by Rodrigo Werle (UW-Madison Extension Cropping Systems Weed Scientist)
Last month we released a blog post entitled “Can brand or generic herbicides be tank-mixed?” and in the first paragraph we wrote “This past week we received several questions regarding herbicide tank mixtures. One common question was whether brand and/or generic S-metolachlor/metolachlor, atrazine and/or mesotrione-based products could be tank-mixed”.
After speaking with industry colleagues, I learned that in the original blog post we described several important aspects to consider when developing a custom herbicide tank mix but did not actually answer if S-metolachlor/safened metolachlor, atrazine and/or mesotrione-based products could be tank-mixed; herein I will attempt to address this question.
As always, the answer is “it depends”.
Lumax EZ is a popular pre-mix corn herbicide that contains S-metolachlor, atrazine and mesotrione. Lumax EZ herbicide can be sprayed PRE and early-POST in corn (according to the label: “Postemergence applications to field corn must be made before crop reaches 12 inches in height”).
If a grower decides to make his/her own “Lumax-equivalent” custom tank mix, that tank mix can be sprayed before corn emergence. After corn emergence, there is a caveat to be considered; the label of mesotrione-based products such as Callisto, Explorer, Mesotrione 4SC and Meso Star state 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”.
S-metolachlor-based products such as Duall II Magnum, Medal EC and Brawl, and safened metolachlor-based products such as Me-Too-Lachlor 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-based products for POST-emergence applications in corn.
- Can S-metolachlor/safened metolachlor be tank-mixed with atrazine and sprayed POST-emergence in corn? YES
- Can mesotrione be tank-mixed with atrazine and sprayed POST-emergence in corn? YES
- Can S-metolachlor/safened metolachlor be tank-mixed with mesotrione and sprayed POST-emergence in corn? NO
- Can S-metolachlor/safened metolachlor, atrazine and mesotrione be tank-mixed and sprayed POST-emergence in corn? NO
Additionally, pay attention to the: i) geographic restrictions (for instance atrazine use is prohibited in parts of Wisconsin), ii) maximum use rate of a pesticide per application and iii) total pesticide use within a season. Always follow the most restrictive tank mix instructions for the products involved.
Check our 2018 post “Geographic Restrictions for Corn and Soybean PRE-emergence Herbicides in Wisconsin” for additional geographic restriction information.
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.