Recently, my country's main cotton producing areas have experienced varying degrees of continuous high temperature weather, often accompanied by drought or rainy and humid weather. It is the critical period of cotton flowering and boll formation. High temperature weather above 35℃ is not conducive to the growth and development of cotton, mainly manifested in reduced pollen vitality, severe bud and boll shedding, and suppressed boll development, thus affecting cotton yield and quality. In response to the adverse effects of high temperature weather, the Crop Management Department of the Ministry of Agriculture and Rural Affairs organized the National Agricultural Technology Extension Service Center and the Cotton Expert Guidance Group of the Ministry of Agriculture and Rural Affairs to study and propose technical guidance opinions on cotton production in response to high temperature weather.

1. Timely irrigation and cooling to reduce high temperature stress

When encountering high temperature and drought during the flowering and boll formation period, timely irrigation should be carried out to alleviate the shedding of buds, flowers and bolls caused by lack of water. When there is no rainfall for more than 7 consecutive days or the average daily temperature is higher than 32℃, if the top 3-4 leaves of the cotton plant become thicker, dark green, and dull, and wilt at noon, and still cannot return to normal at 3-4 pm, it indicates that the cotton plant is short of water and needs to be irrigated in time. Water wells, rivers, ditches, etc. can be used to irrigate in time by means of small ditch irrigation, sprinkler irrigation and drip irrigation. The irrigation time is generally before 10 am or after 6 pm to avoid irrigation during the high temperature period at noon.

2. Carry out scientific fertilization to achieve the "three encounters" of fertilizer, water and temperature

The flowering and boll period is the peak period for cotton fertilizer demand. At the same time as irrigation, quick-acting fertilizers should be applied reasonably to help cotton resist high temperatures. For ditch-irrigated cotton fields, 10 kg/mu of urea and 5-8 kg/mu of diammonium phosphate should be applied. Cotton fields with obvious symptoms of potassium deficiency should also be supplemented with potassium fertilizer. Combined with pest control (red spiders, Spodoptera litura, etc.), 1% urea + 0.5% potassium dihydrogen phosphate solution should be sprayed on the leaves in the early morning or evening, once every 7 days, to prevent premature aging of cotton due to fertilizer and water imbalance caused by high temperature and drought. In addition, continuous high temperature and drought can easily cause boron deficiency in cotton. When the petiole ring rate of cotton in the field is high, the fruit branches are not strong, and the bud and boll shedding rate is high, it shows serious boron deficiency. Depending on the base fertilizer and topdressing conditions, appropriate amounts of borax and other high-content boron fertilizers should be sprayed on the leaves in time, and the high temperature period at noon should be avoided to prevent cotton plants from being burned. If it rains during fertilization, timely ditch application should be chosen after the rain. During the high temperature and drought period, plant growth regulators such as brassinolide plus amino acid fertilizer can also be sprayed as appropriate to enhance the resistance of cotton plants to high temperature and drought.

3. Strengthen field management and improve drought resistance

The first is straw covering. Covering the exposed surface with straw to avoid direct sunlight on the surface can effectively reduce soil moisture volatilization and improve soil moisture retention and drought resistance. Generally, the thickness of straw covering is about 5 cm, which can be increased or decreased according to specific conditions. The second is inter-cultivation and soil cultivation. For cotton fields that have not been closed after irrigation, shallow tillage can cut off soil capillaries, increase water penetration, reduce soil moisture evaporation, improve soil permeability and fertilizer and water supply, and promote cotton plant root development. The third is pruning and shaping. For cotton that grows vigorously, it should be treated by removing leaves and branches, picking old leaves, beating the edge and cutting empty branches to shape the reasonable plant type of cotton, optimize the boll structure, promote growth transformation, and increase the boll rate.

Fourth, clean up ditches in time and do a good job of drainage

For low-lying cotton fields with poor drainage, in case of short-term heavy rainfall, the ditches should be cleaned in time after flooding, and the water in the cotton fields should be drained as soon as possible to avoid high temperature after water accumulation, which will lead to an increase in rotten bolls in the middle and lower parts of cotton, resulting in reduced production and quality. For lodging cotton plants, they should be gently lifted up in time after draining the accumulated water. After the cotton plants are straightened, the soil should be piled up to stabilize the plants so that the plants can grow upright and improve the ventilation and light conditions of the cotton fields. Do not pull hard or step on them with your feet to avoid damaging the roots.

5. Strengthen pest monitoring and do a good job in prevention and control

Under high temperature and drought weather, cotton leaf mites in the early growth stage and leaf moths in the middle and late stages of cotton growth often occur more severely. We must actively monitor pests and diseases and prevent and control them early. It is recommended to use different action mechanism agents alternately. When applying the pesticide, adjuvants can be added to enhance the permeability of the pesticide. Try to avoid using the pesticide when the sun is strong and the temperature is high. Cotton leaf mite control: When the central plant and the spot plant are found, spray with avermectin or pyridamole emulsifiable concentrate in time. Red spider mites should be controlled in time in the intercropped cotton field to prevent the spread of mites and reduce cross-harm. Spodoptera litura control: In areas where Spodoptera litura often occurs, use Spodoptera litura sex attractants in a continuous area, with 1 volatile core and moth-type trap per mu, to kill adults in groups and reduce the amount of eggs laid in the field. Apply biological food attractants in large areas. 1-2 days before the main generation of Noctuidae pests (cotton bollworm, cutworm, clover armyworm, etc.) emerge, apply the pesticides evenly on the top leaves of cotton plants every 50-80 meters to kill the adult insects.