Why do insecticides become less effective the more they are used? To achieve the best insecticidal effect when using pesticides to control crop pests, in addition to selecting appropriate pesticides and using them at the appropriate time, special attention should also be paid to the timing and location of application.

1、 Choose favorable timing for pesticide application based on climate characteristics and the diurnal activity patterns of pests.

It is advisable to apply pesticides between 9-10am and after 4pm. Because after 9 am, the dew on the crop leaves has dried up, and it is also the peak time for the activity of sunrise pests. Applying pesticides at this time will not affect the control effect due to the dilution of dew, and can also directly contact pests with pesticides, increasing the chance of pest poisoning.

After 4 pm, as the sun sets westward, the light weakens and the temperature decreases. It is also the time when flying activities and nocturnal pests are about to emerge at dusk. Applying the pesticide at this time can advance the application of the pesticide to crops, allowing pests to come into contact with venom or die from poisoning when they come out for activities or feeding at dusk and night. At the same time, it can also avoid evaporation loss and photolysis failure of the pesticide.

2、 Different pesticides should be selected and different application methods should be adopted according to the harmful parts of pests, and the pesticides should be delivered in place.

For pests that harm the roots, apply the pesticide to the roots or in the sowing ditch; Spray the medicine on the back of the leaf for pests that feed on it; To prevent and control the red bollworm and cotton bollworm, apply the medicine to the flower buds, green bells, and tips of the group; Spraying poisonous soil to prevent and control stem borers from causing dead seedlings; Spray or splash water to prevent white spikes; To prevent and control rice planthoppers and rice leafhoppers, the medicinal solution is sprayed onto the base of the rice plant; To prevent and control the Spodoptera litura, spray the medicine onto the flower buds and young pods.

In addition, for concealed pests such as cotton aphids, red spider mites, rice planthoppers, and rice leafhoppers, according to their feeding methods through their piercing and sucking mouthparts, insecticides with strong systemic absorption can be selected to be absorbed and transmitted to other parts of the plant, achieving the goal of delivering the pesticide in place. Only by applying pesticides to insects and delivering them in place can we hit the key points and achieve the effect of eliminating insects from the pesticides, allowing them to exert their best effects and achieve ideal insecticidal effects.

Why do insecticides become less effective the more they are used

A pesticide often has a good insecticidal effect when first used, but as the dosage and scope of use continue to increase, cases of increased drug resistance continue to occur. The most prominent one is cis cypermethrin, which is often referred to as the righteous Laifu Ling in advertisements in the 1980s. However, justice can no longer be upheld because even increasing the dosage or concentration by tens or even hundreds of times cannot kill pests.

This is actually because pests develop drug resistance, which is the ability to tolerate the amount of medication that kills most individuals in a normal population and develop it within their population.

In fact, individuals with different levels of sensitivity to pesticides already exist in natural pest populations. The process of using insecticides is actually the process by which insecticides have a selective effect on insect populations. Every time insecticides are used, relatively resistant individuals are left behind, and relatively sensitive individuals are killed, which increases the level of resistance of pest populations to varying degrees.

It has been found that:

(1) The emergence of drug resistance is related to pests and their living habits. Pests with a short life history, multiple generations of reproduction each year, and frequent exposure to pesticides, such as mites, scale insects, aphids, mosquitoes, etc., are most likely to develop resistant populations;

(2) A pest that develops resistance to one pesticide often also has resistance to other pesticides of the same type; The interaction between drugs with different insecticidal mechanisms is less likely to occur;

(3) The same pesticide is used more frequently or at higher concentrations, resulting in faster resistance formation, while the opposite is slower.

Knowing these, we can prevent or delay the increase of pest resistance through rational drug use. To this end, it is advocated to adopt a comprehensive prevention and control policy that includes breeding, promoting resistant varieties, improving cultivation techniques, and carrying out various biological, physical, and other technologies, in order to minimize the frequency and dosage of chemical control.

Next is to choose insecticides with different mechanisms of action for mixed use, rotation, and embedded application.

The third is to improve the application technology, such as targeted medication, timely spraying, selecting efficient equipment, and spraying in place, in order to maximize the killing effect.