Pesticide wettable powders

The stability of toxicant-carrier combinations used in pesticide wettable powder formulations cannot be easily predicted by evaluating various properties of the carrier. Several types of synthetic calcium silicates and their modifications were evaluated for malathion stability and other properties. The carriers were evaluated for pH (slurry), pK (surface acidity), moisture content, absorptive capacity, and/or ion exchange capacity. These properties were correlated with actual malathion stabilities as measured at 40° C. storage for 1, 2, 3, and 7 months. The carrier properties evaluated did not offer a simple means of predicting compatibility in the variety of carriers tested. 

Sucrose distearate Sucrose stearate dispersant, pesticide wettable powders Sodium methyinaphthalenesulfonate dispersant, pesticides... 

Tensiofix CG11 Tensiofix CG21 wetting agent, pesticide wettable powders... 

Schreuder, R. H., A. Martijn, C. van de Kraats, Diisobutyl- and diisopropylnaphthalene-sulphonates in pesticide wettable powders and dispersible granules by HPLC, 7. Chromatogr., 1989,467, 177-184. 

Pesticide Dispersants. Modified ligaosulfates are used ia the formulatioa of pesticides, la wettable powders, suspeasioa coaceatrates, and water dispersible granules, they act as dispersants and prevent sedimentation. They also act as biaders ia the productioa of granular pesticides. Typical usage levels ia these types of products range from 2—10%. 

All lnaphthalenesulfonic Acids. The aLkyLnaphthalenesulfonic acids can be made by sulfonation of aLkyLnaphthalenes, eg, with sulfuric acid at 160°C, or by alkylation of naphthalenesulfonic acids with alcohols or olefins. These products, as the acids or their sodium salts, are commercially important as textile auxiUaries, surfactants (qv), wetting agents, dispersants (qv), and emulsifying aids, eg, for dyes (qv), wettable powder pesticides, tars, clays (qv), and hydrotropes. 

The main purpose of pesticide formulation is to manufacture a product that has optimum biological efficiency, is convenient to use, and minimizes environmental impacts. The active ingredients are mixed with solvents, adjuvants (boosters), and fillers as necessary to achieve the desired formulation. The types of formulations include wettable powders, soluble concentrates, emulsion concentrates, oil-in-water emulsions, suspension concentrates, suspoemulsions, water-dispersible granules, dry granules, and controlled release, in which the active ingredient is released into the environment from a polymeric carrier, binder, absorbent, or encapsulant at a slow and effective rate. The formulation steps may generate air emissions, liquid effluents, and solid wastes. 

Exposure assessments are commonly done using computer modeling (e.g., Pesticide Handlers Exposure Database [PHED]). Computer modeling was not used for cyromazine 75 WG because of the limited information in the database on wettable powders packed in water-soluble bags at the time the study was planned. 

Approximately 55 different commercial formulations of chlordecone have been prepared since its introduction in 1958 (Epstein 1978). The major form of chlordecone, which was used as a pesticide on food products, was a wettable powder (50% chlordecone) (Epstein 1978). Formulations of chlordecone commonly used for nonfood products were in the form of granules and dusts containing 5% or 10% active ingredient (Epstein 1978). Other formulations of chlordecone contained the following percentages of active ingredient 0.125% (used in the United States in ant and roach traps), 5% (exported for banana and potato dusting), 25% (used in the United States in ant and roach bait), 50% (used to control mole crickets in Florida), and 90% (exported to Europe for conversion to kelevan for use on Colorado potato beetles in eastern European countries) (Epstein 1978). 

Agricultural (Ag) formulations that are commonly diluted and applied by means of spray equipment include water soluble liquids, emulsifiable concentrates, wettable powders, and flowable suspensions. The choice of which formulation to develop normally depends upon the solubility properties of the technical pesticide. Scientists often must also consider manufacturing costs, field efficacy and product toxicity. 

Fig. 12.11 Examples of pesticide concentration vs. depth, indicating preferential flow of each pesticide in individual field plots. Symbols C continuous I intermittent P ponding S spiinkhng TG technical grade EC emulsifiable concentrate WP wettable powder U undisturbed D disturbed (Ghodrati and Jury 1990)...

