Always refer to pesticide labels for mixing instructions that may be specific to each product. Here are some general rules for mixing pesticides, taken from the Manitoba Guide to Crop Protection. Feel free to print this out and keep it handy.
1. Fill the spray tank with 1/4 to 3/4 the amount of water required for the application.
2. Turn on the sprayer and agitate.
3. Add any fertilizer** or pH adjuster additives (ex. N-pHuric)
4. Add any wettable powders, dry flowables, dry granules, water dispersible granules (WP, DF, DG, WDG) or flowable liquid suspensions (FL) to the tank. Add dry products slowly to prevent clogging.
5. Allow sprayer to agitate for a few minutes.
6. Shake any containers of liquid pesticide thoroughly to ensure they are well mixed.
7. Add any liquid pesticides that are solutions (SN), such as amines and salts (ex: 2, 4-D).
8. Add any liquid pesticides that are emulsifiable concentrates (EC), such as esters (ex: Puma Super, Horizon, Buctril M).
9. Add any surfactants or other adjuvants (ex: Crop Oils).
10. Add the remainder of the water and agitate.
**Exception to fertilizer rule: Add anything packaged in a water soluble packet into the tank before adding fertilizers. Some of these fertilizer ions (particularly chlorine and sulfur acids) as well as some organic solvents used in the formulation of other adjuvants and solvent based formulations can interfere with the solubility of the bag material. Products packaged in solu-bags should go in the tank first after the water. Make sure solu-bags are fully dissolved before continuing the mix procedure. If they are only part dissolved, and other components are added, the remnants could clump and plug screens. Once dissolved the clumping is not an issue.