Analysis of Limiting Factors in Cotton Production and Countermeasures (Part 2)

7. Main symptoms of premature senescence: First, after the peak boll-setting period of cotton, the leaves show interveinal chlorosis and yellowing; the yellowing leaves begin at the point farthest from the main stem and develop from top to bottom and from outside to inside, and the leaves gradually dry up and fall off. Second, in the late growth stage of cotton, the leaves turn red and lose their function of producing nutrients. The earlier the premature senescence of cotton appears, the more severe the yield reduction.

Causes: First, the soil is poor and the soil fertility is insufficient. The soil nutrients cannot meet the requirements of cotton growth and development; second, fertilization is insufficient. In particular, potassium fertilizer and nitrogen fertilizer are insufficient, and some cotton farmers fear that when the amount of nitrogen applied is large, it will cause excessive vegetative growth of cotton; third, drought or waterlogging in the cotton field causes poor growth; fourth, in excessively vigorous cotton fields, the imbalance between vegetative growth and reproductive growth causes it; fifth, plastic-film cotton develops early and the root system senesces early as well, and if the plastic film is not removed during the growth period, poor root development causes it; sixth, high-yield fields set many bolls, and nutrients cannot meet the requirements of cotton growth and development.

Countermeasures: First, fertilize reasonably. Increase the application of potassium fertilizer and nitrogen fertilizer. Potassium fertilizer is best applied as a base application or early topdressing; for nitrogen fertilizer topdressing, the principle should be steady application of bud fertilizer, heavy application of flowering and boll fertilizer, and supplementary application of topping fertilizer. Second, irrigate when drought occurs. When irrigating, apply light small amounts of water in alternate furrows to prevent excessive vegetative growth after irrigation followed by rain. Third, for plastic-film cotton, remove the plastic film promptly after entering the rainy season to prevent drought under the film and avoid affecting cotton root development. Fourth, drain promptly when waterlogging occurs.

8. Main symptoms of late chemical regulation: When precipitation is excessive or fertilizer and water are excessive, the cotton plants are tall, the field is closed, ventilation and light transmission are poor, and bud and boll shedding in the middle and lower parts is severe, causing yield decline and quality reduction.

Causes: Cotton farmers do not have a good grasp of fertilizer and water management and chemical regulation techniques, and mostly carry out chemical regulation only after cotton has become vigorous or even excessively vigorous.

Countermeasures: First, for cotton fields with a tendency toward vigorous growth, carry out chemical regulation early; do not wait until after vigorous growth to regulate. Second, after topdressing, irrigation, and rainfall, carry out timely chemical regulation according to fertilizer and water conditions. Third, chemical regulation should start from the seedling stage to keep cotton plants growing steadily. The usual dosage of mepiquat chloride is 1-2 ml per mu at the seedling stage, 6-12 ml from full bud stage to early flowering stage, and 12-15 ml at full flowering and boll-setting stage. Fourth, the concentration for chemical regulation should be lower rather than higher; if growth is still vigorous after chemical regulation, regulate once more after 7-8 days, for a total of 3-4 chemical regulations throughout the season. Fifth, irrigate promptly when drought occurs after chemical regulation.

9. Main symptoms of Fusarium wilt and Verticillium wilt: Cotton plants are dwarfed, leaves yellow, and various symptoms such as patches, net-like patterns, green wilt, and leaf drop occur. A longitudinal cut of the cotton stem shows browning of the vascular tissue, few bolls are set, and in severe cases the entire plant dies. Fusarium wilt and Verticillium wilt have a long disease duration. Fusarium wilt begins at the seedling stage, and Verticillium wilt begins at the bud stage. The disease period is more than three months. These two diseases have a relatively large impact on cotton yield.

Countermeasures: The pathogens of Fusarium wilt and Verticillium wilt survive in the soil for a long time, and there is currently no specific control method. Cotton farmers do not have a good grasp of measures to control disease development. First, select improved disease-resistant varieties. Second, cultivate strong seedlings to improve cotton's disease resistance. Third, at the two peak periods of Fusarium wilt and Verticillium wilt, namely the bud stage in mid-to-late June and the flowering and boll stage in August, apply chemicals once every 7-10 days for 3-4 consecutive applications. Fourth, rainfall or irrigation forms a peak of disease incidence, so apply chemicals promptly after rainfall or irrigation. Fifth, select 50% carbendazim wettable powder at 1000 times or 70% thiophanate-methyl at 800 times mixed with humic acid foliar fertilizer for spraying to control disease development.

10. Main symptoms of mirid bug damage: When young buds are damaged at the cotyledon stage, the tips wither and form "male cotton"; when leaves are damaged, "torn-leaf madness" forms; when young buds are damaged, they turn from yellow to black and drop after 2-3 days; when medium-sized buds are damaged, open-mouthed buds form; when young bolls are damaged, water-soaked spots appear, and in severe cases they become stiff and drop; when the terminal bud or side buds are damaged, "broom cotton" forms.

Causes: First, with the promotion and application of insect-resistant cotton, the amount of pesticide used has been greatly reduced, and mirid bugs have risen from a secondary pest to a major pest. Moreover, the insect body is small and mostly active and damaging after evening, so it is not easy for people to detect. Second, because mirid bugs have migratory habits, control by individual households alone has very poor results.

Countermeasures: First, it is best to adopt unified control promptly according to the symptoms of cotton damage. Second, the timing of chemical application is best around evening, and surrounding cotton fields are best controlled uniformly with the village as a unit; unified control by county and township is even better. Third, the chemicals can be acephate plus pyrethroid insecticides, or chlorpyrifos plus pyrethroid insecticides. Fourth, when spraying, pay attention to spraying evenly and thoroughly; the effect is better when both the front and back of the leaves are evenly covered with the chemical.