Sulfur-Based Pesticides. Sulfur (elemental) has been used as an effective acaricide, fungicide, and insecticide. For ease of use, a number of special formulations are available, ranging from sulfur dusts (up to 95% sulfur) a wettable powder (30 to 90%) and paste-like solutions in which the sulfur is ground to a fine colloidal form. Such formulations may contain up to 50% sulfur. Target plant diseases of sulfur when used as a fungicide include apple scab, brown rot. downy and powdery mildew, and peach scab. Against insects, sulfur is effective for mite, scale, and tJirip. Most formulations are not injurious to honeybees. 

After the 1980s, y-HCH was used to produce lindane and other HCHs were mainly used as intermediates of HCB. There was no direct use of a- and (S-IICI after the 1980s. Lindane was used for locust and wheat midge control. Three kinds of lindane formulation were registered in the pesticide registration information system of the Chinese Ministry of Agriculture for wheat midge and locust control 1.5% powder, 6% powder, and 6% wettability powder. 

Tpo understand the physical and colloidal chemical aspects of pesticidal formulations research, one must first understand the objectives of the formulations chemist in his work. Simply speaking, the formulations chemist must take the pure organic chemical pesticide and put it in a usable form for field use. These forms include wettable powders, emulsifiable concentrates, dusts, granules, water-soluble concentrates, flowables, and an aerosol, to name a few types of concentrates. The formulations chemist desires to put together a formulation that (1) is easy and eco-... 

Control of Drop Size w/o Emulsions. Although the control of the drift of herbicide sprays was the initial reason for renewed interest in water-in-oil emulsion sprays, there are other interesting and novel ways of applying pesticides. The physical properties of w/o emulsions are considerably different from those of more conventional types of spray liquids, and the emulsifiers required to form and stabilize w/o emulsions are different from the usual materials employed in oil-in-water and wettable powder sprays. These differences can affect all aspects of spray performance, and a thorough study is required to appreciate the advantages and disadvantages which w/o emulsions may possess over aqueous-based sprays. 

Understanding the relationship between the composition of a mixture and its properties is fundamental to the development of formulated products. In the pesticide industry, formulation chemists seek to translate such an understanding into products that meet criteria established for properties such as suspensibility, emulsibility, storage stability, compatibility, and most importantly, biological activity. The preferable way to acquire the necessary knowledge is to deduce the properties of mixtures in terms of mechanisms that are operative at the microscopic level. However, mixtures are extremely complex systems and the available theory is usually insufficient for developing useful theoretical models. For example, we are unable quantitatively to predict, on the basis of molecular theory, the suspensibility of a wettable powder from a knowledge of its composition. 

The objective of this report is to discuss with the help of an illustrative example, the applicability of computer-assisted methods to the development of pesticide formulations. The example describes the process of planning and conducting a study to obtain an empirical equation which correlates the suspensibility of a wettable powder with its composition. 

The persistence of pesticides in soil is also influenced by their formulations. Granules are generally the most persistent. Wettable powders and dusts are usually less persistent than emulsifiable concentrates (McEwen and Stephenson, 1979). 

Pesticides are more extensively applied as liquids than as solids. Even some dry formulations, such as wettable powders, are diluted or suspended in a liquid before being applied. Different formulations present different hazards to the applicator. Figure 4.2 describes the hazards of various formulations. 

Pyrethroids are formulated as emulsifiable concentrates, wettable powders, granules, and concentrates for ultralow volume application. They may be combined with additional pesticides (sometimes highly toxic) in the technical product or tank mixed with other pesticides at the time of application. AAS-TAR is a combination of flucythrinate and phorate. Phorate is a highly toxic organophosphate. 

The pump must have sufficient pumping capacity to supply the needed volume to the nozzles and to the hydraulic agitator (if necessary) and to maintain the desired pressure. The pump parts should be resistant to corrosion and abrasion if abrasive materials such as wettable powders are to be used. Select gaskets, plunger caps, and impellers that are resistant to the swelling and chemical breakdown caused by many liquid pesticides. Consult your dealer for available options. 

Roller pumps are among the least expensive and most widely nsed of all sprayer pumps. They provide moderate volumes (8 to 30 gpm) at low to moderate pressure (10 to 300 psi). Often used on low-pressure sprayers, roller pumps are positive-displacement, self-priming pnmps. The rollers, made of nylon, teflon, or rubber, wear rapidly in wettable powders but are replaceable. A pump that will be subjected to such wear should have a capacity at least 50 percent greater than that needed to supply the nozzles and agitator. This reserve capacity will extend the life of the pump. The pump case is usually cast iron or a nickel alloy. Roller pumps are best for emulsifiable concentrates, soluble powders, and other nonabrasive pesticide formulations (Figure 14B). 

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