Why not use pesticides under windy, rainy and high temperature conditions?

The control effect and function of pesticides on pests, germs and weeds are often affected by the weather. In windy, rainy, high temperature, high humidity and other climatic conditions, the use of pesticides will affect the pesticide residue period, reduce the efficacy, increase environmental pollution or increase the chance of pesticide damage. Therefore, in some places, old farmers said, "Look at the weather and use drugs skillfully", which is a summary of farmers' practical experience for many years.

(1) gale

Pesticides should not be used in windy weather, and the effect of pest control, disease prevention and weeding is generally poor. The reasons are as follows: First, strong winds are easy to blow away pesticides, especially dusting, which will accelerate the volatilization of pesticides and make the application of pesticides uneven; Secondly, due to the influence of wind, the branches and leaves of plants vibrate and rub against each other, resulting in mechanical loss of chemicals; Third, the sprayed powder or fog spots are easy to fly with the wind, can not fall quickly and attach evenly to the body surface of the trees to be controlled, and will also pollute the atmosphere; Fourth, the wind is strong, and chemicals are easy to fall on operators, which increases the probability of poisoning and is very unsafe for operators.

It's raining.

Rainwater can directly wash away pesticides, causing losses, which will not only affect the effects of insecticidal, bactericidal and weeding, but also pollute river water bodies and cause aquatic animals to die of poisoning. Therefore, pesticides must not be used on cloudy or rainy days. However, different pesticide varieties and dosage forms have different ability to wash away rainwater. For example, trichlorfon has weak resistance to rain, while dimethoate, monocrotophos, triadimefon and carbendazim can be absorbed by plants because of internal absorption, so the impact of rain on them will be less. Among the dosage forms, powder and wettable powder are the least resistant to rain erosion and are easy to lose, while emulsifiable concentrate pesticides have certain resistance to rain erosion because they can form an oil film on plants, but they also have certain limitations.

(3) High temperature

Generally speaking, high temperature will promote the decomposition of pesticides, shorten the duration of pesticides, reduce the control effect and increase phytotoxicity. The main reasons are: first, the use of pesticides at high temperature will accelerate the chemical decomposition of pesticides; Second, high-temperature ultraviolet rays are also stronger, which will also accelerate the decomposition of drugs; Third, high temperature can promote the volatilization of effective components of drugs; Fourthly, in the high temperature weather, the chemical activity of chemicals is relatively strong, and the toxicity of pesticides is also relatively large. In hot weather, the metabolism of trees is relatively strong, and the stomata on the leaves are large and open. When spraying, chemicals can easily enter the body, which is prone to phytotoxicity. For example, lime-sulfur mixture, emulsifiable concentrate and some herbicides are all used at high temperature. Therefore, in hot weather, if it is really necessary to use pesticides, the concentration of herbicides should be lower, and try not to use pesticides at hot noon to avoid phytotoxicity and poisoning accidents of users.

Of course, many pesticides will improve their efficacy and control effect at higher temperatures, especially some pesticides containing organophosphorus and organic sulfur preparations, such as trichlorfon, dichlorvos, dimethoate, parathion and sulfur. For example, when 40% dimethoate EC is used to control cotton aphids, the dilution ratio of water is only 2000 times at 65438 05℃, and it can reach 3000 ~ 4000 times at 25℃.

(4) High humidity

High humidity is different from the scouring effect of rain, which mainly causes the mechanical loss of chemicals, while humidity mainly causes the chemical decomposition of chemicals, making chemicals ineffective or causing phytotoxicity. For example, when the air is humid, foggy and dewy, don't use Bordeaux mixture. Due to the contact of these chemicals with high humidity air and the action of carbonic acid gas, it is easy to increase the water-soluble dosage and increase the phytotoxicity. Moreover, humidity is often related to temperature. Many pesticides decompose at high temperature, which can catalyze decomposition (while microbial pesticides can exert their efficacy better at high temperature).

In addition, sunlight also has an impact on the efficacy, mainly because ultraviolet rays can decompose a variety of pesticides. For example, dimethoate, sodium pentachlorophenol and phoxim are easily decomposed in the sun. Many kinds of pesticides are packed in brown glass bottles to avoid being decomposed by light.