Herbicide Resistance: Are Soil-Applied Herbicides Immune?

The continual evolution of herbicide-resistant weeds is one of the most daunting problems faced by weed management practitioners. According to Aaron Hager, associate professor of weed science at the University of Illinois, biotypes of 12 weed species in Illinois are known to be resistant to one or more herbicide action mechanisms.

“The occurrence of multiple herbicide resistances within individual plants and/or fields is a particular challenge,” Hager said. “Waterhemp has evolved resistance to more herbicide mechanisms of action than any other Illinois weed species.”

Frequently, soil-residual herbicides are proposed as part of an integrated weed management program. They provide several benefits, including reducing the intensity of selection for resistance to foliar-applied herbicides.

Many growers believe that weeds demonstrate resistance only to herbicides applied to the foliage. In fact, weeds can also develop resistance to soil-applied herbicides.

For example, imazethapyr (the active ingredient in Pursuit and some herbicide premixes) is an acetolactate synthase (ALS)-inhibiting herbicide that can be applied to the soil or plant foliage. Worldwide, biotypes of 128 weed species have evolved resistance to ALS-inhibiting herbicides. Many Illinois waterhemp populations contain plants that are resistant to these herbicides whether they are applied to the soil or plant foliage.

The story is similar for herbicides that share a common mechanism of action but that are usually applied to either the soil or the foliage, such as herbicides that inhibit the protoporphyrinogen oxidase (PPO) enzyme.

“Waterhemp resistance to PPO-inhibiting herbicides is becoming increasingly common across Illinois,” Hager said. “Growers began to suspect it was present after a foliar-applied PPO inhibitor failed to control plants that were treated within label guidelines. The treated plants demonstrated injury symptoms, such as leaf necrosis, that are characteristic of this herbicide family. However, the injury was less than normal, and the resistant plants begin to recover within seven to 10 days after the application.”

A common misconception is that resistance to PPO inhibitors exists only to those that are foliar-applied. In reality, biotypes of waterhemp that are resistant to PPO-inhibiting herbicides are resistant regardless of whether they are applied to the soil or foliage. However, when a PPO-inhibiting herbicide is applied in the soil, the waterhemp control level is often comparable to that of a susceptible population.

Why do soil-applied PPO-inhibiting herbicides seem to control PPO-resistant waterhemp populations that foliar-applied PPO-inhibiting herbicides do not control?

“Because the dose of the soil-applied herbicide is high enough to overcome the resistance mechanism, at least for a while,” Hager explained. “Foliar-applied PPO-inhibiting herbicides are applied at rates to control the weeds that are present when the application is made. Rates for soil-applied PPO-inhibiting herbicides are calculated to provide several weeks of residual weed control and thus are much higher than what is needed to control weeds that are present when they are applied. The higher rates overcome the mechanism of resistance to PPO-inhibiting herbicides because the magnitude of resistance is relatively low.”

If a waterhemp population contains a mix of PPO-resistant and sensitive individuals, a soil-applied PPO-inhibiting herbicide will control both resistant and sensitive plants for a period of time after application. As the herbicide degrades, a threshold concentration is reached at which the sensitive individuals are still controlled, but the resistant individuals survive. This provides a selective advantage for the resistant individuals and may partially explain the increasing frequency of PPO-resistant waterhemp populations in Illinois.

Selection for herbicide resistance for any herbicide takes place each time it is applied. However, the overall intensity of selection for resistance to a specific herbicide or mechanism-of-action family is reduced when multiple, different tactics are used to control the weed population.

“Not every individual waterhemp plant is herbicide-resistant,” Hager concluded. “An integrated weed management approach that applies soil- and foliar-applied herbicides at labeled rates in combination with other management tactics can help slow the selection for additional resistances in individual plants and populations.”

Topics:

