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.