4.2 Adjuvants, Surfactants & Performance Enhancers

Adjuvants, Surfactants & Performance Enhancers

In the world of pesticide application, the active ingredient is the star of the show, but adjuvants are the crucial supporting cast. An adjuvant is any chemical added to a pesticide formulation or the spray tank to modify the product's physical properties or enhance its performance. While many commercial pesticide products already contain adjuvants in their formulation, applicators often add specific adjuvants to the tank mix to address local water conditions, weather, or specific target pest characteristics.

Adjuvants are broadly categorized into two main groups: Activator Adjuvants (which improve the pesticide's efficacy on the target) and Utility Adjuvants (which help with the mixing, handling, and application process).

Activator Adjuvants

Activator adjuvants are designed to directly improve the performance of the pesticide. They alter the way the spray droplet behaves on the target surface, increasing coverage, penetration, and ultimately, pest control.

Surfactants (Surface Active Agents)

Water has high surface tension, which causes it to bead up into tight drops. When spraying a water-based pesticide onto a waxy leaf or a hairy insect, this high surface tension prevents the liquid from spreading evenly, leading to poor coverage and runoff. Surfactants reduce the surface tension of water, allowing the spray droplet to flatten out and spread over a larger area of the target.

Surfactants are classified by their electrical charge:

• Anionic Surfactants: Have a negative electrical charge. They are highly effective but can react with other chemicals in the tank, potentially causing compatibility issues.
• Cationic Surfactants: Have a positive electrical charge. They are rarely used alone in agriculture because they can be highly phytotoxic to plants.
• Non-Ionic Surfactants (NIS): Have no electrical charge. Because they do not react with the ions in hard water or other tank mix chemicals, NIS are the most widely used and versatile surfactants. They are excellent at improving coverage on plant surfaces and are recommended on many herbicide labels.

Oils: Crop Oil Concentrates (COC) and Methylated Seed Oils (MSO)

Oils are another type of activator adjuvant used primarily with herbicides to increase the penetration of the active ingredient through the thick, waxy cuticle of plant leaves.

• Crop Oil Concentrates (COC): Formulated from petroleum-based oils mixed with a surfactant (usually 10-20% surfactant). COCs help the pesticide penetrate the plant cuticle better than standard surfactants, making them ideal for post-emergence weed control, especially during hot, dry weather when plants thicken their cuticles.
• Methylated Seed Oils (MSO): Made from plant-based oils (like soybean or canola oil) that have been chemically altered (methylated) to improve performance. MSOs provide even more aggressive penetration than COCs and are often required for certain herbicides targeting particularly tough, woody, or heavily waxed weeds.

Caution: Because COCs and MSOs increase penetration so aggressively, they also significantly increase the risk of phytotoxicity (crop injury) to desirable plants, particularly under high heat and humidity.

Utility Adjuvants

Utility adjuvants do not directly increase the toxicity or penetration of the pesticide. Instead, they solve operational problems in the spray tank or during application, such as bad water chemistry, foaming, or excessive drift.

Buffers and Acidifiers

The pH of the water used in a spray tank can severely impact the effectiveness of a pesticide. Many insecticides and some fungicides are susceptible to alkaline hydrolysis—a chemical reaction where high pH (alkaline) water rapidly breaks down the active ingredient, rendering it useless before it even reaches the target.

• Acidifiers are added to lower the pH of the water in the tank.
• Buffers not only lower the pH but also stabilize it, preventing the pH from changing even if other alkaline substances are introduced. If you know your water source is highly alkaline, adding a buffer before adding the pesticide is critical.

Compatibility Agents

When mixing multiple pesticides and liquid fertilizers in the same tank, the chemicals may physically or chemically clash, creating a thick sludge, clumps, or separating into layers. Compatibility agents act as emulsifiers to help suspend and maintain the stability of complex tank mixes, preventing the ingredients from separating. However, they cannot fix chemical incompatibilities where the active ingredients neutralize each other.

Anti-Foaming Agents (Defoamers)

Some pesticide formulations, particularly those with high surfactant loads, can create excessive foam when subjected to vigorous agitation in the spray tank. Foam can overflow the tank, causing spills and exposing the applicator, or it can cause the pump to lose its prime. Anti-foaming agents (defoamers) are added to the tank to eliminate existing foam or prevent it from forming, ensuring smooth pump operation and accurate volume measurements.

Drift Retardants (Thickeners)

Off-target drift is one of the most significant liabilities for a pesticide applicator. Wind can carry fine spray droplets away from the target, potentially damaging neighboring crops, contaminating water, or exposing bystanders. Drift retardants (thickeners) increase the viscosity (thickness) of the spray mixture. This results in a spray pattern with a higher percentage of large, heavy droplets and fewer fine, drift-prone droplets. While they do not eliminate drift entirely, they are an essential tool for applications in sensitive areas.

Stickers and Extenders

Once a pesticide is applied, environmental factors like rain, irrigation, and UV sunlight immediately begin to degrade or wash it away.

• Stickers increase the adhesion of the spray droplets to the target surface. They form a water-resistant coating that prevents the pesticide from washing off during rain or irrigation.
• Extenders are specialized stickers that protect the active ingredient from ultraviolet (UV) light degradation, extending the residual life of the pesticide on the target.

Making the Right Choice

The decision to use an adjuvant must be guided by the pesticide product label. The label will explicitly state whether an adjuvant is required, recommended, or strictly prohibited. Using an adjuvant when the label prohibits it can lead to severe crop injury, illegal residues, or equipment failure. Conversely, failing to use a required adjuvant (like an MSO for a specific herbicide) will likely result in complete application failure and wasted money.