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.   

Post-Harvest Weed Control Questions (Prostko)

Still getting a few calls about post-harvest weed control.  Here are a few questions and answers for you regarding post-harvest weed management:

1) What's the best option to control volunteer corn (up to 12" tall)?

Select Max 0.97EC @ 6 oz/A or Select 2EC (clethodim) @ 4 oz/A (or generic equivalents) + COC @ 1% v/v.  I have never had much success controlling volunteer corn with either Liberty (glufosinate) or Gramoxone (paraquat).  Don't forget that many of the corn hybrids grown in Georgia today are RR+LL.  The plant-back restriction for wheat after clethodim is 30 days.  A hard freeze also works well with no plant-back restrictions.

2) Can you control Benghal dayflower/tropical spiderwort with 1 herbicide application?

NO! 2 applications (14 days apart) of either Gramoxone, Aim (carfentrazone), or 2,4-D will be required. Dicamba is NOT recommended for the control of this weed.

3) What is the plant back restriction for wheat after an application of dicamba?

All depends upon the application rate (0.25 lb ae/A = 15 days; 0.50 lb ae/A = 30 days).

4) What is your favorite post-harvest treatment?

I have had good success controlling many post-harvest weeds in my field corn plots, including volunteer corn, with the combination of Gramoxone + Tricor (metribuzin).  But, small grains are not a viable rotational crop option after this one.  Gramoxone + Tricor is much more effective on volunteer corn than Gramoxone alone.  Check out the link and picture below: 

https://s3-us-west-1.amazonaws.com/agrian-cg-fs1-production/pdfs/TriCor_4F_2EE1.pdf

5) Will late-season applications of glyphosate have an influence on weed seed viability/germination next year? 

Generally, glyphosate will only affect weed seed viability/germination if applied around flowering or initial seed set.  Later applications will have little effect on weed seed viability/germination for next season.  

6) Any additional info in 2022 UGA Pest Control Handbook about this topic?

Yes, more specific information can be found on pages 74 (tropical spiderwort) and 86 (Palmer amaranth). 

Peanut Weed Control: Success or Failure?

Check out this picture I took yesterday from one of my weed control studies at the UGA Ponder Farm.  I think you would agree that it looks pretty good at 83 DAP.

Figure 1.  Peanut weed control plots at UGA Ponder Farm (Ty Ty, GA) on July 24, 2023. 83 days after peanut planting (DAP).  No rainfall or irrigation until 8 DAP and 17.92" of total rainfall from May 1 - July 24 (6.86" above long-term average). PRE – Applied 1 DAP; POST – Applied on May 25, 2023 - 22 DAP (Cadre + 2,4-DB + Cobra + Dual Magnum).  Weed-free at planting/twin rows. 

How did I make this happen?

1) I started clean and planted in twin rows.

2) Since I did not get to apply any irrigation until 8 DAP due to an irrigation pump problem, I pulled the trigger early on my POST treatment (22 DAP) and also added Cobra to that treatment. 

3) Spraying weeds when they are smaller in size, works almost 100% of time!  In my opinion, timeliness trumps (or desantiss?) GPA, nozzle type, tractor speed, and boom height.  The effects of these other factors on spray coverage are more critical when herbicides are applied to bigger weeds.  

4) Take a quick look at the Cadre (imazapic) label (https://s3-us-west-1.amazonaws.com/agrian-cg-fs1-production/pdfs/CadreR_Herbicide_Labelp.pdf). With the exception of cocklebur and rhizome johnsongrass, maximum labeled heights for all weeds listed are 4" or less.  A recent growth chamber study conducted on sicklepod control with Cadre indicated 16% less control of sicklepod when Cadre was applied at 6" vs 3" (remember that herbicides always work better in the greenhouse or growth chamber).

5) POST treatments in all my peanut tests are applied in 15 GPA, 3.5 MPH, 20" boom height, and with AIXR11002 nozzles (coarse droplets, 402 VMD50). 

