Two or more pesticides may be mixed in the spray tank provided mixing is not prohibited on any of the labels. The dosage rates, timing, and other use directions must conform to the most restrictive requirements on the label for each product. If there are no directions for mixing on any of the labels, the user may be liable for problems associated with the mixture, such as incompatibility, crop injury or reduced performance. The safety of any specific tank mix may depend on potato variety, crop growth stage, the weather, and spray solution concentration.  The higher the number of products in the mix, the less predictable the effect.

A jar test can help to determine if products will be physically compatible in a tank mix. 

Tank-Mixing Pesticides Without Disasters is a guide by Frederick M. Fishel, University of Florida/IFAS Extension. It describes types of incompatibility, performing a jar test, general steps for mixing products, and commercial tank-mixing tools.