Herbicide Adjuvants Explained: A Gardener's Guide to Spray Additives

If you've read a pesticide label, you've likely encountered the term "adjuvant." Broadly defined, an adjuvant is any additive that enhances pesticide effectiveness—improving chemical activity, application, leaf adhesion, or product solubility. Understanding herbicide spray adjuvants and their properties can be confusing, but this guide clarifies these important additives.

Herbicide Adjuvant Guide

Adjuvants are common in herbicides and pesticides, functioning as wetting agents, solvents, stickers, stabilizers, spreaders, and penetrants. They're the catalysts that make chemical formulas work better, faster, and more efficiently. This guide sorts out the various types and their functions.

Surfactants—familiar to many gardeners—are a key category of herbicide spray adjuvants. Technically, surfactants reduce surface tension between spray droplets and leaf surfaces, acting as wetting agents that help chemicals adhere and absorb rather than roll off. Four main surfactant types serve as adjuvants:

• Anionic surfactants – enhance foaming
• Non-ionic surfactants – most common in horticulture; primarily break surface tension
• Amphoteric surfactants – rarely used in gardening, occasionally in specialized formulas
• Cationic surfactants – not used in horticulture; found in industrial cleaners

Three main adjuvant classes are used in horticulture:

• Surfactants, wetting agents, penetrants, and oils – often purchased separately and added to herbicide formulas to boost effectiveness.
• Spray modifier agents – including stickers, spreaders, filming agents, deposit builders, foaming agents, and thickeners; usually pre-mixed in manufactured products.
• Utility modifiers – emulsifiers, stabilizers, dispersing aids, coupling agents, anti-foam agents, and buffers; also typically included in the original formulation.

Choosing and Using Adjuvants with Herbicides

Selection starts with reading the herbicide or pesticide label carefully. The wrong adjuvant can cause severe damage under incorrect conditions, on wrong species, or at improper rates. For large-scale crops, non-ionic surfactants are recommended over oils to prevent widespread injury.

Labels specify recommended surfactant active ingredient percentages (often 75%). Formulas requiring adjuvants will indicate which type and how much. Remember: adjuvants should support—not replace—the action of the purchased product.

If label information is unclear, contact the manufacturer directly to confirm the correct adjuvant type and concentration for that specific product.