4.3 Mixing and Application per Label Instructions

FIFRA and the Label as Law

FIFRA Section 12(a)(2)(G) makes it unlawful to use any registered pesticide in a manner inconsistent with its labeling. For mixing and application, that means the rate, the mixing order, the adjuvants, the tank-mix partners, the carrier, the equipment, and the application timing must all match what the label allows. Deviating in a way the label does not permit is a federal violation, enforceable by EPA and by IDALS under Iowa Code Chapter 206.

FIFRA Section 2(ee) does allow a few specific deviations without being 'inconsistent with labeling': applying at a lower rate or concentration (unless the label prohibits it), applying against a pest not listed if the site is listed, using an application method not prohibited by the label, and mixing with fertilizer when not prohibited. Everything else — a higher rate, an unlisted site, a prohibited tank mix, a different carrier — is a violation.

Rates and Units

The application rate is the amount of product applied per unit area or per unit of spray. Labels express rates in several ways:

Always verify the rate is for the formulation you have, not a different concentration. A 4 lb/gal glyphosate product and a 3 lb/gal glyphosate product are not interchangeable at the same pint-per-acre rate.

Mixing Order: A-A-C-D

The Iowa Core Manual teaches the A-A-C-D mixing sequence as a general guideline for tank-mixing compatible products. The label's specific mixing instructions always override this convention.

1. A — Agitate: Fill the tank half to two-thirds full of clean carrier (usually water) and start agitation. Agitation must continue throughout mixing and application.
2. A — Add dry formulations: Wettable powders (WP), dry flowables (DF), water-dispersible granules (WDG), and soluble powders (SP). Pre-slurry each in a small amount of water before adding to the tank, and allow each to disperse fully before adding the next.
3. C — Add liquids (Compatibility next): Soluble liquids (SL), flowables (F/L), and suspension concentrates (SC), then emulsifiable concentrates (EC). ECs go after soluble liquids because oil-based ECs added too early can cause dry formulations to clump.
4. D — Add surfactants and adjuvants last: Nonionic surfactants (NIS), crop oil concentrates (COC), methylated seed oils (MSO), compatibility agents, and defoamers go in last, after everything else is in suspension.

Other common acronyms (WAMLEGS, WALES) describe the same physical principle: dry formulations first, then soluble liquids, then ECs, then surfactants last, with constant agitation. Always check the label — some products specify a different order or prohibit certain adjuvants.

Tank-Mix Compatibility

Labels often list tank-mix partners explicitly. If a label says 'do not mix with product X,' that mix is prohibited and illegal. If a label is silent on a partner, the general rule is to perform a jar test — mix small amounts in the intended ratio in a clear jar, wait 30 minutes, and check for flakes, gel, separation, heat, or a precipitate. Any of those signs means the mix is incompatible and must not be used.

Compatibility problems are more likely with:

• Hard water (calcium, magnesium ions tie up glyphosate and sulfonylureas).
• Cold water (slows dispersion).
• Multiple products in the same tank (cumulative risk).
• Mixing ECs with dry flowables in the wrong order.

Adjuvants and Surfactants

An adjuvant is any substance added to a spray mix to improve performance or handling. Labels may require, allow, or prohibit specific adjuvants:

• Required: 'Use a nonionic surfactant at 0.25% v/v' — you must add it.
• Allowed: 'A crop oil concentrate may be used' — optional.
• Prohibited: 'Do not use oil-based adjuvants' — using one is a label violation.

Common adjuvant types:

Adding an adjuvant the label prohibits, or exceeding a label rate for an adjuvant, is a label violation.

'Do Not' Statements

Labels list explicit prohibitions. Examples:

• 'Do not apply when wind speed exceeds 15 mph.'
• 'Do not apply within 66 feet of a downwind sensitive area.'
• 'Do not apply through any type of irrigation system.'
• 'Do not graze or feed forage for 30 days after application.'
• 'Do not tank mix with products containing glyphosate.'

Each 'do not' is enforceable. FIFRA Section 2(ee) does not authorize violating a 'do not.'

Following the Rate Exactly

• Under-dosing can fail to control the pest and contribute to resistance. It is allowed under FIFRA Section 2(ee) only when the label does not specify a minimum rate and does not prohibit deviation.
• Over-dosing is illegal unless the label expressly allows a range. It wastes product, risks crop injury, increases residues above the tolerance, and threatens groundwater.

If a label gives a range (for example, '0.5 to 1.0 lb ai/A'), any rate in that range is legal. A rate above 1.0 is a violation.

Spray Drift Precautions on the Label

Labels increasingly carry specific drift management language: wind-speed ceilings, buffer distances, droplet-size requirements (for example, 'apply as a medium or coarser spray'), and boom-height limits. These are mandatory. A label that says 'do not apply when wind speed exceeds 10 mph' sets a legal ceiling, not a suggestion. Iowa applicators working near sensitive crops, beehives, or surface water must read and follow the drift section before spraying.