Can I Add a Dry Fertilizer to My Liquid Herbicide Tank?

Herbicides Are Pesticides

• Herbicides are classified as pesticides, according to the University of California at Davis Online Integrated Pest Management Program. Fertilizer that contains weed control material is also a pesticide. Fertilizer and pesticide labels contain warnings about chemical interactions between products. Incompatible chemicals alter plant metabolism and toxicity to both targeted and nontargeted plants.

Effects of Mixing

• Compatibility of chemicals is critical "and should be tested prior to application even though product labels allow mixing," according to Ohio State University Extension Research. A compatible fertilizer and herbicide mixture does not separate when mixed together in a glass jar. Do not use a fertilizer-herbicide combination in a spray tank if it foams excessively, separates or becomes syrupy.

Synergistic Effects

• Synergism is a chemical combination that produces a greater response than the added effects of each material when used separately. Chemicals in the two products create a third chemical combination that may be toxic or deadly. Many pesticides contain unidentified chemicals labeled as "inert ingredients" that are dangerous in their synergistic effect. Incompatible mixtures of fertilizer and pesticides may also clog the tank sprayer mechanisms.

Clean the Tank Sprayer

• Garden sprayers should be cleaned after every use. The clean-up location should not be near a water supply, vegetable or flower garden, or in an area where children play. Flush the tank, screens, nozzle and hose thoroughly with clean water. Pesticide residues easily accumulate in a cracked hose. Do not use chlorine bleach to clean a sprayer tank that has been used with fertilizer. The ammonia in fertilizer creates a toxic gas when combined with bleach.