How to manage a cotton field after a sudden shift from drought to waterlogging?

Right now, cotton is at the stage when vegetative growth is entering its peak and gradually shifting to reproductive growth, and it is also a period when the crop absorbs more fertilizer and water and is very sensitive. Since June 4, there have been many overcast and rainy days, the air humidity is very high, and the temperature has hovered between 25 and 30°C. Fusarium wilt has been triggered in many old cotton fields that have been planted for years. The rate of wilted plants is generally around 5%, in severe fields the rate of diseased plants is around 10%, and in some sections the incidence rate is around 20%. In some cotton fields, tarnished plant bugs, cotton bollworms, red spiders, and aphids are also causing damage in spots and patches.

At the same time, for cotton that has been given too much nitrogen fertilizer, under conditions of abundant rain, the extreme reversal of fertilizer and water can easily cause excessive vegetative growth, and the average daily increase in main stem length often exceeds 3 cm overnight. This will cause the cotton to close its rows too early, make the cotton field heavily shaded, and cause a large number of squares and bolls to shed. In a small number of waterlogged cotton fields, the cotton suffers flooding after drought, and the ecological environment deteriorates further. Therefore, cotton areas everywhere should adapt measures to local conditions and individual seedlings, strengthen management at the square stage and flowering and boll stage, and strive to fight disasters and secure a bumper harvest.

1. Combine promotion and control to achieve balanced growth. For cotton seedlings that have not yet entered the square stage, quick-acting fertilizers should be the main choice to speed up cotton seedling growth. For cotton seedlings that have entered the square stage and flowering and boll stage, high-content compound fertilizers and slow-release fertilizers should be the main choice, 15 to 25 kg per mu, along with 15 kg of potassium fertilizer, applied by opening furrows or making holes while preserving soil moisture; broadcasting over the field is taboo. Fertilization at this time aims to build a high-yield framework for cotton early, so that cotton can close its rows by late July. For cotton that is growing vigorously or excessively, promptly choose mepiquat chloride or chlormequat for spraying. In the early stage, use 4 mL of mepiquat chloride or 1 g of chlormequat per mu, then gradually increase to 8 to 12 mL or 2 to 3 g. Last year, some farmers blindly increased the dosage and over-regulated growth, sharply reducing the boll-setting rate of cotton; this lesson must be learned.

2. Prevent disease and control insects for safe growth. For cotton fields where Fusarium wilt has already occurred, apply more decomposed organic fertilizer and bio-organic compound fertilizer, and also apply more potassium fertilizer, to enhance defense against and recovery from Fusarium wilt. Pesticides that alleviate Fusarium wilt, such as those in the kuhuangku category, can also be sprayed. For insect pests already observed, priority should be given to preventing tarnished plant bugs while also controlling other pests. Options include mie(su) mangchun at 20 to 30 mL per mu, or 2% emamectin benzoate wettable liquid at 5000 times dilution, or 3% acetamiprid emulsifiable concentrate at 1500 to 2000 times dilution, or imidacloprid wettable powder at 1500 times dilution.

3. Clear the "four ditches" so the field dries after rain stops. The surrounding ditches, bed ditches, waist ditches, and large peripheral drainage ditches of the cotton field should be thoroughly cleared so that waterlogging can be drained and drought can be resisted. At the same time, after rain, break the surface crust and loosen the soil, and earth up to form ridges to prevent lodging.