WALES Mixing Order Guide: Correct Pesticide Tank Mix Sequence

WALES mixing order explained: every letter, every reason

WALES is a mnemonic used in pesticide application training — particularly in UK and European agronomy — to remember the correct sequence for building a spray tank mix. The same underlying principle is taught in the US as WBAS. Both systems exist because adding products in the wrong order is one of the most common causes of tank mix failure.

WALES vs DALES vs WBAS — what's the difference?

These are regional variants of the same principle. WALES is the most widely used UK/European mnemonic. DALES (Dispersibles, Adjuvants, Liquid flowables, Emulsifiable concentrates, Soluble concentrates) is an alternative that combines WDG and WP under a single "Dispersibles" heading. WBAS (Water, Buffer, Active products by formulation type, Surfactants) is common in US extension service guidance. All three produce the same practical result: dry formulations first, oil-based last, surfactants after everything else.

What happens if you mix pesticides in the wrong order?

Mixing order failures aren't always visible immediately — some only become apparent at the nozzle or in the field. Here are the specific failure modes that result from common sequencing mistakes, and why the WALES order prevents each one.

Adding EC before WDG/WP — gelling and incomplete dispersion

Emulsifiable concentrates contain a surfactant package that helps the oil emulsify in water. When an EC is added before dry formulations have fully dispersed, that surfactant package interacts with the undissolved powder particles — coating them and preventing water penetration. The result is partially dispersed powder that clumps, gels, or settles as a paste at the bottom of the tank. These clumps won't fully dissolve during agitation, meaning some nozzles receive under-concentrated spray and the residue can block strainers or nozzle tips.

Adding surfactant before actives — disrupted WDG dispersion

Non-ionic surfactants (NIS), crop oil concentrates (COC), and methylated seed oils (MSO) all dramatically reduce water's surface tension. When added early, this prevents the wicking action that draws water into WDG granule aggregates. Instead of dispersing uniformly, the granules form tight clumps that resist hydration. You may not notice anything wrong until application — when the settled residue clogs nozzles or creates uneven application patterns across a field.

Adding SL glyphosate before AMS in hard water — reduced efficacy

Hard water contains calcium and magnesium ions that bind to glyphosate molecules, forming insoluble calcium-glyphosate or magnesium-glyphosate salts. These salts don't penetrate plant tissue effectively. Ammonium sulfate (AMS) works as a water conditioner by competing with calcium and magnesium for the binding sites — but only if it's added to the water before glyphosate. Adding AMS after glyphosate provides no benefit because the glyphosate is already partially inactivated. This is why AMS always goes in the A step — before any actives.

Adding oil-based ECs together without agitation — phase separation

When two EC formulations are added in quick succession without adequate agitation between additions, their oil phases can coalesce before fully emulsifying in the water. The result is a visible oil slick on the tank surface and an inconsistently mixed load. Once phase separation occurs it can be difficult to re-emulsify without draining and restarting. The fix: add one EC at a time, agitate until the tank looks uniformly milky, then add the next.

The visual test isn't always enough

A tank that looks well-mixed after incorrect sequencing may still have stability problems that emerge over time — especially on long spray runs or in hot weather. Products that separate after 30–60 minutes of sitting in a partially-filled tank on a warm day can cause severe over-application in the first few passes and under-application in later ones. Always maintain agitation during filling, and complete the jar test before building the full tank on any new product combination.

Common pesticide tank mix examples in WALES order

Example 1: Corn pre-emerge — glyphosate + atrazine + acetochlor

Example 2: Wheat fungicide + insecticide + adjuvant

Note: When all products are ECs, the order within the E step is less critical — but jar test first, and add them one at a time while agitating.

Can you mix Roundup and 2,4-D together?

Yes — glyphosate (SL) and 2,4-D amine (SL or EC) are one of the most commonly tank-mixed herbicide combinations in broadacre farming. In WALES order:

1. Fill tank 50% with water
2. Add AMS if using hard water (A step)
3. Add 2,4-D amine (SL formulation) — S step; or 2,4-D ester (EC formulation) — E step before glyphosate
4. Add glyphosate SL — S step
5. Add NIS surfactant if required by label
6. Top off with water

Important: always check both product labels for tank mix restrictions. Note that the governing REI for this combination is 12 hours (2,4-D amine), not the 4-hour glyphosate REI. Use the REI Calculator to calculate the safe re-entry time.