What Is a Fumigant?

Fumigants are a class of pesticides that use vapors generated during volatilization to poison pests. Gaseous molecules enter poisonous organisms to play a toxic and killing effect, and are different from gasified liquid, solid or compressed gas. The dosage is calculated according to the space volume of the fumigation place (unit is g / m3), and the concentration is determined according to the fumigation time, the degree of fumigation place sealing, the amount of fumigated matter, and the fumigant vapor adsorption capacity. It should be applied in warehouses, tents, houses, carriages, cabins, etc. that can be sealed or close to closed conditions. Under the condition of large concentration of fumigated objects, it can effectively eliminate hidden pests or germs.

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Fumigants are produced when volatiles are used

Soil treatment methods are: soil injection method; drip irrigation method. Ditching and soil covering method. mechanical film application method.

The fumigant vapor usually enters the respiratory system directly through the epidermis or valve of the pest, which penetrates into the blood and kills the pest. Its insecticidal effect is generally thought to lie in chemical action on enzymes. For example, methyl bromide can be combined with sulfhydryl groups, which can gradually and irreversibly inhibit a variety of enzymes in pests.

Fumigants can be classified according to chemical structure: Haloalkanes such as carbon tetrachloride, dichloroethane, dibromoethane, methyl bromide, bitter chloride, dichloropropane, dibromochloropropane and the like. Sulfides such as carbon disulfide,

The use of fumigants is affected by the following factors:

Physicochemical properties of pharmaceuticals. Mainly the volatility, molecular weight and flammability of pharmaceuticals. Volatility directly affects the efficacy of the drug, which is generally expressed by the vapor pressure of the drug. The latter is positively correlated with volatility and permeability. Molecular weight is inversely related to gas diffusion rate and permeability. For example, cyanohydrin with a small molecular weight has a higher diffusion rate and permeability, while chloropicrin, which is heavier than air, has a slower diffusion and diffusion rate, which is easy to aggregate On the ground, it should be applied evenly on the fumigant so as to spread downward. The vapor of some fumigants is easy to burn, and its flammability is measured by the minimum ignition concentration and the ignition concentration range. The larger the ignition concentration range and the lower the ignition concentration, the greater the fire danger during storage and use. Generally, after a fumigant gas is mixed with the same amount of air, a small Mars that does not cause combustion at 25 ° C is a safe fumigant. Mixing inert materials such as carbon dioxide and carbon tetrachloride can reduce flammability.

The nature of the object being fumigated. The fumigant's adsorption of fumigant gas molecules is related to the fumigant's permeation, insecticidal, sterilizing effects, and residual problems. Objects of different properties and the use of different kinds of fumigants have different adsorption properties at different temperatures. Generally, when the adsorption is high, the quality of the fumigated object may be affected, such as reducing the germination rate of seeds, causing damage to plant buds, flowers, leaves, and fruits, and reducing the nutritional content of food. Low adsorption and strong permeability can increase the effective insecticidal concentration. If the vapour is chemically reacted with the fumigated substance after desorption, the desorption (ventilated air after fumigation) cannot be removed any more, resulting in residue. But generally the fumigant residue is not very serious.

Temperature and humidity. The temperature has a great influence on the fumigation effect. When the temperature is higher than 10 ° C, the volatility of the agent will increase, and the activity and chemical action of the gas molecules will accelerate. At this time, the pests will also become active, and the poisoning will be accelerated due to the increased respiratory rate. When the temperature is 10 , the pests are less active, the respiration rate is lower, and the fumigant's ability to diffuse and penetrate is also reduced. However, when the temperature is lower than 10 ° C, the low temperature is unfavorable for the physiological activities of the pests. At the same time, although the low temperature reduces the evaporation rate of the pesticide, it also increases the adsorption capacity of the insect epidermis to the vapor, so the fumigation effect is increased. Generally, grains can be effectively fumigated at a temperature of 21-25 ° C. Properly increase the dose when the temperature drops, and vice versa when the temperature increases. Humidity has less effect on fumigation. However, in the case of fumigation in grain processing plants, in order to avoid the corrosion of the metal by the steam, or the mildew of the smoked objects, it is best to choose fumigation under low humidity conditions.

The type and status of the pest. The sensitivity of a pest to a fumigant varies with different types of physiology and structure. Even the same pest is significantly different because of its different developmental stages. For example, the adult's respiration rate is the highest, followed by the larvae, pupae, and eggs. The adult's resistance is the worst. It should be determined according to the above characteristics to achieve the best control effect.