7.3 Adjuvants, Tank-Mix Compatibility, and Dilution

Why mix order and adjuvants sit in the pesticides domain

Rule 40-21-3-.01 groups compatibility and dilution with formulation types. National Core Chapter 4 and the mixing-and-loading chapter overlap here: the General Standards exam does not care which UGA manual chapter you used, only whether you can keep a tank from gelling and a rate from being wrong. Later chapters in this guide cover mix/load site design, closed systems, and spill response. This section is the formulation physics of what goes in the tank, in what order, and at what labeled strength.

An adjuvant is a substance added to the spray mixture (or already built into a formulation) to improve mixing, spreading, sticking, deposition, pH, or foam control. Adjuvants are not a second pesticide, but they can change phytotoxicity, drift, and tank stability. The rule that overrides every trade-name pitcher on a dealer shelf: add an adjuvant only when the pesticide label allows or requires it. Some cotton and peanut herbicide labels require a specific surfactant class—for example a nonionic surfactant or a crop oil concentrate—at a stated rate. Other labels forbid crop oil on a sensitive crop or forbid mixing with certain fertilizers. The spreader always helps is not an exam answer.

Adjuvant classes you must be able to name

Surfactants (surface-active agents) reduce the surface tension of spray droplets so the mix wets waxy peanut, pecan, cotton, or turf leaves instead of beading up. Subclasses you will see on Georgia labels include nonionic surfactants (NIS), crop oil concentrates (COC), and methylated seed oils (MSO). Using a COC when the label called for NIS can burn cotton. Using no surfactant when the label requires one can produce a clean-looking pass and no weed control.

Stickers (and spreader-stickers) help deposit adhere through light rain and irrigation. They matter on pecan and peach foliar programs and on turf. Too much sticker can reduce uptake of some systemic herbicides or leave visible residue on cars parked beside a Category 24 account.

Buffers and acidifiers adjust carrier pH. Many insecticides and some herbicides degrade in alkaline well water common in parts of Georgia. A buffer is not automatic: some products are unstable in acid water, and a buffer added on top of an already acidic mix is wasted chemistry. Measure pH when the label or the product’s technical bulletin makes pH a condition of use.

Drift-control / deposition aids thicken or otherwise change droplet spectrum to cut fines. They do not legalize spraying in an inversion or in wind above the label. They also do not turn a Category 41 ULV mosquito machine into a boom sprayer.

Defoamers knock down foam so a tank does not overflow at the nurse-upstand and so dry products are not stranded on a foam layer where they never wet. Over-agitation of some ECs and surfactants is a foam factory; a defoamer is process control, not a perfume.

Other adjuvants you may see: compatibility agents for liquid-fertilizer carriers, colorants, and attractants. Same rule: label first.

Compatibility: physical versus chemical

Physical incompatibility is what you can see: flakes, crystals, gel, cottage-cheese curd, sludge, oil slick, or layered chocolate milk that will not recombine. It plugs screens, destroys a centrifugal pump, and lays down a streaky rate. Causes include putting two concentrates together before water, mixing a wettable powder into a foam head, using very cold water with a WDG, or combining an EC with a liquid fertilizer the label warns against.

Chemical incompatibility may look like a perfect tank while the active ingredients deactivate each other, become more phytotoxic, or produce a gas. You will not always see it in a jar. Labels and manufacturer compatibility statements are the control. Never mix products the label prohibits.

Undiluted concentrates should not be poured into each other. RTU products are already dilute; do not treat them as tank-mix concentrates unless the label says they may be mixed.

The jar test

Before you commit 300 gallons in a cotton or peanut sprayer, National Core teaching is to prove physical compatibility on a pint-jar scale.

1. Use the same water you will spray—pond, well, or municipal—because hardness and pH change compatibility.
2. Measure proportional amounts of each product (a pint-jar scale of the tank recipe).
3. Add them in the same order you will use in the tank, with agitation (invert the jar) between additions.
4. After all products are in, invert again and let the jar stand about 10 to 15 minutes. Watch for heat, unexpected color change, precipitate, gel, or layers.
5. If the mix stays uniform, or remixes easily after standing, it is probably physically compatible. If it does not, do not scale it up. Adjust order, add a labeled compatibility agent, drop a partner, or spray products separately.

