5.3 Adjuvants, Compatibility, and Dilution

Mixing is a labeled activity

40 CFR 171.103(c)(5)(iii) requires knowledge of compatibility, synergism, persistence, and animal and plant toxicity of formulations. (c)(5)(vi) requires dilution procedures. Oklahoma Core will not make this the chapter where you grind through a full gallons-per-acre tank load—that is Chapter 11. It will ask whether you may combine two products, in what order, with what water, and what you do when labels disagree.

The governing rule is simple: do not tank-mix unless every product’s label allows the combination, and the site and the pest are on each label. A cotton insecticide that allows mixing with a listed fungicide does not authorize adding a pasture herbicide. A 7A bait that says not to apply a repellent spray on the same placement is a mixing and sequencing rule even when nothing is poured into a tank. If labels conflict, stop. Compatibility agents, “we have always mixed these,” and a pretty jar test do not override labeling.

Adjuvants — only when the pesticide label allows or requires them

An adjuvant is added to the spray tank to improve mixing, application, deposition, or uptake. Adjuvants are not pesticides by themselves in the usual Core picture, but they change phytotoxicity, drift, foaming, and efficacy. The pesticide label wins. If the herbicide says do not add surfactant on a stressed crop, you do not add your favorite nonionic surfactant because a salesman likes the sheen on the leaf. If the label requires a specified adjuvant class (for example a crop oil concentrate on a tough pasture weed at a stated rate), leaving it out is also a label problem and an efficacy failure.

Oklahoma well water is often hard and sometimes alkaline. That is why buffers and ammonium sulfate appear on so many glyphosate and 2,4-D amine conversations. They are still optional only when the pesticide label allows them. Do not acidify a product that is unstable at low pH. Do not dump water-softener salt from a house unit into a cotton tank and call it a labeled conditioner.

Tank-mix sequence: WALES, then the labels

A widely taught National Core order is WALES. Some manuals expand it to WAMLEGS so microencapsulated products get their own slot between dry formulations and other liquids. Teach this standard order, then obey any order printed on the products in the tank.

1. Fill the tank about one-quarter to one-half with carrier water (the water you will actually spray).
2. Start agitation and keep it on.
3. W — Wettable powders, dry flowables, water-dispersible granules, and other dry dispersible formulations. Give them time to fully wet and disperse.
4. A — Continue agitation. Do not shut the pump off and assume the powder is “in.”
5. L — Other liquids: true solutions, flowables, and suspension concentrates.
6. E — Emulsifiable concentrates and other emulsifiable liquids.
7. S — Surfactants and other adjuvants last, unless a label says otherwise.
8. Top off with water and keep agitating through the job.

Why the order exists: dry formulations need water and time to wet. Emulsifiable concentrates can oil out or seize a wettable powder into curds if you dump the EC first. Adjuvants can gel some mixtures if they hit concentrates before those concentrates are diluted. Microencapsulated insecticides are easy to strip or clump if they meet a harsh adjuvant or an EC too early—that is why WAMLEGS parks them in their own step.

If two labels specify incompatible orders, or if either label prohibits the mix, do not mix. For 7A, “mixing” may mean sequencing a flush aerosol, a residual liquid, and a gel bait on the same kitchen. That is still a label problem if one product tells you not to contaminate bait placements.

Jar test

When the labels allow a mix but you have not used that combination in this water, run a jar test before filling a 300-gallon pasture rig or a cotton sprayer.

Typical teaching procedure (follow any procedure printed on the product labels):

• Use a clean glass quart jar (or the size the label specifies).
• Use the same water source you will spray. A rural well near Stillwater is not municipal water in Tulsa, and a muddy pond is not either of those.
• Add proportionate amounts of each product in the same order you will use in the tank, with mixing between additions.
• Let it sit 10 to 15 minutes (some labels say longer) and watch. Remix and see whether it returns to a usable suspension or emulsion.

Fail signs: heat, gas bubbles, precipitate, sludge, cottage-cheese curds, an oil layer, gel, or products that will not resuspend. A pass is not a chemical-safety certificate. It only shows physical mixing in that water at that temperature. A mixture can look pretty and still be chemically antagonistic or more phytotoxic than either product alone.

Physical versus chemical incompatibility — and synergism

Physical incompatibility is visible in the jar or the tank: plugged filters, stopped nozzles, layers, sludge, gel, or an oil slick. Common causes include mixing a WP with an EC in the wrong order, combining some liquid fertilizers with pesticides, using very cold water so WDG will not disperse, or hitting extreme pH. The equipment failure is the giveaway. You may also get phytotoxicity from the solvent-rich mess you just created, which is the plant-toxicity piece of 40 CFR 171.103(c)(5)(iii).

