by Rodrigo Werle (UW-Madison Extension Cropping Systems Weed Scientist)
Last week I released a blog post attempting to address the question regarding tank mixing safened S-metolachlor/metolachlor, atrazine and/or mesotrione-based products for weed control in corn (see: “Can brand or generic herbicides be tank-mixed? Part-2”).
The mesotrione products that I checked during my label search (i.e., Callisto, Explorer, Mesotrione 4SC and Meso Star) stated the following restriction: “DO NOT apply this product post-emergence in a tank mix with emulsifiable concentrate grass herbicides, unless specifically directed under one of the tank mix section of this label, or crop injury can occur”.
Safened S-metolachlor products such as Duall II Magnum, Medal EC and Brawl, and safened metolachlor products such as Me-Too-Lachlor II and Stalwart C labeled for use in corn fall under the emulsifiable concentrate grass herbicides formulation category and thus SHOULD NOT be tank-mixed with the aforementioned mesotrione products for POST-emergence applications in corn.
HOWEVER, there are several safened S-metolachlor/metolachlor and mesotrione products out there and of course I missed checking the label of some. This week I received calls from chemical retailers in Wisconsin mentioning that my blog post was not completely accurate. Guess what? They were right. I even stated the following in the previous article “Once this post is released there will likely be a “Part 3” coming next because I will certainly forget to address something important; going through the label exercise is not a simple task! That’s when experience comes into play. Growers should always consult an expert before spraying a custom herbicide tank mix. Always read the product label before spraying.”
Back to the feedback I received, Drexel Chemical Company has a mesotrione product called MesoTryOne 4L. In their label (page 2), instead of having the particular tank mix being discussed herein under RESTRICTIONS, they have it under USE PRECAUTIONS: “Post-emergence applications of this product in tank-mixes with emulsifiable concentrate grass herbicides may cause severe corn injury or yield loss under adverse weather conditions”.
So in this case, the tank mixing of an emulsifiable concentrate grass herbicide with MesoTryOne 4L POST-emergence in corn is considered a legal application; however, the label states that you must apply under “non-adverse weather conditions” to reduce the potential of crop injury.
If you go to “Table 5. Tank-mixtures of this Product for PRE-emergence Application in Corn” (page 9 of the MesoTryOne 4L label), you will see that the mixture of MesoTryOne 4L with Metolachlor (e.g., Me-Too-Lachlor II, Duall II Magnum) is listed; but the same tank mixture is not listed in “Table 6. Tank-mixtures of this Product for Post-emergence Application in Corn” (page 9 of the label). Moreover, the tank mixture of commercial pre-mixes of Atrazine + Metolachlor (e.g., Trizmet, Bicep II Magnum) with MesoTryOne 4L are listed in Table 6, but keep in mind that these pre-mixes are formulated as a suspension concentrate. The concern regarding crop injury comes from having mesotrione tank mixed and sprayed POST-emergence with emulsifiable concentrate grass herbicides.
I truly appreciate the positive criticism and feedback from the clientele and industry colleagues! Though my post was not 100% accurate, I certainly got folks to take a closer look at the labels (mission accomplished!).
Again, going through the label exercise is not a simple task! That’s when experience comes into play. Growers should always consult an expert before spraying a custom herbicide tank mix.
Disclaimer: I am not endorsing Drexel Chemical Company and the use of their product MesoTryone 4L (nor the opposite). I am just using their product as a pertinent example for the discussions regarding custom herbicide tank mixtures and label restrictions.
Always read the product label before spraying.