6) It has been well documented that lower GPA's (10 GPA), faster operating speeds (>10 MPH), higher boom heights (>24"), and extremely coarse/ultra coarse spray droplets (i.e. dicamba tips) provide less spray coverage.   

What does this mean for the grower, especially when behind, treating larger weeds, and needing to get better spray coverage?

a) Regardless of any application tweaks, weed control expectations should be lower.  I have never been able to consistently control large weeds in my 37 year weed science career.  Every once in awhile, there are a few exceptions (i.e. bristly starbur/goathead/Texas sandspur and Strongarm).

b) Apply herbicides in 15 GPA.

c) Avoid using nozzle/pressure combos that produce extremely coarse or ultra coarse droplets (VMD50 > 502).

d) Reduce tractor speeds and boom heights as much as possible/practical.

e) Use full labeled rates.

Tank-Mixes, Perennial Weeds, and Pink Purslane (Prostko)

 A few things for you to chew on:

1)  The following are some pictures of a few peanut tank-mixes that I observed over the last few weeks that were not included in previous slides I sent you.  Nothing too scary here.

2)  Last week, I received numerous inquiries about controlling broadleaf perennial weeds in peanut (dogfennel, horsenettle, maypop passionflower, heliotrope, etc.).  None of the herbicides we have in our peanut arsenal work well on these types of weeds.  Growers who have perennial weeds in their peanut fields might consider the following:

a) If perennial weeds are in small spots and growers are willing to sacrifice the peanuts in those spots, they can be spot treated with a high rate of glyphosate (i.e. Roundup PowerMax3 5.88SL @ 44 oz/A or equivalent).  

b) In the fall after harvest, allow perennial weeds to regrow then treat fields with a high rate of glyphosate (same rate as above).  This fall application of glyphosate must be be applied at least 2 weeks before first frost.  Then in the spring of next year, plant RR-field corn or Xtend soybeans/cotton and plan on using a POST combination of glyphosate + dicamba in those crops.

c) It will take multiple years of fall + spring applications of glyphosate to get perennial weeds under control.  It took more than 1 year for these weeds to become a problem and will take more than 1 year to get them under control.

d) Avoid planting peanuts in fields with known populations of perennial weeds.

3) Pink purslane has been a bur under my saddle for many years.  Consequently, my PhD graduate student (Nick Shay) is conducting POST control studies as part of his dissertation.  Nick already completed 2 trials in the greenhouse last fall and 1 field trial this summer.  The following are the recent results of the field trial that he conducted.  Surprisingly, only Aatrex (atrazine) and Cobra (lactofen) were effective in this POST trial.  This field trial will be repeated again later this summer.

Wet Weather Concerns - Part II (Prostko)

Much of Georgia continues to get hammered with frequent rainfall events.  When will it end? Here are some answers to questions you might be getting: 

1) How much has it rained?

Updated rainfall totals from June 12-June 21, 2023

2) What's my best peanut weed control recipe for a disaster field?

a) Apply Select 2EC (clethodim) @ 8-16 oz/A + COC @ 1% v/v then

b) 3 days after the Select application, apply the following combination:  Cadre @ 4 oz/A + Cobra @ 12.5 oz/A + 2,4-DB @ 16 oz/A + any Group 15 herbicide (either Anthem Flex @ 3 oz/A or Dual Magnum @ 16 oz/A or Outlook @ 12.8 oz/A or Warrant @ 48 oz/A or Zidua SC @ 2.5 oz/A).  Include NIS @ 0.25% v/v when using Anthem Flex, Warrant, or Zidua.

c) Costly for sure but desperate times require desperate measures! 

3) Can I also add Strongarm to that mix?

Yes, I did that in 2022 to clean up a peanut field and observed no major problems. Check out the following pics:

4) Is there a shortage of Cobra (lactofen)?

I have heard from several growers that Cobra was not available.  I contacted my inside sources at Valent and this situation should be remedied.   A e-mail quote from my Valent contact yesterday: "Cobra being shipped this week so no excuses moving forward!"

5) Can peanut herbicides be applied aerially by plane or drone?