Chemical incompatibility is not always visible. One product reduces the efficacy of another (antagonism). Teaching examples include some tank mixes that reduce glyphosate uptake, or insecticide combinations the label warns against. The opposite, synergism, is a greater-than-additive effect. Piperonyl butoxide with some pyrethroids is an intentional synergist on certain labels. Unlabeled synergism that increases cotton or turf burn is still a problem. The federal Core standard names synergism so you know it exists—not so you invent synergistic mixes that no label describes.

Never use a jar-test pass to mix products when either label forbids tank mixing or the site is missing from one label. A compatibility agent might make a forbidden mix look pourable. Looking pourable is not legal authority.

Reading a rate table (conceptual dilution)

Dilution starts with reading, not with a formula. Chapter 11 will make you calculate tank loads, GPA, and percent solutions with numbers. Core still expects you to know what the table is saying.

Look for all of the following before you add water:

• Site row: cotton postemergence is not pasture; a putting-green rate is not a rough rate; indoor crack-and-crevice is not outdoor perimeter; “non-crop” is not a wheat field.
• Pest, weed height, or disease-pressure columns: a 6-inch cocklebur rate is not a 24-inch rate; a preventative turf rate is not a knockdown rate.
• Units: fl oz/A, pt/A, lb product/A, lb AI/A, fl oz/100 gal, fl oz/1,000 sq ft, oz/gal in a compressed-air sprayer, or percent solution.
• Spray volume: many cotton and peanut labels require a minimum gallons per acre. Turf labels often use gallons per 1,000 square feet. Structural labels may use ounces of product per gallon of water for a 1-gallon pump-up.
• Percent AI in the concentrate versus percent solution in the sprayer. A jug that is 41% AI is not a 41% spray. Indoor and ornamental labels that call for a 0.5% finished spray want a diluted mixture; the arithmetic lives in Chapter 11. Here you only need to know those are different numbers in different parts of the label.
• Maximums: do not exceed a yearly maximum, a maximum per crop cycle, or a maximum per application. A second “clean-up” pass can be illegal even when the pump math is tidy.

If the table lists pounds of product and you treat it as pounds of AI, you will underdose an 80WP and overdose a 4 lb/gal EC. That error is a formulation-reading error from Section 5.2 showing up as a dilution error here.

Water quality, pH, and hardness

Carrier water is an ingredient. Oklahoma groundwater can be hard (calcium and magnesium) and alkaline (high pH). Surface fills can be muddy.

• Alkaline hydrolysis: some organophosphate and carbamate insecticides, and certain other chemistries, break down in high-pH water. The spray loses potency while it sits in the tank on a hot cotton afternoon. Buffers help only when the pesticide label allows them. Do not acidify a product that is unstable at low pH.
• Hardness: cations can bind glyphosate and some 2,4-D amine and other weak-acid herbicides, reducing weed control. Labels may allow ammonium sulfate or a named water conditioner. Hardness is also why a pasture renovation burndown can look weak on the same rate that worked with city water.
• Dirty water: clay, silt, and organic matter tie up paraquat, glyphosate, and some other products. A muddy pond fill is a silent rate cut, not free water.
• Temperature: very cold water slows WDG/DF dispersion and can contribute to a jar-test failure that is really a temperature failure.

If control has slipped and the product, pest identification, and weather look right, test the water or change the fill source before you blame the brand. Changing formulation (EC versus amine salt of an auxin, for example) also changes how water quality bites you—another reason types, formulations, and mixing are one Core area under 171.103(c)(5).

Oklahoma use patterns in one mixing frame

• Cotton insecticide: Often an SC or EC in a boom tank. Watch EC burn, water pH for hydrolysis-sensitive insecticides, and WALES order if a fungicide or PGR is in the same load. Do not add a harvest-aid defoliant because the neighbor picked yesterday.
• Pasture herbicide: Amine liquids, some ECs, and pellets. Hard water and AMS rules show up on glyphosate renovation sprays. Auxin products still carry the cotton-injury chemistry from Section 5.1. Grazing and hay intervals are residue rules, not optional mixing trivia. Pellets skip WALES but not the rate.
• Turf: WDG and SC in small tanks foam—use antifoam if the labels allow it. Granules skip the tank but not spreader calibration. Spray dyes stain sidewalks in Edmond as surely as they mark a fairway.
• 7A baits and dusts: Usually not tank-mixed. Sequence and sanitation matter. A void dust is a formulation choice. Do not cut a gel bait with leftover residual spray water.
• 7C fumigants: Not a WALES problem. Rate is often a space or commodity calculation, sealing matters, and extra certification is Chapter 10.

If you remember one mixing paragraph for the exam, remember this: every label must allow the combination and list the site and pest; if labels conflict, do not mix; jar-test unknown physical mixes in the real water; add dry dispersibles first and adjuvants last unless a label prints another order; and do not treat water quality as optional. Worked GPA and tank-load numbers wait for Chapter 11.