More and more people, especially property owners, are becoming aware of problems posed by invasive plant species. On our 80 acres just outside Duluth, we’ve been fighting Buckthorn for more than ten years. After the third year or so, coming across a small new infestation, we realized that we’re making progress, but it’s a never-ending job. Same with another pesky weed, Tansy. When we first moved here, I performed the amazing task of pulling every last Tansy plant out of our septic field. Then I moved on to the verges of the road and got the picture: this is another project with long-term job security.
I have been working with the local group of CISMA, the Collaborative Invasive Species Management Area, which in south St. Louis County has participation from more than 40 public agencies and non-profit organizations. In the process, I’ve learned about other non-local plants that plague our region, including Japanese and Bohemian Knotweed, Garlic Mustard, Non-Native Phragmites, Japanese Barberry, Oriental Bittersweet, Wild Parsnip, Knapweed, and Leafy Spurge.
I won’t pretend the work is easy, but my determination comes from my love for the earth I live on. I know the reality of ecology is not stasis, but change. But I think my little corner of the earth works pretty darn well as it is, and I’d like to see that it has a chance to adapt slowly to changes.
An invasive species is defined as any plant, animal, insect or disease that is not native and can cause harm to the environment or human health. In general terms, these plants tend to out-compete natives, reduce wildlife habitat or disrupt important ecosystem functions.
Several state departments and many counties respond to the problem of invasive species. Minnesota’s Departments of Natural Resources and Transportation publish a list of “Noxious Weeds” that includes the legal category in which the species is placed.
“Prohibited-Eradicate” means not currently known to be present in Minnesota or not widely established. Per state law, they must be eradicated, meaning all the above- and below-ground parts must be destroyed. Examples include Common Teasel, Japanese Honeysuckle, and Grecian Foxglove.
“Prohibited-Control” means plants established throughout Minnesota or in some regions of the state. Efforts must be made to prevent the spread, maturation and dispersal of any propagating parts. My friend Tansy is in this category, along with Purple Loosestrife and Wild Parsnip.
“Restricted” means plants that are already widely distributed and detrimental to human or animal health or the environment, but whose only feasible means of control is to prevent their spread. Here we find Buckthorn, Crown Vetch and Wild Carrot.
“Specially Regulated” means plants that may be native or have shown economic value, but also have the potential to cause harm. Poison Ivy is hiding out here.
No matter where you live, there is likely a culprit causing problems in your ecosystem.
The good news is that people have banded together to counter the threat; they hone their skills and become quite effective at keeping the invasives in check. There are more than 20 such groups in Minnesota alone, typically working in parks or other public spaces. They love to welcome new members, and it’s a great way to make new friends.
What’s lurking in your neighborhood?
Here are a few examples to get your blood moving.
Garlic mustard (Alliaria petiolata) thrives in shade and threatens to monopolize the forest floor wherever it spreads. It shades out native wildflowers and robs the soil of the fungi those wildflowers need to bolster their roots.
Its seeds germinate in spring and grow into clusters of basal leaves (‘rosettes’) in the first summer. Rosettes develop robust taproots, and their leaves stay green all winter. The next spring the plant ‘bolts,’ sending up a leafy stem that produces many small white flowers. When Common Lilac blooms it is a good time to look for flowering Garlic Mustard. If the plant is not controlled the flowers produce long skinny pods, each with about 20 tiny seeds, in this second summer. The pods dry and split, the seeds fall out, then the whole plant dies. In both years the leaves smell like garlic when crushed.
Because these plants can’t live more than two years, the strategy for controlling an infestation of Garlic Mustard is to prevent seed production. Seeds can germinate after lying dormant in soil for 5-10 years, so control is needed every year until no new rosettes appear. Preventing future arrival of seeds from elsewhere is also important. Since infestations commonly occur near creeks, the water flow often spreads the seeds downstream. Look upstream to find the source and you’ve got a good chance to control it.
Garlic Mustard is categorized as Restricted, so it is illegal to import, sell, or move the reproductive parts.
Non-native knotweeds include three look-alike species that I think of as heart-breaking plants: you hate to cut them back because they’re stunningly beautiful, and you hate it when they keep coming back despite your best efforts to defeat them. Japanese Knotweed (Polygonum cuspidatum), Giant Knotweed (P. sachalinense), and Bohemian Knotweed (P. x bohemicum), dieback to the ground each winter, leaving dead bamboo-like stalks. Bohemian Knotweed is a hybrid between Giant and Japanese Knotweeds.
Leaves are broadly oval with pointed tips. Stems are reddish-brown, smooth, stout, hollow and swollen at the joint where the leaf meets the stem. They look a lot like bamboo. Frost-killed stems turn bronze-colored and often remain standing through the winter. In the spring, new stems re-sprout from existing roots. Eye-catching, creamy-white flowers grow in spikes or drooping clusters in late summer/early fall.
The plant sends out rhizomes, stems that grow below the soil surface. They form roots and produce new plants, eventually forming a dense mat. You’ll see it along roadways and stream banks.
Categorized as a Prohibited-Control Noxious Weed, these survivors resprout from stem fragments as small as ½ inch long. Mowing can spread the plant to new locations. The best advice here is to contract with a professional to control this beautiful beast.
Canada Thistle (Cirsium arvense) is a Prohibited-Control Noxious Weed, meaning that efforts must be made to prevent the spread of seeds or other propagating parts. The familiar spiny plant blooms with clusters of tiny pink/purple flowers with feathery tufts to catch the wind. Seeds can be viable in the soil for up to 20 years. Roots can also produce new plants. It spreads quickly, replacing native plants and reducing diversity. You can hand-pull Canada Thistle, hauling up as much of the root as possible. Mowing will weaken roots and is most effective when flower buds are just about to open. Do not mow when the seed is present, as that will spread the seed.
Now we come to my favorite adversary, Common Buckthorn (Rhamnus cathartica) and Glossy Buckthorn (Frangula alnus). I see hedges of Buckthorn in yards in Duluth and Minneapolis, and always wish the landowners would pull them out. Thanks in part to birds eating seeds, Buckthorn has spread all over the state, forming dense thickets, crowding out native plants and displacing mid-layer trees where many birds typically nest. Common Buckthorn also worsens pest problems for farmers of soybeans and grains, and the dead leaves are harmful to amphibians.
Buckthorn has brown bark with silvery corky projections, but native plums and cherries have similar bark, so it’s easy to confuse them. Berries ripen to black in fall. The leaves stay green late into the fall, making the trees stand out in the woods. Fall is the best time of year to control Buckthorn.
You can easily pull small plants by hand. Plants with thicker stems are best controlled by cutting the stem at the soil surface and then covering or treating the stump with herbicide to prevent re-sprouting. We once used small paintbrushes to apply full-strength Roundup, but were delighted to discover the Buckthorn Blaster, a small plastic bottle with a sponge on top, that makes it easy to treat a stump without getting Roundup all over your clothes.
Battling invasive plants can be a lot of work, but when you think about how much the earth gives us, to me it seems the least we can do.
Information and images in this article come from:
Bugwood Center for Invasive Species and Ecosystem Health, University of Georgia
Minnesota Noxious Weeds, MnDOT
