Key Points of Cotton Chemical Topping and Detailed Explanation of Application Methods

Cotton chemical topping is the use of chemical regulation measures to shape cotton into an ideal plant architecture and create a high-photosynthetic-efficiency population.

1. Status and role of chemical topping

Cotton is a typical light-loving crop. High yield, early maturity and high quality in the early-maturing cotton region of eastern Hebei need to be achieved through rational close planting, but rational close planting will inevitably intensify the contradiction between individual plants and the population in terms of space and light energy utilization in the middle and late stages. Therefore, cotton chemical topping has become an important supporting measure for rational close planting, and is also the core content of early promotion and stress resistance, especially the simplified cultivation technology system.

At present, mepiquat chloride is the most widely used in cotton chemical topping, and its effect is also relatively ideal. It can reduce cotton plant height, decrease the number of fruiting branches, promote the transfer of photosynthesis to reproductive growth, reduce boll shedding (physiological shedding caused by nutritional deficiency), increase the number of set bolls, coordinate the contradiction between individual development and population development, and improve population photosynthetic utilization. In addition, it can reduce pest occurrence: first, it lays a good foundation for pesticide spraying operations against pests; second, it improves the expression capacity of insect-resistant genes, because experiments have proved that growth rate is negatively correlated with the expression level of resistance genes.

2. Chemical topping goals

To achieve high quality and high yield in cotton, it is necessary to establish a population with high light energy utilization. Synchronous cultivation theory holds that the best boll-setting position should be synchronized with the best boll-setting period (the warm-rich period), increasing the setting of high-quality large bolls within the 12th node and inner positions, so as to maximize the population's yield-increasing potential. Therefore, its management goal is "synchronization of the best boll-setting position with the best boll-setting period." Appropriately advancing the sowing period, rationally increasing planting density, and field management such as fertilizer and water regulation all aim at this goal, and chemical topping is the same. Other cultivation management aimed at "reducing pre-dog days bolls, increasing dog days bolls, and controlling autumn bolls," and cultivation management aimed at "synchronization of three highs (the period of high photosynthetic efficiency of leaves, the peak period of cotton boll growth, and the local high-energy period of resources such as light and heat)," have similar chemical topping goals.

3. Chemical topping principles

3.1 According to the "weak early, vigorous late" characteristics of insect-resistant cotton and the soil and climate characteristics of our region, the principle of "promote early, control middle, prevent late decline" is suitable. During the seedling stage, apply growth-promoting regulators, such as Huafu, Lufeng 95, etc.; during the bud stage and flowering and boll stage, use mepiquat chloride for regulation; after entering the boll-opening stage, root absorption function declines and the load is large. If there are signs of premature senescence: foliar spray with 15% urea water combined with 1% potassium dihydrogen phosphate.

3.2 Principles for using mepiquat chloride for chemical topping

① The principle of light first then heavy, preferring light over heavy, and small amounts multiple times. Grasp the initiative and stability, and avoid excessive vegetative growth and stiff seedlings. This principle should be noted, because cotton farmers in our region generally apply mepiquat chloride relatively late, starting chemical topping only after entering the early flowering stage or discovering excessive growth. ② The principle of "five observations" (observe the sky, observe the soil, observe the seedlings, observe the variety, observe the density), comprehensively consider and flexibly master the timing and amount of chemical regulation. Rationalize chemical topping according to weather, soil fertility and cotton growth; promote weak seedlings, control vigorous seedlings, generally place equal emphasis on promotion and control for ordinary cotton, and be cautious when encountering drought. Accurately judging the growth state of cotton seedlings is also very important. For example, in June and July 2004, rainfall was heavy and concentrated. At that time, although the cotton leaves all appeared yellow on the surface, growth was in two states: one was the waterlogging-controlled type, and the other was the abundant-rain vigorous-growth type. For the former, chemical topping should be stopped immediately; for the latter, seize the time for chemical topping. Cotton varieties (lines) differ in their sensitive response to mepiquat chloride. For example, SGK321 special-grade product and ordinary type are insensitive, while the premium-grade product is sensitive. Different varieties also grow differently at each growth and development stage. Some varieties have weak growth vigor throughout the whole growth period; some have strong growth vigor throughout the whole growth period; some have weak early growth and strong late growth; some have strong early growth and premature senescence late, etc. This requires carefully reading the variety introduction and understanding in detail the characteristics and traits of the variety, so as to facilitate flexible chemical topping. ③ The principle of combining with other cultivation management measures.

High yield is the result of the coordination of multiple factors. Chemical topping must be combined with other cultivation measures. For example: for fields with higher cotton plant density, early chemical topping must be combined with early topping; for excessively vigorous seedlings at the full bud stage when chemical topping is temporarily difficult to be effective, adopt measures such as stepping the cotton plants crooked with the foot, and after a few days stepping them toward the other side, etc.

4. Basic model of mepiquat chloride chemical topping

Taking local soil, a density of 5000 plants/667 sq m, and medium-to-above fertility plots as an example, mepiquat chloride is basically applied in 4 times.

4.1 Bud stage (June 20-25) fine adjustment: use 0.51 g per 667 sq m in 20 kg water, which is beneficial for controlling the top and promoting the bottom, stabilizing growth and increasing buds.

4.2 Early flowering stage (July 5-10): use 1.51 g per 667 sq m in 30 kg water, which can prevent excessive growth and increase bolls.

4.3 Flowering and boll stage (one week after cotton topping, that is, around July 25) heavy control: use 34 g per 667 sq m in 30 kg water, focusing on spraying the plant canopy and the top of fruiting nodes, so as to help shape a good plant architecture.

4.4 In early to mid-August, if there is a "running tall" phenomenon, heavy control can be applied: use 34 g per 667 sq m for topping, so as to help control late buds, shorten upper fruiting nodes, and prevent the increase of ineffective fruiting nodes and the clustering of redundant buds.

The above model can be used as a reference. In the production process, it should be flexibly mastered according to the principles of use and actual conditions.

5. Several issues related to chemical topping

5.1 Use the secondary dilution method, especially during fine adjustment of chemical topping at the full bud stage, which can more accurately grasp the actual amount of mepiquat chloride. Secondary dilution method: dissolve 10 g of solid mepiquat chloride in 1000 mL of water to dilute it into a 100-fold mother solution, that is, 10 mL of mother solution contains 0.1 g of mepiquat chloride. When using, add it to the sprayer with a pipette.

5.2 Mepiquat chloride must be a product from a legitimate manufacturer, so as not to miss the chemical topping timing.

5.3 Spray after the morning dew has dried, and pay attention to weather changes.

5.4 When spraying mepiquat chloride in the early stage, spray large plants but not small ones, spray tall plants but not short ones, spray vigorous plants but not weak ones, and spray the top of the main stem and the tips of fruiting branches.

5.5 If the dosage is excessive, causing slow cotton plant growth, upper fruiting branches unable to extend, an excessively compact and dwarfed plant architecture, and a high rate of flower bud shedding, spray (30-50) x 10E-6 gibberellin or strengthen watering and fertilization, which can alleviate or eliminate the phytotoxicity.