Adjuvant is a broad term for anything that is added to a herbicide that helps with performance or handling. Adjuvants can be added by the manufacturer for a variety of purposes such as improving solubility, shelf life, handling, compatibility, stability and other characteristics. Most people, however, think of an adjuvant as those products that they add to the spray tank. The most common type of adjuvants are surfactants or surface-active agents that are used to improve spreading and/or absorption of the applied solution. There are many other uses for adjuvants. These include deposition agents, drift control agents, anti foam agents, buffering agents, compatibility agents, water conditioners, tank cleaners and others.

Rarely are adjuvants used with soil applied herbicides. There has been interest, however, in using adjuvants with two of the soil applied herbicides used in lettuce to improve weed control. The intent is to use an adjuvant to either increase the movement of Prefar down into the soil or to reduce the movement of Kerb too far into the soil.

Prefar(bensulide) is normally applied to the soil surface and incorporated with water. It adheres very strongly to the surface and can be difficult to move down to the germinating weed seed in many fine textured soils. Some growers and pest control advisers have used non-ionic surfactants, crop oil concentrates or other specialty adjuvants to improve movement into the soil and have reported improved weed control. In our trials, however, we have not been able to measure a consistent improvement in weed control from any of the adjuvants that we have tested.

Kerb(pronamide), on the other hand, does not adhere strongly to the soil and can often be leached below germinating weed seeds by irrigation water before they germinate. Adjuvants that are used to increase the adsorption of products to foliage have been tested with Kerb to reduce leaching. In our trials, we have again been unable to measure a consistent benefit from these.

Irrigator: "You lissen ta me... tddiss an ADJUVANT!"

Tickes/J.Pena

To contact Barry Tickes go to: btickes@ag.arizona.edu.

For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
College of Agriculture, The University of Arizona, Tucson, AZ.