How should the timing and method of cotton chemical growth control be handled?

Although cotton was sown late, the cotton seedlings also developed late. By early June, well-growing cotton fields in the north had already produced 7-8 true leaves, and some had already produced squares. Around June 10, most cotton fields will successively enter the squaring stage. In previous years on June 10, most cotton fields had already produced 3 fruiting branches; this year there will be two fewer fruiting branches, with no pre-dog-days bolls or few pre-dog-days bolls. This is not necessarily a bad thing: it can save the operations of removing early squares and removing the lower 1-2 fruiting branches, and it helps reduce rotten bolls and hard-walled bolls.

According to the fixed-plant survey results of Guoxin Cotton Institute: June 10 to July 10 is the period of fastest main stem growth in cotton, with an average daily growth of 1.5 cm, and this is also the period of most vigorous root growth. If aboveground growth is too fast, it will affect root growth, causing an imbalance between aboveground and belowground growth, and it is also unfavorable for controlling plant height. Therefore, most cotton fields should be sprayed with the first application of mepiquat chloride in early to mid-June.

The exact day to begin chemical control mainly depends on the growth of the cotton seedlings. For cotton fields with fast development, large leaves, and tall plants, starting in early June is preferable. Large cotton seedling leaves indicate that vegetative growth is too vigorous, so chemical control is needed. The effect of chemical control mainly depends on controlling the dosage. For ordinary cotton fields, use 0.3-0.5 g of mepiquat chloride per mu; for vigorously growing cotton fields, the dosage should be increased. Be sure to eliminate worries about chemical control at the squaring stage; once chemical control is late, management will become passive. Specifically, the following key points should be mastered:

1. Choose mepiquat chloride that meets national standards, that is, with an active ingredient content above 97% and impurities below 1.5%. Do not use other chemical control drugs that do not indicate impurity content or have unknown ingredients. Problems that have occurred in cotton farmers' chemical control in the past, whether ineffective or excessive, were all caused by unqualified mepiquat chloride or regulators with unknown ingredients.

2. When spraying, be sure to make the cotton tip receive the pesticide, because mepiquat chloride is absorbed quickly after being sprayed on the cotton plant but translocates very slowly. The new leaves, fruiting branches, and stems that the cotton plant will produce are all contained within the cotton tip. If the cotton tip does not receive the pesticide, the goal of making the next 3 leaves smaller and the next 3 internodes shorter cannot be achieved. Therefore, when spraying and large leaves cover the cotton tip, be sure to spray the liquid onto the cotton tip from the side.

3. Adapt measures to the seedlings and the field. Within the same plot, large seedlings should be sprayed more, and small seedlings should be sprayed less or not at all.

4. Check the effect. If 3 days after spraying, the newly emerged tender leaves show no change, it means the dosage was too low and an additional spraying may be done as appropriate; if the newly grown tender leaves are dark in color, glossy, and obviously wrinkled, it means the treatment has taken effect.

5. Increase the dosage on fertile land. On fertile melon, vegetable, and garlic land and on first-year cropped land, a small dosage has no effect. How much is suitable to spray? You can first conduct a test. Do not let your thinking be restricted. On especially fertile land, even 1-2 g per mu may be ineffective. As long as the dosage is increased, there is no cotton field that cannot be controlled.

6. Mainly control the dosage per mu. The dosage per mu is 0.3-0.5 g; 10-15 kg of water per mu is enough at the seedling and squaring stages.

7. If the seedlings are uneven, carry out chemical control separately. Spraying mepiquat chloride alone can prevent large and small seedlings from receiving the same dosage. If pesticides are added for mixed spraying, chemical control must still be the main purpose. Even where pests are severe, do not spray more pesticide, so as not to affect cotton plant growth.

8. After starting chemical control, it cannot be interrupted. The effective period of mepiquat chloride is 10-15 days. If chemical control is not continued after the first application, cotton plant growth will rebound, and the previous chemical control may even be completely wasted. Therefore, after starting chemical control, apply chemical control once every 8-10 days, gradually increasing the dosage. The interval and dosage can be determined according to cotton plant growth conditions and weather conditions.

9. The dosage differs depending on whether chemical control is early or late. If chemical control starts early, use less; if it starts late, use appropriately more.

10. The dosage differs with different densities. High density requires controlling the plants shorter, so chemical control should be appropriately earlier and the dosage larger; low density has less strict requirements for plant height, so chemical control can be appropriately relaxed.

11. Do not forget topdressing when doing chemical control. After chemical control, cotton plant leaf color becomes darker, but this does not mean there is no fertilizer deficiency. When topdressing is needed, it must be done. In plots with uniform growth and relatively low soil fertility, 1% urea can also be added during chemical control, which both controls the seedlings and supplements nutrients; however, do not add fertilizer in cotton fields with uneven cotton seedlings, otherwise the large seedlings will become even larger.

12. Combine with the weather forecast. It is best to carry out chemical control before rainfall; waiting until after rainfall to carry out chemical control can easily make management passive.

13. If chemical control is too strong, it can be remedied. If chemical control is carried out according to the above methods, the problem of excessive chemical control generally will not occur. Excessive chemical control often occurs in four situations: first, the dosage was calculated incorrectly or spraying was not properly controlled; second, rain was forecast but it did not rain after spraying; third, nutrient drugs with unknown ingredients, such as those containing regulators, were mixed with mepiquat chloride for spraying; fourth, after chemical control had no effect, spraying was continued with an increased dosage. If chemical control is too strong, spray 1% urea solution to alleviate it; if spraying urea is ineffective, spray "920".