By John Garr and Jerry Green, GarrCo Products
If you have not already done so, now is the time to determine how you are going to use adjuvants next season. Adjuvants do a lot of useful things, but figuring out which adjuvants to use when can be a bit difficult. We will try to help make it a little easier for you.
Many adjuvant functions
Adjuvants can be any substances that have no biological activity when they are applied alone but when you apply the “right” ones with pesticides and other types of biological products, they enhance activity or improve application characteristics, usually eliminating real and potential mixing and spraying problems. When adjuvants are added to pesticide formulations, they are called “in-can” adjuvants. When added separately, they are called “tank-mix” adjuvants.
Many pesticide formulations contain in-can adjuvants. However, building a total adjuvant system into a formulation does not always work well because of the need to apply different spray volumes. Adjuvant efficacy often depends on its concentration, the percent of the spray volume, and an in-can adjuvant can only be the right concentration at one spray volume. For example, if the manufacturer designs the surfactant system to be the right concentration at 5 gal/A, it will be 4X too high at 20 gal/A and 5X too low at 1 gal/A.
Our experience is that pesticide manufacturers rarely put the full amount of surfactants and other adjuvants needed in their formulations. Tank-mixing additional adjuvant usually helps. Pesticide manufacturers generally feel that putting the full amount of adjuvant “in-can” requires too much volume and thus overly dilutes the amount of pesticide in the product. And maybe even more importantly, pesticide manufactures need to cooperate with the distributors who sell their pesticides. All distributors have their own brand of adjuvants, which their sales force is strongly encouraged to sell.
Tank-mix adjuvants are generally regarded as safe and largely exempted from regulation by the U.S. EPA. They do not kill pests and usually do not show any effect on plants. At most, adjuvants may cause a little cosmetic damage on sensitive plant tissue, usually by solubilizing waxes and allowing the plant tissue under the spray deposits to desiccate and result in some leaf burn or necrotic spotting. This cosmetic damage is not usually of concern unless the leaf or fruit is sold directly to the consumer. In these cases, using a lower concentration or a milder adjuvant usually solves the problem.
Adjuvant and formulation inert functions
Adjuvants are commonly grouped into two categories: activator adjuvants that enhance biological activity and utility adjuvants that improve application characteristics. One well-known expert once declared that different spray adjuvants do different things in different applications. It’s a catchy phrase, but what adjuvants do is not a mystery. The beneficial functions of adjuvants are well defined and can be at any stage of the application process, from the product formulation to the pest (see figure).
Key adjuvant functions from the product formulation to the pest.
How to use
Applicators must consults pesticide labels to determine what adjuvants to add to the spray tank. The label directions can be specific requirements, general recommendations or prohibitions. When adjuvant use is not mentioned, the applicator has the discretion on what to use. Hopefully you never have to deal with a situation where pesticide label directions contradict each other. If that occurs, do not mix those products and contact the manufacturer for guidance.
Applicators need to network with suppliers and local experts to ensure they are using adjuvants correctly. Nobody wants to spend more time on adjuvants than they have to. However, as our friends from the “show me” state know, just because someone tells you that an adjuvant performs a certain way does not mean that it will. Applicators must evaluate the adjuvants they use and ensure they are getting the improved performance they promise.
Pesticide manufacturers know adjuvant quality varies greatly and their products will not always be in the spray tank with the best products. The solution for most pesticide manufactures is to recommend their products at rates high enough to work even with the poorer quality adjuvants. Even when you use the best adjuvants, it is still generally not a good idea to cut pesticide rates below label recommendations because pesticide manufacturers usually only stand behind their products when the full rates are used. In addition, full pesticide rates and the best adjuvants together help prevent the evolution of the slowly creeping types of pest resistance.
Special consideration for aerial application
Develop your plans for adjuvants now before you get too busy. Anticipate pest problems and determine which adjuvant functions you will need. Aerial applicators know better than anyone how to apply pesticides at low spray volumes and have a high reputation to keep. However, the pressure to be perfect is increasing. Aerial applicators apply too much, too quickly to wait to see unwanted biological responses or product on their windshields to make corrections. Today’s yield monitors show uneven spray patterns and the grower is more likely to blame you than the products he asked you to apply for any streaks in the field. You will give your customers more uniform applications and better efficacy when you use adjuvants properly.