Adjuvant
- Also known as
- spray adjuvant, agricultural adjuvant, activator adjuvant, spreader
An adjuvant is an ingredient added to a spray mixture, or built into a formulation, to improve how a crop protection or nutrient product performs or how the mixture handles. Surfactants, crop oils, drift reducers and water conditioners are common types.
What is an adjuvant?
An adjuvant is anything added to a pesticide or nutrient spray to improve its effectiveness or make it easier to apply. Adjuvants do not control pests themselves. They change how the spray mixes in the tank, how droplets form and land, how well they wet and stick to the target, and how much of the active ingredient gets into the plant.
Adjuvants can be added by the applicator to the spray tank, called tank-mix adjuvants, or included by the manufacturer in the product, called built-in or formulation adjuvants.
Main types of spray adjuvants
Adjuvants are usually divided into two broad groups.
Activator adjuvants improve the biological performance of the active ingredient:
- Surfactants, especially nonionic surfactants, which lower surface tension so droplets spread over the leaf instead of beading.
- Crop oil concentrates and methylated seed oils, which help some herbicides penetrate the waxy leaf cuticle.
- Organosilicone surfactants, which produce very rapid, extensive spreading.
- Nitrogen fertilizers such as ammonium sulfate, used with certain herbicides to improve uptake and overcome hard water.
Utility or special-purpose adjuvants improve handling and application:
- Water conditioners, which counter the calcium, magnesium and other ions in hard water that reduce some herbicides’ activity.
- Compatibility agents, which help products mix without separating; see tank-mix compatibility.
- Drift reduction agents, which increase droplet size to limit spray drift.
- Deposition aids and stickers, which improve retention and rainfastness.
- Buffers and acidifiers, which adjust spray pH.
- Defoamers, which control foaming in the tank.
How surfactant adjuvants work
Most leaf surfaces are waxy and water-repellent, so water droplets bead up and roll off. A surfactant adjuvant lowers the droplet’s surface tension and the tension between droplet and leaf, reducing the contact angle so the droplet spreads, covers more area and stays on the leaf. Speed matters, because a droplet lands in a fraction of a second: surfactants that reach new surfaces quickly perform better in sprays than their equilibrium surface tension alone would suggest.
Choosing an adjuvant
The pesticide label is the first guide: it often specifies which adjuvant types to use, at what rates, or which to avoid. Beyond that, the choice depends on the target, the weather, the water quality and the other products in the tank. More is not always better; excessive adjuvant can damage the crop or increase drift.
In most U.S. states, adjuvants are not registered as pesticides with the Environmental Protection Agency, although some states, including California and Washington, require them to be registered. Industry certification programs, such as that of the Council of Producers and Distributors of Agrotechnology, check that products meet stated specifications.
Adjuvants at Locus
Locus supplies its Amphi glycolipid biosurfactants to adjuvant formulators as co-surfactants, describing them as improving spray wetting, spreading and on-target delivery across complex tank mixes.
Frequently asked questions
Adjuvant describes the job: improving a spray’s performance or handling. A surfactant is one type of chemical that often does that job, by improving wetting and spreading. Many adjuvants are surfactants, but oils, fertilizers and polymers are also used as adjuvants.
No. Many products already contain the adjuvants they need. Others require one on the label, and some should not be used with certain adjuvants. The label is the guide.
It is a surfactant with no electrical charge on its head group, used to improve spray wetting and spreading. Nonionic surfactants are the most common general-purpose activator adjuvants because they are compatible with a wide range of products.
Sources
- Adjuvants for enhancing herbicide performance; spray adjuvant guides, Penn State Extension and Purdue University Extension
- Compendium of Herbicide Adjuvants, Purdue University and partners
- Council of Producers and Distributors of Agrotechnology (CPDA) adjuvant certification, CPDA