Row Pattern, Burial Depth, and Tillage Effects on Tropical Spiderwort/Benghal Dayflower (Prostko)

At the recent UGA Weed Science Agent Training on December 5, I was asked for more specific data regarding the effects of row spacing, burial depth, and tillage on tropical spiderwort/Benghal dayflower (TSW/BDF).   For those wanting to know, here you go.

1) TSW/BDF control in peanut is better with twin rows.

2) TSW/BDF emergence is significantly reduced with deeper burial depths.  No emergence of TSW/BDF occurred at a depth of ~4.8".

3) TSW/BDF control is better in conventional tillage (moldboard plow) systems.

4) TSW/BD dayflower seed viability was < 2% when buried for 36 months at a depth of 8".

Wheat Circular is Ready! (Culpepper)

The 2018/2019 wheat weed control circular is ready. For those not familiar with the circular, it is a two page laminated handout with a programs approach for controlling ryegrass and wild radish in wheat. If you would like a copy prior to it being uploaded on the UGA Weed Science web-site (www.gaweed.com) in January of 2019 do the following: Email 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.


Vegetable weed management laminated circulars will be provided at the Vegetable conference in Savannah.

Cotton weed management laminated circulars will be delivered to you and your growers during your weed meeting. If I am not visiting your county for a weed meeting or UPW meeting then let me know and I will send them through the cotton team when they visit.

Dicamba Registration Update (Culpepper)

Agents, please refer below to last nights (Oct 31, 2018) EPA press release regarding dicamba registration for 2019 and 2020.  Additionally, MAKE SURE you attend the weed science training Prostko has set up in Tifton on December 5.  In addition to our normal training approach, we will have two special speakers coming in to talk about auxin labeling/training in GA for 2019 as well as how Extension should handle pesticide drift calls/cases.

--------------------------------------------------------------------------------------------------------------------------------

EPA Announces Changes To Dicamba Registration

WASHINGTON (October 31, 2018) – Today, U.S. Environmental Protection Agency (EPA) announced that it is extending the registration of dicamba for two years for “over-the-top” use (application to growing plants) to control weeds in fields for cotton and soybean plants genetically engineered to resist dicamba. This action was informed by input from and extensive collaboration between EPA, state regulators, farmers, academic researchers, pesticide manufacturers, and other stakeholders. 

“EPA understands that dicamba is a valuable pest control tool for America’s farmers,” said EPA Acting Administrator Andrew Wheeler. “By extending the registration for another two years with important new label updates that place additional restrictions on the product, we are providing certainty to all stakeholders for the upcoming growing season.”

The following label changes were made to ensure that these products can continue to be used effectively while addressing potential concerns to surrounding crops and plants:

Dicamba registration decisions for 2019-2020 growing season

·         Two-year registration (until December 20, 2020)

·         Only certified applicators may apply dicamba over the top (those working under the supervision of a certified applicator may no longer make applications) 

·         Prohibit over-the-top application of dicamba on soybeans 45 days after planting and cotton 60 days after planting

·         For cotton, limit the number of over-the-top (OTT) applications from 4 to 2 (soybeans remain at 2 OTT applications)

·         Applications will be allowed only from 1 hour after sunrise to 2 hours before sunset

·         In counties where endangered species may exist, the downwind buffer will remain at 110 feet and there will be a new 57-foot buffer around the other sides of the field (the 110-foot downwind buffer applies to all applications, not just in counties where endangered species may exist)

·         Clarify training period for 2019 and beyond, ensuring consistency across all three products

·         Enhanced tank clean out instructions for the entire system

·         Enhanced label to improve applicator awareness on the impact of low pH’s on the potential volatility of dicamba

·         Label clean up and consistency to improve compliance and enforceability

The registration for all dicamba products will automatically expire on December 20, 2020, unless EPA further extends it.  EPA has reviewed substantial amounts of new information and concluded that the continued registration of these dicamba products meets FIFRA’s registration standards. The Agency has also determined that extending these registrations with the new safety measures will not affect endangered species.

Learn more: https://www.epa.gov/ingredients-used-pesticide-products/registration-dicamba-use-genetically-engineered-crops

Do Harvest-Aid Applications of Paraquat Reduce Soybean Seed Germination? (Prostko)

Historically, glyphosate has always been a no-no for use as a harvest-aid in soybeans grown for seed because of its potential negative effects on seed germination.  But, what about paraquat?

Since I have never conducted any harvest-aid research, I would not really consider myself an "expert" on this subject.  I can only go by what I read and who I talk to (usually my weed science colleagues who work more on soybeans).  Also, hope that we can all agree that we are never too old to learn new stuff.   A few thoughts about this paraquat/soybean seed germination issue:

1) A quick review of the published literature is as follows:

a) Whigham, D.K. and E.W. Stoller.  1979.  Soybean desiccation by paraquat, glyphosate, and ametryn to accelerate harvest.  Agronomy Journal  71(4):630-633.

"Paraquat applied 4, 3, or 2 weeks before harvest did not affect soybean seed germination."

b) Cerkauskas, R.F., O.D. Dhingra, J.B. Sinclair, and S.R. Foor.  1982.  Effect of three desiccants on soybean (Glycine max) seed quality.  Weed Science 30:484-490.

"Paraquat applied at R7 stage (50% defoliation) caused 16% to 29% reductions in soybean seed germination, depending upon cultivar and seed germination test (potato dextrose agar or rolled celluose towels).

c) Ratnayake, S. and D.R. Shaw.  1992.  Effects of harvest-aid herbicides on soybean (Glycine max) seed yield and quality.  Weed Technology 6:339-344.

