The pesticide dosage forms that need to be diluted can be mainly used for dilution with water. In China, there is no pesticide dosage form registered with organic solvent dilution, mainly including emulsifiable concentrate, wettable (soluble) powder, suspension (milk), and water. , water emulsion, microemulsion, water dispersible granules, etc.
The common feature of this type of pesticide formulation is that no matter what form, it must be diluted with water to prepare a liquid before use, and then applied by spraying.
Almost all of the original pesticides can be processed into spray formulations, and depending on the formulation characteristics, they can be adapted to different volume spray methods. In addition, most of these preparations contain suitable surfactants (emulsifiers, dispersants, wetting agents, etc.), which can be better dispersed and suspended in water when formulated with pharmaceutical solutions, and can form wetting and adhesion on the target after application. This is the basic premise for its effective use. Spraying the liquid of the liquid and forming droplets of different fineness onto the object to be controlled depends mainly on the selection of the spray method and the performance of the spray implement.
It can be seen that the use of pesticide formulations after dilution with water is more complicated and must be taken seriously according to the characteristics of the dosage form and the requirements of the use technology.
First, emulsifiable oil
The emulsification of emulsifiable concentrate is greatly affected by water quality (such as water hardness) and water temperature. It is best to use a small amount of test after use, and emulsified and then prepared in large quantities according to requirements. If there is oil slick or precipitated liquid during use, it will not be sprayed evenly, resulting in the failure of the drug to function properly and even phytotoxicity. The emulsion formed by emulsifiable concentrate on water is a thermodynamically unstable system, the stability of the emulsion changes with time, and most of the active ingredients of the pesticide are easily hydrolyzed. Therefore, the pharmaceutical liquid should be stirred, and the liquid should be used up as soon as possible. For the motorized sprayer, the mixing tank must be added with a stirring device. Emulsifiable oils are generally not sprayed directly, but can be diluted with water to different concentrations to suit different volumes of spray.
Second, wettable (soluble) powder
Since the granules of the wettable powder are generally coarse, the granules settle faster, and the agitation should be enhanced during the application, otherwise the concentration of the medicated liquid before and after spraying may be inconsistent, which may affect the efficacy. The granules of wettable powders may agglomerate in high-hardness water. Therefore, the effect of water quality on the suspension properties of wettable powders must be considered when formulating pharmaceutical liquids.
The wettable powder is a solid pesticide preparation. When a low-volume spray liquid is prepared (generally less than 2 liters per acre of application liquid), the viscosity will be too large to be effectively sprayed. Therefore, wettable powders are generally used as a constant spray. In addition, the wettable powder can not be directly sprayed, and care should be taken to prevent moisture absorption during storage or use, so as not to affect the use.
Third, suspension (milk) agent
The suspension system formed by the water-insoluble solid drug is called a suspension agent, and the suspension system formed by the water-insoluble liquid original drug is called a suspoemulsion. The suspension system of both original drugs is called a suspension emulsion. It is diluted with water to form a uniformly dispersed and suspended emulsion, and the operation requirements are similar to those of emulsifiable concentrates and wettable powders. However, the suspension (milk) agent uses water as the dispersed phase, and can be uniformly mixed and dispersed with water at any ratio. When used, it is less affected by water quality and water temperature, and is convenient to use and does not pollute the environment. It is an ideal pesticide dosage form for dilution.
Suspension (milk) must be visually inspected when used. If it is stratified or precipitated, it can be recovered by shaking. It can be used normally after water dispersion and suspension. Otherwise, it can not be used, so as to avoid the difference of active ingredients in the upper and lower parts of the pesticide or the dispersion of the preparation. The unsatisfactory suspension is caused by uneven distribution in the liquid medicine tank, so that the active ingredients of the pesticide before and after the sprayed liquid are different, which may affect the efficacy and even cause phytotoxicity.
Fourth, water agent
The pesticide in the water agent has good solubility in water and is chemically stable. It can be diluted with water to form a very stable aqueous solution, which can be used in various spray methods. Since the pesticide original drug is very soluble and stable in water, it is generally not encountered in the preparation of the drug solution. However, since the processing of Chinese water agents generally does not add a wetting aid, the sprayed liquid has poor wettability to the target, which easily causes the loss of the liquid, affects the control effect and pollutes the environment. Therefore, the use of the water agent should be appropriately added to the wetting aid according to the actual use.
Five, water emulsion
The water emulsion is a pesticide dosage form which is sprayed after being diluted with water. When diluted with water, it is similar to the emulsifiable oil, and is uniformly dispersed in water to form a relatively stable emulsion with a very small oil bead (1 to 5 μm) for the spraying method. Apply.
When using an aqueous emulsion, it is generally required to check the appearance of the preparation. The ideal aqueous emulsion product should be a homogeneously stable emulsion with no delamination and water evolution. If there is slight stratification or water leaching, it can be restored to homogeneity after shaking, and it can also be used. Water emulsions, like emulsifiable concentrates, are also required to form a relatively stable emulsion by spontaneous emulsification or a little agitation.
Since the water emulsion contains more water, a certain amount of antifreeze is generally added to the preparation. Care must be taken during use to ensure proper storage of the aqueous emulsion, especially for unused preparations, which must be sealed and placed above 0 °C.
Six, microemulsion
The microemulsion is similar to the aqueous solution when applied in diluted water, and the water spontaneously disperses and forms an almost transparent emulsion. It should be noted that the microemulsion is diluted with water to be a nearly transparent emulsion, rather than a concentrated milky white emulsion like emulsifiable concentrate. It is not the traditional practice that the emulsion is more concentrated and whiter. The better the microemulsion is diluted with water, it indicates that the quality of the microemulsion product is unqualified. Both water emulsions and microemulsions are water-based pesticide formulations developed to replace emulsifiable concentrates with good environmental compatibility.
Seven, water dispersion granules
The water-dispersible granules are generally spherical or cylindrical particles, which can be disintegrated rapidly in water, dispersed into fine particles, and shaken or stirred to form a highly suspended pesticide dispersion system for spray application. It is more like a wettable powder and a suspension (milk).
Water-dispersible granules should avoid excessive extrusion during production, storage and use, so as to avoid particle-based crushing and lose the dosage form advantage. The water-dispersible granules are free of granules and have the properties of granules. However, due to the production and processing costs, they generally have a high effective content and cannot be used for direct application.
Other pesticides used after dilution include oil dispersing powders, milk granules, dispersible tablets, effervescent tablets, dispersible liquids, and microcapsule suspensions.
(Source: "Pesticide Application Guide")
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