Glyphosate-resistant Palmer Amaranth Still a Formidable Challenge
Most growers would be thrilled to control 98 percent of the weeds in their fields and, in most cases, pulling it off would mean a job well done. But glyphosate-resistant Palmer amaranth (pigweed) is such a game-changer, attaining even this seemingly adequate benchmark now indicates you are actually losing ground rather than achieving successful management of this notorious weed.
“Over the past two seasons Arkansas has seen an explosion in glyphosate-resistant Palmer amaranth and controlling 98 percent of it in any given field is unacceptable.” This was one of several important messages from Dr. Jason Norsworthy, University of Arkansas weed scientist, during his presentation at a recent Syngenta sponsored meeting of southern crop consultants. Dr. Norsworthy, along with fellow weed scientists across the South, has been working diligently to provide growers with best management practices and recommendations to keep this weed from annihilating crop yields.
Success Requires a Program Approach
Perhaps the most important thing growers can do to successfully manage glyphosate-resistant Palmer amaranth is develop a season-long weed management program. In the new era of weed resistance, pre-emergence residual herbicides have become indispensable. And while these products do a good job of keeping crops clean early, some producers make one pre-emerge herbicide application and assume the heavy lifting for the season has been done. “Growers have had tremendous success with pre-emergence herbicides, but these early applications are not a complete solution,” said Norsworthy. “To be truly successful against Palmer amaranth, growers need to be prepared with a total weed management program that protects their crop from preplant through harvest.”
Residuals are Not Just for Early Season
Palmer amaranth emerges throughout the season and can create quite a predicament for growers once it’s up and competing with the crop. “Never let Palmer amaranth germinate,” said Norsworthy. “Because it can grow several inches a day, we only have a small window for effective chemical control before it gets too big.” From bad weather to breakdowns, there are too many things that can go wrong to keep growers out of the field and allow glyphosate-resistant pigweed to get to a height at which it is virtually impossible to control. Pre-emergence herbicides are a good start, but the use of overlapping residual herbicides such as Dual Magnum®, Sequence® and Flexstar® GT should be incorporated post-emergence and into the season to continually guard against emerging Palmer amaranth.
Syngenta Recommendations
Below are recommendation options from Syngenta for controlling glyphosate-resistant Palmer amaranth in soybean and cotton.
Soybeans
Burndown | At-planting or pre-emerge | In-crop | Late-season | Harvest aid |
Gramoxone Inteon® (40oz/A) | Boundary® (1.5 to 2 pt/A) | Flexstar® GT (3 pt/A) | Touchdown Total® (24 oz/A) | Gramoxone Inteon (16 oz/A) – apply when seeds have reached physiological maturity |
OR |
Prefix® (2 pt/A) | Sequence® (2.5 pt/A) |
OR |
Sequence (3 pt/A) | Flexstar GT (3 pt/A) |
Cotton
Fall application | Early burndown | Early preplant (2 to 3 weeks) | At-planting or behind the planter | Post-emerge (1 to 4 leaf) | 8 to 10 leaf | Lay-by |
Dual Magnum (1.33 to 1.67 pt/A) + Gramoxone Inteon (40 oz/A) | Dicamba or 2,4-D + Touchdown Total (24 oz/A) or Gramoxone Inteon (40 oz/A) | Reflex (1 pt/A)* + Gramoxone Inteon (40 oz/A) | Caparol® 4L (1.5 to 2 pt/A) | Sequence (2.5 pt/A) | Envoke® (0.15 oz/A) + Touchdown Total (24 oz/A) | Suprend® (1 to 1.25 lb/A) + Valor® + MSMA |
Glyphosate-resistant Palmer amaranth has changed the fundamentals of weed management, and growers need to adjust their approach to stay ahead. Being prepared with a season-long program and incorporating multiple residual herbicides can mean the difference between successful management and crop that can not be harvested due to uncontrolled weeds.
©2010 Syngenta Crop Protection, 410 Swing Road, Greensboro, NC 27409.Important: Always read and follow label instructions before buying or using Syngenta products. Gramoxone Inteon is a Restricted Use Pesticide.
Flexstar GT and Reflex are not currently registered for sale or use in all states. Please check with your state or local extension service before buying or using these products. Reflex may be used on cotton in AL, AR, LA, MS, MO and TN in accordance with the Special Local Needs provisions of the EPA under a FIFRA Section 24(c) registration. You must have a copy of the approved 24(c) registration in your possession in order to use Reflex, and you must comply with all of the limitations for use set forth in the 24(c) registration.
Boundary®, Caparol®, Dual®, Envoke®, Flexstar®, Flexstar® GT, Gramoxone Inteon®, Prefix®, Reflex®, Resistance Fighter™, Sequence®, Suprend®, Touchdown Total® and the Syngenta logo are trademarks of a Syngenta Group Company.
Valor® is a registered trademark of Valent U.S.A. Corporation Agricultural Products. Roundup® is a registered trademark of Monsanto Technology LLC.