Home Yard & Garden Newsletter at the University of Illinois
Canada thistle (Cirsium arvense) is a noxious (and obnoxious) weed that I occasionally get questions about. This plant is listed in 43 states’ noxious weed laws meaning that its control is required by law. Illinois is no exception. If Canada thistle is growing on land that you own or manage, you are required to control it. Failure to do so may result in your being slapped with an unwanted fine. However, because this law is poorly enforced in many counties, we see more Canada thistle growing happily and spreading wildly than we should. It is commonly found along roadsides and in pastures, lawns, gardens, crops, and meadows.
Many thistles are biennials meaning that they require two years to complete their life cycle and produce seeds. Unlike many other thistles, Canada thistle is a rhizomatous perennial. That means that shoots can arise from their extensive underground system. These shoots are erect and donot form a rosette as seedlings do. Roots and rhizomes commonly extend 3 to 6 feet down in the soil profile which makes physically and completely uprooting the plant quite difficult to do. This plant is well known for its rapid spread by rhizomes and also by seed. One plant is capable of producing 1,500-5,000 long-lived (20 years or more), airborne seed. Seeds are capable of germinating within 8 to 10 days after the flowers open. If that weren’t enough, one plant can also produce 6 meters of rhizomes per year. Most of the rhizomes stay within 1 foot of the soil surface. It is ranked as being an invasive plant of "major concern" by Elizabeth J. Czarapata, author of "Invasive Plants of the Upper Midwest."
It’s a cool season perennial and actively grows in the spring and fall. It produces flowers very early in summer, usually in early to mid June. Growth slows during hot weather. By early July, seeds are fully developed. This can vary depending on the year’s growing conditions of course. Above ground portions can be killed by frost. Brown, erect stems may persist into the winter.
Canada thistle growing in a lawn.
Plants can grow 2 to 5 feet tall. The stems are hairy and seedling leaves are covered with short bristly hairs. The leaves of mature plants are simple, alternate, and lobed with spiny margins. The upper leaf surface is dark green and hairless, while the lower surface is light green and may or may not have hairs. Flowers are numerous, small (less than 1”), spineless (unlike most other thistles), and bear pink-to-purple, sometimes white, flowers. Plants are dioecious and grow in patches of all male or all female plants. Cross pollination is necessary. Only the females produce seed.
Canada thistle in bloom.
The key to controlling Canada thistle is to control it early before it has a chance to produce seeds and a serious network of rhizomes. Mowing or repeated cutting may be used to help prevent the spread by preventing the production of seeds and starving the plant. Mowing too late, however, can spread the seed. Postemergent applications of a systemic herbicide may be used. Fall is typically the best time for these treatments. Other good times are during the early bolting stage when plants are 6-10" tall and during the bud to flowering stage. In lawns, some herbicide options are 2,4-D, MCPP, MCPA, dicamba, triclopyr, carfentrazone, and quinclorac. Clopyralid is quite effective on thistle. Non-selective herbicides such as glyphosate may also be used. Lawns should be properly maintained to promote a healthy, dense turf that will compete well with weeds.
Canada thistle growing in a landscape bed.
Perhaps your site is not a lawn but instead a landscape bed. Many of these products are not labeled for this use due to the variety of species present. Be sure that the product you use is labeled for the intended area. Often times, careful spot treatments of non-selective herbicides are your only chemical option. Nearby sensitive plants may be covered with plastic prior to application. The plastic may be removed as soon as sprays dry. Applications may also be painted on using a brush or sponge. Be sure to read and follow all label directions carefully. Realize that multiple applications may be needed to eradicate this weed.–Michelle Wiesbrook
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What is Bermudagrass and how is it bad for your yard?
Cynodon dactylon, better known as Bermudagrass, is a perennial warm-season grass that is widely used as both lawn grass and pasture grass. Its toughness, adaptability, and creeping growth habit attract either appreciation or disdain from the homeowners, gardeners, landscapers, and others who plant it or are invaded by it.
Is Bermudagrass a grass lover’s dream?
Bermudagrass can help you achieve a lush green lawn. It quickly grows from seed or sod into a dense lawn that is capable of out-competing weeds and is highly tolerant of insect and disease pests. It thrives in heat and is drought tolerant. It grows roots deep underground to access hard-to-reach moisture and simply goes dormant in the driest of weather. And Bermuda grass is extremely resilient. If a large patch is damaged, it has an incredible ability to regenerate from the deep, creeping roots, and via mower clippings that land on bare soil and then root in. This kind of tough resiliency makes it a grass lover’s dream, but the adjacent landscape, and adjacent landowners, may disagree.
