Thursday, June 19, 2008

Turf, Landscape, and Nursery - Pesticide Adjuvants

An adjuvant is a chemical that is added to a pesticide, either in the pesticide formulation, or as an additive in the spray tank, that enhances the action of the pesticide by modifying its characteristics in relation to the target. The following is basic information on adjuvents.

The world of adjuvants is very confusing with much information being proprietary. Often it is recommended by manufacturers or by researchers that specific adjuvants be used with systemic pesticides including herbicides, insecticides, and fungicides, to improve their activity or efficacy. Terms such as surfactant, penetrant, and activator are used to describe what the adjuvant does, and to some degree, the general nature of the additive.

There are two basic actions that must be successful for a systemic pesticide to be effective. First, the chemical must enter into the plant. Second, it must be distributed in the plant to the site of action. Adjuvants are used to enhance entry into the plant.

Adjuvants are added to help the chemical pesticide cover over the leaf surface, move through the cuticle, and in some cases, move into the stomata. Surfactants are a major category of adjuvants. They reduce the surface energy of chemicals applied and water, allowing the chemical to spread over the leaf surface more readily. They have both hydrophilic and hydrophobic components thus working with a wide range of pesticides (whether hydrophilic or hydrophobic). Depending on their formulation, they may work to emulsify, disperse, spread/wet, or solubilize the added pesticide as they interact with the leaf surface.

Surfactants act in a number of ways depending on formulation. They may increase the area of contact of spray droplets with the leaf, increase spray retention, act as a humectant to keep spray droplets moist for a longer time, modify the cuticle by allowing dual solubility in hydrophilic and hydrophobic components as the pesticide moves through the cuticle, produce hydrophilic channels for those pesticides with that characteristic, increase the permeability of the cuticle and cell membrane of the underlying leaf cells, complex with pesticides and lower their surface tension, lower tensions allowing movement between cell walls of the leaf, and enhance entry into stomata.

Organosilicone adjuvants have been shown to enhance the movement of chemicals into the stomates as a major mode of entry for pesticides.

Oil based adjuvants are diverse with two broad catagories: petroleum based and vegetable based. Oils work to reduce vapor loss of a pesticide and for some pesticides, improve entry into the leaf by a number of mechanisms.

Gordon Johnson, Extension Horticultural Agent, UD, Kent County

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