Understanding The Threat Of Palmer Amaranth: Management Recommendations For The 2014 Season

Palmer amaranth is a weed species that must be thoughtfully and carefully managed. Simply attempting to control Palmer amaranth often leads to ineffective herbicide applications, substantial crop yield loss, and increased weed infestations, said a University of Illinois weed sciences researcher.

“If ignored or otherwise not effectively managed, Palmer amaranth can reduce corn and soybean yield to nearly zero,” said Aaron Hager. “The threat of Palmer amaranth during the 2014 growing season is very real across a large portion of Illinois.”

The U of I weed science program has developed recommendations for management of Palmer amaranth in agronomic crops. These recommendations were developed in accordance with the unique growth characteristics of this weed species. The goals of the recommendations are twofold: to reduce the potential for Palmer amaranth to negatively impact crop yield, and to reduce Palmer amaranth seed production, which ultimately augments the soil seed bank and perpetuates the species.

Three general principles of Palmer amaranth management include:

  • Prevention is preferable to eradication. Prevention refers to utilizing tactics that prevent weed seed introduction and weed seed production.  “Palmer amaranth is not native to Illinois so any population discovered in the state originated from seed that somehow was moved into the state,” Hager said. “The myriad of ways in which Palmer amaranth seeds can be transported, however, makes preventing seed introduction extremely challenging. Once Palmer amaranth populations become established, utilizing any and all tactics to prevent seed production becomes of paramount importance.”
  • It is not uncommon for annual herbicide costs to at least double once Palmer amaranth becomes established. There are simply no soil- or foliar-applied herbicides that will provide sufficient control of Palmer amaranth throughout the entire growing season.
  • Control of Palmer amaranth should not be less than 100%. “In other words, the threshold for this invasive and extremely competitive species is zero,” the researcher said. “Female Palmer amaranth plants produce tremendous amounts of seed, and in less than five years a few surviving plants can produce enough seed to completely shift the weed spectrum in any particular field.”

Recommendations based on Palmer amaranth germination and emergence characteristics include:

  • Be certain to control all emerged Palmer amaranth plants before planting corn or soybean. Burn-down herbicides or thorough tillage are effective tactics to control emerged Palmer amaranth plants before planting. Keep in mind, however, that glyphosate will not control glyphosate-resistant Palmer amaranth and that growth regulator herbicides (such as 2,4-D or dicamba) are most effective on Palmer amaranth plants less than 4 inches tall.  If pre-plant scouting (which is especially important prior to planting soybean) reveals Palmer amaranth plants taller than 4 inches, consider using tillage instead of herbicides to control the plants.
  • Apply a full rate (based on label recommendations for soil texture and organic matter content) of an effective soil residual herbicide no sooner than seven days prior to planting and no more than three days after planting. Many soil residual herbicides that are effective for controlling waterhemp are also effective for controlling Palmer amaranth. In soybeans, products containing sulfentrazone (Authority) or flumioxazin (Valor) have provided effective control of Palmer amaranth. Application rates of products containing these active ingredients should provide a minimum of 0.25 lb ai/acre sulfentrazone or 0.063–0.095 lb ai/acre flumioxazin.

Hager said growers should not rely solely on glyphosate to control Palmer amaranth. “Molecular assays have indicated that resistance to glyphosate appears to be relatively common among recently identified Palmer amaranth populations in Illinois,” he explained.

Recommendations based on Palmer amaranth growth rate include:

  • Begin scouting fields within 14 to 21 days after crop emergence. “We recommend this interval even for fields previously treated with a soil residual herbicide applied close to planting,” he explained.
  • Foliar-applied herbicides must be applied before Palmer amaranth plants exceed 4 inches in height. The effectiveness of most foliar-applied herbicides dramatically decreases when Palmer amaranth plants are taller than 4 inches.  Postemergence herbicides that demonstrate control or suppression of Palmer amaranth include synthetic auxin herbicides (dicamba, 2,4-D), diphenylethers (acifluorfen, lactofen, fomesafen), glufosinate, glyphosate, and HPPD inhibitors (mesotrione, tembotrione, topramezone).
  • Consider including a soil residual herbicide during the application of the foliar-applied herbicide. A soil residual herbicide applied with the foliar-applied herbicide can help control additional Palmer amaranth emergence and allow the crop to gain a competitive advantage over later-emerging weeds.
  • Fields should be scouted 7 to 14 days after application of the foliar-applied herbicide to determine herbicide effectiveness; if the soil residual herbicide included with the post application is providing effective control; and if additional Palmer amaranth plants have emerged.

