GardenLine | Yard & Garden | Quackgrass: A Tough Weed To Beat

Wood was an instructor with the Department of Horticulture Science. This column is an extension service provided by the Division of Extension and Community Relations and the Department of Horticulture Science, University of Saskatchewan.

Quackgrass is one the most troublesome perennial grassy weeds in our lawns. Also called couchgrass, this herbaceous perennial dies back to "rhizomes" for the winter, only to appear again early the following spring. Rhizomes are underground stems capable of producing new plants. Because quackgrass is very aggressive and produces many rhizomes, it can quickly dominate a lawn.

Choosing a Herbicide Quackgrass is more complicated to control than other weeds. Many weeds can be controlled with "selective" herbicides - ones that kill specific plants and leave all others unaffected. Unfortunately, there is no selective herbicide available to control quackgrass in lawns. To control quackgrass chemically, a "non-selective herbicide" is required. A non-selective herbicide will kill all growth it contacts.

The non-selective herbicide glyphosate can be used by the homeowner to effectively control quackgrass. Glyphosate is a "systemic" herbicide; it is absorbed by the leaves of the plant and moves to the root system, where it kills from within. Glyphosate can be purchased as a concentrate or in prediluted form under various trade names, including Erase, Roundup and Sidekick.

In applying the chemical, carefully follow the instructions supplied by the manufacturer. If the solution is too strong, the chemical will not be transported to the roots; if it is too weak, it will kill only part of the root system.

Methods of Controlling Quackgrass

With Chemicals - If most of the lawn has been affected by quackgrass, spray the entire lawn with glyphosate (Erase, Roundup, Sidekick or other commercial products) according to the manufacturer's instructions. Spray when the lawn is growing actively, preferably in the spring. The application will kill the lawngrass as well as the quackgrass. In about two weeks, when all the grass is dead, rototill thoroughly and remove as much dead sod as possible. Then prepare the soil for seeding or sodding.

If a small area of the lawn is affected, spray only the affected area with glyphosate; in this case, it is not necessary to spray the entire lawn.

If the problem amounts to no more than a few spears of quackgrass in an area of your lawn, paint the individual spears with diluted glyphosate, taking care to avoid painting the lawngrass.

Without Chemicals - If only a small area of the lawn is affected, it may be worth trying to dig out the quackgrass; but all the rhizomes must be removed because rhizomes as small as 1-2 cm (about 1/2 in.)) can produce new growth if left in the soil.

Frequent, close mowing can be an effective way to control quackgrass on lawns of bluegrass or fescue. Quackgrass grows faster than bluegrass and fescue and is therefore more susceptible to damage from the mowing. If you use this method, fertilize and water your lawn according to recommended practice. A healthy lawn is less likely to be damaged from the stress of close, frequent mowing - though there is always the risk of some damage, even to a healthy lawn. For bluegrass and fescue lawns, mow not closer than 4 cm (1.5 in.).

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Sustainable horticultural information, offered free of charge to the public with the support of the University of Saskatchewan Extension Division, the Department of Plant Sciences and the Provincial Government.