Pest control is an important part of high quality and high yield cultivation of crops. However, in the current situation, the prevention and control of crop pests and diseases can not be separated from chemical control. To reduce the pressure of chemical control, improve the effectiveness of prevention and control, and reduce environmental pollution, we must grasp the appropriate period of time in order to achieve the effect of less drugs, high efficiency, and less pollution.
I. Infant young age In recent years, some farmers have reported that the effectiveness of pesticide control is poor. According to the survey, most cases are caused by long-term use of certain pesticides or certain types of pesticides, increased insecticide resistance, and inadequate control of insect pests during appropriate period of time. What period of time is the appropriate period of pest control? In general, the young period before the third instar is the control period. This period of medication can receive more effective results. This is because the wall of the 3rd instar of the insect pest is very thin, and there are many micro-hairs on the body wall. The epidermis of the micro-hair area is very thin, and the medicine can easily penetrate through these thin layers. At this time, the pests are small, eat less, endanger lightly, have a small range of activity, and are weak in drug resistance. For borers, no matter whether it is a borer pest or a borer pest of a flower or fruit, the newly hatched larvae have not yet penetrated into the plant, and the control effect is naturally better. Therefore, to determine the appropriate period of control, should be mastered before the pest 3rd instar. 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 pests, thereby greatly reducing the insecticidal effect. In addition, as the pest age increases, the amount of fat in the insect body 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.
2. Dangerous growth period For crops, the growth period that is susceptible to susceptibility to disease and susceptibility to insects and is likely to cause major losses is the dangerous growth period. For example, vegetable crops in early spring are most susceptible to damping-off and damping-off, and early-season dry nursery and seedlings are susceptible to bacterial wilt and cotton rot in the seedling stage. The period from heading to filling stage of wheat is most susceptible to aphid, and the period from breaking to full flowering is the period most susceptible to head blight, so this second stage is the risk of susceptible aphids and susceptible scab. period. The risk of growth of rice borer borer and rice borer borer is from tillering, booting to heading. The risk of panicle blast of rice is from breaking to heading and flowering. Therefore, the control of pests and diseases should catch the drug during the dangerous growth period, and during the dangerous growth period, the young insects of the pests should be used to catch the drug during the prosperous period.
Third, natural enemies sensitive to crops more natural enemies, most of the natural enemies are also insects, such as all kinds of ladybugs, grasshoppers, hoverfly and parasitoids, parasitic flies and so on. There is a large class of natural enemies, that is farmland spiders. In the period when these natural enemies are relatively sensitive to chemical reactions, they should use as little or no germicide as possible to protect their natural enemies and maintain their ecological balance. If you need to apply pesticides, try your best to choose pesticides that are not sensitive to pesticides. For example, natural enemies of egg parasitism are sensitive to pesticides before parasitism, and insensitive to pesticides after parasitism. Because parasitoids are protected from the eggs of pests, these parasitic natural enemies have the egg membrane protection of the host pests, and insecticides are less toxic to them. The natural enemies that have developed in the dead locusts and scale insects are also difficult to be poisoned by pesticides because of the protection of the thick solid walls of the host. At this time, the application of insecticides has almost no effect on them. The larvae of Plutella xylostella larvae were parasitized by larvae, and the most sensitive period to insecticides was the parasitic larvae of the second and third instar larvae, while the larvae of 1st and 4th instar larvae parasites had enhanced resistance. Other pests have the same phenomenon. The increased resistance of host pests will reduce the impact of pesticides on parasitic natural enemies, which in effect means that natural enemies have been protected.
IV. Safety intervals for pesticides For the sake of safety, use of pesticides is stopped for a predetermined number of days before the vegetables are harvested.
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