7.3 Adjuvants and Tank Mixes

7.3 Adjuvants and Tank Mixes

Quick Answer: Use adjuvants only when the pesticide label allows or recommends them. Never tank-mix products without label (or other lawful) compatibility guidance. When mixing is allowed, follow label mix order, keep agitation running for suspensions, and use a jar test when compatibility is uncertain. Labels override any classroom sequence.

Sections 7.1 and 7.2 covered what is in the container and how it is applied. This section covers what happens when you combine materials in one tank—or add a helper product meant to change spray behaviour. Tank-mix mistakes cause crop injury, clogged equipment, illegal use, and wasted product. Core exams test the rules and habits, not brand recipes.

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What adjuvants are

An adjuvant is a substance added to a spray mixture to improve mixing, application, or effectiveness—or to reduce a problem such as foam or drift—without being the primary pesticide active for the pest. Common teaching categories:

Adjuvants are not automatically safe or legal to add. Some pesticide labels require a specific type of surfactant; others prohibit oil adjuvants, extra wetters, or any additive. Adding the wrong adjuvant can increase runoff, burn foliage, raise bee hazard, or void the legal use pattern.

Hard rule for Ontario Core

Use adjuvants only when the pesticide label allows or recommends them (and follow any named product type or concentration limits). “The salesperson said it always helps” is not a label. “We always add dish soap” is not a labelled adjuvant program and can injure plants or change spray behaviour unpredictably.

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Surfactants, stickers, drift retardants, and antifoams in practice

Surfactants

Wetting agents help spray films cover hard-to-wet targets. Too much surfactant can increase runoff from the leaf or increase uptake to the point of crop injury. Dose adjuvants by their own labels and by the pesticide label’s limits.

Stickers

Stickers aim to improve rainfastness or adhesion. They do not replace waiting for the labelled rain-free period when the pesticide label states one. They also do not authorize application immediately before a storm contrary to label weather statements.

Drift retardants

These products may reduce the fraction of very fine droplets for some systems. They are not a licence to spray in high wind or to ignore buffers and sensitive sites. Weather, nozzle choice, pressure, and boom height remain primary drift controls. Never use a drift aid to justify an otherwise reckless application.

Antifoams

Foam hides true liquid level in the tank, causes overflow, and wastes time. Antifoams solve a physical problem during mixing. Add only products intended for pesticide sprays when the program allows them; household experiments are poor practice.

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Tank mixes: legal and physical compatibility

A tank mix combines two or more pesticide products (and sometimes fertilizers or adjuvants) in one spray tank for a single application.

Legal compatibility

Both (or all) products must:

1. Be registered and legal for the site, pest, and timing
2. Allow the mix (label language such as tank-mix partners, or clear permission to mix with other products under stated conditions)
3. Remain within rate, PPE, REI, and other constraints—use the most restrictive relevant precautions when labels differ
4. Comply with Ontario class, licence, permit, and cosmetic-ban rules for the intended land use

Never mix products without label compatibility guidance (or other lawful written support recognized in your training/program). If labels are silent or conflicting, do not invent the mix. Apply products separately if both uses are legal, or choose a single labelled product that covers the need.

Physical and chemical compatibility

Even when legally allowed, products can:

• Form sludge, gels, or crystals that clog screens
• Separate into layers
• Lose efficacy
• Become more phytotoxic together

That is why labels and technical bulletins discuss partners—and why field practice uses caution.

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The jar test concept

A jar test is a small-scale trial of the planned mix in a clean jar before filling a large tank.

Typical teaching steps (illustrative):

1. Wear PPE appropriate for handling the concentrates
2. Use the same water source and approximate ratios as the field mix
3. Add components in the intended order, mixing between additions
4. Observe for heat, precipitate, oil globs, severe separation, or sludge
5. Let the jar stand and re-check after a labelled or practical waiting period
6. If the mix fails physically, do not scale it up

Limits of a jar test:

• A jar test that “looks fine” does not by itself make an unlabelled tank mix legal
• It does not prove long-term chemical stability or field efficacy
• Temperature and water hardness in the field can still differ

Use jar tests as a compatibility screen when the label allows the mix type but physical behaviour is uncertain—not as a substitute for reading labels.

