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DEVIL'S GRASS APT PSEUDONYM FOR PESKY QUACK GRASS
I was inspecting my December gardens the other day and discovered several thriving patches of quack grass. Each stem I yanked from the ground was connected to a lengthy rhizome (underground stems) that, try as I might, broke before I could remove it all from the still-unfrozen soil. I know from experience that quack grass quickly re-grows from the smallest piece left in the ground.
Laura Paine, a University of Wisconsin extension educator, says quack grass is everywhere, perhaps rivaling corn as the most frequently encountered plant in the Upper Midwest.
You would be either a rare or a gifted gardener if no quack grass grows in your soil.
Quack grass has a number of traits that account for its widespread presence, according to Paine. It is winter hardy, adaptable to a wide pH range (4.5 to 8.0) and, while it can survive under low fertility conditions, it readily sucks up available soil nutrients, absorbing as much as 45-55% of soil nitrogen, phosphorus and potassium.
The trait that has earned quack grass its notoriety is its ability of to spread underground. A single plant can produce more than 500 feet of rhizomes and more than 200 tillers. Couple that with the fact that each seed head can produce 25 to 400 seeds and you can appreciate several common aliases for quack grass: devil's grass and witch grass. Other aliases for this pesky plant include couch grass, dog grass, twitch grass, cough grass, cutch grass, quitch grass, quake grass, scutch grass and durfa grass.
Quack grass rhizomes 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 in. thick in the upper part of the soil.
Controlling quack grass, either with chemicals or by other means, is a challenge. One non-chemical method that won't work is to use a roto-tiller, because the churning action of the roto-tiller blade effectively chops up the rhizomes and efficiently propagates thousands of new plants.
The most effective way to eradicate quack grass, according to Deb Brown, University of Minnesota extension horticulturist, is by using a herbicide that contains glyphosate (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, so apply glyphosate only to the plants you want to eradicate.
One problem with using glyphosate on quack grass, Brown says, 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 seven days the glyphosate degrades and the dormant lateral buds will start to grow new shoots.
Brown says 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 two weeks after each application. Always wear rubber gloves and eye protection to avoid skin contact with the liquid.
If a roto-tiller isn't the answer, what non-chemical solutions are there for quack grass?
Several spring cultivations should sprout and kill any weed seeds before they develop rhizomes. Extremely shallow cultivation works best where there is existing quack grass because cutting rhizomes leads to rapid multiplication of plants.
Mulch can be used to smother plants, but Brown cautions that the plant's tenacious rhizomes will creep along until there is an area in which it can send up a shoot. 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 quack grass. 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.
Young blades of quack grass can be repeatedly cut 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.
For a more detailed discussion of quack grass control, refer to the Yard & Garden Brief titled Controlling Quack Grass in Gardens at the Master Gardener website: www.mg.umn.edu.
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