Post-Harvest (Field Corn) Weed Management Reminders (Prostko)

Field corn harvest is well underway in much of south Georgia.  Please remind your growers that it is a great idea to think about managing weeds such as Palmer amaranth and Benghal dayflower at this time of year.  Remember that Palmer amaranth seed is viable within ~2 weeks after pollen shed and Benghal dayflower can go from seed to seed in about 42 days.  Thus, there is ample time to produce lots of seed in those harvested corn fields from now until first frost.  Check out the UGA Pest Control Handbook (pages 74 and 86) for more specific information.

 https://secure.caes.uga.edu/extension/publications/files/pdf/SB%2028-15_3.PDF

a) For growers who will not be planting a small grain this fall, here is one of my favorite post-harvest treatments.  The rate for Gramoxone 3SL (paraquat) would be 32 oz/A. Tricor = metribuzin.

b) For those fields that are plagued by Benghal dayflower, splits shots (7-14 days apart) of either Gramoxone or 2,4-D.

Recent Peanut Problems (Copperleaf, Roundup, Mixing Order, 2,4-DB Rain-Free Period) - Prostko

A few interesting things that crossed my path over the last few weeks:  

1) From Macie Mosteller in Turner County.  Hophornbeam copperleaf in peanut.  Way too big now for herbicides (but not hands or hoes).  Ultra Blazer (acifluorfen) and Cobra (lactofen) are 2 POST control options for smaller copperleaf plants.  Check out this older fact sheet for more info about hophornbeam copperleaf in peanut:

https://secure.caes.uga.edu/extension/publications/files/pdf/C%20882_5.PDF

2) From former legendary Dodge Co. Agent Greg Slaughter (now with RW Griffin).  Roundup (glyphosate) contamination on peanut.  Grower sprayed Cadre (imazapic) + 2,4-DB + Basagran (bentazon) + Dual Magnum (s-metolachlor) + COC.  Sadly, this happens a lot (too much) in south Georgia.  Tissue samples sent to Waters Lab in Camilla confirmed the presence of glyphosate (0.3 ppm). How did it get there? Jug management????? Check out this older fact sheet for more info about peanut tolerance to glyphosate:  

https://archive.ces.ncsu.edu/wp-content/uploads/2014/10/PEANUT-NOTES-No.-104-2014-UGA-Glyphosate-on-Peanut.pdf?fwd=no

3) From Bill Tyson in Bulloch Co. The tank-mix blues strike again! Mixing order is important!! A slight change in mixing order helped fix this problem.  Check labels for proper mixing orders. Tons of good info in those labels!

4) It has come to my attention that the rain-free period for 2,4-DB listed in the peanut section of the 2025 UGA Pest Control Handbook of 1 hour (page 222) is NOT correct.  Not sure where I came up with the 1 hour since nothing specific is listed on any label nor is it consistent with other sources? After talking with technical folks at Albaugh, LLC (makers of Butyrac 175 or Butyrac 200), the rain-free period for 2,4-DB should be 6 hours.

Florida Beggarweed in Peanut (Prostko)

I was texted the following picture (slightly blurry) early yesterday morning from a SW-GA crop consultant.  He commented that it was all over the field.

This is Florida beggarweed (kidney-shaped cotyledons).  When I first got to GA in 1999, Florida beggarweed was the #1 peanut weed.  It became less troublesome when Valor (flumioxazin) was registered in 2001 (very effective) and when Palmer amaranth exploded. Florida beggarweed tends to be a later emerging weed and prospers during wetter conditions. 

At this point in the growing season, there are not many good options for controlling Florida beggarweed in peanut. The first option is a POST (60 days after peanut emergence) application of Classic (chlorimuron).  The other option is to use Gramoxone (paraquat) in a non-selective applicator (wiper, sponge, rope-wick).  Both of these options are described on page 224 of the 2025 UGA Pest Control Handbook and/or listed below. Please carefully read the comment sections of these recommendations.  Peanut cultivar tolerance to Classic is a major concern.  If a newer peanut cultivar is not listed in the comment section (i.e. Arnie, TifNV-HG, etc.), that means I DO NOT have any tolerance data and have no clue what will happen.

