Over the weekend, I fielded a few questions about the potential use of a Roundup + Liberty tank-mixture for weed control in field corn. A few years ago, I was not really a huge fan of this tank-mix because I was worried about possible antagonism (i.e. less weed control) since they are very different herbicides. Roundup is a systemic (translocated) herbicide while Liberty is a contact herbicide (limited movement within a plant). I have heard ASC talk positively about this tank-mixture in cotton over the years but he has also observed some reduced grass weed control with this combo.
In my field corn research thus far, I have not seen this antagonism (yet?) but I am also adding either Aatrex (atrazine) and/or Prowl (pendimethalin) to the mix. Aatrex 4L @ 2 qt/A brings much to the table. Check out the field pictures below. You might also observe in these pictures that I did not add any additional adjuvants to these treatments because a) I do not have hard water [excessive Ca, Fe, K, Mg, Na] and b) “loaded” glyphosate formulations [formulations already have adjuvants included] were used. If you are not sure about which glyphosate formulations are “loaded” or not, check out the following (no need to reinvent the wheel) :
https://www.ag.ndsu.edu/publications/crops/north-dakota-weed-control-guide (From North Dakota State University, page 93)
https://extension.msstate.edu/sites/default/files/publications/publications/P1532_web.pdf (From Mississippi State University, pages 12-13)
A few other things to think about? 1) Not all field corn hybrids are tolerant to both Roundup and Liberty so that needs to be confirmed before application and 2) Labeled cutoff stages for over-the-top applications for each herbicide are very different (Atrazine = 12″; Liberty = V6; Prowl = 30″ or V8; Roundup = 30″ or V8).
