The Role of Adjuvants

Weather, the severity of host infection, and the stage of development of the irritant pest are all factors in the effectiveness of a pesticide. To waste time and/or product on a control effort that is ineffective is both eco­nomically and environmentally unsound. That is what happens when a pesticide rolls off the waxy epidermis of a plant, or when it settles to the bottom of a sprayer tank rather than staying mixed in the water carrier. Add to that concern the dangers of a pesticide being blown as particles or vapors onto nearby plants, soil, or animals for which it was never intended and environmental alarms go off throughout the region. Adjuvants address those problems.

Adjuvants are chemical additives that improve the performance of the pesticide with which they are combined. There are an increasing number available for horticulturists to select from, but not all have the same qualities and not all are used for the same purpose. Table 6-3 lists some of the types of adjuvants available and describes their modes of action when combined with pesticides. Because of the differences in both type and mode of action, growers and others who apply pesticides must be careful in their selection of a particular adjuvant. Increasingly, the manufacturers of pesticides are specifying the appropriate adjuvant on the pesticide label. When a manufacturer’s recommendation is not available, pesticide applicators need to work with a reputable supplier who can help them select the proper adjuvant to meet their needs.

Certification

During the last two decades of the twentieth century, concern about the use of pesticides grew within all segments of the national and interna­tional populations. Stories and anecdotes of misuse—some true, some exaggerated, and some totally fabricated—resulted in government regulatory reactions that ranged from wise and overdue to knee jerk and hyperpolitical. The green industry, while not welcoming every change, particularly those perceived as restrictive and unwarranted, has gener­ally complied.

Types of Adjuvants and How They Work

Type of Adjuvant

Mode of Action

Anti-Foams

Reduce the foaming that occurs when spray mixtures are agitated as they are prepared and/or applied

Foaming Agents

Used to reduce pesticide drifting by promoting the cohesiveness of small droplets

Buffering Agents

Permit the mixing of two or more materials that would otherwise be incompatible due to pH differences

Emulsifiers

Permit petroleum-based pesticides to be mixed with water for application

Invert Emulsifiers

Permit water-based pesticides to be mixed with carriers containing oil for application

Penetrants

Enable the pesticide to reach the inside of what is being treated

Safeners

Reduce the toxicity of a pesticide to the plant being treated and/or to the person applying it

Spreaders

Improve the uniformity of application over the surface being treated

Stickers

Increase the time a pesticide remains on the treated surface

Thickeners

Used to reduce drifting by increasing the size and weight of droplets

Wetting Agents

Allows pesticides in dry powder form to mix with water for application

The Role of AdjuvantsOne of the outcomes of the concern was regulation. Some well – known and widely used pesticides were either removed from manufac­ture or reformulated into diluted, less toxic forms. Many pesticides are no longer available in high potency forms to nonprofessionals such as home gardeners. The formulations that have their active ingredients in high percentages or require special techniques to apply are now avail­able for purchase and use only by professionals who are certified pes­ticide applicators. The certification is conferred by state governments after an applicant passes an examination that demonstrates knowledge of safe pesticide use. Renewal of the certification is mandated every few years to ensure that applicators stay current with new knowledge and regulations.