A compatible jar does not prove crop safety. Phytotoxicity still needs a labeled use and, when you are trying a new partner mix the label allows but you have never used on peanuts or cotton, a small test strip in the field.

Mixing order without inventing a Georgia mnemonic

GDA Rule 40-21-3 does not adopt an official state mixing-order acronym. You will not find WALES in the Georgia Rules of the Department of Agriculture, and this guide will not invent a fake official Georgia mnemonic. What you will find in National Core teaching and in nationwide extension training is a sequence concept: after the tank is partly filled with carrier and agitation is running, add the products that are hardest to disperse first, then the ones that form emulsions, then true solutions and adjuvants—unless a label states a different order.

Industry study aids you may meet in manuals include WALES (wettable powders, agitate, liquid flowables, emulsifiable concentrates, surfactants) and newer expansions such as WAMLEGS that insert microencapsulated products, glyphosate or other solutions, and water-conditioning agents. Treat those letters as a memory hook for the physics, not as a Georgia statute. Labels that say add this product last or do not mix with beat any acronym.

A practical Georgia order that matches that physics:

1. Fill the tank about one-half to two-thirds with clean water (more if the carrier is liquid fertilizer).
2. Start agitation and keep it on.
3. Add water-soluble packets and let them dissolve completely.
4. Add dry suspensions: WP, then WDG/DF (often premixed as a slurry in a bucket of water).
5. Add liquid flowables / suspension concentrates / microencapsulated liquids.
6. Add emulsifiable concentrates.
7. Add true solutions (including some soluble liquids and, when labeled, liquid nitrogen).
8. Add adjuvants—surfactants, oils, stickers, drift-control agents—generally last, with defoamers as needed to control foam rather than as a substitute for lowering agitator speed.

Water conditioners such as ammonium sulfate, when the label wants them on a herbicide, often go in early so the water is conditioned before the herbicide hits it. That is a label detail, not a reason to invent a Georgia AMS rule.

Dilution procedures

Dilution is how a concentrate becomes a labeled rate per acre, per 1,000 square feet, or per gallon of finished spray. Chapter 13 of this guide works the arithmetic. This chapter is the procedure.

• Read the Directions for Use for site, pest, rate, carrier volume, and any adjuvant requirement. The label is the law; Rule 40-21-3 does not create a second rate table.
• Wear the mix/load PPE on the label. Mix/load exposure is often higher than application exposure, especially with WP dust and EC solvent.
• Measure with dedicated devices. Dry products are measured by weight when the label gives pounds; volume cups are a last resort and a source of error with fluffy WPs.
• Never fill by glugging from a 2.5-gallon jug over a tank opening on a windy peanut field.
• Partial-fill, agitate, add, then top off so the last product meets moving water, not a whirlpool of concentrates.
• Mix only what you can apply legally that day. Leftover mix is a disposal problem and a recordkeeping problem under Rule 40-21-5 when you are a contractor or when the product is restricted-use.
• Triple-rinse or pressure-rinse emptied concentrate containers into the tank during filling when the label and recycling program allow that rinsate to be part of the application.

If you supervise an uncertified mixer, Rule 40-21-6 still makes you responsible, and the label still governs whether a certified person must be physically present. Formulation competence includes not handing a WP bag to an untrained helper to dump upwind of the fill station.

Georgia scenario: the jar that looked like yogurt

A Category 21 applicator near Albany wants a cotton tank of a WDG residual, an EC herbicide, and a crop-oil adjuvant the EC label allows. The helper dumps both concentrates into a five-gallon bucket to premix, then pours the paste into a quarter-filled tank. The mix ropes into gel. A jar test done that morning with the well water, WDG first, EC second, oil last, had stayed pourable. The failure was order and lack of carrier, not bad product. They rebuild following the label and the hard-to-mix-first sequence, with agitation on from the start. They also skip adding a mystery sticker from the shop shelf because neither label mentions it.

The same discipline applies on a Category 24 turf route in Gwinnett County and on a Category 27 right-of-way mix along I-75. Adjuvants, jar tests, and dilution are General Standards, not a Category 21-only skill.