The collateral damage it causes
Ornamental beds, vegetable gardens, paver patios, driveway, and other lawns adjacent to Bermuda lawns are at risk of invasion. Typical maintenance includes regular mechanical and chemical edging during the growing season when Bermuda grass creeps out of bounds both above and below ground. Homeowners and landscapers use lawn edgers to sculpt crisp edges along driveways and lawn borders, then follow behind with glyphosate weed killer to prevent Bermuda shoots from sprouting in mulched areas, pavement cracks, and other non-lawn areas. Unfortunately, that’s not the end of it.
Neighbors of Bermudagrass owners, who don’t wish to grow it themselves, must contend with it. A real challenge ensues, since the chemical controls, both conventional and organic, that kill Bermuda grass also kill other types of lawn grass. Getting rid of Bermuda grass is not an easy task, and it is a task that is never finished.
Are salt and vinegar an eco-friendly way to kill Bermudagrass?
Salt and vinegar are more eco-friendly than pesticides, although they aren’t as eco-friendly as other solutions. A mixture of 1 cup salt and 1 gallon of vinegar will kill any plant, and it’s so effective that if it soaks into your soil, nothing will grow there for a long time. Spraying a light mist over the plants is safe, as only a few drops will make their way into the soil, and such small quantities will neutralize and disperse quickly.
Do not dispose of any leftover mixture by pouring it into the soil. Vinegar is acidic, which kills plants but can also cause chemical burns on skin in high concentrations, so wear safety gear when mixing and applying vinegar as an herbicide. The acidity of salt and vinegar will kill any plant when applied to it, not just Bermuda grass, so this is best for killing a broad area. Otherwise, you’ll need to target the Bermuda grass specifically, which can be tedious.
Can you dig up Bermudagrass?
You can dig up Bermudagrass, but it can be difficult. Digging up Bermudagrass is only the best solution if the grass is in a small area and no other options are available. Bermudagrass doesn’t just have its roots underground, but it also has rhizomes. Rhizomes are thick, underground stems that grow sideways. New grass shoots can grow from them, so if the rhizomes are left behind, your work will have been for naught. When digging up Bermudagrass, you want to dig at least 6 inches, to make sure you’re getting the entire plant. The part of ginger that we eat is the rhizome, so be on the lookout for anything that looks like ginger or an oddly shaped potato.
Think control not eradication
Owners of zoysia, centipede, and fescue lawns often battle Bermudagrass. Unfortunately, it is impossible to kill Bermudagrass organically when it invades another type of lawn without killing both types of grass. Organic herbicides only “burn out” the foliage, leaving the energy stored in the roots to regenerate new foliage.
However, there are systemic lawn herbicides that can help. A systemic herbicide is absorbed through the foliage and then translocates throughout the tissue of the weed to kill the plant. Fluazifop is an active ingredient that kills Bermuda grass and is safe for use on fescue and zoysia lawns. Use a product with the ingredient Sethoxydim to control Bermuda grass in centipede lawns. Be sure to follow the label instructions, including concentration rates, precisely to avoid damaging the good grass.
You should also scalp your Bermudagrass annually. While this treatment is aggressive and shouldn’t be used on most other grasses, scalping your Bermudagrass is helpful to the lawn as irrigation and fertilizer.
How to kill Bermudagrass organically
It takes patience and persistence to kill Bermudagrass organically, and these methods are non-selective, which is to say they kill off all vegetation in the area. The most effective ways to organically kill Bermuda in large areas, such as a lawn renovation or preparing a garden bed, are soil solarization and smothering.
Soil solarization must be done at the hottest part of the summer. It requires at least four weeks with daytime high temperatures above 85 degrees. Hotter and longer is even better. Mow the grass as short as possible. Rototill the area to a depth of 12 inches. Slowly irrigate with one to two inches of water. Cover the area, plus a 2-foot margin all around, with a single sheet of clear plastic. Anchor the plastic in place with landscape staples or by shoveling soil onto the entire perimeter (a good seal is required for the best effect). Leave the plastic in place for four to six weeks.
To smother Bermudagrass, begin by scalping the upper layer with a garden spade or sod cutter. You can rent a sod cutter from your local power equipment rental place. Pile the sod in an out-of-the-way location and cover it with a heavy plastic tarp to decompose. Cover the scalped ground with three or four layers of heavy-duty cardboard. Then cover the cardboard with four to six inches of mulch. Leave everything undisturbed for six months before planting.
After removing Bermudagrass, stay vigilant. This tough grass is capable of reestablishing as quickly as before by roots, stems, mower clippings, and seeds. Learn to recognize it, and dig it out whenever you spot it. It is impossible to eradicate troublesome Bermudagrass, but with constant suppression, you can keep it under control.