11/15/2013 - By Dr. Raymond Snyder

Adjuvants are intended to enhance the performance or handling characteristics of pest control products.  Proper adjuvant selection or in some cases exclusion can greatly impact the effectiveness of control products used for weed, insect, and disease management.  In addition, consistency of control from site to site can be increased when adjuvants are properly utilized.

A number of different adjuvant types are available for use in weed, insect, and disease management programs.  Activator-type adjuvants are designed to increase the performance of pest control products.  These activator adjuvants include nonionic spreader-stickers and penetrants, organosilicone surfactants, and crop oils.  Each has their own intended purpose and aggressive characteristics.

Nonionic spreader stickers are intended to reduce the contact angle of water and promote adhesion of applied control products on waxy leaf cuticle surfaces.  Reducing the contact angle promotes lateral spread of applied control products across greater surface area thereby increasing the opportunity for contact with target pests.  The sticker component increases the chances that the control product will remain on the plant surface minimizing run-off or wash-off following rainfall.  Some products specifically recommend spreader sticker-type adjuvants in which case one should be utilized to maximize the effectiveness and consistency of the applied product.

Nonionic penetrants are generally more aggressive and designed to promote the penetration of applied control products through the plant cuticle.  Nonionic penetrants also have more potential to reduce the contact angle of water relative to many spreader sticker-type adjuvants.  Nonionic penetrants help to promote the efficacy and consistency of herbicides when applied to tough-to-control weeds.  Many herbicides specifically recommend nonionic penetrants to increase the effectiveness of control.

Crop oil concentrates are usually derived from non-phytotoxic petroleum oil-based materials, mineral oil, or vegetable oil.  Crop oil concentrates can be even more aggressive than nonionic penetrants.  Their main function is to aid in the movement of herbicides across tough, waxy plant cuticle surfaces.  In addition, crop oil concentrates can reduce the drying time of applied herbicides thereby reducing the time necessary for absorption.  Herbicides designed to control difficult weeds often recommend the addition of a crop oil concentrate adjuvant.

Organosilicone surfactants are perhaps considered to be the most aggressive among adjuvant types.  Organisilicone surfactants significantly reduce surface tension.  Reduced surface tension can result in rapid rainfast characteristics, reduced volatilization and photodegredation, and increased stomatal infiltration of many applied control products.  In many cases, the use of organosilicone surfactants permits for the use of the lowest label rate while still achieving good control.  Caution, however, should be exercised when using organosilicone surfactants due to their aggressive characteristics.

In summary, adjuvants can be very useful in improving the effectiveness and overall consistency of applied control products.  Adjuvant types vary depending on their chemistry and intended function.  Finally, be sure to always consult and follow product label instructions.

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