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). 

Coverage, Coverage, Coverage (Prostko)

In support of Dr. Bob "Hole in My Roof" Kemerait's 6:29 am e-mail earlier today, I would like to add a few comments about spray coverage.  I don't sleep that much this time of year especially when its field corn planting time and it's too rainy/windy to plant/spray.  Three quick reminders about spray coverage that we often talk about (with some data to back them up):

1) Increased tractor speeds result in decreased spray coverage. 

2) Lower water volumes result in decreased spray coverage.

3) Larger spray droplets result in decreased coverage.

In the words of Forrest Gump, "That's all I have to say about that!"

Zalo Herbicide Registration (Prostko)

The registration for AMVAC's Zalo herbicide (glufosinate + quizalofop) was recently granted by the US EPA on February 13, 2024. Considering the current shortage of the over-the-top dicamba products (Engenia, Tavium, and Xtendimax) in Georgia, cotton and soybean growers will very likely be interested in any or all glufosinate formulations. For more information, check out the slides below.  

Adjuvants-Part II (Prostko)

You might recall that I provided you with some general information about spray adjuvants in a December 11, 2023 UGA Weed Science blog post.  I was not aware of (or more likely forgot) that there is an Adjuvant Certification Program spearheaded by the Council of Producers and Distributors of Agrotechnology (CPDA).  Adjuvants that have this certification have met 17 benchmark qualifications of a consistent and quality adjuvant. More information and a complete list of CPDA certified adjuvants can be found at https://cpda.com/adjuvant-certification-history-2/.

Ryegrass Control/Reviton-Peanut Rotation Restriction Change (Prostko)

 A few things you might be interested in:

1) Lately, I have received a few questions about controlling Italian/annual ryegrass in preplant burndown situations.  Assuming resistance is not an issue, glyphosate can be effective but remember that rate and timing are very import (Figure 1).  If you suspect that glyphosate-resistance (GR) is an issue, check out page 85 of the 2024 UGA Pest Control Handbook.  On the bottom of page 85, I have more detailed information about controlling GR-ryegrass.

 https://secure.caes.uga.edu/extension/publications/files/pdf/SB%2028-15_2.PDF  

Figure 1.  Ryegrass Control with Roundup WeatherMax at Different Rates
and Stages of Growth.

2) Via a FIFRA Section 24(c) label, the crop rotation restriction for peanut in Georgia following an application of Reviton (tiafenacil) has been reduced to 0 days (1 oz/A ) and 7 days (2 oz/A).  Refer to the 24(c) label below.  Check out the February 7, 2022 and March 31, 2023 posts on the UGA Weed Science Blog for some earlier comments about Reviton.  

Figure 2.  Section 24(c) Label for Reviton (tiafenacil) in Georgia