"Paraquat had no effect on soybean seed germination when applied at R5 (beginning seed), R6 (full seed), R7 (beginning maturity), or R8 (full maturity) stages of growth."

2) I did not realize this but the Gramoxone SL 2.0 paraquat formulation (Syngenta) has a label for use on soybeans grown for research, field trials, and seed production.  This label includes a 3 day PHI which is very different from the regular soybean harvest-aid PHI label of 15 days. Other commercial formulations of paraquat, including Firestorm (Arysta), Parazone (AMVAC) and Helmquat (HELM Agro), do not have this harvest-aid/soybean seed production use on their current labels.  

Gramoxone SL 2.0 Label (check out page 41)
https://s3-us-west-1.amazonaws.com/www.agrian.com/pdfs/Gramoxone_SL_2.0_Label1q.pdf

3) Dr. Wilson Faircloth, Syngenta's local Agronomic Services Representative, provided the following information about this subject:

“The PHI for soybean grain is set to avoid paraquat residue in grain.  The application for soybeans grown for research or seed does not allow seed to enter grain channel, these soybeans must not enter normal grain channel.  So if the question is around concerns over impact on seed germination, neither application will cause a problem with germination when applied to mature seed.”

Weed Science Update - August 21 (Prostko)

A couple of things you might find of interest:

1) A local crop consultant recently sent me this picture of prostrate globe amaranth (Gomphrena celosioides).  I have never seen this plant before and for the record, Dr. Mark "The Czar" Czarnota (UGA-Griffin Campus) identified it for me.  It is a member of the Amaranthaceae (pigweed) plant family.  For more general information about this weed, please refer to the following link: http://wssa.net/wp-content/uploads/Gomphrena-celosioides.pdf

2) Had a peanut grower ask me if 2,4-DB applied to large sicklepod plants would have any effect on seed production.  A quick review of the literature would suggest that 2,4-DB applications made at the initial flower to peak flower stages of growth will cause significant reductions in the number of sicklepod seed produced.  However, applications before or after that time have no effect on seed production (only initial flower and peak flower seed numbers were statisicially different than the NTC-none).

Reductions in Grass Control in 2018? (Prostko)

Getting plenty of calls about perceived reductions in grass control after applications of ACC-ase inhibiting herbicides, such as Select (clethodim) or Poast (sethoxydim), have been applied.  Some folks first reaction to this "lack" of control is that we suddenly have widespread ACC-ase resistance.  When its comes to the issue of resistance, I will never say never.  But, before traveling down that bumpy road, I would like for you and your growers to consider the following:

1) Currently, only 2 grass species have been "officially" confirmed to have evolved ACC-ase resistance in Georgia including large crabgrass and Italian ryegrass. Scientific confirmation of herbicide resistance takes lots of time, manpower, and greenhouse space.

2) Labeled heights for optimum control of various common grasses with Select, including crabgrass, Texas panicum crowfootgrass, and goosegrass, are 2"- 6".  

3) The following is some data illustrating the effect of Select rate and timing on the control of goosegrass.  Please note that goosegrass control was reduced by 16-23%, depending upon rate, when applied at the 4-6 tiller stage of growth.

Figure 1.  Goosegrass control with Select applied at different rates and timings.

4) If Cadre (imazapic) was applied prior to the grass herbicide application, it is very likely that grass control will be reduced.   Research has shown that Cadre can reduce the photosynthetic rate of goosegrass which then reduces the sensitivity of the ACC-ase enzyme to clethodim (Burke and Wilcut.  2003.  Physiological basis for antagonism of clethodim by imazapic on goosegrass.  Pesticide Biochemistry & Physiology) 

5) At this time of the year, peanut plants are kinda tall (> 12").  Thus, any grass plants peaking out of the top of the peanut canopy are not likely to be adequately controlled due to size and coverage issues.

6) Before dropping the R-bomb, please double-check use rates, stages of growth, adjuvants, rain-free periods, and field history.  The threat of herbicide resistance is definitely real but it does not happen in one night.

Peanut Tank-Mix Thoughts (Prostko)

     Rain delays and/or late planting have resulted in continual inquiries about peanut herbicide + fungicide tank-mixes and their potential effects on weed control and crop injury. UGA will never be able to adequately address all concerns with 90,000+ potential tank-mixtures in peanuts.   Here is a quick review of some of the published data:

1) When 2,4-DB is tank-mixed with a postemergence graminicide, grass control can be reduced by 8% to 15% approximately 45% of the time.

2) When averaged across 5 grass species, Cadre (imazapic) + Select (clethodim) tank-mixtures provided 19% less effective grass control than Select alone.

3)  Abound (azoxystrobin), Absolute (tebuconazole + trifloxystrobin), Bravo (chlorothalonil) and Headline (pyraclostrobin) are 4 fungicides that have caused significant grass antagonism when tank-mixed with Select (~12% to 30% reductions in grass control).

4) Grass efficacy with Poast (sethoxydim) and Select has not been consistently reduced by tebuconazole (various trade names including Folicur, Orius, TriSum, Integral, Ebustar, Muscle, Tebuzol).  However, when reductions have been significant, grass control was reduced by 4% to 13% with tebuconazole mixes.

5) Palmer amaranth (PA) control was not reduced when 2,4-DB was tank-mixed with Bravo, Provost (prothioconazole + tebuconazole), Headline, or Absolute.  But, 2,4-DB is not that great on PA anyway though?

6)  Sicklepod control with 2,4-DB was reduced by 14% when applied with Abound but not with Bravo or tebuconazole.