Managing Herbicide-Resistant Weeds
in Peanuts in the United States

 
Some members of a weed species can survive and reproduce after exposure to a rate of herbicide that normally kills other weeds of the same species. Such plants are said to be herbicide resistant. Herbicide resistance is the inherited ability of a weed species to survive and reproduce following exposure to a rate of herbicide that was previously effective in controlling this species. Application of herbicide may reveal biotypes within the population that can survive exposure to the herbicide. Applying herbicides with the same mechanism of action repeatedly and successively allows these resistant plants to continue to survive and reproduce. Increasingly, peanut growers must consider the mechanism behind development of herbicide-resistant weeds and approaches to delay, curtail and prevent development of resistant weed populations. Prevention is the most effective way to manage herbicide resistance.

The probability that a weed will develop resistance to a herbicide (and to related herbicides with the same mechanism of action) depends upon three factors:

• specificity of the mechanism of action (Table 1),

• degree of selection pressure exerted on the population, and

• ability of the species to reproduce.

The grower can only control the amount or degree of selection pressure exerted on the weed population. To prevent development of herbicide resistance, it is most effective to reduce selection pressure on resistant biotypes. Do not apply herbicides with the same mechanism of action repeatedly and successively. Use a herbicide with a different mechanism of action to kill weeds that survive the previous herbicide application. Table 1 lists mechanisms of action for various herbicides and also groups herbicides by the likelihood of resistance development.

Poor weed control may be caused by a number of factors other than herbicide resistance. Be diligent in determining if a weed control failure is in fact due to herbicide resistance. Consider all factors when diagnosing weed control failures (Table 2). Several key indicators may be used to determine if herbicide resistance is the cause of poor weed control. If herbicide resistance is confirmed or highly suspected, approaches to managing herbicide resistance need to be incorporated into weed management strategies immediately for the species in question. The Web site that contains the most conclusive summary of documented cases of herbicide-resistant weeds is www.weedscience.org/in.asp.

Herbicide resistance is prevalent in peanut-growing regions (Table 3), and specific herbicide programs are suggested to help the grower manage herbicide-resistant weeds in peanut fields (Table 4). Growers lose effective herbicide options if populations of several weed species in a given field develop significant herbicide-resistant biotypes.

Table 1. Herbicide Families and Relative Propensity of Developing Resistance to Herbicides.
Trade Name Active ingredient Herbicide family Mechanism of action
Herbicides with high potential to select for herbicide resistance
Cadre, Impose Imazapic Imidazolinone Inhibition of acetolactate synthase (ALS)
Pursuit Imazethapyr Imidazolinone Inhibition of acetolactate synthase (ALS)
Strongarm Diclosulam Triazolopyrimidine
sulfonamide
Inhibition of acetolactate synthase (ALS)
Classic Chlorimuron Sulfonylurea Inhibition of acetolactae synthase (ALS)
Herbicides with moderate to high potential to select for herbicide resistance
Arrow, Select, Select
Max, Volunteer
Clethodim Cyclohexanedione Inhibition of acetyl CoA carboxylase
Poast, Poast Plus Sethoxydim Cyclohexanedione Inhibition of acetyl CoA carboxylase
Herbicides with moderate potential to select for herbicide resistance
Prowl, Pendimax Pendimethalin Dinitroaniline Inhibition of microtubule assembly
Sonalan Ethalfluralin Dinitroaniline Inhibition of microtubule assembly
Treflan Trifluralin Dinitroaniline Inhibition of microtubule assembly
Herbicides with low potential to select for herbicide resistance
Basagran Bentazon Benzothiadiazole Inhibition of photosynthesis
Cobra Lactofen Diphenylether Protox inhibitor (PPO)
Firestorm, Gramoxone
INTEON, Parazone
Paraquat Bipyridilium Acceptor of electron transfer in Photosystem I
Dual Magnum, Parallel
PCS, Stalwart
Metolachlor Chloroacetamide Inhibition of nucleic acid formation, other
Outlook Dimethenamid Chloroacetamide Inhibition of nucleic acid formation, other
Storm Acifluorfen + Bentazon Diphenylether +
Benzothiadiazole
Inhibition of photosynthesis and
protox inhibitor (PPO)
Ultra Blazer Acifluorfen Diphenylether Protox inhibitor (PPO)
Valor SX Flumioxazin N-phenylphthalimide
derivative
Protox inhibitor (PPO)
Butyrac 200, Butoxone 2,4-DB Phenoxy Plant growth inhibition

