Tank Mix That Turns to Sludge
An applicator plans a tank mix of a wettable powder (WP) fungicide, an emulsifiable concentrate (EC) insecticide, and a liquid fertilizer carrier in a 300-gallon tank. The plan: add fertilizer first, then the WP, then the EC, with agitation running throughout. After adding the WP to the fertilizer, thick curds form and the mixture will not disperse. The applicator adds more water and increases agitation, but the curds persist. The EC has not yet been added. The label for the WP specifies "add to water, agitate to a slurry before adding other products" and warns against mixing with high-salt carriers without a compatibility test.
1. Explain what went wrong chemically and physically, and what the correct mixing order and procedure should have been.
Read the worked answer
The WP was added directly to a high-salt liquid fertilizer carrier without first forming a slurry in water. High electrolyte concentration salts out the WP's dispersing agents, causing the clay particles to flocculate into curds that cannot be re-dispersed by agitation alone.
Correct procedure:
- Jar test the full mix (WP + EC + fertilizer) before committing 300 gallons.
- Fill tank ~half to two-thirds with water.
- Add the WP first as a slurry in a separate container, then add to water with agitation (per label).
- Add the EC next (emulsifiable concentrates generally go after dry formulations).
- Add liquid fertilizer last, or per compatibility-test result, with continued agitation.
General order: water → dry formulations (WP/WDG) → liquid flowables → ECs → surfactants/adjuvants → fertilizer. The curds indicate the batch is unusable; it must be disposed of per label and state rules, not sprayed.
2. What should the applicator do with the failed batch, and how should future mixes be screened?
Read the worked answer
The curded batch is not sprayable - spraying it risks nozzle plugging, uneven application, and illegal off-label use. Disposal:
- Do not dump on soil, in drains, or in waterways.
- Follow the label's disposal instructions and state hazardous-waste rules; a 300-gallon failed mix may require a licensed waste hauler or an approved land-application/rinseate procedure.
- Triple-rinse containers and add rinseate to the spray tank only if the batch is usable; for a failed batch, contain and dispose per regulation.
Future screening:
- Perform a jar compatibility test (small clear jar, same ratios, same order, observe for curds, separation, heat) before every new combination.
- Read all labels for mixing restrictions and carrier incompatibilities.
- Keep a written record of tested combinations and results.
Prevention is far cheaper than disposing of 300 gallons.