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Teaching sequence for mixing order

Many training manuals teach a default order so products disperse properly and reduce instant incompatibilities. A common classroom sequence is:

1. Start with clean water in the tank (half or as directed)—never pour concentrates into a dry tank as a habit
2. Water-soluble packets / WSP — allow packets to dissolve fully before adding other materials when using WSP products
3. Dry formulations (WP, DF/WDG, SP) — slurry or add with agitation so powders wet and disperse
4. Other liquid formulations (solutions, flowables/suspension concentrates as directed)
5. Emulsifiable concentrates (EC) — often added after aqueous systems are established
6. Adjuvants — frequently last, so they do not interfere with wetting of dry products or create unexpected gels early

Critical override

Product labels override this teaching sequence. If Product A says “add this product last” or “do not mix with X,” follow the label. If two labels conflict on order, do not force a single tank—seek guidance or apply separately.

Agitation should run during addition and continue as required for suspensions.

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Agitation requirements for WP, DF, and flowables

Wettable powders, dry flowables/WDGs, and many suspension concentrates do not form true solutions. Particles stay solid and will settle without agitation.

Consequences of poor agitation:

• First spray out of the tank may be weak; later spray may be overly concentrated
• Uneven pest control and possible crop injury from concentrated bottoms
• Clogged screens, nozzles, and pumps
• Inaccurate effective rate versus the label

Practice points:

• Start mechanical or hydraulic agitation before adding dry products when the system requires it
• Keep agitation running during application for WP/DF/SC mixes
• Do not leave a loaded suspension tank sitting overnight without a plan to resuspend fully and check filters
• After settling, do not assume a quick stir without inspection is enough—follow equipment procedures

True solutions (many SL/SP mixes once dissolved) need less continuous particle suspension, but still require thorough initial mixing. ECs need proper emulsification and may cream if left static—follow label and equipment guidance.

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Foam, water quality, and other mix factors

• Foam: Controlled with allowed antifoams; reduce cascade filling that beats air into the tank
• Water pH and hardness: Can affect some products; labels or technical sheets may advise buffers—do not add random acids/bases
• Temperature: Cold water may slow WSP dissolution; hot conditions may increase volatility or phytotoxicity risk for some mixes
• Leftover mix: Apply to a labelled site at labelled rates when possible; do not dump; do not store mystery multi-product leftovers for “next week” unless labels and stability allow

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Scenarios Core candidates should answer cleanly

Scenario A — Unlabelled mix. A client wants Herbicide A and Insecticide B together. Neither label mentions the other. Correct action: do not tank-mix without compatibility authorization; treat separately if both uses are legal, or pick another labelled option.

Scenario B — Extra wetter. Fungicide label says “do not use surfactants.” Adding dish soap “for better stick” is wrong and may be phytotoxic or off-label.

Scenario C — Drift aid misuse. Wind exceeds sensible (or labelled) limits. Adding a drift retardant does not make the application acceptable.

Scenario D — Settled WP. Mid-job the boom sputters and the tank bottom looks thick. Likely agitation or filter failure with a suspension—stop, correct agitation/filtration, and do not accept striping as “normal.”

Scenario E — Mix order. Training sequence says adjuvant last, but the pesticide label requires a specific surfactant premix step. Follow the pesticide label.

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Field checklist for tank mixes and adjuvants

1. Read every product label for mix permission, prohibited partners, and adjuvant statements.
2. Confirm Ontario legal use for the site (class, licence, cosmetic ban).
3. Choose the most restrictive PPE, REI, and environmental statements among partners.
4. Plan mix order from labels first; use teaching order only as default when labels agree.
5. Jar-test when physical compatibility is uncertain and the mix is otherwise allowed.
6. Fill with water, engage agitation, add components carefully, rinse containers as required.
7. Watch for foam, sludge, heat, or separation—abort the tank if the mix fails.
8. Apply promptly with correct nozzles/pressure; keep agitation for suspensions.
9. Clean the system thoroughly before the next incompatible product.
10. Record products, rates, adjuvants, batch notes, and weather when your program requires records.

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Exam focus points

• Adjuvants only when label allows/recommends
• Know roles: surfactant, sticker, drift retardant, antifoam
• No unsupported tank mixes
• Jar test = small-scale physical check, not a legal free pass
• Teaching order: water → WSP → dry → liquids → EC → adjuvants, labels override
• Agitation critical for WP/DF/many flowables
• Most restrictive label precautions win when products are lawfully mixed

Master formulations (7.1), equipment (7.2), and mixing rules (7.3) together: they are one operational system. The next chapter turns to mixing/loading sites, calibration, and rate math that make these tools deliver the labelled dose on the ground.