Technical Guidance on Cotton Management During the Flowering and Boll-setting Stage

The flowering and boll-setting stage of cotton is a critical period when vegetative growth and reproductive growth proceed together. During this stage, the plant gradually shifts from being dominated by vegetative growth to being dominated by reproductive growth. The plant grows vigorously with a large daily growth increment. It is the peak period of fertilizer and water demand in the plant's entire life cycle, and also the key period for forming economic yield. Timely and meticulous management is essential, adapted to local conditions and to the condition of the seedlings. Attention must be paid to pest and disease control, chemical regulation, pruning, and intertillage loosening of the soil, while at the same time rationally and scientifically formulating fertilizer and irrigating promptly and in appropriate amounts, so that individual plants grow steadily, the plant architecture and field population structure are reasonable, ventilation and light penetration are good, the root system is well developed, and the leaf color is deep green, achieving stability in July, tenderness in August, and no premature senescence in early September, with many squares setting into bolls and few shedding, striving to achieve the management goals of "no excessive vegetative growth, no premature senescence, many bolls set, and few rotten bolls" during the flowering and boll-setting stage, and ensuring a bumper harvest. This year, during the sowing and emergence period of cotton in our city, rainfall came at the right time and the subsoil moisture was sufficient. In the fields, the seedlings were complete, uniform, and even, and the young seedlings grew robustly with good vigor. However, in the second half of June, during the squaring stage, no effective rainfall occurred, and moreover the temperature was high, evaporation was large, and drought and moisture deficiency were present, which was unfavorable to cotton plant growth. On June 30, moderate rain fell citywide, alleviating the drought, which is favorable for flowering and boll setting. Management during the flowering and boll-setting stage should be combined with moisture conditions, plant growth vigor, and soil fertility status, combining promotion and control, with scientific management, preventing high temperature, drought, autumn waterlogging, and pest and disease damage, striving to set more high-quality bolls, increase boll weight, and prevent rotten bolls, premature senescence, and late-season excessive vegetative growth and delayed maturity.

I. Scientifically apply heavy fertilizer for the flowering and boll-setting stage. The flowering and boll-setting stage is the period of greatest fertilizer demand in the entire growth cycle of cotton. Rationally applying heavy fertilizer at the flowering and boll-setting stage is the key to high yield, achieving sufficient flowering and boll-setting fertilizer and supplemental top-dressing fertilizer. For cotton fields with sufficient soil fertility, good moisture conditions, and robust cotton plant growth, the flowering and boll-setting fertilizer can be applied as a small amount of top-dressing at the full flowering stage or delayed; generally, 8-10 kg of urea and 5-10 kg of potassium sulfate or potassium chloride are applied per mu; for cotton fields with insufficient base fertilizer, poor moisture conditions, and weak cotton plant growth, the flowering and boll-setting fertilizer should be applied early and heavily, preferably at the initial flowering stage; generally, 10-15 kg of urea + 5-10 kg of potassium sulfate or potassium chloride are applied per mu; for cotton fields with excessive early fertilization, vigorous growth, and a daily growth increment exceeding 3 cm, the flowering and boll-setting top-dressing should be delayed until the cotton plant has set 1-2 bolls, and the amount of nitrogen fertilizer applied should be appropriately reduced. After topping, an additional 5-7 kg of urea per mu should be applied as top-dressing fertilizer. Top-dressing should mainly be done by hole application or band application, applied below 10 cm of the soil surface, 25-30 cm away from the cotton plant. At the same time, in combination with pest and disease control, spray a mixed solution of 0.2% monopotassium phosphate + 1% urea + 0.2% borax 2-3 times, to promptly and rapidly supplement plant nutrition, regulate the nutrient structure within the plant, and reduce flower and boll shedding. From early July to early August, according to soil fertility and cotton plant growth vigor, select suitable foliar fertilizers, supplement and apply top-dressing fertilizer well, improve the plant's nutritional status, extend the functional period of green leaves, prevent premature senescence, increase boll weight, and promote early maturity; for cotton fields with weak growth, spray 1% urea; for fields with robust and vigorous growth, spray 0.2% monopotassium phosphate solution.

II. Timely irrigation and prompt drainage. In our city, during the cotton flowering and boll-setting stage, rainfall is generally abundant in normal years, which can meet the water requirements for growth and development during this period, affecting normal cotton plant growth, but the interannual variation is large. In some years, there may be excessive rainfall, causing water accumulation and waterlogging in low-lying fields, or there may be a long period without rainfall, with poor soil moisture, causing massive square and boll shedding, slow extension of fruiting branches, and affecting yield. Therefore, corresponding irrigation and drainage measures should be taken according to weather changes, soil moisture conditions, and cotton plant growth vigor. Generally, if there has been no rainfall for 10-15 days, the relative water content of the soil tillage layer is below 60%, leaves wilt and droop at noon, leaves are thick, small, and dark green, and fruiting branches extend slowly, irrigation should be carried out promptly; irrigation should preferably be small furrow irrigation, avoiding large-scale flooding irrigation; if rainfall is excessive, drainage should be carried out promptly to prevent soil oxygen deficiency caused by water accumulation, causing root diseases and excessive field humidity causing flower and boll shedding.

