facebook_pixel

When Glyphosate Fails – Management Strategies For Resistant Palmer Amaranth

In journalism school, professors teach aspiring writers to never use clichés, especially not two in the same sentence. But if the shoe fits, I say wear it.

Glyphosate-resistant Palmer amaranth grows like a weed, and according to emerging research, it could spread like wildfire too. That sentence is no good for college professors across the country, and its truth is even worse for producers throughout the Cotton Belt. Glyphosate-resistant Palmer amaranth ruined a few cotton fields in Georgia last year, and if not properly contained and controlled, it will become a problem elsewhere.

According to Dr. Stanley Culpepper, Extension Agronomist for Weed Science at the University of Georgia – Tifton, producers with glyphosate-resistant Palmer amaranth need to take precautions from preplant to layby. For those growers who haven’t dealt with the problem yet, Culpepper offers a few words of wisdom, another cliché if you will – an ounce of prevention is worth a pound of cure. The reason is simple:

“Palmer amaranth is an extremely competitive weed, and when you think about managing it, the first thing you’ve got to think about is that Palmer is going to grow 1-3 inches a day in good growing conditions. Even in areas of Macon County where we didn’t have good growing conditions last year, it was growing an inch a day,” Culpepper said.

Unfortunately, that’s just one half of the equation. Palmer amaranth produces hundreds of thousands of seeds, and if a tolerant gene emerges, that trait can be reproduced through non-resistant plants. A field with few resistant plants one year can become choked by weeds in just a few seasons. Culpepper explains:

“One of the biggest problems we’ve got is due to the ability of this weed being able to reproduce very rapidly. If you look at average seed production per plant, when it is producing 400,000-600,000 seed per plant, this plant can quickly come in and take over a situation,” he said. “The first field we found resistance in two years ago, 25% of the population was resistant to glyphosate, which meant 75% was sensitive to glyphosate. Within two years, 75% of the population in that field is glyphosate-resistant and 25% is sensitive. That shift occurred in two years and it has got to be because of the ability of reproduction. So that’s how quickly Palmer in general can come in and take over … which in essence, in my opinion, means we go from having a chance to harvest a field to probably not being able to harvest the field at all.”

The Common Denominator

Glyphosate-resistant Palmer amaranth did not randomly. It developed a tolerance and adapted after application and application of glyphosate. If Culpepper could stress anything, he would harp on the fact that producers need to use herbicides that feature different modes of action. Overusing a single weed management tool, especially a broad-spectrum herbicide like glyphosate, can be devastating. At the very least, this single-pronged weed management system got many growers in the situation they are in today.

“If you look at the growers who had problems in 2005, there are several things that are very common. First of all, we were very dependent on a single management tactic. These growers had mostly Roundup Ready cotton, and they sprayed around 3-5 times a year, and that was predominantly the tool they used to manage this pest. Now they certainly were not alone in the single management tactic. Currently, there is over 100 million acres of Round-up Ready technology being grown, and in most of these cropping systems, glyphosate is the predominate weed management tool,” Culpepper said.

In addition to the heavy reliance on glyphosate as a panacea for weed management, Culpepper also said some producers use lower-than-recommended rates, a premise he understands, but the worst possible thing to do in the current situation. “Many of us are guilty of cutting herbicide rates. But I never understand why we want to cut the rate of glyphosate. It is the most effective and economical herbicide in the world, and we will cut the rate to save 25% or 50%,” he said. “I am from a family farm, so I know there are situations when it will pay to cut the rate and add an adjuvant. I am all for promoting adjuvants, but do not cut the rate. That is something that we do not need to do, especially in the situation that we are currently in.”

Is it Really That Bad?

Continuing on the path of monoculture crop systems and single-pronged weed management plans is disastrous. If the most effective and economical herbicide is deemed useless by resistance, it will be a major blow to producers everywhere. That, Culpepper said, is a reality producers need to understand.

“In this situation where we have resistance, and you take a 4X rate of Roundup, and you put it on the Palmer when it is 1 inch, the same Palmer when it is 4 inches and the same Palmer when it is 12 inches (and the palmer survives), you can clearly see we have lost the most effective and economical herbicide in the world,” Culpepper said. “And I think it is arguably the most important herbicide in the world in all production systems in agronomics today and in our state. So we have lost that in these fields, and we are going to continue to lose it as it spreads throughout our state, especially in circumstances where growers are too dependent on glyphosate.”

Grower-induced glyphosate resistance isn’t the only problem. As discussed in the weed management article in the March issue of Cotton Grower, a glyphosate-resistant Palmer amaranth plant can pollinate another plant from at least 200 meters away, and it is very possible that pollination can occur at even farther distances. Not only do producers have to worry about developing resistance on their farms, they also have to contend with it spreading from other areas.

“Obviously, when you have 100 million acres that you are treating with glyphosate, glyphosate, glyphosate, you will, and we did, find resistance. The problem we’ve got now is that it is going to spread, and we have to deal with it,” Culpepper said. “What we really need to do is to delay the arrival or the spread of this resistance. Once we get some number and are able to model this situation, we will be able to tell people we think it will be here in 2 years, here in 3 years, and here in 4 years. But also keep in mind that people who continue to spray glyphosate, glyphosate, glyphosate can create their own biotype in their own area, and it may be completely non-related to pollen movement.”

