 times solution can be used for root drenching (0.5 kg per plant), or a mixture of 500 times fulvic acid salt solution plus 500 times Fang Si Le solution can be sprayed for control.