III. Intertillage and earthing up to prevent lodging. Generally, intertillage in cotton fields should be shallow rather than deep, with an intertillage depth of 7-10 cm between rows and 5 cm between plants. For cotton fields with a tendency toward excessive vegetative growth, deeper intertillage should be appropriately carried out to cut some lateral roots and control excessive vegetative growth; after irrigation or rainfall, intertillage and loosening of the soil should be carried out at appropriate moisture to reduce field humidity, reduce weed growth, and prevent rotten bolls. Sandy soil and cotton fields that have not yet flowered and closed rows can be deeply intertilled and earthed up high; cotton fields that have already flowered and closed rows should no longer be deeply intertilled, to prevent excessive root damage and affect cotton plant growth. Combine intertillage with rational earthing up to enhance plant lodging resistance and ventilation and light penetration. Generally, the earthing-up height is 13-16 cm, and the final height should be lower than the first fruiting branch. When earthing up, do not bury branches, damage branches, or knock off flower buds; the furrows should be straight and level, convenient for irrigation and later management.

IV. Rational chemical regulation to inhibit excessive vegetative growth. The appropriate timing of chemical regulation, dosage, and number of applications should be determined according to rainfall conditions and cotton plant growth vigor. Generally, chemical regulation should be carried out when the daily growth increment of the main stem is 2.5 cm at the initial flowering stage and 3 cm at the full flowering stage. For fields with vigorous growth and robust plants, apply 1-1.5 g of mepiquat chloride per mu (or 5-10 ml of chlormequat) in 30 kg of water at the initial flowering stage, and apply 2-3 g of mepiquat chloride per mu or 8-15 ml of chlormequat in 40-50 kg of water for uniform spraying at the full flowering stage; for fields with poor growth, delay application or reduce the dosage and number of applications, generally applying about 2 g of mepiquat chloride per mu or about 8 ml of chlormequat, and subsequently decide whether to carry out chemical regulation again according to growth conditions. For vigorously growing cotton fields, 5 days after topping, apply 4-5 g of mepiquat chloride per mu for a heavy spray and heavy regulation once, to inhibit ineffective flower buds, concentrate nutrients, and strengthen bolls and increase weight. Note that chemical regulation should not be carried out within 5 days before or after topping; in rainy conditions, appropriately increase regulation, and in drought conditions, appropriately reduce regulation.

V. Meticulous pruning to reduce nutrient consumption and enhance ventilation and light penetration. Adhere to the pruning principle of "determining branches by density, determining time by branches; when branches are sufficient, do not wait for time; when time is due, do not wait for branches." At the initial flowering stage, remove the growing points of the lower 3 or 4 fruiting branches; around July 15, remove the growing points of the middle 4 or 5 fruiting branches; in early August, remove all the tips of the upper fruiting branches. Alternatively, for cotton fields with good growth, once each plant has grown 13 fruiting branches (the number of fruiting branches varies by variety), the group branches and the main stem tip can be removed at one time; for cotton fields with poor growth, topping can be appropriately delayed, but not later than the Beginning of Autumn, with July 25-30 being suitable. For cotton fields with high water and fertilizer, low density, and strong cotton plant growth, remove axillary buds at any time in combination with topping. For densely shaded cotton fields, remove old leaves from the main stem in stages from bottom to top to improve ventilation and light penetration conditions in the cotton field.

VI. Timely removal of plastic film to promote downward root extension. At the end of June or early July, in combination with watering or after a thorough rain, remove the film at appropriate moisture, and immediately intertill and loosen the soil and earth up, to enhance soil permeability, promote downward root extension, improve drought resistance, and prevent lodging and late-stage premature senescence. When the soil is dry and moisture-deficient, the film should not be removed, to avoid incomplete film removal in one go, or root damage during film removal, affecting normal plant growth. After film removal, 300-500 kg of straw per mu can also be used for field mulching, to lower soil temperature, reduce water evaporation caused by film removal and high temperature, favor root growth, and at the same time achieve the effects of returning straw to the field to build soil fertility and improve soil structure.

VII. Closely monitor pest and disease dynamics and carry out timely control. At present, cotton varieties in the city are mainly insect-resistant cotton. The 2nd and 3rd generations of cotton bollworm generally do not need control, and the 4th generation is controlled according to circumstances. However, cotton aphids, mirids, and red spider mites have become the focus of control. Control should adhere to the principle of prevention first and scientific pesticide use. When controlling, select two pesticides with different active ingredients corresponding to the pest species and mix them for spraying, controlling multiple pests at once, alternating several formulations, and at the same time do not arbitrarily increase the dosage, to prevent pests from rapidly developing resistance. When spraying, spray finely and evenly, so that the underside of leaves receives the pesticide, and prevent missed spraying, which affects control effectiveness.