How can the boll-setting rate be increased in cotton cultivation?

Types of square and boll shedding in cotton include physiological shedding, shedding caused by pests and diseases, and shedding caused by mechanical damage. As for the causes of physiological shedding: first, excessive application of fertilizer and water causes excessive vegetative growth, with nutrients consumed too heavily in the early stage and supply falling short of demand in the later stage; second, excessive planting density in the cotton field causes severe shading by branches and leaves, reducing light, weakening photosynthesis, and decreasing the nutrients produced; third, some cotton fields are deficient in boron, causing cotton to flower but not set fruit; fourth, high temperature and drought, insufficient fertilizer and water, or excessively high temperatures cause cotton pollen sterility; fifth, frequent rainy weather leads to poor pollination. As for pest and disease damage, inadequate control of cotton mirids, cotton bollworms, Fusarium wilt and Verticillium wilt can easily lead to massive square and boll shedding. As for mechanical damage, it is mainly caused by improper operation during field management. In addition, in the past two years, blind application of herbicides has occasionally caused square and boll shedding.

Therefore, in order to increase the boll-setting rate of cotton, we must adopt comprehensive measures focused on strengthening fertilizer and water management, aiming mainly for a good crop of midsummer bolls, abundant autumn bolls, and the setting of all three types of bolls, so as to achieve a high and bumper cotton harvest.

First, apply fertilizer scientifically. At present, this is the critical period for applying flower and boll fertilizer and boll fertilizer to cotton according to the seedlings' condition. Combined with the rainfall recently forecast, first, for cotton that is flowering and setting bolls, apply 30 to 50 jin of high-content compound fertilizer per mu, together with 30 jin of potassium fertilizer; second, for cotton that has already set 2 to 3 bolls per plant, apply 20 to 30 jin of urea per mu, and in potassium-deficient cotton fields, an additional 20 jin of potassium fertilizer should also be applied; third, when a single plant has set 8 to 10 bolls, apply about another 30 jin of urea per mu; fourth, for cotton fields with severe boron deficiency, spray boron fertilizers such as Sule boron 2 to 3 times at intervals of about 7 days.

Second, improve ventilation and light transmission conditions. In order to enhance the permeability of the cotton field, increase light intensity from two aspects: first, thoroughly prune branches and remove unwanted shoots, completely removing the wood branches and superfluous buds from cotton fields with heavier shading; for cotton with relatively sparse density, 1 to 2 wood branches may be retained, the growing tip removed, and 2 secondary fruit branches kept; second, spray with the retarding-type plant growth regulators mepiquat chloride or chlormequat, applying according to the seedling condition per mu, using 1 to 2 grams of mepiquat chloride or 4 to 8 milliliters of chlormequat, which can better control the cotton plant type, prevent row closure too early, and ensure ventilation and light transmission.

Third, prevent pests. The third generation of cotton bollworms and cotton mirids occurs to varying degrees in various places, so timely prevention should be carried out before the peak period arrives, and prevention can be carried out respectively with 2% emamectin benzoate wettable liquid, 40% chlorpyrifos, and Lorsban emulsifiable concentrate. Applying additional potassium fertilizer in cotton fields with Fusarium wilt can enhance defense and recovery ability.