Brassinolide has functions such as promoting cell division and elongation, promoting photosynthesis, delaying aging, and improving stress resistance. Cotton is a crop with a long growth period, and its growing season undergoes a process from low to high temperature, then to low temperature, and from high humidity to drought. Reasonable spraying of brassinolide throughout the entire growth period of cotton plays an important role in promoting cotton growth, improving stress resistance, promoting early maturity, increasing yield, and improving quality. Its usage is to use 0.4-0.6 grams of brassinolide 0.15% soluble powder per acre, and spray 30-45 kilograms of water. If it can be sprayed together with trace elements such as boron and zinc and foliar potassium fertilizer (such as high-energy red potassium), the effect will be better. The effects and frequency of spraying at different stages are as follows:

       1. Application of brassinolide during seedling stage: During cotton seedling stage, there are many cloudy and rainy weather, low temperature, high humidity, and many diseases, which are not conducive to early emergence of strong seedlings. Spraying brassinolide 1-2 times can promote the improvement of low temperature resistance during seedling stage, promote root growth, reduce the occurrence of diseases such as stem blight, promote early emergence of strong seedlings, and promote flower bud differentiation, compete for more and stronger buds, increase the number of dormant peaches, laying the foundation for high yield.

       2. Application of brassinolide during the bud stage: Spraying brassinolide during the bud stage can promote the growth and development of buds and cotton plants. However, in the southern cotton region, it is during the rainy season, with high temperature and humidity, and cotton is prone to vigorous growth. Therefore, it is generally not advisable to spray brassinolide at regular concentrations to avoid introducing excessive growth. However, for cotton fields with weak growth or well controlled plant types in the early stage, spraying once is also possible. For thriving cotton fields, increasing the dosage appropriately can quickly enhance the hormone levels in the plant, redirect nutrient supply towards reproductive growth, and indirectly play a role in controlling the growth.

       3. Application of brassinolide during the flowering and boll stage: The flowering and boll stage is the most vigorous period for cotton's nutritional and reproductive growth, as well as a critical period for yield formation. The competition between nutritional and reproductive growth nutrients is fierce, and at this time, the cotton area enters a high-temperature and drought period, which can easily lead to the shedding of buds and bolls. Spraying brassinolide can increase the level of growth promoting hormones in cotton plants, increase photosynthesis, promote the production of assimilates, and transport them to the buds and bolls, Increasing pollen activity, promoting normal fertilization, improving cotton's resistance to high temperature and drought, reducing physiological buds and bolls, and promoting the growth and development of young bolls. Generally, spraying 2-4 times has a significant yield increase effect.

        4. Application of brassinolide during the boll opening period: The boll opening period is a critical period for determining boll weight and fiber quality, during which temperature begins to decrease, root absorption capacity gradually weakens, and nutrient growth gradually declines. Spraying brassinolide can prevent premature aging, maintain high photosynthetic capacity, promote nutrient transport to cotton bolls, increase boll weight and lint percentage, increase the number of autumn peaches, and prevent rotten peaches. Generally, it can be sprayed 3-4 times.