Quack grass is a weed worthy of many names. In Latin its name is Elymus repens, but it is also referred to by a previous name, Agropyron repens. It has an abundance of common names across the country, including couch grass, dog grass, quick grass, quitch, scutch, twitch and witchgrass. Whatever you call it, this weed is a common problem on many vegetable and berry farms, especially in temperate growing areas. A native of Europe, it is also found in pastures, gardens, roadsides and other disturbed but unshaded areas.
Integrated quack grass management includes bare fallow tillage with a spring or spike-tooth harrow, ideally starting in the hottest, driest part of the summer, going no more than 4 inches deep and repeating as soon as new shoots that come up have three to four leaves.
Photos by Vern Grubinger.
One obvious characteristic of this grass is its system of underground stems, or rhizomes. The rhizomes allow quack grass to spread out widely from the "mother plant" in little time. New shoots sprout up from nodes on the rhizomes, and these can survive on their own if separated by mechanical cultivation. The rhizomes also provide a place for the plant to store energy for future growth. These are some of the reasons why quack grass can be hard to control.
The following information is taken from the fact sheet titled "Quackgrass Management on Organic Farms," written by Heather Westwood, Kara Cox and Eric Gallandt and produced by the University of Maine Sustainable Agriculture Program.
Plant biology - Aboveground quack grass stems grow from 1 to 4 feet high. These stems and the upper leaves can be somewhat hairy, but the undersides of leaves are smooth. The plant can spread by seeds as well as rhizomes. The seed spikes look a lot like those of Italian ryegrass, but if you roll them between your fingers, the quack grass spikes will feel round and the Italian ryegrass spikes will feel flat.
Although seeds contribute to long-distance dispersal, local infestations of quack grass result from prolific rhizome growth. These rhizomes, in addition to the fibrous root system, comprise 60 to 70 percent of total plant weight. Rhizomes can grow more than an inch per day and extend 10 feet or more from the mother plant.
Quack grass is a perennial, so it needs a reservoir of energy to survive from year to year. It stores sugars in its roots and rhizomes in the late summer and fall so it can survive the winter. In the spring, the plant has energy available that puts it ahead of crops that start from seed.
Quack grass is most vulnerable just as the shoots are emerging - sugar from the roots is being used to promote new growth, but since the young leaves are not photosynthesizing to their full ability yet, little sugar is being sent back to the roots.
The annual cycle of this cool-season grass starts early in the spring. Aboveground growth is limited during the hottest days of summer, but belowground rhizome production is greatest then. In the fall, the tops of the parent plants die off. The rhizomes stop growing horizontally and instead form new shoots that emerge from the soil. Even following repeated disturbance throughout the summer, if soil moisture is adequate, quack grass may begin to flourish in the fall after most crops have been harvested or have died back.
After repeated summer tillage, fall cover crops should be planted, sometime in August for most Northeast locations. Possible covers include winter rye or oats plus hairy vetch. Another option is to plant a winterkilled cover crop like oats or oats and peas. A thick, even stand of cover crop is necessary to suppress any quack grass that continues to sprout.
An integrated approach to quack grass management is necessary: prevention, tillage, depletion of rhizome sugar stores (accomplished by grazing or mowing) and a competitive crop that will keep surviving rhizome buds from thriving.
Mechanical suppression - Hand-digging, mulch (like a fabric weed barrier) and careful monitoring may be sufficient for small, recently established quack grass patches. Disrupting the root system activates dormant rhizomes, causing the grass to regrow abundantly. You must dig the new plants again before they have more than three leaves, but repeating the process several times will usually eradicate the stand.
When dealing with more widespread quack grass, it is recommended that you till repeatedly with a spring or spike-tooth harrow, starting in the hottest, driest part of the summer. This will expose the roots and rhizomes to the sun, so they will dry out; be aware that this method will not be as effective for rhizomes that have adapted to drought-like conditions. Again, rhizome buds will separate from the parent plant and sprout due to the disruption, so tillage has to be repeated when the new plants put out three leaves.
Pull up a quack grass plant and you'll see long white rhizomes up to a yard long, with nodes every couple of inches. Each node can form new plants, and are more likely to if the rhizomes are separated from the mother plant by tillage. New plants started from rhizomes are more vigorous than those started from seed.
Rhizome fragments buried in the top 4 inches of soil tend to sprout at the same time, making it easier to kill the shoots at the correct stage. Therefore, tillage methods should be designed to keep rhizomes as close to the soil surface as possible. Tillage should be repeated every time new shoots come up and develop three to four leaves. If young quack grass plants are allowed to grow any more leaves, they will begin to send out new rhizomes, and they will also begin accumulating new stores of sugar in the roots. Each tillage operation removes the new shoot growth and forces the plant to sprout again, until its belowground food reserves are completely exhausted.
While a substantial amount of quack grass rhizomes can be killed in the first year of management, at least two years of tillage may be required for good control. If a quack grass stand remains relatively thick after the first year, tillage must be continued until the middle of the next summer. Soil type can influence the amount of cultivation needed to eradicate quack grass. Two to three rounds of cultivation may suffice on lighter soils, but with heavier clays it may take as many as six. Once your perennial weed problems are under control, the length of the summer fallow can usually be shortened.
Left unchecked, quack grass can quickly become a serious problem in vegetable fields.
Mowing or intensive grazing can also be used to manage quack grass. Mow as close as possible to the soil level to reduce new rhizome growth. Intensive grazing that encourages the animals to eat the shoots down to the soil level would also help reduce rhizome growth.
Cover cropping - Following a sequence of repeated tillage throughout the summer, a fall cover crop should be planted. Overwintering cover crops include winter rye or rye plus hairy vetch. You could also plant a winterkilled cover crop like oats or oats and peas. To prevent quack grass reinfestation in years without a summer fallow, competitive fall cover crops such as rye or oats should be planted soon after harvest of the cash crop. The key with fall cover crops is to establish a good, competitive stand. This means you would want a seeding rate of 2 to 2.5 bushels per acre of oats, for example.
Sanitation - Quack grass has a tendency to spread from weedy field edges into fields, where occasional tillage encourages further spreading by separating buds from the parent plant. Mow your field margins on a regular basis - this causes the same sort of reduction in energy reserves as repeated digging.
Rhizomes can easily be moved from an infested area to a clean one, so to prevent re-establishment, it is necessary to thoroughly clean tillage equipment after it is used in infested fields.
Conclusions - Multiple strategies need to be employed in order to successfully manage quack grass. Of particular importance is well-timed tillage, repeated when regrowth reaches three to four leaves. Thus, summer fallowing is critical to controlling quack grass if it is already well-established in a field. If possible, take fields with quack grass out of production every other year for a summer fallow, or at least try doing a summer fallow every four years. Periodic fallowing of field edges should also be done to reduce movement of rhizomes into fields. Harrows with S or C-shaped spring shanks are useful for bringing quack grass rhizomes to the soil surface, where they will dry out and die, weather permitting. Crop rotations that include vigorous fall cover crops, both after summer fallowing and summer cash crops, can help reduce quack grass infestations.
The author is a vegetable and berry specialist with University of Vermont Extension based at the Brattleboro office.