It is not uncommon for multiple pesticides and fertilizers to be mixed together in the same sprayer tank so they can all be applied in one go. Most pesticides labels provide information on compatibility with other pesticides and fertilizers, but testing of all combinations is impossible. If a substance is not specifically mentioned as compatible, follow the label to perform a compatibility test.
To minimize the risk of active ingredients of different formulations interacting with each other, the following mixing order should be used, from first to last:
- Wettable Powders (WP or W) – finely ground solids, typically mineral clays, to which an active ingredient is sorbed. They provide an effective way to apply an active ingredient in a water spray that is not readily soluble in water. These dry preparations look like dust, contain a high percent active ingredient (usually 50 percent or more) and are mixed with water for application. Wettable powders form a suspension rather than true solution when added to water. Good agitation (mixing) is needed in the spray tank to maintain the suspension.
- Dispersible Granules (WDG) – manufactured in the same way as wettable powders except that the powder is aggregated into granular particles. They are mixed with water and applied in a spray exactly like a wettable powder. This dry formulation usually contains 70 to 90 percent active ingredient.
- Flowable or Aqueous Suspension (F, L or AS) – very finely ground solid material suspended in a liquid. Liquid flowables usually contain a high concentration (4 pounds or more) of active ingredient and are mixed with water for application.
- Emulsifiable Concentrate (E or EC) – usually contains the active ingredient, one or more petroleum solvents, and an emulsifier that allows the formulation to be mixed with water. These concentrates are soluble in oil and form an emulsion in water. The emulsion-forming characteristic results from the addition of adjuvants to the herbicide formulation.
When using a sprayer:
- Calibrate the sprayer
- Read the herbicide label and wear personal protection equipment
- Fill the tank half way with water, never mix concentrated chemicals in an empty tank
- Measure chemicals you are adding to the tank.
- Apply the pesticide according to label directions.