Prevention and treatment of premature senescence of cotton in the later stage

The internal reason for the premature senescence of cotton in the later stage is that after the cotton growth entered August, there was a fierce competition for nutrients among roots, stems, leaves and bolls, resulting in an imbalance between supply and demand of nutrients; the external cause was the lack of water and fertilizer in the later stage of cotton fields, such as phosphorus or potassium deficiency; and some cotton fields caused serious damage to cotton leaves because of excessive spraying times or excessive concentration of pesticides in the later stage.

It should be pointed out that the fundamental measure to prevent premature senescence of cotton is to strengthen the basic construction of cotton fields, that is, to carry out deep ploughing and fine harrowing of cotton fields, increase the application of organic fertilizer and maintain the balance of various elements in the soil. When cotton enters the late growth stage, only the following remedial measures can be taken:

1. Fertilizer and water management: it is necessary to re-apply flower and boll fertilizer according to seedling condition, climate and soil condition. if flower and boll fertilizer is insufficient, cover top fertilizer should be applied again. After entering the middle of August, if the maximum water holding capacity in the field is less than 60%, and when it is less than 55% in the first ten days of September, it is necessary to water in time and promote fertilizer with water to ensure that the fertilizer effect is brought into full play in time. If the premature senescence of cotton is caused by the lack of potassium in the soil, the application of potassium sulfate or potassium chloride should be increased by 5kg of potassium sulfate or potassium chloride at the seedling stage while applying base fertilizer. When applying fertilizer, we must plough more than 20 centimeters, apply fertilizer to the bottom of the plow, apply fertilizer deeply, promote the root system, reduce fertilizer loss, and improve fertilizer use efficiency. Water should be watered in case of drought during flowering and boll setting period, ditch boxes should be carefully cleaned to prevent further water stains, and waterlogging should be drained in time when waterlogging occurs.

two。 Reasonable chemical control: in order to prevent premature senescence caused by early onset of plants, chemical control time and dosage of zhuangsu should be comprehensively considered in combination with climate, soil fertility and appearance. Generally, a small amount of regulators such as zhuangsu are sprayed many times at 8-leaf stage, bud stage, early flowering stage, full flowering stage and after topping, in order to achieve the purpose of reasonable regulation.

3. Extra-root topdressing: after August, the cotton fields deficient in phosphorus and potassium can be sprayed with 300 × 500 times of potassium dihydrogen phosphate every 10-15 days, 60,80kg per 667 square meters (1 mu). For nitrogen deficient cotton field, 200 times urea solution can be sprayed. Topdressing outside the root can be sprayed all day in cloudy days and in sunny days in the evening to avoid burns to leaves.

4. Break the hardening: for the unsealed cotton fields, especially in the hilly areas, the soil should be loosened in time to break the hardening after the rain. Do not loosen the soil too deep, so as not to damage the root system and destroy the soil. It can also be sprayed with soil conditioner "no deep tillage". Spraying "no-deep tillage" can break the consolidation, loosen the soil, improve the soil structure, give full play to the fertilizer effect, promote the normal growth of the root system, and improve the root absorption capacity. The method of spraying "no deep tillage": every 667 square meters, 200 ml of medicine is mixed with 50 kg of water and sprayed evenly on the soil cultivation line.

5. Topping and pruning: first of all, fine pruning in time, removal of ineffective buds, buds after the Beginning of Autumn or flowers after White Dew should be removed to reduce consumption. Secondly, there should be fewer fruit nodes for the lower fruit branches, one for the first and second fruit branches, and two for the third and fourth fruit branches. This method can save organic nutrients and prevent cotton from premature senescence in the later stage.

6. Protection against insects and leaves: the functional period of normal leaves is generally about 8 weeks, but due to the influence of pests such as cotton bollworm, blind Toona sinensis, red spiders and diseases such as Fusarium wilt, Verticillium wilt and red leaf stem blight, the leaves are damaged or shedding, reducing the function of leaves and speeding up premature senescence. Therefore, it is necessary to control insect pests, reduce diseases and prolong leaf function. In the early stage of the onset of Verticillium wilt, the root can be irrigated with 1000 times of carbendazim (0.5kg / plant), or sprayed with fulvic acid and Fangjiele.