“If scouting reveals additional Palmer amaranth plants have emerged, make a second application of a foliar-applied herbicide before Palmer amaranth plants are 4 inches tall,” Hager said.

In regard to Palmer amaranth seed production, Hager said research has demonstrated that female Palmer amaranth plants are capable of producing numbers of seed comparable to that of waterhemp (several hundred thousand to over one million). “Physically remove any remaining Palmer amaranth plants before the plants reach the reproductive growth stage. Plants should be severed at or below the soil surface and carried out of the field. Severed plants can root at the stem if left on the soil surface, and plants can regenerate from stems severed above the soil surface,” he said.

University of Illinois Extension provides equal opportunities in programs and employment. If you need a reasonable accommodation to participate in this program, please contact the County Office at least two weeks prior to the event.  University of Illinois Extension offers practical, research-based programs that help people improve their lives and address critical community issues involving youth, families, economics, health and natural resources.

Source: University of Illinois Extension

Topics:

Leave a Reply

Herbicides Stories

HerbicidesScouting Key To Next Season’s Soybean Herbicide Program
August 12, 2014
When growing soybeans, growers need to think ahead to stay one step ahead of weeds. That means examining weed threats and evaluating which herbicides work best. Read More
HerbicidesArysta Touts Burndown Herbicide For Brome Management In Wheat
June 4, 2014
Arysta LifeScience North America recommends PRE-PARE Burndown Herbicide for effective brome management in winter wheat. Read More
HerbicidesFall Herbicide Applications More Effectively Manage Resistant Italian Ryegrass
May 14, 2014
Field studies show that a fall application of certain herbicides before weed emergence, leads to more successful crop planting and weed control in spring. Read More
Waterhemp in soybean stubble
HerbicidesThe Weed Resistance Problem: A Matter Of Billions
April 1, 2014
Not only is the amount of money being spent to control these yield robbers high, but the toll it has taken on the human population is growing lager by the day. Read More

Top 100 Articles

CropLife 100CHS: Driving Momentum To Help Farmer-Owners Grow
December 11, 2014
CHS Inc., the nation’s leading farmer-owned cooperative and a global energy, grains and foods company, must capture new opportunities to Read More
CropLife 100BRANDT, Verdesian Ink Distribution Agreement
December 9, 2014
The agreement grants BRANDT the exclusive right to sell and market Verdesian’s patented Steric chemistry in the Turf and Ornamental and eastern U.S. ag markets under the BRANDT Reaction product line name. Read More
CropLife 100CropLife 100: The Colors Of Custom Application
December 5, 2014
Although many color spray rigs are in the yards of the nation’s top ag retailers, the majority of them still come in only a few shades. Read More
CropLife 100Pinnacle Invests In Meridian Agriculture Distribution
December 4, 2014
Meridian will provide retailers with supplier-branded products and numerous opportunities to differentiate themselves from their competitors. Read More
CropLife 100CropLife 100: Entering A New Seed Era
December 4, 2014
The seed category has been re-vitalized during the past few years, and more good news (and varieties) are headed the industry’s way in 2015. Read More
CropLife 100CropLife 100: The Depressed State Of Fertilizer
December 3, 2014
Following downright giddy growth earlier this decade, fertilizer sales have fallen back down to earth the past two years. Read More

