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Pesticide Safety Education Program (PSEP)
Part of the Pesticide Management Education Program
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Pesticide Compatibility

COMPATIBILITY - MIXTURES OF PESTICIDES

It is often economical and convenient to apply a mixture of two or more pesticides when a wide range of pests must be controlled. Some pesticide products, particularly many of those intended for home garden and home orchard use, already contain two or more pesticides. In most instances the pesticide user must add separate products to the spray tank. These products must be compatible with each other. Incompatibility can cause:

  • lumps, globs, sediments, gums and separated liquids which
  • cause poor distribution as well as clogged or damaged equipment.
  • loss of effectiveness
  • increased toxicity to man and other non-target animals
  • phytotoxicity
  • damaged to treated surfaces

The label on many pesticide products contains a list of compatible pesticides. Some labels even contain directions for mixing the product with certain other pesticides. Compatibility charts are available (REDBOOK AND CORNELL RECOMMENDS). However, there is still need for caution.

Label instructions and compatibility charts usually refer to only two pesticide active ingredients. They do not cover mixtures of three or more pesticides and usually give no information on the compatibility of inert ingredients such as emulsifiers and wetting agents. In addition, factors such as type or variety of crop, weather and water chemistry (especially pH) may be important.

Recommendations, labels and compatibility charts are certainly helpful but the pesticide user should take additional precautions. When trying new mixtures, he should mix up a pint or quart of the pesticide(s) and water (or other solvents) in the relative proportions that he plans to use them. Everything should mix well when the mixture is stirred or shaken and should not settle out rapidly upon standing. New mixtures should be applied initially on a small scale. In general, it is riskier to mix two different types of formulations, for example wettable powders with emulsifiable concentrates.

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