Agent Training Follow Up (Prostko)

Just a few things to follow up on after our recent weed science training on December 2:

1) If you are looking for something to help you better understand herbicide modes of action (MOA), check out the Herbicide Resistance Action Committee's (HRAC) 2020 MOA Classification Chart.  A good one for your pickup truck library.

https://hracglobal.com/files/HRAC_Revised_MOA_Classification_Herbicides_Poster.pdf

2) We had some discussion about the potential residual effects of glyphosate on crops and some of the research that we are conducting.  It's a very complicated issue influenced by many factors (soil type, OM, pH, other soil cations, application rate, timing, species sensitivity).  However, I am not really worried about the residual effects of glyphosate on most major row crops grown in Georgia.  

I was asked specifically about the effects of soil pH on the adsorption of glyphosate.  In general, as soil pH increases, soil adsorption of glyphosate decreases (Figure 1).  This also happens with herbicides in other families such as the triazines (atrazine) and sulfonylureas (chlorimuron).  But, just because glyphosate adsorption is decreased as soil pH increases, it does not automatically mean it will cause excessive crop injury. 

 

Wheat Weed Management Circular for 2020-2021 (Culpepper and Vance).

Agents, our wheat weed control circular is finalized. For the most part, it remains very similar to last seasons except that we have added Axial Bold and updated our recommendations in regards to a large amount of research with Quelex.

If you would like a copy, e-mail Jenna Vance at jcsmith3@uga.edu and ask for one of the following options:

Option 1: Request laminated circulars to be mailed to you. Provide the number of circulars that you would like and provide and address to send them.

Option 2: Request a pdf version.  An email response will provide the PDF as an attachment.

Dicamba Update (Culpepper)

Extension agents, I am optimistic that we are nearing a decision by our U.S. EPA regarding registrations for XtendiMax, Engenia, FeXapan, and Tavium and their potential uses for 2021. We certainly need to thank the EPA for the tremendous effort that they have invested in this challenging process. As I have shared several times, I am optimistic that labels will be approved for use in dicamba-tolerant cotton and soybean but I am also concerned about additional restrictions that may be added to labels challenging our farmers……….of course, that is just my guess. We will have in-depth discussions regarding this topic at our Using Pesticide Wisely training platform for 2021 and at our annual extension weed training on Dec 2………….make sure you attend! Of course, Prostko is organizing the training so send him an e-mail if you have questions or thoughts.

"New" Field Corn Herbicides for 2021 (Prostko)

In the last few weeks, I have seen some publicity about potential “new” herbicides in field corn.  In many cases, these “new” herbicides are not really new just a new pre-mix of older active ingredients.  The following table summarizes a few of these “new” field corn herbicides that growers might be asking you about for use in 2021.  FYI, none of these herbicides will appear in 2021 UGA Pest Control Handbook because I currently do not have enough data to support their widespread use.  It is the general practice of the UGA Weed Science Team to collect at least 2-3 years of solid data before a new product in "officially" recommended in the Pest Control Handbook.   

Company	Trade Name	Active Ingredients	WSSA MOA	Label
AMVAC	Sinate™	glufosinate + topramezone	10 + 27	https://s3-us-west-1.amazonaws.com/agrian-cg-fs1-production/pdfs/Sinate_Label1.pdf
	Impact Core™	topramezone + acetochlor	27 + 15	https://s3-us-west-1.amazonaws.com/agrian-cg-fs1-production/pdfs/Impact_CORE_Label.pdf
Summit Agro USA	Shieldex®	topyralate	27	https://www.summitagro-usa.com/wp-content/uploads/2019/09/SHIELDEX-400SC-Herbicide-Label.pdf
Syngenta	Acuron GT	bicyclopyrone + s-metolachlor + mesotrione + glyphosate	27 + 15 + 9	Not yet labeled

Here are few pictures of these products from my field research in 2020 (click on pictures to make them larger):

 

Late-Season Applications of Glyphosate and Weed Seed Production (Prostko)

Now that many growers are finishing up with field corn harvest, I have been getting lots of questions about the potential effects of late-season applications of glyphosate on the production of weed seed. Very glad to see that growers/agents are thinking about this issue.  Preventing weed seed-rain back into a field is a great long-term strategy for improving future weed control programs.  

Bottom line on this issue is that late-season applications of glyphosate can be very helpful in reducing weed seed production BUT ONLY IF APPLIED AT THE RIGHT TIME!  

