Herbicide Resistance in Waterhemp and Palmer Amaranth
15 Nov 2019
Brushing up on what it takes to keep weeds from putting a damper on your next crop is always a good idea. Waterhemp and Palmer amaranth are two significant pests you should be scouting for prior to, during, and after planting.
Why Are Waterhemp and Palmer Amaranth Resistant to So Many Herbicides?
Both waterhemp and Palmer amaranth belong to a special group of the Amarathus genus, which are dioecious -- meaning male and female flowers grow on separate plants. For successful reproduction, pollen must transfer from the male plants to female plants.
Because of this, genetic diversity within these two species tends to be greater than that of most agronomic weeds. This increases the potential for evolving and spreading herbicide resistance genes and other traits that improve survival.
These two plant species have an amazing ability to adapt and develop resistance to herbicides. To date, both have confirmed resistance to eight herbicide groups: Group 2, 3, 4, 5, 9, 14, 15 and 27.
Here is a quick summary of these herbicide groups and some examples of products they include:
Group 2: Acetolactate Synthase (ALS) Inhibitors
Includes products such as Accent® Q, components of Authority® Assist and Authority® First, Beacon®, Classic®, components of Clearpath®, components of Fierce®, FirstRate®, Londax®, Newpath®, Permit®, Pursuit®, Scepter®, Staple®, Synchrony®, and components of Valor® XLT
Group 3: Root Growth Inhibitors
Includes products such as Prowl® H2O and Treflan®
Group 4: Plant Growth Regulators
Includes products such as 2,4-D, Banvel®, Clarity®, components of Clearpath®, Engenia®, components of Enlist Duo®, Enlist One® and Facet®
Group 5: Photosystem II (PSII) inhibitors
Includes products such as atrazine, components of Authority® MTZ, components of Bicep II Magnum®, components of Boundary®, Caparol®, components of Harness® Xtra and metribuzin
Group 9: EPSP Synthase Inhibitors
Includes all glyphosate products.
Group 14: PPO Inhibitors
Includes products such as Aim®, components of the Authority® family of herbicides, Cobra®, Envive®, components of Fierce®, Flexstar®, components of Gangster®, Reflex®, Sharpan®, Spartan® and Valor®
Group 15: Shoot Growth Inhibitors
Includes products such as Dual Magnum® (s-metolachlor), Harness®, Warrant®, Degree®, Surpass® (acetochlor), Zidua® (pyroxasulfone) and Outlook® (dimethenamid-p)
Group 27: Pigment Synthesis (HPPD) Inhibitors
Includes products such as Balance Flexx®, Callisto®, components of Halex® GT, Laudis®, components of Lexar® EZ and components of Realm Q®
But these challenges don't mean farmers are out of options to combat these pests.
What to Consider When Developing a Weed Management Plan
Although waterhemp and Palmer amaranth have shown resistance to multiple herbicide groups, it is important to remember that there are few, if any, cases that have resistance to all the listed herbicide groups in this article. These herbicide groups are still important options to control the weed pests that we have in agronomic crops in the U.S.
By taking advantage of multiple modes of action, along with crop and chemistry rotation, these difficult to control species can be effectively managed.
What is important is that you rotate your chemistries and crops to most effectively deal with these difficult to control species. As always, consult with your trusted FBN agronomist to design the best herbicide plan for your operation and talk to your FBN account executive about adjuvant options to maximize weed control.
Soybean Herbicide Options
Here are some suggested herbicide options for common soybean cropping systems:
Conventional Soybean
Spring Burndown 2,4-D, glyphosate or glufosinate + paraquat
Pre-Plant*1,4 Authority® Elite, Fierce®, Envive®, Sharpen®, Sonic®, Surveil®, Valor® SX, Valor® XLT, or Verdict® + Group 15 herbicide
Pre-Emerge**2,4 Boundary®, Authority® MTZ, Canopy®, or metribuzin + Group 15 herbicide
Post-Emerge*** Cobra®, fomesafen, or Ultra Blazer® + Group 15 herbicide
Salvage Dicamba
Glyphosate-tolerant Soybean
Spring Burndown 2,4-D, glyphosate or glufosinate + paraquat
Pre-Plant*1,4 Authority® Elite, Fierce®, Envive®, Sharpen®, Sonic®, Surveil®, Valor® SX, Valor® XLT, or Verdict® + Group 15 herbicide
Pre-Emerge**2,4 Boundary®, Authority® MTZ, Canopy®, or metribuzin + Group 15 herbicide
Post-Emerge*** Glyphosate + fomesafen + Group 15 herbicide
Salvage Glyphosate + Cobra® or Ultra Blazer®
LibertyLink®-tolerant Soybean
Spring Burndown 2,4-D, glyphosate or glufosinate + paraquat
Pre-Plant*1,4 Authority® Elite, Fierce®, Envive®, Sharpen®, Sonic®, Surveil®, Valor® SX, Valor® XLT, or Verdict® + Group 15 herbicide
Pre-Emerge**2,4 Boundary®, Authority® MTZ, Canopy®, or metribuzin + Group 15 herbicide
Post-Emerge*** Liberty® 280 + fomesafen + Group 15 herbicide
Salvage Liberty® 280
Enlist E3™ Soybean
Spring Burndown Enlist Duo™ + paraquat
Pre-Plant*1,4 Enlist Duo™ + Authority® Elite, Fierce®, Envive®, Sharpen®, Sonic®, Surveil®, Valor® SX, Valor® XLT, or Verdict® + Group 15 herbicide
Pre-Emerge**2,4 Boundary®, Authority® MTZ, Canopy®, or metribuzin + Group 15 herbicide
Post-Emerge*** Enlist Duo™ + Group 15 herbicide
Salvage Enlist Duo™
Roundup Ready 2 Xtend® Soybean
Spring Burndown XtendiMax® + glyphosate or glufosinate + Paraquat
Pre-Plant*1,4 XtendiMax® + Authority® Elite, Fierce®, Envive®, Sharpen®, Sonic®, Surveil®, Valor® SX, Valor® XLT, or Verdict® + Group 15 herbicide
Pre-Emerge**2,4 Boundary®, Authority® MTZ, Canopy®, or metribuzin + Group 15 herbicide
Post-Emerge*** XtendiMax® + glyphosate + Group 15 herbicide
Salvage XtendiMax® + glyphosate
Effectively Manage Waterhemp and Palmer Amaranth in Your Fields
Herbicide diversity plays an important role in fighting weed resistance. FBN Direct® offers a diverse product portfolio to provide a wide range of herbicide options for growers like you to develop a proactive, effective integrated weed management strategy.
Sources:
http://iwilltakeaction.com/weed/common-waterhemp
http://iwilltakeaction.com/weed/palmer-amaranth
http://iwilltakeaction.com/uploads/files/55620-1-ta-hrm-weed-chart-poster-fnl-hr.pdfhttp://bulletin.ipm.illinois.edu/?p=4498
https://www.ksre.k-state.edu/news/stories/2019/03/palmer-amaranth-resistance-to-herbicides.html
https://emergence.fbn.com/agronomy/common-herbicide-mode-of-action-groups-for-weed-management
Map Credit:
Heap, I. The International Survey of Herbicide Resistant Weeds. Online. Internet. Friday, October 18, 2019
15 Nov 2019