Latest News

Seed/BiotechKaren Arthur Joins AgriThority As Seed Treatment Produc…
December 19, 2014
Prior to joining AgriThority, Arthur directed research and development programs, overseeing laboratory and field research, to build the Valent U.S.A. seed treatment portfolio. Read More
EquipmentJohn Deere To Sell Crop Insurance Business
December 19, 2014
Deere & Co. has reached a definitive agreement to sell its crop insurance business, subject to regulatory approval, to Farmers Mutual Hail Insurance Co. of Iowa. Read More
Crop InputsNufarm Fills Regulatory VP Position
December 18, 2014
Nufarm announced today that Rob Schwehr has been promoted to the position of Vice President of Innovation & Regulatory Affairs for Nufarm Americas. Read More
Seed/BiotechReport: China Approves Viptera Corn, U.S. Officials Awa…
December 17, 2014
Chinese authorities have informed some agriculture industry officials the government has approved U.S. imports of a type of genetically modified corn developed by Syngenta. Read More
FertilizerMonty’s Plant Food Brings In New Sales Rep
December 16, 2014
Monty's Plant Food Company has hired Warren Kearns as its newest Sales Representative for the South Carolina area. Read More
EquipmentHagie Wins 2014 CropLife IRON Product Of The Year Award
December 15, 2014
The self-propelled sprayer maker has a hit on its hands with the new STS Series model. Read More
Syngenta
Seed/BiotechSyngenta Sees China Approving Contentious GMO Corn Soon
December 15, 2014
Syngenta will make an announcement when it receives official documentation from China that Agrisure Viptera corn, known as MIR 162, has been cleared for import. Read More
Crop InputsVerdesian Life Sciences Names Vice President Of Communi…
December 15, 2014
Amy Bugg will oversee the execution of all promotional strategies for the corporate brand and the complete product portfolio. Read More
StewardshipFarmers, Retailers Attend 4R Certification 4U Workshop
December 15, 2014
More than 160 farmers and ag retailer attended the “4R Certification 4U” workshop December 12 to learn more about the 4Rs of nutrient stewardship, water quality research in the area and cost-sharing opportunities. Read More
Matt Hopkins10 Best New Agriculture Apps For 2015
December 15, 2014
These new agriculture apps are certain to help ag professionals do their jobs more efficiently in 2015 and beyond. Read More
ManagementARA Learnings, Retail Buying Intentions: Welcome To Cro…
December 12, 2014
This informal video program puts news and events effecting retailers into context, and features Editors Paul Schrimpf and Eric Sfiligoj. Read More
Seed/BiotechMonsanto Herbicide-Tolerant Technology Closer To Commer…
December 12, 2014
The final EIS moves Monsanto one step closer to the introduction of Bollgard II XtendFlex cotton and Roundup Ready 2 Xtend soybeans, paving the way to provide access to dicamba-tolerant soybeans and cotton. Read More
Seed/BiotechUSDA Issues Final Environmental Impact Statement On Her…
December 12, 2014
The USDA Animal and Plant Health Inspection Service (APHIS) is issuing a final environmental impact statement on varieties of cotton and soybeans that have been genetically engineered for resistance to several herbicides, including the one known as dicamba. Read More
CropLife 100CHS: Driving Momentum To Help Farmer-Owners Grow
December 11, 2014
CHS Inc., the nation’s leading farmer-owned cooperative and a global energy, grains and foods company, must capture new opportunities to Read More
LegislationARA Applauds CFATS Passage Prior To Holiday Adjournment
December 11, 2014
The streamlined bill provides a four-year authorization of the CFATS program and guidance to DHS on key issues of chemical facility security Read More
Seed/BiotechBayer CropScience’s ILeVO Approved By EPA
December 11, 2014
EPA has approved ILeVO, the only seed treatment that protects the root system against infections caused by the Sudden Death Syndrome fungus and has activity against dangerous nematodes. Read More
Biologicals in Emerging Markets Map.
Crop InputsBiocontrols Could Quadruple By 2025; Will Regulators Pl…
December 11, 2014
The European experience with GMOs offers caution — and a promise — for biologicals. Read More
Crop InputsBASF Donates $75,000 To Feeding America
December 10, 2014
The donation will support Feeding America’s National Produce Program, an initiative that helps with planning, transportation and logistics to ensure fresh produce deliveries to the 200 member food banks around the country. Read More