Recommendations

During UGA research on glyphosate-resistant Palmer amaranth last year, Culpepper’s team experimented with 168 different herbicide systems on 12 acres of small plot research. Of those systems, 155-160 plots had to be mowed under because of Palmer resistance, making it easy to identify possible solutions, but also emphasizing the resilience of the weed. “It makes it easy on what we are going to recommend,” Culpepper said, “because most of the things we tried simply do not work.”

For glyphosate-resistant Palmer amaranth in Roundup Ready cotton, Culpepper recommends Prowl or Treflan PPI combined with Reflex PRE during preplant or preemergence. Postemergence in 1-to 4-leaf cotton, he believes a glyphosate and Dual Magnum mix is effective if no Palmer has emerged, while a glyphosate/Staple mix should be used in Palmer that is 1-2 inches tall. For layby, MSMA combined with one of the following – Direx, Layby Pro, Suprend or Valor – is producers’ best bet. He stresses that vigilance is key to fighting gylphosate-resistant Palmer amaranth, emphasizing that managing resistant Palmer taller than 2 inches in Roundup Ready cotton is even more difficult – if not impossible.

Culpepper realizes his program will cost producers more money, especially when compared to just spraying a few applications of glyphosate. But he stresses that the program protects glyphosate, an important concept that he believes cannot be said enough, and keeps growers from an even worse scenario – mowing down there crop.

“If you look back at this program, first of all, you are going to say that I am costing you money. And I admit that. But the second thing you see is, yes, we are still using Roundup. It is still the most effective tool in 98-99% of our acreage. But what we are doing is surrounding that most important tool with three kinds of alternative herbicide chemistries with different modes of action,” Culpepper said. “This will protect the glyphosate, it will delay or help hold down ALS resistance, and it will also prevent or reduce the likelihood of resistance developing to these chemistries too, because we have three maybe four modes of action in one program. That is a sound program.”

University of Georgia Herbicide Programs for Palmer Amaranth in Cotton

Managing Glyphosate-resistant Palmer Amaranth in Roundup Ready Cotton
Preplant Incorporated (PPI)
or Preemergence (PRE)
Postemergence
(1-4 leaf cotton)
Layby Directed
Prowl or Treflan PPI + Reflex PRE Glyphosate + Dual Magnum (no Palmer emerged) or
Glyphosate + Staple
(1-2″ Palmer)
MSMA + Direx, Layby Pro, Suprend or Valor
Managing Heavy Glyphosate-sensitive Palmer Amaranth in Roundup Ready Cotton
At Plant Postemergence
(1-4 leaf cotton)
Layby Directed
Prowl/Treflan PPI or Prowl PRE
+ Cotoran, Direx, Reflex or
Staple PRE
Glyphosate +
Dual Magnum or Staple
MSMA + Direx, Layby Pro, Suprend or Valor OR Glyphosate + Direx, Layby Pro, Suprend or Valor
Managing Light to Moderate Glyphosate-sensitive Palmer Amaranth in Roundup Ready Cotton
At Plant Postemergence
(1-4 leaf cotton)
Layby Directed
Prowl/Treflan PPI or Prowl Glyphosate + Dual Magnum or Staple MSMA + Direx, Layby Pro, Suprend or Valor OR Glyphosate + Direx, Layby Pro, Suprend or Valor
PRE Prowl/Treflan PPI or Prowl PRE + Cotoran, Direx, Reflex or Staple PRE Glyphosate as needed
Topics:

Leave a Reply

Weed Control Stories
Weed Control

Dicamba’s Defenders

August 22, 2017

Amid a chorus of complaints, many cotton producers express worry over losing an invaluable tool for weed control.

Weed Control

Best Management Practices to Mitigate Dicamba Drift

June 27, 2017

To help offset potential dicamba drift issues, Tennessee Weed Specialist Larry Steckel offers best management practices to help reduce off-target movement.

Weed Control

Avoid Inversions When Spraying Weeds

June 19, 2017

Dr. Larry Steckel offers tips to help avoid potential problems when spraying dicamba in inversion conditions, even when proper guidelines are being followed.

Soybeans

Tips to Prevent Dicamba Drift

June 15, 2017

In a video presentation, Tennessee Weed Specialist Larry Steckel discusses three actions to help reduce dicamba drift and volatilization.

Soybeans

Dicamba Damage Reports Increasing in Arkansas

June 12, 2017

Forty complaints from off-target movement of dicamba have already been reported to the Arkansas State Plant Board, as of June 12.

Weed Control

Glyphosate-Resistant Johnsongrass Focus of New Webcast

May 22, 2017

A new webcast on effective management of glyphosate-resistant johnsongrass has been added to the Focus on Cotton online series from the Plant Management Network and Cotton Incorporated.