 

Table 2. Detection and Approaches to Management of Herbicide Resistance.
Possible reasons why herbicides do not control weeds that are not associated with herbicide resistance
• Improper herbicide choice or rate.
• Improper application of herbicide, including poor incorporation.
• Poor timing of herbicide application.
• Weather conditions were not favorable when herbicides were applied.
• Weeds emerged after application of postemergence herbicides that do not have residual activity, or weeds emerged prior to application of herbicides that do not have postemergence activity.
Indicators suggesting that weeds are resistant to herbicides
• Performance of the herbicide poor on the species in question while other weed species that are normally controlled are controlled well.
• Herbicide normally controls the weed in question.
• Poor control is confined to spots in the field.
• Some plants of the same species controlled well while other plants of the same species controlled poorly.
• Field history of a single herbicide or heavy use of herbicides with the same mechanism of action.
Steps to take to prevent or manage herbicide resistance
• Rotate to herbicides having different mechanisms of action.
• Use tank mixes or sequential applications of herbicides having different mechanisms of action.
• Be especially vigilant when using herbicides with a high potential for selecting for herbicide resistance.
• Integrate non-chemical controls, such as cultivation and hand-removal of weeds, when possible or spot sprays using non-selective herbicides.
• Do not allow weeds to produce seeds when herbicide resistance is suspected.

 

Table 3. Prevalence of Herbicide Resistance in Peanut in the United States.
Southeastern region (Alabama,
Florida, Georgia)
Southwestern region (New
Mexico, Oklahoma, Texas)
Virginia-Carolina region (North
Carolina, South Carolina, Virginia)
Acetolactate synthase inhibiting (ALS) herbicides (Cadre, Classic, Impose, Pursuit, Strongarm)
Palmer amaranth Palmer amaranth Common cocklebur
Pigweed species Pigweed species Common ragweed
    Palmer amaranth
    Pigweed species
Dinitroaniline herbicides (Prowl, Sonalan, Treflan)
Goosegrass   Goosegrass
Palmer amaranth   Palmer amaranth

 

Table 4. Specific Herbicide Programs to Manage Herbicide-Resistant Weeds in Peanut.
NOTE: Consult local recommendations and product labels for effectiveness and restrictions on uses of    herbicides.
Weeds suspected
to be resistant
 
