Tank mixes of two or more pesticides, and applications of one pesticide immediately or shortly following the application of another, have been put into three categories by the Environmental Protection Agency:
- Category 1 – The use is indicated on the label of one or more EPA-registered products.
- Category 2 – The use is covered by state registration.
- Category 3 – The use has been tested and recommended by Agricultural Experiment Stations (Universities) or State Departments of Agriculture, or is a common agricultural practice.
Applications that meet Category 1 or Category 2, are legal.
Other uses (Category 3) will be permitted if dosages do not exceed label instructions for any product in the mix used singly for the same pests on the same crop and if labels do not explicitly instruct against such a mixture.
The EPA has not reviewed the effectiveness or the human or environmental hazards of combinations of products in Category 2 and Category 3. The user is at risk in applying these mixtures with respect to effects on crops and equipment, applicator safety, environmental effects, and preharvest tolerance intervals.
If a particular mixture causes adverse effects, the EPA will, on a case-by-case basis, rule that it is not permitted.