The short answers is yes (but not Cadre. It does not have an aerial application label) but I have some concerns.  I have been conducting weed control research since 1987.  During this 36 year time frame, I have never applied herbicides in water volumes less than 10 GPA. Coverage, crop injury, and efficacy are my concerns.  There is a ton of work being conducted with drones but I have not seen a sufficient amount of replicated university data to confirm true weed control efficacy.  But in this current rainy situation, perhaps something is better than nothing??????

6) What are the minimum labeled GPA requirements for aerial applications of peanut herbicides?

Butyrac 200 (2,4-DB) = 5 GPA; Classic = 3 GPA; Cobra = 7 GPA; Gramoxone = 5 GPA; Select = 3 GPA; Storm = 5 GPA; Ultra Blazer = 5 GPA 

7) Is Classic still available for late-season Florida beggarweed control in peanuts?

Yes! Check out page 224 in 2023 UGA Pest Control Handbook for updated information about peanut cultivar tolerance to Classic.

https://secure.caes.uga.edu/extension/publications/files/pdf/SB%2028-24_1.PDF

8) Is Gramoxone (paraquat) still labeled for use in peanuts in a non-selective applicator such as a rope-wick or weed wiper? 

Yes!  Check out page 224 in 2023 UGA Pest Control Handbook. Gramoxone applied in this fashion is very effective on Palmer amaranth, Florida beggarweed, and sicklepod.

https://secure.caes.uga.edu/extension/publications/files/pdf/SB%2028-24_1.PDF

For more info:

TopCrop Super Sponge: https://www.smucker.net/weed-wiper-products

GrassWorks Weed Wiper:  https://grassworksmanufacturing.com/

LMC-Cross Wick-Bar: https://www.lmcag.com/

Dayflower Control in Peanut (Prostko)

Here are some quick pics from data collected earlier today about spreading (?) dayflower control in peanuts from our strip-plots in Berrien County (Thanks Gentle Ben and Nick Shay!).  Generally, these are the same herbicide treatments that I typically recommend for tropical spiderwort/Benghal dayflower control as well.  Note that Cadre + Dual Magnum was no bueno!  FYI, Broadloom is a generic formulation of Basagran (bentazon) from UPL (https://s3-us-west-1.amazonaws.com/agrian-cg-fs1-production/pdfs/Broadloom_Label1i.pdf).

Wet Weather Concerns (Prostko)

Over the past few days, many locations in south Georgia have received significant rainfall (Figure 1). 

Figure 1.  Georgia Rainfall (June12-June15, 2023)

A few things to think about:

1) Keep an eye on rain-free periods for postemergence (POST) herbicides.  For my crops, these are listed in the UGA Pest Control Handbook (Remarks and Precautions).  If I am missing one, please let me know.

2) Cool, cloudy, wet weather has a significant influence on the cuticles of plant leaves (i.e. makes them thinner).  Thus, pesticides applied during this type of weather can cause more crop injury symptoms.

3) Residual weed control will likely be compromised (shorter than normal).  Applications of additional residual herbicides should be strongly considered  (Anthem Flex, Dual Magnum, Outlook, Warrant, Zidua).

4) It is also very likely that some growers will not be able to get back into their fields on a timely basis to make POST herbicide applications.  There are no POST herbicides, in any of my crops, that can consistently control a pigweed that is bigger than about 3-4" tall.  Thus, applying herbicides to very large weeds (revenge spraying) is a waste of time and money!  Hand-weeding, mechanical cultivation, non-selective applicators, and mowing are the only effective options for large weeds.

5) Since applications of POST herbicides will be delayed, experience tells me that many growers will want to apply broadleaf and grass herbicides together.  Tank-mixing grass herbicides with broadleaf herbicides (Cadre + Select or 2,4-DB + Select), is labeled/legal but will often result in reduced grass control (~10-20%).  Growers can increase the rate of the grass herbicide (within label) but I prefer a split application (grass herbicide first then broadleaf herbicide ~3-5 days later).