Tank Mix Gone Wrong Before a Sensitive Application
An applicator is preparing a 500-gallon tank mix for a turfgrass site adjacent to a pond. The plan combines an herbicide, a liquid fertilizer, and a surfactant. The applicator adds the herbicide first to a nearly full tank, then the fertilizer, then the surfactant, and notices curdling and clumping in the tank. The label lists the herbicide as toxic to aquatic invertebrates and requires a buffer to surface water. The applicator plans to spray anyway after stirring, and intends to rinse the tank into a grassy ditch near the pond afterward. Wind is calm and a temperature inversion is forming as evening approaches.
1. Diagnose the tank-mix problem and explain the correct mixing order and compatibility practice that should have been followed.
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The curdling and clumping indicate an incompatible tank mix or improper mixing order. Adding the herbicide to a nearly full tank and then adding fertilizer and surfactant can produce precipitation, especially with fertilizer salts and certain formulations. The correct approach:
- Perform a jar test before mixing a new combination, using the same products and water in the same proportions.
- Follow the label's mixing order - generally fill the tank partway with water, add products in the label-specified sequence (often compatibility agent, then dry products, then liquid products, then adjuvants/surfactants last), with agitation throughout.
- Add the surfactant last and only if the label permits it.
- Use continuous agitation to keep products suspended.
A curdled mix should not be sprayed. Spraying a precipitated mix can clog nozzles, cause uneven application, and damage the turf. The tank should be cleaned per label directions and the mix discarded properly.
2. Evaluate the applicator's plan to spray the curdled mix and rinse the tank into a ditch near the pond. What environmental and legal problems arise?
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Both parts of the plan are problematic:
Spraying the curdled mix:
- Precipitated product means unknown and uneven active-ingredient delivery - possible under- or over-application and turf injury.
- Off-label if the mix no longer matches labeled use directions.
Rinsing into a ditch near the pond:
- The label identifies the herbicide as toxic to aquatic invertebrates and requires a buffer to surface water. A ditch draining to the pond is a direct route to the water body.
- Dumping rinsate into a ditch is generally a violation of label directions and can violate water-quality rules; rinsate should be applied to a labeled site at labeled rates or disposed of per label and state rules.
- The temperature inversion forming in the evening traps spray and vapors near the ground, increasing drift and deposition risk to the pond and surroundings. Calm conditions with an inversion are a stop condition, not a green light.
The applicator should not spray and should not dump rinsate near the pond.
3. What should the applicator do with the tank and rinsate, and how should the buffer and inversion conditions factor into timing?
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Tank and rinsate:
- Stop and do not spray the curdled mix.
- Clean the tank per label directions, collecting rinsate in a container.
- Apply rinsate to a labeled turf area at or below labeled rates, away from the pond, or dispose of it according to label and state rules - never into a ditch or water body.
- Triple-rinse (or equivalent) and document disposal.
Buffer and timing:
- Maintain the label-required buffer to surface water; verify the distance from the spray edge to the pond before applying.
- Do not spray during a temperature inversion. Inversions keep droplets and vapors suspended and can carry them to the pond and off-site. Wait until the inversion breaks and conditions are stable, with light wind moving away from the water.
- Recheck the mix with a jar test and correct mixing order before resuming.
Documenting the decision to stop and the disposal method protects the applicator if questions arise later.