Spray Adjuvants

Several different types of products are available that may help to improve pesticide efficacy. Known as spray adjuvants, they perform a variety of functions. A given adjuvant may perform more than one function, and the functions performed should be specified on the label.

Be careful when using adjuvants, particularly with EC formulations. Improper selection or use can result in either plant injury or reduced effectiveness.

Activator - Increases the biological efficacy of the pesticide.

Acidifier - Lowers the pH of alkaline spray water to reduce the potential breakdown of certain pesticides in the spray tank. Not necessary unless spray solution has a pH above 7. The amount of acidifier necessary to lower the pH to the desired level depends on the pH of your water source. Follow label recommendations carefully.

Buffer or Buffering Agent - Lowers the pH and maintains it at a certain level of acidity. Some pesticides break down rapidly at a solution pH above 7. Add a buffer if the water source has a pH above 7 and the product label indicates sensitivity to alkaline (high pH) solutions. Check the pH of your spray water source periodically, as it may change during the season.

Defoaming Agent or Antifoaming Agent - Eliminates foam or prevents foam formation in the spray tank.

Drift Control Agent or Drift Reduction Agent - Reduces drift of spray droplets onto nontarget areas.

Surfactant, Spreader, Wetting Agent - Different names for products which reduce the surface tension of spray droplets, allowing them to spread out more evenly on the surface of the leaf or fruit. Some surfactants used in combination with certain pesticides can cause plant injury. This can be a problem on several types of fruit trees and is particularly a problem on Anjou pears. Consult the label or chemical supplier for more information.

Sticker - Causes spray droplets to adhere or stick to the target surface after the spray dries, thereby reducing the potential for loss from rain or overhead irrigation.

Spreader-Sticker - A term commonly misused when referring to a surfactant or spreader. A true spreader-sticker combines the characteristics of a surfactant with that of a sticker.

Water Conditioning Agent - Reduces or eliminates antagonism between the pesticide and ions present in the water.

WSDA requires registration of spray adjuvants that are distributed in Washington. To determine if an adjuvant is registered in Washington visit the PICOL website at https://extension.wsu.edu/wsprs/ .