Insecticide/Herbicide Tankmix Safety

Many calls have came in over the past week to ten days regarding mixing insecticides and herbicides and the resultant effects on crop safety.  There are many factors that go into phytotoxicity observed on crops from pesticide applications; however, I will attempt to briefly summarize our recommendations below.

Generally speaking, the safest insecticides (for use on thrips) to mix with herbicides are listed below (in order from safest to most injurious):

1.  acephate/Radiant

2.  Bidrin

3.  dimethoate

Having given this list, keep in mind that the herbicide you are tankmixing with plays a strong role in observed phytotoxicity as well.  Normally, when mixing any of the above with glyphosate or Liberty the potential for crop injury is reduced compared to when you tankmix glyphosate or Liberty + metolachlor (or S-metolachlor).  The general thought is that the emulsifiable concentrate (EC) formulations tend to increase the level of crop injury observed when mixed with any of the products mentioned above.

Variety and technology contained therein can also play a role in the level of crop injury observed.  Crop injury from Sequence or glyphosate + metolachlor (or S-metolachlor) with or without an insecticide is usually similar across all varieties and technologies.  Environmental conditions appears to play a large role in crop injury observed from these combinations.  When applying Liberty and potentially mixing metolachlor (or S-metolachlor) and/or an insecticide with it, variety and technology contained therein must be considered.  Liberty Link varieties (GLB2; GLT) appear to be the most tolerant to two and three way tankmixes of herbicides and insecticides.  This is not to say you will never see injury on these varieties; however, all other things being equal, injury appears to be less pronounced from tankmixes on these varieties.  Caution should be exercised with Xtend varieties and Phytogen varieties.  These varieties appear to be more sensitive to two and three way combinations of herbicides and insecticides.  Injury we have observed from these two and three way combinations does not usually result in death of the crop; however, the level of damage can be unnerving.  Keep in mind that in many cases this injury is transient and tends to disappear with time.  However, given the weather conditions so far this spring combined with the lateness of the crop and slow early season crop growth, care should be taken to not delay crop maturity.