For the Doubting Thomas (Prostko)

Here is a quick picture from my research plots earlier today.  Further proof that herbicides work well when applied on time.  Generally, I do not have any preference for what Group 15 herbicide is used in this EPOST + POST program (Anthem Flex, Dual Magnum, Enversa, Outlook, Warrant, or Zidua).  But, I would prefer that our growers not tank-mix Anthem Flex with Cadre + Cobra + 2,4-DB (POST) at this time (i.e., I need more data).  Also, please keep in mind that these are average prices and prices may be more or less depending upon the grower.  

If you need more info about herbicide mechanisms of action (Groups), check this out from the Weed Science Society of America:

https://wssa.net/wp-content/uploads/WSSA-Mechanism-of-Action.pdf

More Tank-Mix Stuff (Prostko)

 1) Here is a quick picture of a recent peanut tank-mix from JB in Wilcox Co. that was applied without a hitch. I would welcome more pictures from any County Agent of good and bad tank-mixes.  If you send me a tank-mix picture, try to get planting date, application date, and picture date. 

2) Here is an example why conducting meaningful tank-mix research is nearly impossible.  

Grower Tank-Mix Application:

 

My tank-mix application of same treatment: Looks nothing like what grower saw?

3) This ain't starting clean and no way any soil residual herbicide will work on a large, buried pigweed plants!!!! Notice buried stems/roots.  

Palmer Amaranth Control Update (Prostko)

About 2 weeks ago, I put out a small Palmer amaranth control test in Wilcox Co. with John Bennett and Macie Mosteller.  The goal of the test was to investigate potential PPO-resistance.  About 10 minutes after we were done spraying, it rained 0.7".  I went back to the field 2 days later and re-treated in another area of the field.  Here are a few things that we learned:

a) Sometimes the weatherman is correct.  

  

b) Cobra was rain-fast in those 10 minutes (label says 30 minutes) but Gramoxone + Ultra Blazer + Basagran + Dual Magnum was not (need 4 hour rain-free period).  FYI, I have most rain-free periods listed in the comment sections of my various chapters in the 2025 UGA Pest Control Handbook.

c) Applications of Cobra made just 48 hours later were significantly less effective.  In that short time period, average Palmer heights went from 3.54" to 5.05".  Using average heights is NOT a great idea because at both application times 30-50% of the measured plants were larger than the average.

d) Had we and the farmer been in the field 7 days earlier (with no rain), I am certain that a "cracking" application of Gramoxone + Ultra Blazer + Basagran + Dual Magnum would have cleaned up this mess.  TIMELINESS is everything!!!

e) Pretty sure that this population of Palmer amaranth is not PPO-resistant since the 1st application of Cobra was effective.  We also sent some plant samples to the University of Illinois Plant Clinic since they can test for PPO-resistance.  Have not received any results at his time.  

https://extension.illinois.edu/plant-clinic

"Cracking" Time - 2025 (Prostko)

Check out this picture taken from my plots earlier today.  A friendly reminder for peanut growers who need an early-postemergence treatment (aka "cracking" spray) in peanut.  Program can be tweaked according to growers preferences/needs/experiences as follows:

1) Grower can replace Ultra Blazer + Basagran (aka "Georgia Storm") with commercial Storm 4SL @ 16 oz/A.  Storm is a pre-mix formulation of Blazer + Basagran.

2) If grower does not want to use any Ultra Blazer, can just use Basagran 4SL (8 oz/A) or Basagran 5SL (6.4 oz/A).

3) If grower does not want to use Dual Magnum, can use the following:  Anthem Flex 4SE @ 3.0 oz/A; Enversa 3ME @ 48 oz/A; Outlook 6EC @ 16 oz/A; Warrant 3ME @ 48 oz/A; or Zidua 4.17SC @ 2.5 oz/A.  Generally, I have no preference.  When using either Dual Magnum or Outlook in this mix, additional NIS (1 qt/100 gals) is not needed.   

The "Program" Works (Prostko)

Here is a picture taken from my peanut plots earlier this morning.  A friendly reminder that "The Program" really works (starting clean, twin rows, moisture activated residual herbicides) and has been for 28 years of peanut weed control research.

