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 

2024 Peanut Herbicide Prices, Field Corn Hybrid Herbicide Tolerance Guides - Prostko

 1) Thought you might be interested in the current prices of peanut herbicides.  These prices were obtained by averaging numbers from at least 4 local retailers.  Also, need to realize that every grower will likely pay a different price than listed below based upon many factors (probably lower).

Anthem Flexx = $621/gal; Basagran = $60/gal; Brake = $187/gal; Butyrac 1.75SL (2,4-DB) = $21/gal; Cadre = $250/gal; Cobra = $181/gal; Dual Magnum = $69/gal; Gramoxone 3SL = $40/gal; Outlook = $134/gal; Prowl H2O = $49/gal; Select Max = $92/gal; Sonalan = $50/gal; Storm = $90/gal; Strongarm = $756/lb; Ultra Blazer = $46/gal; Valor EZ = $461/gal; Warrant = $30/gal; Zidua SC = $710/gal.

Using these numbers then ......

Sonalan 3EC @ 32 oz/A + Valor EZ 4SC @ 3 oz/A + Strongarm 84WG @ 0.225 oz/A (PRE) fb Cadre 2AS @ 4 oz/A + Dual Magnum 7.62EC @ 16 oz/A + Butyrac 1.75SL @ 16 oz/A  (POST) =  $53.01/A

2) Check out the most recent editions of the field corn hybrid herbicide tolerance information from Pioneer and Dekalb.  Always a good idea to double-check BEFORE spraying.

Amides: Dual Magnum, Outlook, Warrant

Benzoic Acid/Phenoxy: 2,4-D, dicamba

Isoxazole: Callisto, Laudis, Impact

Sulfonylurea: Accent, Revulin Q, Sandea, Steadfast Q 

Pioneer:

Dekalb:

Herbicide Adjuvants (Prostko)

At the recent UGA Weed Science Update (12/06/23), Cale Cloud from Grady County asked me if I could talk about herbicide adjuvants.  Since I had my talks already prepared, I did not have the time to go into this interesting and very important topic.  Here are few things for you to consider: 

1) There are numerous adjuvants in the market.  Thus, almost impossible for UGA weed scientists to adequately test all of them.  I could have spent my whole career just testing adjuvants.  

2) Generally, adjuvants can be put into 3 categories including non-ionic surfactants (NIS), oils [crop oil concentrates (COC) or methylated seed oils (MSO)], and fertilizers [usually dry or liquid ammonium sulfate (AMS) or liquid urea-ammonium-nitrate (UAN)].

3) All POST herbicide labels will have a section on recommended adjuvants. 

4) Generally (not always), COC/MSO adjuvants will cause more crop injury and provide slightly better weed control than NIS adjuvants.

5)  Many COC's are actually made from petroleum oils while MSO's are made from vegetable oils (soybean or sunflower).  Both types contain 80-85% oil + 15-20% surfactant. High surfactant oil concentrates (HSOC) contain at least 50% oil + 25-50% surfactant.

6) In my own herbicide testing program, I routinely use Induce (NIS) or Agri-Dex (COC) from Helena unless somebody asks/provides something special.  For over 25 years, both of these have worked just fine for me.  

Induce: https://s3-us-west-1.amazonaws.com/agrian-cg-fs1-production/pdfs/Induce_Label1g.pdf

Agri-Dex: https://s3-us-west-1.amazonaws.com/agrian-cg-fs1-production/pdfs/Agri-Dex_Label1i.pdf

7) Historically, North Dakota State University (NDSU) has been one of the leading land-grants that regularly tests herbicide adjuvants. I included some very good information about adjuvants from the 2023 NDSU Weed Control Guide (W253-23) in the e-mail that I sent to you regarding this specific blog. This info would make a great edition to your "truck" reference materials.

2023 NDSU Weed Control Guide (https://www.ndsu.edu/agriculture/sites/default/files/2022-12/223214_Weed_Color.pdf)

8) Another good resource for herbicide adjuvants is the Compendium of Herbicide Adjuvants.  This publication used to be updated yearly but is no longer.  The latest edition (2016) can be found at the following web-address:  https://mssoy.org/uploads/files/herb-adjuvants-purdue-siu.pdf 

9) If someone is using an adjuvant in your county that you would like to see researched more thoroughly, I can try to fit it into my testing program.  This may or may not happen given my time and space constraints.