By Barry Tickes, UA Area Agriculture Agent

Adjuvant is a broad term for anything added to a herbicide that helps with performance or handling.

Adjuvants can be added by the manufacturer for a variety of purposes including improving solubility, shelf life, handling, compatibility, stability, and other characteristics. Most people think of an adjuvant as products they add to the spray tank.

The most common adjuvants are surfactants or surface-active agents used to improve spreading and/or the absorption of the applied solution. Other uses for adjuvants include deposition agents, drift control agents, anti-foam agents, buffering agents, compatibility agents, water conditioners, tank cleaners, and others.

Adjuvants are rarely used with soil applied herbicides. There has been interest in using adjuvants with two soil-applied herbicides in lettuce to improve weed control.

The intent is to use an adjuvant to 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 well 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.

Results of our trials have been variable. We have not measured a consistent improvement in weed control from any of the tested adjuvants.

Kerb (pronamide), on the other hand, does not adhere well to the soil and can often be leached below germinating weed seeds by irrigation water before germination. Adjuvants used to increase the adsorption of products to foliage and soil have been tested with Kerb to reduce leaching. Results have been variable and inconclusive.

Contact Tickes: (928) 580-9902 or btickes@ag.arizona.edu.