4.3 Adjuvants, Water Quality, Jar Tests & Label-Directed Mixing
Key Takeaways
- Use an adjuvant only when the pesticide label requires or permits it and verify that the chosen adjuvant is legal for distribution in Maine.
- Surfactants, oils, conditioners, buffers, antifoams, humectants, stickers, and drift agents perform different functions and can also increase injury or exposure.
- Water pH and hardness effects are active-ingredient-specific; there is no universal requirement to acidify every tank to pH 5.5–6.5.
- A proportional jar test screens physical compatibility but cannot prove label legality, efficacy, or crop safety.
- The labels control mixing order; WALES is only a mnemonic for a common sequence and may not fit the products in a particular tank.
Adjuvants, Water Quality, Jar Tests, and Mixing Order
An adjuvant is added to improve handling or performance, but it can also increase crop injury, drift, foaming, exposure, or incompatibility. Use an adjuvant only when the pesticide label requires or permits it and the chosen product is currently legal for distribution in Maine.
Major functions
Surfactants reduce surface tension and improve spreading or wetting. Nonionic surfactants are common, but the label can specify a type and concentration.
Crop oil concentrates and methylated seed oils can improve penetration of waxy plant surfaces. Their oil and surfactant composition varies; do not memorize one universal 80-to-85-percent formula. Heat, drought stress, crop stage, product, and rate can affect phytotoxicity.
Ammonium sulfate and other water conditioners can bind ions or improve performance for certain herbicides. Buffers or acidifiers change or stabilize pH. Antifoam agents reduce foam. Humectants slow drying. Stickers improve retention. Drift-reduction agents can change viscosity or droplet spectrum.
No adjuvant guarantees performance or legalizes a prohibited application. A drift agent does not permit excess wind, and an acidifier should not be added merely because water pH exceeds 7.
Water quality
Hardness, pH, alkalinity, turbidity, temperature, and suspended material can affect products differently. Calcium, magnesium, iron, or other ions can antagonize some active ingredients. Some pesticides hydrolyze faster at high or low pH, but the rate is chemical-specific.
Test source water when the label, local experience, or failure history justifies it. Use the label or reliable technical information for the desired range and conditioner. Automatically forcing every tank to pH 5.5 to 6.5 can damage a product or crop and is not a general rule.
Compatibility versus legality
Physical compatibility means products stay mixable and can pass through equipment. Chemical compatibility means ingredients remain stable. Biological compatibility means the mixture remains effective and does not injure the crop. Legal compatibility means every label permits the mixture, site, rate, timing, and adjuvant.
A jar test can screen physical compatibility; it cannot prove crop safety, efficacy, or legality.
Jar test
Use the same water, relative product proportions, and intended adjuvants as the full tank. Wear label PPE. Add ingredients in the proposed order, agitate as the tank will, and observe immediately and after a useful standing period.
Warning signs include heat, gas, pressure, persistent foam, flakes, crystals, curds, gel, sludge, or layers that do not redisperse. A dangerous reaction is not tested in open glass or by leaning over it; stop and consult the manufacturers.
If the test remains uniform, the mixture may be physically compatible, but a small labeled test area may still be needed for crop safety.
Mixing order
The pesticide labels control. A mnemonic such as WALES is only a memory aid for a common sequence: water-soluble packets or dry products, agitation, liquid suspensions, emulsifiable concentrates, and solutions or surfactants. Labels and compatibility agents can require a different order.
A safe framework is:
- inspect and calibrate the sprayer;
- fill partway with compatible carrier and start agitation;
- add water conditioners required before pesticide;
- add each product in label order, allowing full dispersion or dissolution;
- add oils, surfactants, drift agents, or antifoam at the stated point;
- finish filling while maintaining agitation; and
- apply promptly within label directions.
Do not place an unopened water-soluble packet through a strainer that prevents it reaching the tank. Do not add concentrate directly to another concentrate unless the labels provide that procedure.
Problems and correction
Settling points to inadequate agitation, excessive delay, or an incompatible suspension. Crystals can reflect cold water, poor solubility, or concentrated contact. Gel can result from packet film, incompatible polymers, salts, or wrong order. Foam can come from surfactants or excessive return agitation.
Stop before forcing an incompatible mix through the pump. Consult product technical support and manage the material according to the labels and waste requirements. Never add an unapproved chemical to “break” a gel.
Record the decision
Record source-water concerns, products and EPA numbers, adjuvant brand and rate, order, jar-test result, batch quantity, and any problem. If the label requires an adjuvant, omitting it can be misuse. If it prohibits one, adding it can be misuse.
The exam-ready answer puts the exact label first, then uses water testing and a proportional jar test to prevent physical failure.
When may an adjuvant be added to a pesticide tank?
What does a jar test establish?
How should an applicator manage carrier-water pH?
What determines tank-mixing order?