Check out Figures 1 & 2.  You will note that glyphosate applications only reduced weed seed production when applied early.  Generally, glyphosate applications made to plants with maturing seed were not as effective and would likely be a waste of time and money.  

Many weeds in Georgia fields after corn harvest might already have maturing or mature seed.  Thus, growers (with the help of their local county extension agent) should look very closely before blindly applying glyphosate with the sole hope of reducing weed-seed rain.  

How much 2,4-DB can be applied in peanuts? (Prostko)

2,4-DB is a very popular and inexpensive peanut herbicide that is used on at least 35% of the acres in GA.  There are a few labels out there and use rates/time of application/PHI vary depending upon the specific label.  The following is a general summary of the 2,4-DB labels that I could find on the Agrian web-site (https://home.agrian.com/):

 

Product	Manufacturer	Rate/A (oz)	Time of Application	Total # Applications /Year	PHI (days)
2,4-DB 175	Winfield	16.0-28.0	No later than late bloom (90-100 DAPb)	2	60
2,4-DB 175	ACETO	16.0-28.0	No later than late bloom (90-100 DAP)	2	60
2,4-DB 200	Winfield	12.8-16.0	2-12 WAPa	2	60
2,4-DB 200	ACETO	14.4-25.6	No later than late bloom (90-100 DAP)	2	60
Butyrac 175	Albaugh	14.4-17.6	2-12 WAP	2	45-60
Butyrac 200	Albaugh	12.8-16.0	2-12 WAP	2	45-60
2,4-DB DMA 175	Drexel	14.4-17.6	2-12 WAP Do not apply later than 100 DAP	2	60
2,4-DB DMA 175	Drexel	12.8-16.0	2-12 WAP Do not apply later than 100 DAP	2	60

^aDAP = days after planting; ^bWAP = weeks after planting.

Peanut Weed Control Update - June 30 (Prostko)

Just a few comments based upon recent phone calls/texts/e-mails:

1) Be on the lookout out for pink purslane (Portulaca pilosa).  Best options for control at this time are either Ultra Blazer or Cobra (yes, these herbicides will burn peanuts). Do not spray Ultra Blazer or Cobra if peanut plants are 60-75 days old.

 

2) Select (clethodim), or Poast (sethoxydim), or Fusilade DX (fluazifop-P) for POST grass weed control? Is one better than the other? For whatever reason, many GA growers seem to prefer Select or generic Clethodim over the other grass herbicides.  What do I think?  Check out a summary of these previous peanut weed control studies:

a) Grichar, W.J.  1991.  Control of Texas panicum (Panicum texanum) and southern crabgrass (Digitaria cilaris) in peanuts (Arachis hypogaea) with postmergence herbicides.  Peanut Science 18:6-9.

    

    - EPOST applications (1-6" tall grass) of clethodim, fluazifop-P, and sethoxydim provided similar control of Texas panicum (>88% control).

    - In 1 of 2 years, control of southern crabgrass with EPOST applications of fluazifop-P was lower than with either clethodim or sethoxdim. 

b) Wilcut, J.W.  1991.  Efficacy and economics of common bermudagrass (Cynodon dactylon) control in peanut (Arachis hypogaea).  Peanut Science 18:106-109 

    - Split applications (21 days apart) of either sethoxydim (0.28 + 0.14 lb ai/A), fluazifop-P (0.19 + 0.10 lb ai/A). or clethodim (0.25 + 0.25 lb ai/A) provided at least 90% control of common bermudagrass. 

c) York, A.C., J.W. Wilcut, and W.J. Grichar.  1993.  Interaction of 2,4-DB with postemergence graminicides. Peanut Science 20:57-61.

    - At 28 DAT, clethodim provided 98% control of broadleaf signalgrass, sethoxydim provided 97% control of broadleaf signalgrass, and fluazifop-P provided 92% control of broadleaf signalgrass.

d) **Please review page 233 of 2020 UGA Pest Control Handbook for a summary of peanut grass herbicides.  

3) Check out these new pictures from my research plots taken earlier today.  I observed no differences between Sonalan or Prowl.  Also observed no differences between Anthem Flex/Dual Magnum/Outlook/Warrant/Zidua programs.  

 

4) As always, I am readily available for any formal or in-formal field visits upon request (FYI, I will be on vacation from July 11-18).