The appropriate application of pesticides can not only save pesticides, reduce costs, but also improve the effect, reduce pesticide residues, effectively control pests and diseases, and ensure the normal growth of crops. In determining the appropriate period of application, should consider from the following aspects: Pest period. For pests, the period of occurrence of pests can be the period of egg hatching, larvae emergence, and the age of adult worms. The timing of the application of pesticides depends on the circumstances. In principle, we must master the living habits of pests and carry out the stages where they are the most vulnerable to killing insects and can effectively control the damage. Generally, pesticides should be applied at a young age before the third instar of pests. At this time, they can receive a multiplier effect. The reasons for this are: 1. The young insect pests are very thin at the 3rd instar precursor wall and have a lot of micro-hairs on the body wall. The epidermis on the micromathematical part is very thin, and the medicine can easily penetrate this layer. At this time, the insect body is small, the food intake is small, the hazard is light, the activity range is small, and the drug resistance is weak. Therefore, it is necessary to determine the appropriate control period and control the pesticide before the third instar, which can achieve the best control effect. When pests reach 4-6 years of age, pest food intake and body wall thickness are greatly increased, and their thickness can reach 50-100 times that of 1st instar larvae. There is also no microscopic hair on the body wall, so the medicine is not easy to adhere to the body. On the wall and through the body wall, it is more difficult to reach the pests, which greatly affects the insecticidal effect. 2. After the age of pests increases, the amount of fat in the insects also increases, which has the effect of accumulating and decomposing many pesticides. The higher the body fat content of pests, the more obvious this effect is and the stronger the drug resistance is. Natural enemies are sensitive. In the period when natural enemies of pests are sensitive to drug reactions, they should use as little or no medicine as possible to protect their natural enemies and maintain their ecological balance. Sensitive growth period. For diseases, the growth period of susceptible diseases is the appropriate time for prevention and treatment. If seedlings are most susceptible to bacterial blight, they can be seeded with fungicides or sprayed at the seedling stage before sowing. Weed sensitive period. Herbicides should generally be applied during the sensitive period of weeds. For weeds that are seed-grown, seedlings and young shoots are more sensitive to herbicides, so this period is often the right time to control weeds. When broad-spectrum herbicides are used, such as glyphosate and Gramoxone, they are more sensitive to growth in weeds. If we control spring grass and summer grass, we spray best when the weeds bloom early. Mice break fast food. From the effective control of rodent density, the bait should be placed in the fasting phase of rodents better. Years of experiments have proved that the best effect of spring rodent control is due to the exhaustion of winter rat food and the corresponding increase in the consumption of poisonous baits. Plant safety period. The safety of the agent to the plant is a prerequisite for determining the appropriate period of application. For example, when 2,4-dbutyl ester is applied after the jointing stage of winter wheat, it is easy to make wheat not strong. Therefore, it is advisable to apply the winter wheat till the end of the till till the jointing stage. Therefore, in the application of pesticides, we must choose to spray the crop during the period of strong resistance to pesticides, so as not to cause crop phytotoxicity. Safety interval. During the application period of pesticides, pesticides shall also be applied within the safety interval according to the standards for the safe use of pesticides so as to avoid excessive pesticide residues and adverse consequences.