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Preparing Spray Solutions: Mixing Order

A red, tractor-mounted sprayer with its tank being flushed by a hose connected to a large truck.
Courtesy: University of Arkansas

Originally written by Gared Shaffer, former SDSU Extension Weeds Field Specialist.

Before mixing any pesticide always check the pesticide label for instructions on compatibility of two or more pesticides. Some herbicides and carriers require a compatibility agent, some are not compatible with a compatibility agent.

Mixing Order Recommendation:

  1. Fill the spray tank with one-third of the carrier (water, fertilizer, or mix) to be used. Have the agitator on.
  2. Add ammonium sulfate for glyphosate products.
  3. Always add compatibility agent before herbicides, if compatibility problems exist. Refer to label.
  4. Use a defoamer if excessive foam is produced by the pesticide mixture. Refer to the label.
  5. If needed, add dry wettable powders (WP), dry flowables (DF) materials or water dispensable granules (WDG). Water soluble packets need time to soak with a small amount of water before being added to the tank. It is always recommended for pre-slurry wettable powders and dry flowables to be at a 2:1 ratio with water before being added to the partially filled spray tank. Some pesticides need presoaking.
    • Agitation is used to uniformly disperse the added herbicides. Agitation means a rolling surface action. Be cautious of over agitating due to the possibility to reducing compatibility or excessive foaming.
    • In most situations it is best to continue the agitation until the spray solution is applied. If agitation is stopped, make sure the suspension is satisfactory before application.
  6. After herbicides are dispersed, increase the carrier to 80 percent of the spray solution to be used.
  7. If needed add Liquids and flowables next.
  8. Then add emulsifiable concentrates (EC). Microencapsulated formulations should be added after the emulsifiable concentrates.
  9. Add surfactants and oils last. Some surfactants can cause excessive foaming. If applicator is concerned about the possibility of drift, a drift control agent could be added at this point.
  10. Add carrier to 100 percent of the spray solution to be used and make sure spray solution is mixed thoroughly before starting application.

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