Key Integrated Cultivation Techniques for the Prevention and Control of Premature Senescence in Cotton

Cotton premature senescence refers to the phenomenon in which cotton leaves wither, turn yellow and drop prematurely under suitable climatic conditions. In the field, it appears as interveinal chlorosis and yellowing of the leaves after the full flowering stage. The yellowing leaves begin at the point farthest from the main stem and develop from top to bottom and from the outside inward, with the leaves gradually drying up and dropping. Premature senescence has a considerable impact on cotton yield and quality; the earlier it occurs, the greater the impact, and it can generally reduce yield by 10%-40%.

Cotton premature senescence occurs because the fertilizer and water requirements for normal growth during the vigorous growth period cannot be met, leading to premature aging and early leaf drop. The specific manifestations are as follows: first, insufficient or unbalanced fertilization in the cotton field makes it difficult to meet the growth needs of cotton; second, poor root development or adverse environmental influences in the middle and late stages weaken root absorption capacity, and the nutrients absorbed by the roots cannot meet the needs of normal cotton growth; third, Verticillium wilt and Fusarium wilt affect the transport capacity of the vascular bundles, so that water and inorganic nutrients absorbed by the roots cannot be delivered in time to the stems, leaves and other organs that need them. Therefore, cotton premature senescence can be classified as a physiological disease, often caused by the interaction of multiple factors, and it is easy to prevent but difficult to cure.

In view of the above causes of cotton premature senescence, it can be seen that preventing premature senescence first requires sufficient fertilizer application, then the cultivation of strong seedlings and protection of the root system, and finally timely disease control. The author summarizes the following nine integrated control measures from the perspective of cultivation techniques, to discuss with everyone:

First, crop rotation is the most effective. Rotation not only avoids the shortage of medium and trace elements in cotton fields caused by long-term continuous cropping, but also effectively reduces soil-borne diseases, especially the occurrence and harm of Fusarium wilt and Verticillium wilt. In central and southern Hebei, it is recommended to rotate cotton with @#@245@#@.

Second, sufficient soil moisture before sowing is very important. Cotton should not be sown by seizing whatever soil moisture is available, because this often means irrigation is needed soon after emergence. Irrigation creates low temperature and high humidity in the cotton field, which can easily cause an outbreak of seedling-stage diseases and is unfavorable for cultivating strong seedlings.

Third, fertilizer application must be reasonable. The three major elements nitrogen, phosphorus and potassium must not only be applied in sufficient amounts, but also in a balanced way. The general fertilizer requirement pattern of cotton is approximately 3:1:3, so, excluding soil available nutrients, the pure nitrogen, phosphorus and potassium application rates per mu should be no less than 12 kg, 4 kg and 12 kg respectively. While applying the major elements in sufficient amounts, an appropriate amount of trace fertilizer should be supplemented; for example, when plowing, apply 2 kg of borax and 1 kg of zinc sulfate per mu as base fertilizer. Paying attention to foliar fertilizer spraying in the middle and late stages of cotton can also effectively prevent premature senescence.

Fourth, sowing at the appropriate time benefits strong seedlings. Sowing too early makes seedlings vulnerable to cold waves or low temperatures before emergence, and after emergence they are susceptible to low-temperature-induced disease infection. In central and southern Hebei, the suitable sowing period for plastic-film cotton is after April 20, and it is best not to sow before this time.

Fifth, hoe and cultivate frequently during the seedling and bud stages. Hoeing and cultivation not only reduce weed damage, but also effectively raise soil temperature and cultivate strong seedlings. Especially during the seedling and bud stages, the effect of hoeing and cultivation is more obvious.

Sixth, slightly delay the first pruning. During the seedling stage, the cotton root system develops faster than the aboveground part. Retaining as much green tissue as possible to synthesize nutrients can promote root development. Therefore, it is recommended to postpone the first pruning and removal of unnecessary branches until after squaring, and do not "strip the pant legs" when pruning.

Seventh, film removal during the bud stage must not be delayed. The main purpose of plastic film mulching in cotton fields is to raise soil temperature and reduce water evaporation. Before the bud stage, the effect of plastic film is very great, but after mid-to-late June, because temperatures have already risen and the rainy season has arrived, the plastic film no longer serves a purpose and may even easily cause the root absorption capacity to decline prematurely under high temperature and high humidity. Therefore, we should remove the film in time, no later than the end of June.

Eighth, pest and disease control must be timely. Damage from seedling-stage diseases, Fusarium wilt and Verticillium wilt, late-stage leaf spot disease, aphids and red spiders can all promote the occurrence of cotton premature senescence and should be controlled in time. Also, when spraying pesticides normally, a little carbendazim, chlorothalonil, etc. for disease control and imidacloprid, dicofol, etc. for pest control can be added. This has a certain preventive effect on such pests and diseases.

Ninth, do not neglect irrigation in drought and drainage in waterlogging. Drought in the early stage affects root development, while water accumulation in the cotton field in the middle and late stages promotes root death. Because of irrigation, any standing water in the field should be drained in time.