Valor Injury Likely (Again) - Prostko

Valor (flumioxazin) was first registered for use in peanut in 2001.  Since that time, we have observed injury symptoms EVERY year across the state.  Thus, it should no longer be a shock or surprise to anyone when it happens.  The current predicted rainfall events over the next few days will likely result in Valor injury in some peanut fields, particularly in fields where peanuts are cracking.  I do not feel the need to reinvent the wheel, so please check out the following previous 6 blogs where I have addressed the Valor/peanut injury issue: 

June 3, 2013: https://ugaweedscience.blogspot.com/2013/06/valor-injury-on-peanut-prostko.html

May 20, 2014: https://ugaweedscience.blogspot.com/2014/05/peanut-injury-update-prostko.html

May 26, 2017: https://ugaweedscience.blogspot.com/2017/05/valor-injury-or-sky-is-falling-prostko.html

May 21, 2020: https://ugaweedscience.blogspot.com/2020/05/valor-injury-on-peanut-is-likely-prostko.html

May 23, 2021:https://ugaweedscience.blogspot.com/2021/05/irrigating-peanut-fields-treated-with.html

May 13, 2023: https://ugaweedscience.blogspot.com/2023/05/valorpeanut-injury-again-prostko.html

**TAKE HOME POINT FOR THE VALOR/PEANUT INJURY ISSUE: VALOR INJURY IS LIKELY BUT YIELD LOSS IN NOT!

Recent Preventable Problems (Prostko)

Here are a few pictures of recent weed science related problems.  Both could have been avoided by reading and following the label. Label recommendations are NOT suggestions.

1) Problem: Reflex 2SL (fomesafen) applied to snapbean in the fall (2024) with field corn planted this spring (2025).  What does label the label say? Crop rotation restriction for field corn after Reflex is 10 months.

2) Problem: Clarifier 4SL (dicamba) @ 8 oz/A applied 3 days before planting soybeans not tolerant to dicamba.  What does the label say?  Following applications of Clarifier and a minimum accumulation of 1" rainfall or overhead irrigation, a waiting interval of 14 days is required for 8 fluid ounces per acre or less, and 28 days for 16 fluid ounces per acre.

Home-Made Halex GT/Cobra and Soybeans (Prostko)

 A couple of things for you to chew on based upon recent questions that I have been getting from growers, consultants, and county agents:

1) Can I make my own Halex GT to save money?

First, let me remind you that Halex GT is a postemergence field corn herbicide from Syngenta that many Georgia growers use.  Halex GT is a pre-mixture of the following active ingredients: mesotrione + glyphosate + s-metolachlor.   In 2025, many growers have figured out that they can make their own version of Halex GT for much less money ($$) using generic formulations of these same active ingredients. However, the big issue is that the s-metolachlor in the Halex GT is not exactly the same formulation as in the generic products.  Thus, there could be some problems with increased corn injury and perhaps even physical compatibility with a home-made mix. In fact, it clearly states on the labels of mesotrione (if you look for it) that there can be some enhanced crop injury when mixing mesotrione with other emulsifiable concentrate (EC) herbicide formulations such as Dual Magnum (s-metolachlor) or Outlook (dimethenamid-P).  I have talked to just a few folks who have made their own Halex GT without any major issues except where overlapping occurred.  However, since I have no personal research to support this practice, I am not recommending growers make home-made Halex GT at this time.  I am in the process of conducting a field trial this summer to address this research issue and reserve the right to change my position in 2026.  Here is a quick summary of what I just discussed:

 

2) Do early postemergence applications of Cobra (lactofen) in soybeans increase yield?

The short answers is HELL NO!  This is a myth that has been permeating around the high-yield grower community for years. There have been several replicated field studies to show there is absolutely no evidence to support this claim.  Please check out this recent white paper (December 2024) from the Mississippi Soybean Promotion Board to access the data summary:

https://mssoy.org/sites/default/files/2024-12/LACTOFEN%20YIELD%20WHITE%20PAPER%20DEC%202024.pdf

3) On a personal note, I am currently dealing with some difficult issues with my aging parents who are both 88 years old.  If you try to reach me and I do not respond in my typical prompt fashion, please also send me a text and I will respond as soon as possible.  Over the last few days, I have had to spend some time in the hospital with my parents but have continued to answer any and all questions that I received via text.  If I can respond to your phone call I will.  If not, assume I am spraying plots (6 am to 9 am) or I am assisting my parents, especially over the next week.  If you have a Charlie Foxtrot situation (youngsters please look this term up), I will prioritize your needs and I am always more than glad to troubleshoot in-person.  Do not hesitate to reach out to me, I will respond!! (229-392-1034).    

