Notes on Adjuvants: Introduction

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Excerpt from Chapter 5, Publication 75, Guide to Weed Control, Order this publication

Table of Contents

1. Introduction
2. Activators and spray modifiers
3. Utility modifiers
4. Notes on Adjuvants
5. Tables on Adjuvants
   • Adjuvants Used in Ontario (Table 5-1) (PDF 25 kb)
   • Adjuvant Rates per Sprayer Tank Water Volume (Table 5-2) (PDF 11 kb)
6. Other topics on Notes on Herbicides (Chapter 4)
   • Introduction
   • Notes on Herbicides: Active Ingredients
   • Notes on Herbicides: Trade Names
7. Tables on Herbicides (from Chapter 4)
   • Herbicides Used in Ontario (Table 4-1) (PDF - 207 kb)
   • Glyphosate Products and Their Registered Uses (Table 4-2) (PDF - 54 kb)
   • Herbicide Crop Rotation & Soil pH Restrictions (Field Crops) (Table 4-3) (PDF - 80 kb)
   • Herbicide Crop Rotation & Soil pH Restrictions (Horticultural Crops) (Table 4-4) (PDF - 82 kb)
   • Herbicide Groupings for Ontario (Table 4-5) (PDF - 23 kb)
   • Interval Before Rainfall (Postemergence) (Table 4-6) (PDF - 49 kb)
8. Related Links

Introduction

An adjuvant is any substance added to a spray solution to modify and enhance the effectiveness of the herbicide.

Adjuvants are an important part of the spray solution and, if not used will negatively affect the degree of weed control obtained. Some products have adjuvants formulated into the product while other products require that the user add the adjuvant. The selection of adjuvants is key to getting the right balance between maximizing weed control and minimizing crop injury. In some cases the rate of adjuvant varies depending on conditions of weather, crop stage, weed species, water quality, etc. Some herbicide labels recommend particular adjuvant products and some recommend particular types of adjuvants. Always use adjuvants as directed on the product label.

Most adjuvant recommendations in this guide are listed as the amount (in litres) added to 1,000 L (L/1,000 L) of spray solution. If you wish to convert to % volume/volume (v/v) use the following conversion:

10 L/1,000 L = 1 % v/v

There are 2 broad categories of adjuvants:

• Activators and spray modifiers
• Utility modifiers

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Activators and spray modifiers

• Surfactants (also known as "surface active agents") are the largest class of adjuvants. Surfactants can be non-ionic, anionic, cationic or amphuteric. Most surfactants are non-ionic (NIS); they do not ionize. A NIS is used to enhance herbicide penetration into a waxy cuticle. Wetting agents and detergents are primarily anionic and when ionized in solution, the water soluble portion is negatively charged. Cationic surfactants exhibit a net positive charge in solution. Amphuteric surfactants can be either anionic or cationic. Cationic and amphuteric are not widely used in agricultural chemicals.
• Oils solubilize the waxy cuticle layer on a weed to increase spray penetration through the leaf cuticle. Oils can be refined mineral oils (petroleum based) or seed oils. Seed oils can be categorized as triglycerides, methylated seed oils (MSO) or crop oil concentrates (COC). Crop oil concentrates are a combination of seed oil and surfactants.
• Spreaders are wetting agents that reduce the surface tension to create better contact between the spray solution and the treated surface (leaf, etc). A sticker increases the herbicide adhesion to the leaf surface.

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Utility modifiers

• Compatibility agents improve mixing, especially when using a liquid fertilizer carrier.
• Drift control agents increase the droplet size to reduce drift.
• Anti-foaming agents are used to reduce foaming in the spray tank.
• Foaming agents are used with specialized equipment to produce and apply a foam.
• Buffering agents can be used enhance solubility or adjust pH.
• Dyes in some instances are used to enhance visibility of spray foam solutions.

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Notes on Adjuvants

Read the Notes on Adjuvants together with the recommendations given later in this publication. Additional information on use, toxicity and safety precautions is given here. With a few exceptions the adjuvants are listed under their trade or product name. See Table 5-1, Adjuvants Used in Ontario for a summary of adjuvants listed in this publication.

Complete information on each adjuvant is available on the product label which is located on the product container. The federal Pest Management Regulatory Agency also lists pesticide labels on their website.

Many pesticide manufacturers also list product labels and/or Material Safety Data Sheets (MSDS) on their websites which are listed on the last page of this publication.

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Related Links

• Weeds in Ontario
• Pesticide Application and Safety
• Pesticide Companies and Agents
• OMAFRA Sprayer Calibration Calculator
• PMRA website
• OMAFRA Publication 505: Ontario Weeds
• OMAFRA Publication 75: Guide To Weed Control

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