Key Technical Points for Cotton Management in the Mid-to-Late Growth Stage

"Major Heat" has passed, and "Start of Autumn" is approaching. Cotton in the southern Hebei region has entered the peak period of full flowering and boll setting. The main problems currently are: first, due to excessive rainfall in the earlier period and delayed chemical regulation, some fields are growing too vigorously with excessively tall cotton plants; second, due to recent sustained high temperatures, aphids, red spider mites and other pests have broken out more severely in some cotton fields, adversely affecting cotton growth. Currently it is the cotton flowering period, which is also the critical period for mid-to-late stage cotton management. In view of this year's climate characteristics, seize the favorable opportunity, adapt measures to local conditions, provide classified guidance, and effectively strengthen mid-to-late stage cotton management to secure a bumper cotton harvest.

I. Fertilizer and Water Management: On the basis of heavily applying flowering and boll fertilizer in mid-July, a top-dressing fertilizer should be supplemented. First, apply 10-15 kg of urea per mu around "Start of Autumn"; second, apply another 5-10 kg of urea per mu around "End of Heat" according to seedling conditions; third, after August 20, combine pest control with comprehensive foliar spraying, using a mixture of 1%-2% urea and 0.2%-0.3% potassium dihydrogen phosphate, spraying once every 7-10 days until mid-to-late September, to nourish roots and preserve leaves, achieving a top canopy full of autumn bolls.

After flowering, cotton fields enter the peak water demand period. Irrigation should be carried out during drought according to weather and actual field conditions. The irrigation indicator is when the top leaves of cotton plants wilt at 4 PM, irrigation can be applied. Generally, during the hot summer-autumn period, when there has been no thorough rain for 7-10 consecutive days, immediately carry out furrow irrigation for drought relief before drought symptoms appear, ensuring timely water supply. At the appropriate time, break the soil crust while moisture remains to prevent cracking, enhance the drought resistance of cotton plants, and reduce bud and boll shedding.

II. Pruning and Branch Removal: Most cotton fields have already been topped. The time for removing terminal buds of fruiting branches is generally before August 10. Lower fruiting branches should retain 2-3 fruiting nodes, middle fruiting branches should retain 3-4 fruiting nodes, and the number of upper fruiting nodes depends on the growth vigor of the cotton plant. When removing terminal buds of fruiting branches, be careful to retain the leaves on the outermost fruiting branch. Promptly pull out empty plants and remove empty branches to improve ventilation and light penetration. For water sprouts, remove them as soon as they appear. After entering the flowering and boll stage, overly vigorous cotton fields tend to become prematurely closed. Old leaves on the middle and lower parts of the main stem can be removed in batches, and empty fruiting branches should also be removed, but never remove leaves from fruiting branches.

III. Pest and Disease Control: August and September are the rampant period for various cotton pests, and also the critical period for protecting buds and bolls and wresting cotton from pest damage. Pest and disease control should adhere to the strategy of "focusing on cotton bollworm and Verticillium wilt, while also controlling other pests and diseases," following the principles of applying pesticides according to pest and disease type, mixed application, and rotational application, to keep various pests and diseases, especially cotton bollworm damage, under control at the early stage.

1. Cotton bollworm. When 5 or more 3rd-instar or older larvae are found per 100 plants, chemical control should be carried out. Choose pyrethroid, organophosphate pesticides or compound formulations with contact or stomach poison action, with a spray volume of no less than 60 kg per mu.

2. Summer aphids. Spray 15 g of 10% imidacloprid per mu for control; alternatively, spray 3% acetamiprid at 2000x dilution or 0.3% matrine aqueous solution at 1000x dilution. During prolonged drought, pay attention to controlling red spider mites. When chemical control is needed, use a mixture of 15% saomanting (pyridaben) at 1500x dilution + 1.8% abamectin at 2000x dilution, which also has a significant effect on cotton leaf mites, achieving the effect of "one spray, multiple controls."

3. Cotton Verticillium wilt. Change flood irrigation to fine-flow furrow irrigation, which can reduce disease incidence by 50%. Drain promptly, ensuring irrigation and drainage are matched. Conduct timely field surveys. Spray diseased plants with hymexazol or ethylicin 2-4 times, which has the effect of controlling disease spread and reducing damage. While spraying, within a one-square-meter range around diseased plants, use one of the above chemicals for root drenching, which can significantly improve the effect compared to spraying alone.

IV. Chemical Regulation: For cotton with good fertilizer and water conditions and strong growth potential, 7-10 days after topping or when the top fruiting branches have grown 2-3 fruiting nodes, spray 8-10 mL of 25% chlormequat per mu diluted in 50-75 jin of water once, to control autumn growth of water sprouts, reduce shedding, and achieve a top canopy full of autumn bolls. For late-developing and late-maturing cotton fields, when most cotton bolls are over 45 days old, during the period from "Cold Dew" to "Frost's Descent," choose a period of 3-5 consecutive days with daily maximum temperatures above 20°C, apply 100-150 mL of 40% ethephon per mu diluted in 40-50 kg of water, and spray evenly over the entire plant on a sunny day.

V. Careful Harvesting and Fine Picking: To improve cotton quality and grade, the key is careful harvesting and fine picking. During cotton harvesting and selling, first, "pay attention to three findings, adhere to four cleans, and implement five separations." The three findings are: finding fallen cotton, stiff-petal cotton, and "eye-crust" cotton (referring to small flower heads left in the boll shell); the four cleans are: clean shells, clean stalks, clean fields, clean roads; the five separations are: grading, separate drying, separate storage, separate ginning, and separate selling, ensuring every boll is harvested for a bumper harvest. Second, when harvesting and selling cotton, always use cotton cloth bags, prohibit chemical fiber bags, and strictly prevent foreign fibers from mixing in.