Tank mix order and compatibility basics

The label governs, then the jar test

Purdue's PPP-122 lists what labels can tell you that no chart can: tested tank mixes, loading order, minimum carrier volume, required or prohibited adjuvants, agitation, temperature sensitivity, pH and mineral warnings, and forbidden partners. Labels change between purchases, so read them each time.

In Canada, only products registered by Health Canada's PMRA (look for the PCP number) may be used, and the Canadian label, not the US one, sets the supported tank mixes and mixing instructions. A US label or compatibility chart does not transfer across the border.

Run a jar test whenever the labels do not answer the question, when you add a product you have not mixed before, when the water source or fertilizer carrier changes, or when a batch number changes, because inert ingredients change without notice. Nebraska's G2350 procedure, which matches Purdue's:

1. Read every label and write down the loading order and any required adjuvant.
2. Use carrier water from the same source as the sprayer, at the same temperature. Do not warm it.
3. In a clear 100 mL jar, 1 mL represents 1 gallon (3.8 L) of tank mix; work out each product's share of a 100-gallon load and scale to millilitres.
4. Fill the jar one-third to one-half with carrier, add the first product, cap and invert, and let it disperse before the next. Repeat in order.
5. Top up to 100 mL, invert again, and let it stand about 30 minutes. Purdue suggests leaving a second jar overnight if the load will sit.
6. Look for layering, fast settling, floating particles, residue on the glass, gel, curds, fizzing, foaming, heat or clotting. Nebraska's example is 28 percent UAN with 2,4-D amine, which turns into a mayonnaise-like mass.
7. A clean jar proves physical compatibility only. Chemical antagonism does not show in a jar; a small test strip is the only field check.

If the jar fails, change the order, add a label-approved compatibility agent, or drop a partner.

Loading order: WALES, APPLES and what they mean

The mnemonics describe formulation chemistry, not brands. Dry products need time and clean water to disperse; oils and emulsifiers coat granules and stop that. SDSU's 2026 publication explains the older acronyms and adds one:

In practice, drawing on Purdue, Nebraska and SDSU:

• Fill the tank to about half with clean water (50 to 75 percent if the carrier is liquid fertilizer) and start agitation. Keep it running until the tank is empty.
• Add water conditioners such as ammonium sulfate first if the label calls for them, and let AMS dissolve fully; one Purdue reviewer timed 22 minutes at 40°F (4°C).
• Add dry formulations one at a time (water-soluble packets, wettable powders, dry flowables, water-dispersible granules), slurried first if the label suggests it. Wait 3 to 5 minutes between products and never put two in the inductor together.
• Add liquid flowables and suspension concentrates, then microencapsulated products, then emulsifiable concentrates. Shake every jug first.
• Add soluble liquids and salts; SDSU puts glyphosate last among the herbicides.
• Add surfactants, crop oils and methylated seed oils, then any anti-drift agent.
• Top up with water, agitate until uniform, and check pH only at the end.

Nebraska's table states that label directions override this order and that adjuvant order in particular varies by product. If a label says "add this product first," that is the order, whatever the acronym.

Water quality: pH, hardness, AMS and conditioners

Water is most of what goes through the nozzle and the ingredient most people never test. Iowa State recommends testing each source for pH and hardness with an inexpensive pool kit or a lab analysis.

Hardness is dissolved calcium and magnesium, with iron, aluminium and sodium also counted as problem cations; Purdue's rule of thumb is that 200 ppm or more is hard. Those cations bind negatively charged herbicides, glyphosate above all, so part of the rate never reaches the weed. Glyphosate labels address this with ammonium sulfate added to the water before the herbicide. AMS replacement products can soften water but, as Iowa State notes, often lack AMS's separate benefit for uptake and translocation.

pH works differently. In alkaline water many products hydrolyse to inactive forms; Purdue cites captan, with a half-life of about 32 hours at pH 5 but about 10 minutes at pH 8. Some products prefer higher pH, so the answer is not "always acidify": Purdue warns that acidifying the tank raises copper solubility and can make copper fungicides phytotoxic, that phosphorous acid products are already acidic, and that carbonate fungicides lose activity when acidified. Follow the pH range on the label, and if you use a buffer, measure after the whole load is mixed.

Adjuvants and the mixes that commonly fail

Adjuvants have their own labels and go last for a reason. The failures extension specialists see repeatedly:

• Oil before dry granules. Oil or EC added before a water-dispersible granule coats the granule, which never disperses and plugs screens.
• Dry granules into liquid fertilizer. WDG added straight to 32 percent UAN floats and blocks screens. High-salt fertilizer has fewer free water molecules to dissolve products, so premix in water.
• Amine herbicides with nitrogen solutions. The 2,4-D amine and 28 percent UAN example above is the classic jar test fail.
• Micronutrients with glyphosate. Purdue trials summarised by Vyn and colleagues found that manganese tank-mixed with glyphosate cut weed control, an amino-acid chelate dropping control from 100 to 85 percent while Mn-EDTA caused no loss. Their advice is not to tank mix manganese with glyphosate and to apply foliar Mn 7 to 10 days later. Nebraska adds that non-chelated copper, iron, manganese and zinc can fall out of solution.
• Sulfur and oils. Sulfur labels carry their own restriction; the Microthiol Disperss label, for example, prohibits use within two weeks of an oil spray outside dormant and post-harvest timings.

None of these are solved by a higher rate of anything. Rates and intervals are on the label registered in your state or province.

Temperature, agitation and timing

Cold water slows everything. Purdue puts the threshold around 42°F (6°C): below it, allow at least 3 to 5 minutes per product or premix a slurry in warmer water, expect ECs and oils to gel rather than form a milky emulsion, and expect water-soluble packets to dissolve slowly enough to plug a pump intake.

Agitation should be moderate: the surface moves but does not boil. Too little and dispersed products settle and hard-pack; too much and wettable powders foam, emulsions separate into curds, and polymer drift agents shear apart. SDSU's rule of thumb is to return 5 to 6 percent of the tank volume per minute; if the pump cannot, mix smaller batches.

Spray the load promptly; if it must sit, keep agitation on.

Record keeping

Purdue recommends writing down, for every mix that worked or failed: the carrier and water source, water temperature, pH and hardness, each product with its rate, batch number and order added, and the agitation time between products. The same record feeds the application records many states and provinces require, and lets you repeat a good mix next season without starting from scratch.