In one situation the mixture produced a thick “sludge” like product, while the other just required extra agitation to keep it in solution.
This is a reminder: Pesticides are not always compatible with each other or with the water or liquid fertilizer carrier. Lack of compatibility may result in the formation of a gel, precipitate, or sludge that plugs up screens and nozzles. But extreme incompatibility may produce a settling out of material that can harden like concrete in the bottom of the tank and in hoses, pumps, and other internal parts of the sprayer. The result may be total loss of the pesticide and use of the sprayer.
Other types of incompatibilities also can reduce effectiveness or cause crop injury. Foliar activity may be enhanced and result in crop leaf burn, or the activity of one or more of the pesticides may be reduced (“antagonism”).
Good information is scarce concerning the physical compatibility of herbicides with specific fertilizer solutions and sometimes other pesticides. Some of this information is more well known by commercial applicators that regularly apply a diverse number of products over many acres, but is less well known by those that don’t do a lot of spraying. Tank-mixing several pesticides and fertilizers, although convenient, may create other problems. Physical compatibility problems are more likely to result when concentrated herbicides are mixed together, so a compatibility test should be done before new mixtures are tried.
Use only labeled tank mixtures or mixtures recommended by experienced agriculturalists whose recommendations are backed by research. For all unlabeled tank mixtures, a jar test is strongly recommended to test for compatibility. The compatibility of herbicide-fertilizer combinations should be tested before large batches are mixed. In some cases, adding a compatibility agent (e.g. Combine, Unite, or comparable compatibility agents) may help maintain component dispersion.
Remember to use a “jar test” if in doubt to test the compatibility of herbicides with each other or of herbicides and other pesticides with liquid fertilizers. Click here for more details about the jar test .
( Source – http://extension.psu.edu/plants/crops/news/2013/05/consider-physical-incompatibility-of-pesticides)