Weed Control

Weed Control Options in Light of Herbicide Shortages

May 9, 2017

Tennessee Extension Weed Specialist Larry Steckel outlines several options for early season cotton weed control in light of shortages of Caporol, Cotoran and Diuron.

Around The Gin
Product News

Improved Bollworm Management Expected in 2018

August 23, 2017

Southeast Texas cotton farmers should have new tools available in 2018 to better manage bollworms and other potentially damaging pests.

Product News

Maximizer Club Honors Top FiberMax Dryland Growers

August 17, 2017

The FiberMax Maximizer Club honored 121 growers who yielded at least 1,000 lb/A on dryland acres with FiberMax varieties in 2016.

Product News

Monsanto, Valent Expand Roundup Ready PLUS Partnership

August 7, 2017

Monsanto and Valent U.S.A. are expanding their crop protection partnership for the 2018 Roundup Ready PLUS Crop Management Solutions platform.

Product News

New Broadleaf Burndown Option Coming from Dow AgroSciences

July 31, 2017

A new burndown option for tough broadleaf weeds has shown excellent promise in trials across the Mid-South and Midwest.

Product News

Protect Cotton Potential from Weeds, Worms and Diseases

July 12, 2017

Southeast cotton producers say latest technologies from PhytoGen help protect yield and quality.

Product News

Monsanto “Troubled” by Arkansas Dicamba Decision

June 26, 2017

Monsanto has weighed in on the Arkansas Plant Board’s proposed ban of dicamba use in the state.

Product News

Drexel Adds Two Regional Sales Reps

June 16, 2017

Kyle Herring and David Davis have joined Drexel Chemical Company as regional sales representatives.

Product News

Dow AgroSciences Launching Enlist Corn in 2018

June 16, 2017

Following the launch of Enlist cotton, Dow AgroSciences will make Enlist corn commercially available for 2018 after receiving Chinese import approvals.

Latest News
Weed Control

Dicamba’s Defenders

August 22, 2017

Amid a chorus of complaints, many cotton producers express worry over losing an invaluable tool for weed control.

Soybeans

Arkansas Researchers Share Dicamba Volatility Studies

August 11, 2017

Work done by University of Arkansas weed scientists has found that every dicamba formulation tested this spring and summer demonstrated a level of volatility.

Weed Control

Post-Direct or Hooded Options for Layby Weed Control

July 6, 2017

Tennessee’s Larry Steckel offers recommendations for post-direct or hooded herbicide applications at layby.

Weed Control

Best Management Practices to Mitigate Dicamba Drift

June 27, 2017

To help offset potential dicamba drift issues, Tennessee Weed Specialist Larry Steckel offers best management practices to help reduce off-target movement.

Weed Control

Avoid Inversions When Spraying Weeds

June 19, 2017

Dr. Larry Steckel offers tips to help avoid potential problems when spraying dicamba in inversion conditions, even when proper guidelines are being followed.

Soybeans

Tips to Prevent Dicamba Drift

June 15, 2017

In a video presentation, Tennessee Weed Specialist Larry Steckel discusses three actions to help reduce dicamba drift and volatilization.

Soybeans

Dicamba Damage Reports Increasing in Arkansas

June 12, 2017

Forty complaints from off-target movement of dicamba have already been reported to the Arkansas State Plant Board, as of June 12.

Weed Control

Glyphosate-Resistant Johnsongrass Focus of New Webcast

May 22, 2017

A new webcast on effective management of glyphosate-resistant johnsongrass has been added to the Focus on Cotton online series from the Plant Management Network and Cotton Incorporated.

Weed Control

Weed Control Options in Light of Herbicide Shortages

May 9, 2017

Tennessee Extension Weed Specialist Larry Steckel outlines several options for early season cotton weed control in light of shortages of Caporol, Cotoran and Diuron.

Soybeans

Cooperation, Preparation Are Keys to Ag Sustainability

May 5, 2017

Georgia’s Stanley Culpepper outlines the training efforts for auxin herbicides in the state and praises the people who make it all work.

Weed Control

Upgrading Cotton Weed Control Step by Step

May 2, 2017

To control yield-robbing weeds, farmers need a step by step strategy, starting with a clean, weed-free field, followed by timely applications of herbicides with multiple modes of action.

Weed Control

Foliar Auxin Injury Not Good Indicator of Yield Loss

May 1, 2017

According to High Plains cotton and weed specialists, the relationship between injury from auxin herbicides and potential yield loss is difficult – if not impossible – to accurately predict.

Weed Control

Multiple Pre-Emerge Residual Options for Cotton

April 20, 2017

An apparent shortage of Caparol has some cotton growers scrambling to find alternatives for their pre-emergence residual herbicide program.

Weed Control

More Responsibilities with New Cotton Technologies

March 30, 2017

From a cotton farming standpoint, it may be more important now than ever to match your surroundings with your weed control responsibilities.

Weed Control

Hit Right Where You’re Aiming

March 20, 2017

Extension experts say hooded booms like Willmar’s Redball hooded sprayers increase accuracy and minimize drift.