At present, pesticide spraying is still the main method to control crop diseases and insect pests. However, in production practice, it is often encountered that the efficacy of qualified pesticides is not ideal. The reasons are as follows:

Cause 1: medicine is not right

First, treat diseases as pests, treat insects as diseases, and use drugs incorrectly. For example, if the dead seedlings caused by tomato bacterial wilt are misdiagnosed as the dead seedlings caused by the root biting of underground pests, no matter how many drugs are used, they will not be effective.

Second, although the diagnosis is correct, the medication is not correct. For example, Jinggangmycin was used to control rice blast, dicofol was used to control wheat aphid, and dicofol was used to control rice planthopper.

Reason 2: bungling the opportunity

For pest control, the effect of pesticide application is good at the peak of adult oviposition or before the 3rd instar of larvae. If the larva is more than 3 years old, the effect will be poor no matter how much pesticide is applied.

Cause 3: inaccurate dosage

Too much medicine is easy to cause drug damage, and too little medicine can not achieve the purpose of disease and pest control. Therefore, it is necessary to prepare according to the pesticide application instructions to obtain satisfactory control effects.

Reason 4: improper mixing

If the weak acid or neutral pesticides such as dimethoate, phoxim and dichloromethane are mixed with basic pesticides such as sulfur mixture, it will cause pesticide decomposition and failure; The mixture of alkaline pesticide sulfur mixture and Bordeaux liquid will produce excessive soluble copper, which will cause drug damage.

Cause 5: blind spraying

Spraying should be sprayed on the key parts to achieve the desired effect. For the prevention and control of sunflower sclerotinia disease, it should be sprayed on the field before sclerotinia germination according to the rule of sclerotinia overwintering in the soil. The control effect is only good. If the drug is sprayed on the diseased part, the effect is not good. Rice blast, bacterial leaf blight and other diseases mainly occur on the leaves. When applying drugs, spray on the leaves; In order to control cotton red spider, it is necessary to spray the medicine on the back of the leaves to achieve good control effect.

Cause 6: adverse weather

The efficacy is closely related to meteorological factors such as temperature, humidity, rain, dew, wind and light. If emulsion pesticide is applied, the effect will be good if there is no rain for at least the next 24 hours after spraying. It takes at least two days for the application of stomach poison and contact pesticide to have a good effect. Therefore, it is necessary to choose fine weather for spraying according to the local weather forecast.

Reason 7: poor quality of medicine and equipment

The good or bad efficacy is also related to the spray tools used. Good quality spray tools not only save medicine and labor, but also improve the efficacy.