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Compatibility with Adjuvants

Many pesticides require no additives (adjuvants). But if there are concerns about pesticide degradation and coverage, an additive such as a buffer or a spreader/sticker may be needed. There are many types of adjuvants (tank additives), including emulsifiers, de-foamers, drift retardants, spreaders, stickers, wetting agents, anti-caking agents, cuticle cutters, penetrants, buffers, translocation aids, nutrient buffers, thickeners, emulsion inverters, UV screens and evaporation inhibitors.

Adjuvants can be sorted into two categories:

1. The activators improve the application and/or effectiveness of products (wetters, spreaders, stickers, emulsifiers, emulsifiable oils and plant penetrants or translocators)
2. Some adjuvants have special purposes (drift retardants, defoamers, buffers, stabilizing agents and feeding stimulants, among others).

Surfactants are “surface acting agents” and are active ingredients in most adjuvants. Surfactants are either non-ionic, anionic (negatively charged) or cationic (positively charged). The pesticide’s label will tell you whether the pesticide is compatible with the different kinds of surfactants. Surfactants work either as spreaders or stickers.

Spreaders break the surface tension of water and allow water-based sprays to spread out on a leaf rather than beading up. Soaps and detergents should not be used for this purpose. Soaps are alkaline and will break down many pesticides. Detergents containing sulfates and phosphates are highly reactive and may react with the spray mixture.

Stickers are used to stick solid pesticide particles to leaves, reduce pesticide volatilization and waterproof the pesticide. Many stickers also act as spreaders (alkylarylpolyethylenates). Most products that won’t wash off with rain or irrigation contain latex (rubber), polyethylenes (plastic), resins (rosins), polymenthenes (resin-like compounds) or other long-chain polymers.

Buffers neutralize alkaline water, which normally breaks down insecticides through alkaline dehydrolysis. Phosphoric acid is the active ingredient in many buffering agents.

In Texas, it is legal to apply pesticides in any adjuvant as long as the percentage concentration of adjuvant in the spray is lower than the percentage concentration of water (carrier) in the tank. Tank mixes must contain at least 50 percent water carrier.

Consult the pesticide label before using an adjuvant. Many labels make specific reference to spreaders/stickers. If not, make a test application on a small number of plants to see if the mixture is beneficial. Determining whether pest control has been enhanced is more difficult. Be cautious. New, untested tank mixtures may cause phytotoxic reactions in plants.

There are so many products available that there are many possible combinations of pesticides and adjuvants. Few have been tested, however, so the grower must determine the usefulness of these products. Contact manufacturers of the pesticide as well as the adjuvant for specific questions about any combination.