Burndown Bummers (Prostko)

Over the last several days, I have received numerous inquiries about the reduced performance of preplant burndown herbicide applications.  Several factors can help contribute to reduced performance of burndown herbicides including application rate (too low?), weed size (too big?), environmental conditions (too cold?), small grain cover crop stage of growth (generally more susceptible prior to boot and after heading), droplet size (too big?), and time (too soon after application?).  

For today, let's just focus on air temperatures.  I like to use a cold temperature threshold of <50 F as a benchmark for when herbicides start to not work like they should,  If you check out Table 1, there have been many days this month below that temperature threshold.  On average, 73% of the days in March at these Georgia locations had low temperatures below 50 F.  In my opinion, this may be one of the main factors that has influenced the performance of some burndown herbicides.  Good news is that the low temperatures forecasted for next week will be above 60 F so that should help improve burndown efficacy.  Although I usually am not a huge fan of using AMS with glyphosate, unless hard water has recently been confirmed with a lab test, I think AMS might help improve glyphosate performance when air temperatures dip below 50 F.  

Beware of Google/AI Answers (Prostko)

Just got an interesting phone call from an established crop consultant. He asked me about the use rate for Sonalan (ethalfluralin) in field corn.  I replied to him that as far as I know, after working in field corn since 1987, that Sonalan was never or is not now labeled for field corn and I that I would never recommend it, especially PPI or PRE.  Remember, Sonalan is a grass herbicide for use in broadleaf crops.  I then asked him where he got his information.  His reply was that I "Googled" it.  If you Google Sonalan and field corn, here is what shows up:

What would I expect if Sonalan was used in field corn?  Stunting, stubby roots, poor stands, excessive lodging, replanting to a labeled broadleaf crop (i.e. soybean or peanut).  A picture of "yellow" herbicide injury on field corn (Source: S. Berger, IFAS).

This is not the first time I have seen an error with a Google/AI search.  Bottom line, growers/consultants/county agents should not be getting weed control recommendations from Google/AI. 

Enlist® Field Corn Weed Control System (Prostko)

Many Georgia growers are very familiar with the Enlist® (i.e. 2,4-D choline) weed control systems for soybean and cotton.  However, I have not talked very much about the Enlist® weed control system for field corn.  This was primarily due to the fact that there was not a good Enlist® corn hybrid adapted for the SE. I recently learned that Pioneer now has one (P13777PWUE).  Check out this 2024 yield data from Pioneer: 

Consequently, some Georgia growers might now be more interested in trying the Enlist® field corn weed control system (on a limited basis).   A few thoughts about this system:

1) I have not conducted very many weed control trials with the Enlist® system.  My weed science research colleague in Athens (Dr. Nick Basinger) has.  Between his work and mine, it looks like a pretty good weed control system.  I will be conducting additional trials this year.  Check out the following picture from a field trial I conducted in 2018: 

2) Enlist® field corn hybrids are tolerant to 4 different herbicides including 2,4-D choline, Roundup® (glyphosate), Liberty® (glufosinate), and Assure® II (quizalofop).

3) P13777PWUE has the following characteristics:   

4) Because of the previous lack of adapted field corn hybrids, I do not have any specific information listed in the 2025 UGA Pest Control Handbook.  But, I will update for 2026.

5) For more general information about the Enlist® field corn weed control system, check out the following Corteva™ publication:

https://www.corteva.us/content/dam/dpagco/corteva/na/us/en/files/trait-stewardship/product-use-guides/DOC-2025-US-PUG-Corn.pdf

6) Enlist® One Label:

https://s3-us-west-1.amazonaws.com/agrian-cg-fs1-production/pdfs/Enlist_One_Label1gu.pdf

7) Enlist Duo® Label:

https://s3-us-west-1.amazonaws.com/agrian-cg-fs1-production/pdfs/Enlist_Duo_Label1gu.pdf

8) Assure® II Label (pages 10, 14-15 for Enlist® information)

https://s3-us-west-1.amazonaws.com/agrian-cg-fs1-production/pdfs/Assure_II_Label1j.pdf

9) As always, please feel free to reach out to me if you have any questions.

