Quackgrass (Elymus repens) is a highly persistent perennial weed that often invades lawns and gardens. Since it is a cool-season grass, it shares many biological similarities with desirable turfgrass species, making selective removal extremely difficult. Most common weed killers target broadleaf weeds, so controlling this grassy weed requires specialized chemical or mechanical methods. The tenacious nature of quackgrass is rooted in its extensive underground network, demanding a targeted approach for lasting control. This article guides you through identifying this weed and implementing selective control strategies to protect your desirable grass.
How to Identify Quackgrass
Correct identification is the first step toward effective control, as quackgrass possesses distinct features that separate it from typical lawn turf. The most definitive characteristic is the presence of slender, claw-like appendages called auricles located where the leaf blade meets the stem. These auricles wrap around and clasp the stem, a feature absent in many other common grassy weeds.
Another key identifier is the aggressive, underground root structure known as rhizomes. These rhizomes are long, white, and wiry, often possessing sharp tips that allow them to penetrate and spread through hard soil. Digging up a patch of the weed reveals the interconnected network of these rhizomes, confirming the identification.
The visible plant growth is typically coarse and a dull, often blue-green color that stands out noticeably against the finer, brighter green of many lawn grasses. Quackgrass also tends to grow faster and taller than the surrounding turf, creating distinct patches visible shortly after mowing.
Targeting Quackgrass with Selective Herbicides
Eradicating quackgrass without damaging desirable turfgrass relies on specialized post-emergent herbicides known as “grass-in-grass” control. These chemicals exploit subtle biological differences between the weedy grass and the turfgrass to achieve selectivity. Two main classes of active ingredients are used for this purpose: sulfonylurea herbicides and ACCase inhibitors.
A primary example is the sulfonylurea herbicide sulfosulfuron, often commercially available for use in established turfgrass. This chemical works by inhibiting the acetolactate synthase (ALS) enzyme, which is required for the synthesis of essential branched-chain amino acids. The targeted quackgrass absorbs the chemical through its foliage, and the resulting lack of amino acids causes the weed to stop growing and die.
The selectivity of sulfosulfuron and similar sulfonylurea compounds is metabolic. Desirable turfgrasses, such as Kentucky bluegrass or Bermudagrass, rapidly metabolize and break down the herbicide into inactive, non-toxic compounds. This swift detoxification prevents the chemical from accumulating to lethal concentrations within the turf, while the slower-metabolizing quackgrass succumbs to the enzyme inhibition.
Another class, the ACCase inhibitors, including chemicals like fenoxaprop-p-ethyl, targets the acetyl-coenzyme A carboxylase (ACCase) enzyme. This enzyme is crucial for the biosynthesis of fatty acids and lipids, which are necessary for cell membrane production. Blocking ACCase starves the weedy grass of the components needed for new growth.
ACCase inhibitors are effective against many grass weeds because they target the specific form of the ACCase enzyme found in the grass family. Selectivity is achieved either because the desirable turfgrass quickly metabolizes the chemical, or because the turfgrass species possesses an ACCase enzyme form that is naturally less susceptible. Applying these selective chemicals allows for the targeted disruption of quackgrass physiology while minimizing harm to the surrounding lawn.
Cultural and Manual Removal Methods
For smaller infestations or for homeowners who prefer non-chemical control, cultural and manual removal methods can be effective if performed diligently. Manual removal involves carefully digging up the entire quackgrass plant, including every piece of the extensive underground rhizome network. Leaving even a small fragment of the wiry rhizome behind allows the weed to quickly regenerate into a new plant.
This labor-intensive process is best suited for small, isolated patches and is most successful when the soil is moist, allowing for easier removal of the entire root system. For larger areas, a process called solarization uses heat to eliminate the growth. This technique involves covering the infested area with clear plastic sheeting during the hottest months of summer.
The plastic traps solar radiation, raising the soil temperature to levels lethal to the quackgrass shoots and rhizomes. The sheeting must be left in place for six to eight weeks to ensure the soil is sufficiently heated to kill the tough, deep rhizomes. Solarization is a highly effective, non-chemical option but requires sacrificing the treated area for the duration of the summer.
Another approach centers on competitive planting, which aims to outcompete the quackgrass. Heavily overseeding the lawn with desirable turfgrass and maintaining a dense, healthy stand helps to choke out the invading weed. Aggressive fertilization and proper mowing techniques favor the growth of the turf, reducing the light and nutrients available to the quackgrass.
Optimizing Treatment for Long-Term Control
Achieving long-term control of quackgrass requires more than a single application due to the weed’s extensive rhizome system. The timing of chemical treatments is important for maximizing effectiveness and ensuring the herbicide is translocated to the underground storage organs. The optimal time for a post-emergent herbicide application is late summer to early fall, typically between August and October.
During this period, the quackgrass actively moves carbohydrates and energy reserves down to its rhizomes in preparation for winter dormancy. Applying a systemic herbicide at this time allows the chemical to be pulled down with those reserves, concentrating the dose in the structures responsible for the weed’s perennial survival. This process ensures that the entire plant, not just the visible foliage, is targeted.
Because the rhizomes contain numerous dormant buds, repeat applications are usually necessary. A second treatment, often applied two to three weeks after the first or the following spring, targets new shoots emerging from surviving rhizome fragments. Consistent cultural practices, such as maintaining a dense, deep-rooted turf through proper watering and fertilization, help prevent re-infestation by outcompeting new quackgrass seedlings.