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Controlling quackgrass in gardens

Illustration: Weeds of the North Central States

Quackgrass--Agropyron repens--is a perennial weed in Minnesota, and a troublesome weed to eliminate from the home landscape. The Latin name means a 'sudden field of fire', and attests to its ability to take over lawns, fields and gardens. The plant is hardy to zone 3 and is actually native to Europe. It has been growing in the U.S. for over 200 years in all states except Hawaii, Arizona and Florida.

In older books quackgrass may be referred to as couch, quitch, devils, wheat, scutch, twitch, witch, dog or durfa grass. This plant is listed in 41 states as a noxious weed because of the detrimental effects it has on agricultural crops, though it does help control erosion.

In the home garden, quackgrass can invade gardens containing perennial flowers or vegetables, making it extremely difficult to eradicate. This sheet will discuss both chemical and non-chemical methods to control this weed in gardens.

An understanding of how the quackgrass grows will help avoid common errors in battling this plant. Quackgrass grows from underground rhizomes to an unmowed height of 1 to 4 feet. It has thin, flat, bright ashy green leaf blades. The seed spike grows from 3 to 8 inches long and appears in July. Quackgrass seed is often found in rye straw, so you may want to avoid using this as mulch in your garden. Each quackgrass plant produces about 25 seeds; they remain viable 3 to 5 years in the soil. It takes 2 to 3 months for a newly germinated plant to develop rhizomes. It is very important to eliminate the plants before they reach this stage.

Rhizomes (underground stems) are yellow to white, 1/8" in diameter, with distinct joints or nodes every inch or so. Each node is capable of producing fibrous roots, and sending a new blade of grass through the soil. The creeping rhizomes are so tough they can grow through a potato tuber, or push up through asphalt pavement. If left to grow, they will form a dense mat 4" thick in the upper part of the soil. One plant can produce 300 feet of rhizomes each year. Never use a rototiller where quackgrass is growing, because it amounts to propagating thousands of new plants from the chopped up rhizomes.

Chemical control

The most effective way to eradicate quackgrass is by using a herbicide that contains glyphosate (Monsanto Roundup). It should be applied when there is no wind and when there will be no rain for 48 hours. The plant must be green and actively growing for best results. Glyphosate is a non-selective herbicide that will kill almost any green plant it contacts, and also can injure or kill woody plants. It is important to apply glyphosate only to the plants you want to eradicate.

One problem with using glyphosate on quackgrass is that up to 95% of the lateral buds on the rhizomes are dormant even though the plant is actively growing. Since herbicides are translocated from the leaves to actively growing plant tissue, after about 7 days the glyphosate degrades and the dormant lateral buds will start to grow new shoots. It may take more than one application to completely eradicate quackgrass.

One way to overcome lateral bud dormancy is to apply nitrogen fertilizer. This will break lateral bud dormancy, and the herbicide will be translocated to the now actively growing plant tissue and kill the entire plant. Repeat the application of glyphosate every 30 to 45 days; avoid cultivation for 2 weeks after each application.

In daylily beds or other perennial flower beds quackgrass can be very difficult to control. You will need to use a small applicator like a child's paint brush or small sponge, then be extremely careful to apply the herbicide only to the quackgrass leaves. If you contact the daylily leaves with glyphosate, it can kill them, too.

In perennial gardens, a selective systemic herbicide containing fluazifop (fusilade) (Ortho-Grass-B-Gon) can also be used successfully. It is important to apply this only to the quackgrass leaves as it may damage or kill all monocots (daylilies, iris, gladiolus, lilies) once it contacts the leaves. This product can also be used with asparagus (non-bearing plants only; you cannot harvest for 12 months after application), rhubarb, spinach, garlic, peppers, onions and non- bearing trees and vines. Grass-B-Gon is best applied to young quackgrass plants with 2 to 4 leaves; two applications are sometimes required to completely eradicate quackgrass. Apply this herbicide when no rainfall is expected for 24 to 48 hours.

Annuals are a different story. To avoid problems during the growing season, eradicate quackgrass before planting vegetables or annual flower gardens. It is important to wear rubber gloves and eye protection to avoid personal contact with the liquid.

Eliminate quackgrass before putting in any garden, annual or perennial, roses or raspberries. It will never be as easy as prior to planting.

Non-chemical control

In vegetable gardens or flowering annual beds there are other successful methods for controlling quackgrass. Several spring cultivations should sprout and kill any weed seeds before they develop rhizomes. Extremely shallow cultivation works best where there is existing quackgrass as any cutting of the rhizomes means rapid multiplication of plants.

Mulch should be used as much as possible to smother plants, but you can be assured that the rhizomes will creep along until there is an area in which it can send up a shoot. Rhizomes will have to be hand dug as much as possible without breaking them off in the soil, then dried and disposed of. The main thing is to repeatedly eliminate the blades by slicing them off with a hoe. Without photosynthesis the plant will not be able to store food reserves in the rhizomes and will eventually die. Any newly germinated plants can be easily hoed out and they will dry up and die rapidly on a sunny day.

Another way to kill this plant is to smother it by planting a cover crop. A rotation of winter rye and crown vetch followed by buckwheat is a good way to clear an area of quackgrass. This could take a few months to grow and till the cover crops in, but you will add valuable organic matter to the soil in the process.

Mowing the perimeter of the garden is very important to prevent quackgrass seeds from blowing into the garden and germinating. Grass clippings should not be used to mulch the garden if there is quackgrass seed in them. It would be better to compost the clippings. If you are mowing without a mulcher, always blow the clippings away from your garden area.

Quackgrass is a tough weed to eliminate, but by using the proper methods it can be eradicated successfully.


Reviewed 1999

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