What are the key management techniques for cotton during the flowering and boll stage?
Cotton enters the flowering stage in early July, and the period from late August to early September when bolls open is the flowering and boll stage. The flowering and boll stage is the period of most vigorous cotton growth and development, and also the key period that determines yield. This year, due to higher temperatures, cotton growth and development has generally been faster, which has planted hidden risks for boll rot. Because production conditions and cotton field appearance vary from place to place, and climatic conditions are constantly changing, management during the cotton flowering and boll stage should be adapted to local conditions and carried out by category.
1. Apply flowering and boll fertilizer well. For cotton fields that flower earlier and suffer severe drought, flowering and boll fertilizer should be applied well in combination with watering. Flowering and boll fertilizer should be applied early at the initial flowering stage, as this helps set more bolls. For cotton fields with good fertility and vigorous growth, fertilizer can be applied when one or two large bolls have set on the lower part of the plant. Flowering and boll fertilizer should be applied heavily, generally about 15 kg of urea per mu, and if basal phosphorus and potassium fertilizer are insufficient, additional application may be made as appropriate. Flowering and boll fertilizer should be applied deeply, preferably by furrow application after rain at a depth of more than 10 cm. Topdressing fertilizer has the effects of preventing premature senescence, preventing shedding, setting more bolls, and increasing boll weight. Whether topdressing fertilizer should be applied depends on soil fertility and cotton plant growth. For late-maturing cotton fields with sufficient fertility, sustained potential, and strong plant growth, as well as saline-alkali land and clay land, topdressing fertilizer should be applied less or not at all to prevent excessive vegetative growth and late maturity; for sandy land with weak cotton plant growth and cotton fields showing a trend of premature senescence, it should be applied early and in greater amounts. Topdressing fertilizer is generally applied at 3-5 kg of urea per mu, usually in late July to early August. In the middle and late stages of the flowering and boll stage, the ability of the cotton root system to absorb fertilizer and water gradually weakens, and premature senescence is often caused by insufficient nutrient supply. Foliar spraying can effectively supplement nutrients and has a significant effect on increasing boll weight and preventing premature senescence. Cotton fields showing signs of premature senescence can be sprayed with 2% urea solution + 0.5% potassium dihydrogen phosphate solution, generally 2-3 times from mid-August to early September.
2. Water the flowering and boll stage well. When soil water-holding capacity drops below 70%, or cotton plant growth slows, the red stem rises rapidly, leaf color becomes dark green, and at noon the top leaves of the cotton plant slightly wilt and droop, this indicates that the cotton field lacks water and should be watered in time. The amount of watering should not be too large, and field drainage works should also be well managed to prevent waterlogging and damage after watering if rain follows.
3. Prune branches during the flowering and boll stage. For cotton fields that flower too early, early flowers and young bolls before July 5 can be removed along with pruning, which helps prevent premature senescence and boll rot. The timing of topping should be adapted to local conditions, generally around July 20; for weak growth and wide row spacing, it may be appropriately earlier, while for strong growth and low density, it may be postponed to July 25; for no-pruning cultivation, the topping time should be moved earlier to July 15, and the main stem tip and leaf branch tips should be topped all at once and thoroughly.
4. Chemical regulation during the flowering and boll stage. In general high-yield fields, on the basis of chemical regulation at the full bud stage, the second and third chemical regulation should be carried out according to cotton growth after entering the flowering and boll stage. At this time, because temperatures are high and humidity is great, cotton plants grow vigorously. Each interval depends on climate and cotton field growth, generally 10-15 days, with 1-3 g of mepiquat chloride per mu, focusing on spraying the top of the cotton plant and the top of the fruiting branches. The last chemical regulation should preferably be carried out 7-10 days after topping, when the top fruiting branches have grown 3 fruiting nodes. At this time the branches and leaves have aged, so the amount should be increased, generally 3-5 g of mepiquat chloride per mu.
5. Control pests and diseases. The main insect pests during the flowering and boll stage are lygus bugs, summer aphids, cotton bollworms, and thrips, while the main diseases are verticillium wilt, fusarium wilt, alternaria leaf spot, red leaf stem blight, boll blight, and so on. Forecasting should be done well in time, and control should be carried out promptly.