Pesticide resistance: refers to the resistance produced by the offspring of the organism after long-term contact with the pesticide.
Causes
(1) Self selective evolution of pests
After using chemical pesticides for many years, the self structure of the surviving population (including immune function, gene change, epidermis thickening, detoxification ability enhancement, etc.) has changed, resulting in drug resistance.
(2) The growth characteristics of harmful organisms make them resistant to drugs
In the case of aphids, resistance is easy to occur for several generations in a year; the pathogen of wheat rust, with large amount of spores, strong explosiveness, is prone to resistance.
（3） Drug resistance is easy to occur if drug is not used properly
Long term single drug use, random increase in the use of concentration, uneven spraying of drugs, leakage of nets and other individuals are prone to drug resistance.
Classification of resistance
(1) Single resistance: refers to the resistance of an organism to only one drug.
(2) Multiple resistance: resistance to several or several types of drugs.
(3) Cross resistance: the simultaneous resistance of an organism to a drug or a class of drugs other than those that have already developed resistance and have never been exposed to.
(4) Negative cross resistance: when resistant to one agent, it is more sensitive to another or a class of pesticides.
Delayed resistance
(1) Use in combination. Different kinds of drug compounding: for example, the combination of organophosphorus pesticide and pyrethroid pesticide; the combination of egg killing agent and non egg killing agent; the mixture of pesticides with different killing methods: for example, the mixture of inhaling insecticide and contact killing or fumigation insecticide, etc.
(2) Intermittent use of pesticides. A pesticide can not be used continuously even if the effect is good after it is put on the market. After a period of time, it should be suspended, replaced with other pesticides, and reused after a period of time.
(3) In the most sensitive period of harmful organisms. Generally speaking, insecticides are used in larval stage, herbicides in seedling stage and fungicides in early stage.
(4) It is not allowed to increase the times of medication at will. According to the instructions, the dosage on the pesticide label is the result of repeated test and verification by the relevant national departments, do not increase the dosage at will. If it is not effective to use according to the dosage, except for the factors of fake medicine, it can only prove that pests (pests and weeds) have developed resistance to this pesticide. It is better to change a new medicine if the dosage is increased.
Erroneous understanding
(1) The longer the validity period is, the better
Most people think that pesticides, especially pesticides, have a longer shelf-life, the better. This is a wrong understanding. Such pesticides are more likely to induce resistance. For example, an insecticide has a shelf-life of more than 20 days, but in the process of its slowly declining efficacy, it migrates into a group of pests from other places. The residual concentration of pesticide on the crops can no longer kill the foreign pests. Then after the new group of pests eat the leaves and fruits of these crops, their offspring will soon become resistant to the drug. It can also be understood that residual pesticides induce them to produce drug resistance.
(2) The higher the concentration is, the better the effect will be. The higher the concentration is, the better the effect will be. This is a wrong understanding. Not to mention that arbitrarily increasing the dose has potential damage to crops, it is not advisable to only for pesticide resistance. No matter how thick the medicine is, there are also pests that leak through the net. Then the resistance of their offspring rises very fast.
Once the resistance of harmful organisms to pesticides is formed, it is difficult to eliminate them. The results showed that the resistance of housefly to diazinon was 7-23 times after 11 years. This shows that the renewal speed of pesticide is far behind the development speed of pest resistance, so please use pesticide reasonably.