Leave a Reply

Herbicides Stories

HerbicidesREUTERS: Anti-GMO ‘Scientist’ Calls For New Review Of Glyphosate
August 20, 2015
EDITORS NOTE: We feel that it is important to note that there are those that believe one of the lead Read More
Mature Waterhemp in Corn
HerbicidesAustralia’s Seed Destructor Could Be Midwest’s New Tool Against Weed Resistance
August 17, 2015
It’s a piece of equipment that probably isn’t on many Midwest farmers’ radars at this time, but could eventually be Read More
HerbicidesExpert: IARC Herbicide Classifications Leading To Confusion, Misinformation
July 24, 2015
Few people in the crop protection industry had heard of the International Agency for Research on Cancer (IARC) before this Read More
Palmer pigweed seedhead in cotton
HerbicidesUSDA Deregulates Dow AgroSciences’ Enlist Cotton Trait
July 23, 2015
The USDA today issued its decision deregulating Dow AgroSciences’ Enlist cotton trait in the U.S. The USDA has now completed its Read More
Top 100 Articles
Crop InputsLand ‘O Lakes, United Suppliers Finalize Merger
August 24, 2015
According to a press release on August 24, owners of United Suppliers, Inc. and members of Land O’Lakes, Inc. “have Read More
West Central Cooperative, Jefferson, IA
CropLife 100Iowa Cooperatives To Explore Unification
August 19, 2015
The boards of directors at two of Iowa’s leading farmer-owned cooperatives yesterday signed a letter of intent to study the Read More
CropLife 100Southern States Coop Hosting Drone Flight This Friday
August 3, 2015
Southern States Cooperative — No. 9 on the CropLife 100 — is hosting an FAA-approved drone demonstration at Grandview Farms Read More
CropLife 100Aligned Ag Distributors Adds Four New Owners
July 30, 2015
Aligned Ag Distributors LLC has announced the addition of four new customer/owners to Franklin Holding Co. LLC. They are: The Read More
CropLife 100Pinnacle Purchases California-Based Specialty Crops Retailer
July 20, 2015
Pinnacle Agriculture Holdings has successfully acquired California-based NH3 Service Co.  Operating as part of Pinnacle’s Performance Agriculture brand, the new locations Read More
Asmus Farm Supply liquid fertilizer facility features 20,000 square feet
CropLife 100Slideshow: Asmus Farm Supply Shows Off Its New Liquid Fertilizer Facility
July 15, 2015
Asmus Farm Supply, Rake, IA, recently added a new liquid fertilizer facility to its company operations. The new liquid fertilizer Read More
Latest News
Crop InputsNFU: Monsanto Decision To Withdraw Syngenta Bid ‘…
August 26, 2015
National Farmers Union (NFU) President Roger Johnson said the organization was very pleased by the news that Monsanto has withdrawn Read More
Crop InputsMonsanto Withdraws Bid For Syngenta
August 26, 2015
Monsanto Co. abandoned its latest effort to acquire Syngenta AG, the world’s top maker of pesticides, after a sweetened bid Read More
Syngenta Sign
Crop InputsSyngenta Comments On Monsanto Announcement
August 26, 2015
The Board of Syngenta confirms that it received a verbal proposal from Monsanto to acquire the company at a price Read More
Case IH Patriot 2250 Sprayer
EquipmentHigh-powered Case IH Patriot 2250 Sprayer Pushes Throug…
August 26, 2015
Engineered with more muscle, the new 660-gallon-capacity Patriot 2250 sprayer features best-in-class horsepower, along with the fuel efficiency that comes Read More
Crop InputsLand ‘O Lakes, United Suppliers Finalize Merger
August 24, 2015
According to a press release on August 24, owners of United Suppliers, Inc. and members of Land O’Lakes, Inc. “have Read More
TMX-2050 In-Cab Display Launch Run Screen
Eric SfiligojPrecision Ag Could Shine In Increased Spotlight On Agri…
August 24, 2015
By any measure, 2015 is turning into one of the most challenging years agriculture has ever experienced. All throughout good Read More
ManagementCrop Conditions In Minnesota and Traveling Time
August 21, 2015
Editors Paul Schrimpf and Eric Sfiilgoj discuss the crop outlook from a field trip to Minnesota and upcoming travel plans. Read More
HerbicidesREUTERS: Anti-GMO ‘Scientist’ Calls For New…
August 20, 2015
EDITORS NOTE: We feel that it is important to note that there are those that believe one of the lead Read More
Rendering of Syngenta Seedcare Institute expansion
Seed/BiotechSyngenta Announces Seedcare Application And Resource Ce…
August 19, 2015
Syngenta recently announced the Seedcare Application and Resource Center, a collaborative new website designed exclusively for Syngenta Seedcare customers to Read More
Winter Wheat
Industry NewsArysta LifeScience Announces Two New Regional Sales Man…
August 19, 2015
Arysta LifeScience North America recently announced Steve Vining and Phil Reding have each accepted new positions as Regional Sales Managers. Read More
West Central Cooperative, Jefferson, IA
CropLife 100Iowa Cooperatives To Explore Unification
August 19, 2015
The boards of directors at two of Iowa’s leading farmer-owned cooperatives yesterday signed a letter of intent to study the Read More
Golden Harvest Corn healthy leaves
Industry NewsAligned Ag Distributors Names Vice President, Crop Prot…
August 18, 2015
Aligned Ag Distributors LLC have appointed Warren Hragyil to VP Crop Protection. Hragyil comes to Aligned Ag Distributors LLC with Read More
Industry NewsH.J. Baker Hires Manager For Crop Performance Division
August 18, 2015
H.J. Baker has announced Donald Sutton has joined the company’s Crop Performance Division as a part of the U.S. sales Read More
Radish cover crop taproot
Crop InputsSoil Health Field Days Promote Agricultural Evolution
August 18, 2015
Brent Bible practiced no-till farming and the use of cover crops on his farm in Lafayette, Indiana, but until recently, Read More
Cover Crop on corn
Industry NewsMore Farmers Find Healthy Soil Works For Crops, Bottom …
August 17, 2015
Doug Toussaint’s field was in critical condition — and he was the one killing it, reports Dan Gunderson on MPRNews. Read More
Deere tillage
Crop InputsTillage Practices Have A Direct Correlation To Soil Hea…
August 17, 2015
Many areas, including Michigan, have experienced a heightened sense of awareness of the importance of soil quality, according to Michigan Read More
Eric SfiligojAn Interesting Water Issue On The West Coast
August 17, 2015
A few weeks ago at the 2015 Environmental Respect Awards event in Wilmington, DE, one of the speakers talked about Read More
CF Industries' Donaldsonville, LA, nitrogen complex expansion site.
Industry NewsBleak Outlook Sparks Frenzied Dealmaking In Nitrogen Fe…
August 17, 2015
Sinking crop prices and frenzied output growth by producers have sparked a flurry of dealmaking worth nearly $10 billion in Read More