Herbicides that no
longer control this
weed due to resis-
tance
Herbicides effective on these herbicide-resistant weeds
Preplant
incorporated
Preemergence Postemergence
Palmer amaranth,
pigweed
Prowl Dual Magnum Outlook 2,4-DB
  Sonalan Outlook Dual Magnum Cobra
  Treflan Parallel PCS Parallel PCS Cobra + 2,4-DB
    Pursuit Pursuit Cadre or Impose
    Stalwart Stalwart Cadre or Impose + Cobra
    Strongarm Strongarm Cadre or Impose + 2,4-DB
      Valor SX Cadre or Impose + Ultra Blazer
        Classic
        Paraquat (Gramoxone INTEON,
Firestorm or Parazone)
        Paraquat + Dual Magnum or
Parallel PSC or Stalwart
        Paraquat + Outlook
        Paraquat + Storm
        Pursuit
        Pursuit + 2,4-DB
        Pursuit + Ultra Blazer
        Roundup Weather MAX*
        Storm
        Storm + 2,4-DB
        Ultra Blazer
        Ultra Blazer + 2,4-DB
Goosegrass Prowl Dual Magnum Outlook Arrow, Poast, Poast Plus, Select
  Sonalan Outlook Dual Magnum Max or Volunteer
  Treflan Parallel PCS Parallel PCS Cadre or Impose
    Pursuit Pursuit Paraquat (Gramoxone INTEON,
Firestorm or Parazone)
    Stalwart Stalwart Paraquat + Dual Magnum or
Parallel PCS or Stalwart
        Paraquat + Outlook
Palmer amaranth,
pigweed
Cadre Dual Magnum Dual Magnum 2,4-DB
  Classic Outlook Outlook Cobra
  Impose Parallel PCS Parallel PCS Cobra + 2,4-DB
  Pursuit Prowl Valor SX Paraquat (Gramoxone INTEON,
Firestorm, or Parazone)
  Strongarm Sonalan Stalwart Paraquat + Dual Magnum or
Parallel PSC or Stalwart
        Paraquat + Outlook
        Roundup Weather MAX*
        Storm
        Storm + 2,4-DB
        Ultra Blazer
        Ultra Blazer + 2,4-DB
Common cocklebur Cadre None None Basagran
  Classic     Basagran + 2,4-DB
  Impose     Cobra
  Pursuit     Cobra + 2,4-DB
  Strongarm     Paraquat (Gramoxone INTEON,
Firestorm or Parazone) + Basagran
        Storm
        Storm + 2,4-DB
        Ultra Blazer
        Ultra Blazer + 2,4-DB
        2,4-DB
Common ragweed Strongarm None Valor SX Cobra
        Paraquat (Gramoxone INTEON,
Firestorm or Parazone)
        Roundup Weather MAX*
        Storm
        Ultra Blazer
Goosegrass, Palmer
amaranth, pigweed
Cadre Dual Magnum Dual Magnum Cobra
  Classic Outlook Outlook Cobra + 2,4-DB
  Impose Parallel PCS Valor SX Paraquat (Gramoxone INTEON,
Firestorm, or Parazone)
  Prowl Stalwart   Paraquat + Dual Magnum or
Parallel PSC or Stalwart
  Pursuit     Paraquat + Outlook
  Sonalan     Paraquat + Storm
  Strongarm     Ultra Blazer
        Ultra Blazer + 2,4-DB

 
* Apply Roundup Weather MAX with a rope-wick applicator in row middles with no contact with the peanut canopy. This treatment will not control glyphosate-resistant weeds.

Prepared by
Dr. David Jordan, Professor, North Carolina State University; Dr. Eric Prostko, Associate Professor, University of Georgia;
Dr. Peter Dotray, Professor, Texas Tech and Texas A&M Universities; Dr. John Wilcut, Former Professor, North Carolina State University; Dr. Todd Baughman, Associate Professor, Texas A&M University; Dr. Barry Brecke, Professor, University of Florida;
Dr. Jay Chapin, Professor, Clemson University; Dr. Joel Faircloth, Assistant Professor, Virginia Tech; Dr. Wilson Faircloth, Research Agronomist, National Peanut Research Lab, USDA-ARS; Dr. Jason Ferrell, Assistant Professor, University of Florida; Dr. Timothy Grey, Assistant Professor, University of Georgia; Mr. James Grichar, Research Scientist, Texas A&M University; Dr. Greg MacDonald, Associate Professor, University of Florida; Dr. Case Medlin, Assistant Professor, Oklahoma State University.

Dedicated to the memory of Dr. John Wilcut, Professor, North Carolina State University, who was involved in many research projects associated with weed management in peanuts.

Published by NORTH CAROLINA COOPERATIVE EXTENSION SERVICE
College of Agriculture and Life Sciences, NC State University, Raleigh, NC
For more information on herbicide-resistant weed management and for a listing of the review committee for this publication, go to www.ncsu.edu.

AG-692