Halex GT Mixing Problem in Corn/Valor Applied PPI (Prostko)

 A couple of things to bring to your attention based upon my week:

1) A field corn grower in Macon Co. experienced a significant problem when Halex GT (mesotrione + S-metolachlor + glyphosate-K salt) was tank-mixed with a different type of glyphosate formulation (IPA salt) (Figure 1).  This problem did not occur when other K salt formulations (Roundup PowerMax3 or Honcho K6) were used (Figure 2). Remember that all glyphosate formulations are not created equal.  They have different concentrations of active ingredients, are formulated as different salts (K, IPA, DMA), and may/may not be formulated with adjuvants. In my April 8 blog, I provided you with a couple of links where you can get some handy information (charts) about the different glyphosate formulations.

Figure 1.  Halex GT tank-mixing problem in Macon County, 2024.

Figure 2.  Different glyphosate formulations tank-mixed with Halex GT + Atrazine +
Mustang Max + NIS + Defoamer

2) Please remind your growers that UGA does not recommend that Valor be applied pre-plant incorporated (PPI) for weed control in peanut!  Valor is not labeled for that type of application and pigweed control will be significantly reduced (PPI is 25-35% less effective than when applied PRE behind the planter).   

 

Figure 3.  Palmer amaranth control in peanut with Valor applied PPI or PRE.

Wet Weather and PRE Herbicides (Prostko)

In the last 2 days, many locations in south Georgia received lots of rain (Figure 1).  Thus, I have been getting many texts and telephone calls about what might happen to any PRE herbicides that were applied to field corn.  In general, I would say that if runoff/washing was minimal, there is a good chance that the herbicides are still in the field, especially if the PRE treatments were watered in soon after application.  Research in Georgia has shown that runoff of Dual II Magnum and Prowl EC in conventional tillage systems was reduced 1.2-2X when irrigation occurred shortly after application (Potter et al. 2008.  Herbicide incorporation by irrigation and tillage impact on runoff loss.  Journal of Environmental Quality 37:839-847).

In 2022, a very similar weather event occurred in my research plots during the first 7 days after planting (3.84" of irrigation/rainfall).  All my PRE herbicides worked just fine (Figures 2, 3, 4).  Note in Figure 2 that there are some wild radish plants in the plot but no pigweed or grasses.  In general, all of the Group 15 herbicides (Anthem Maxx, Dual Magnum, Outlook, Warrant, Zidua) do not provide adequate residual control of wild radish so this should not be a surprise.  FYI, Anthem Maxx/Zidua are slightly better on wild radish than the other Group 15's.

Bottom line, no way to know for certain how much herbicide will be left in the field.  My best advice would be to keep eyes on/feet in the field and pull the trigger earlier on POST treatments when/if needed.  

Figure .  South Georgia Rainfall, April 10-11, 2024.

Figure 2.  Weed control with Everprex in a rainy year.

Figure 3.  Weed control with Acuron in a rainy year.


Figure 4.  Weed control with Maverick in a rainy year.

Roundup (glyphosate) + Liberty (glufosinate) for Weed Control in Field Corn (Prostko)

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).