Weed Control in Conventional Corn (Prostko)

Yesterday while attending the Georgia Peanut Commission Research Update, I had the pleasure of sitting next to Tift Co. Extension Agent, Justin Hand.  He mentioned to to me that several of his growers are interested in weed control programs for conventional field corn.  I suspect that many of you might also be interested in this topic so here are a few thoughts:

1) Conventional field corn hybrids are available from several companies.  Here are a few:

Dekalb: DKC59-80, DKC111-30, DKC63-58, DKC66-02, DKC68-37

https://www.cropscience.bayer.us/corn/dekalb/seed-catalog

Dyna-Gro: D57CC51

https://dynagroseed.com/seed-finder/corn?cropsId=dynagroseed:crops/corn

Pioneer: P1197, P1870, P1608, P17677 all have conventional versions but supply might be limited

https://www.pioneer.com/us/product-catalog/crop-corn.html

Please contact our new Extension Grains Agronomist, Dr. Nick J. Shay (Nicholas.Shay@uga.edu) for more information about field corn hybrids. 

2) Here is a slide from my 2025 county presentation about weed control in conventional field corn. Growers need to double-check labels since some herbicide tank-mixes are prohibited (i.e. Callisto and Dual Magnum or Outlook).  Also, growers need to confirm the tolerance of any field corn hybrid to the WSSA/HRAC Group 2, Group 15, and Group 27 herbicides. If Counter is used in-furrow for soil insects/nematodes, Callisto, Revulin Q, and Steadfast Q cannot be applied POST. 

3) Here are some field pictures of these herbicide programs from my 2023 and 2024 research plots. This research was partially supported by the Georgia Corn Commission.

4) Feel free to contact me at any time via phone/text (229-392-1034), e-mail (eprostko@uga.edu), carrier pigeon, or smoke signal. I am available to you 365/24/7!

National Pesticide Safety Education Month (Prostko)

February 2025 is the 8th Annual National Pesticide Safety Education Month (NPSEM).  The NPSEM web-page has lots of good information about basic pesticide safety principles, storage, drift, wildlife protection, etc.  Check out the following web-page for more information:  

https://pesticidestewardship.org/national-pesticide-safety-education-month/

Does Roundup + Atrazine Applied POST in Field Corn Reduce Yields? (Prostko)

    I recently received a phone call from a south Georgia corn farmer who told me that someone was going around saying that a Roundup + Atrazine tank-mix, applied POST in field corn, will reduce yields.  My response was show me the data.  Here is my data from 3 on-farm field trials conducted in a high yield environment (250+ Bu/A) from 2014-2016.  Bottom line, yields from plots treated with Roundup + Atrazine + AMS applied POST were NOT statistically different from the untreated check in all trials.  

    As long as growers follow the label (i.e. rates and timing), I am not concerned at all.  A quick look at the Roundup PowerMax3 label:

USE INSTRUCTIONS: This product may be applied alone or in a tank-mix over the top of field corn hybrids with Roundup Ready 2 Technology from emergence through the V8 stage (8 leaves with collars), or until corn plant height reaches 30 inches (freestanding), whichever comes first, unless otherwise directed. Use drop nozzles for optimum spray coverage and weed control when corn plant height is 24 to 30 inches. When corn plants are 30 to 48 inches tall (freestanding), apply this product using only ground application equipment fitted 16 with drop nozzles aligned to avoid spraying into the whorls of the corn plants. Maximum single in-crop application rate of this product up to 48-inch field corn is 30 fluid ounces per acre. Total in-crop application of this product from corn plant emergence through 48 inches in height must not exceed 60 fluid ounces per acre.

    If a grower uses higher rates than listed above and/or applies Roundup later than suggested, yield losses can occur.  This is what what happens to corn ears when glyphosate is applied at tassel (i.e. way off-label).  

As a reminder, atrazine is only labeled for POST use in field corn up to 12" tall.