Most pesticide instructions provide recommended concentrations, which can be followed. However, it's best to apply fungicides based on concentrations recommended by local plant protection authorities after efficacy trials. Reduce concentrations during dry or hot summers to avoid phytotoxicity. Secondly, pay attention to the timing and frequency of application. Mastering the timing of spraying is crucial for understanding the disease's occurrence and development patterns, conducting disease forecasting, or preparing for fungicide application based on local plant protection department forecasts. Generally, fungicide spraying is done in the early stages of disease, such as rice blast, especially in hot weather when rice blast develops rapidly and should be sprayed immediately. Peanut leaf spot develops more slowly; do not spray at the onset of symptoms, and certainly not before. Spray only after symptoms have established a certain development trend. Spray immediately when climatic conditions are favorable for rapid disease development; sometimes, spraying is necessary even during light drizzle to control the disease. The timing of pesticide application depends not only on the disease's development pattern but also on the crop's growth stage, as many diseases are linked to specific growth stages. Furthermore, it's crucial to consider the crop's tolerance to fungicides at each growth stage to prevent phytotoxicity. Plant diseases often develop over time, and multiple applications of fungicides are rarely sufficient to resolve the problem in one go. The number of applications depends primarily on pathogen reinfection, the residual effect of the fungicide, and climatic conditions such as light, temperature, and rainfall. Seedling disinfection: Seed soaking should use emulsions and solutions, not suspensions, and wettable powders should not be used. The key to seed soaking is the concentration of the pesticide solution and the soaking time; improper operation can lead to poor sterilization or phytotoxicity. Other factors such as temperature, seed type, and the location of the pathogen also affect the soaking effect. Generally, once the seed type, temperature, and pesticide type are determined, the pesticide concentration and soaking time can be coordinated; a higher concentration allows for a longer soaking time. If the pathogen is located deep within the seed or the seed coat is hard, the soaking time can be appropriately extended; if the temperature is high, the soaking time can be appropriately shortened. Both the seeds and the pesticide powder must be dry before seed treatment; otherwise, uneven treatment will occur, causing phytotoxicity and affecting the germination rate. The amount of pesticide powder used is generally 0.2% to 0.5% of the seed weight. When treating seeds, the pesticide and seeds should be added in 3 to 4 batches, and then the container should be rotated appropriately to ensure even mixing. With the advent of systemic fungicides, a new seed treatment method has emerged-wet treatment. This involves moistening the pesticide powder with a small amount of water and then treating the seeds, or mixing dry pesticide powder onto wet seeds, allowing the powder to adhere to the seed surface. After sowing, the pesticide slowly dissolves and is absorbed into the plant and transported upwards. For soil-borne diseases such as cotton wilt and cucumber wilt, in addition to seed soaking or treatment, soil disinfection can also be used for control. Soil disinfection first requires selecting an appropriate fungicide based on the type of disease, and then choosing a suitable soil treatment method based on the physicochemical properties of the fungicide and the soil structure and properties. Irrigation is suitable for water-soluble fungicides. After adjusting the fungicide to an appropriate concentration, approximately 5-10 kg of solution is applied per square meter of ground. When the soil is relatively dry, a lower concentration of solution can be used, with an increased irrigation volume; when the soil is moist, a higher concentration with a smaller volume can be used. For fungicides with high vapor pressure, application can be done by plowing the bottom or furrows. The powder or solution is evenly sprinkled into the bottom of the furrow of the first plow, and then covered with soil turned over by the second plow. This method is not suitable for overly heavy clay soils. Alternatively, the powder or solution can be applied to the soil surface and then immediately turned over to bury the fungicide in the soil.
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