Quackgrass, a perennial lawn weed, can be difficult to remove. Quackgrass produces perennial growth by storing energy over the winter in its extensive network of underground roots. These roots are the cause of the trouble. Cut back quackgrass and the roots produce new growth. Dig it too shallowly, and any cut root sections left behind will regenerate to form new plants. To make matters even more frustrating, quackgrass is resistant to almost all selective herbicides. But quackgrass is not impossible to remove. You must, however, apply the appropriate control measures over a season or more to ensure that it is gone for good.
Dig up small patches of quackgrass with a shovel or trowel. Dig deep enough to remove the bulk of the quackgrass roots. Then slowly expand your hole and remove root pieces until you cannot find anymore. Bag and dispose of any grass and roots that you dig up. Do not compost them.
Spray quackgrass with a non-selective herbicide in the spring when it is actively growing. The horticulturalists at the University of Saskatchewan recommend a glyphosate herbicide. Coat patches of quackgrass with the herbicide following the manufacturer's instructions for application rates and amounts. Quackgrass only responds to non-selective herbicides. Unfortunately, these herbicides will kill not only your quackgrass but any other plants they come into contact with.
Re-seed any bare areas two weeks after the quackgrass has been killed by herbicide or immediately after digging. Sprinkle small bare patches with seed (roughly 1 cm between each grass seed is an average rate acceptable for most species of grass) and walk over it to ensure its contact with the soil. If your entire lawn has been killed, rotary-till the lawn to a depth of 6 inches and remove as much of the dead grass as possible before laying seed (at the rate recommended for the grass species) or sod.
Monitor your lawn. Where quackgrass has grown before, it is likely to creep up again. As soon as you notice a few sprouting blades of quackgrass, dig them or treat them with herbicide. Quackgrass is much easier to treat when it is in its early stages of growth.