Space Invaders

Over 800 alien plant species have invaded Canada, more than 400 in Ontario alone. Most recently, kudzu vine, bane of the southeastern United States, has made its way northwards and in 2009 slipped across the border near Leamington.  Fortunately, it was soon spotted and is being closely monitored. Other pesky invaders are already well established here in meadows and woodlands, beside trails and waterways, and quite possibly in your own backyard.

According to Stephen Murphy, Professor and Chair of the Department of Environment and Resource Studies, University of Waterloo, garlic mustard is number one on his list of most troublesome plants in this region. Challenging garlic mustard for top place is common buckthorn followed by dog strangling vine, Japanese knotweed, and dame’s rocket (Hesperis matronalis). Dame’s rocket is often referred to as wild phlox — yes, that plant with the lovely purple and mauve flowers. Yet it’s a serious menace, posturing as a native flower in a beautification project while quietly intruding into woodlots, overwhelming early spring ephemerals.

Garlic mustard (Alliaria petiolata), meanwhile, may sound like a perfect condiment, and has been called poor man’s mustard, but it’s a prolific self seeder, and is unthreatened by the insects and fungi that keep it under control in its native habitat — Europe, Asia, and parts of Africa. Deer rarely eat it but can aid its spread by disturbing the soil, creating optimum conditions for further regeneration. Garlic mustard also has a negative allelopathic effect by producing chemicals that suppress soil organisms required for optimum growth of native plants like blue cohosh, trout lily, and bloodroot. Even our beloved trillium faces eviction. “Garlic mustard overwhelms these smaller understorey plants,” says Professor Murphy, “while buckthorn moves in on the overstorey plants.”

Common buckthorn (Rhamnus cathartica) can grow to a height of two to three meters or more. It produces berry-like fruit that is eaten by animals and birds, particularly starlings. In return, these helpful critters carry out a handy seeding program by making deposits far from the source, resulting in new colonies. Like many invasive plants, it was originally introduced as an ornamental plant, often used as a hedge or windbreak. It’s one of the first plants to leaf out in spring, forming a dense canopy leaving seedlings of native plants and trees in the dark.

Almost as troublesome is the ominous sounding dog strangling vine (Cynanchum rossicum). If you’re regularly kept awake by a hound from hell, a dog strangling weed may not sound like a bad idea to you. It’s an herbaceous perennial twining vine that forms a loose, ropy canopy, choking out competing vegetation. I’m not aware of dogs actually meeting their demise due to this plant, but I might be concerned if Rover vanished into a patch with a magazine or Sudoku puzzle. DSV has become the number one problem for Joshua Shea, Natural Area Coordinator with the City of Kitchener. “It’s widespread, particularly in the Huron Natural Area,” he says.

A member of the milkweed family, DSV doesn’t have any natural enemies as it does in its native Europe, but monarch butterflies are attracted to it. This concerns environmentalist Sean James, a graduate of the Niagara Parks School of Horticulture and expert on invasive plants. “The monarchs lay their eggs on the plant, but the plant doesn’t support the development of the larvae. Regrettably, this has an impact on the number of butterflies.”

Even if the DSV is physically removed, it readily re-roots (picture the scene in "The Sorcerer's Apprentice" where the broomstick chopped up by Mickey Mouse becomes an army of brooms). Nothing appears to have a permanently damaging effect on this plant as it even tolerates burning and resists herbicides.

Perhaps the most aggressive invasive plant is the dreaded Japanese knotweed (Fallopia japonica). It, too, was introduced as an ornamental plant back in the nineteenth century, and has since made tremendous headway in its quest to take over the world. If it appears in your garden, moving may be the only option as it is notoriously difficult to eradicate. By the time it’s stuck its head above ground — even through asphalt or concrete, vigorous roots are already spreading laterally as far as ten meters and up to three meters deep — try digging that up! Leave behind the tiniest fragment and it will sprout a new plant, while parts of the stem will produce shoots and roots within days when dropped into soil or even floated in water.

The above plants cause the greatest problems, but there are many garden plants that given the opportunity will make a break for freedom. They may appear innocuous; I mean, who could be concerned about the delightfully fragrant lily of the valley, periwinkle with its cute blue flowers, or goutweed, the oh so efficient ground cover. They may be acceptable, even useful — if restrained by concrete, but given the chance they’ll take over flowerbeds or whole gardens and potentially create rifts in an otherwise peaceful neighborhood.

These sneaky plants recognize no boundary and will quickly overrun or crowd out native plants. “It’s important for the municipality to monitor for early detection,” says Josh Shea, “particularly the border between private gardens and parks or wilderness areas.”

Although there are limits on the use of herbicides, particularly in private gardens, digging and removing as much as possible of the plant then stifling it with a black plastic cover for as long as a year or more can be effective.

While there may not be easy solutions to deal with invasive plants, there has been success with Purple loosestrife, the plant once feared would colonize every wetland in the province. It has been brought under reasonable control thanks to the release in the late 1980s of a pair of leaf eating beetles, but only after extensive research was done to ensure the helpful bugs would not move on to native plants.

This may be viable solution for other problem plants, and research is underway but it takes years of study and sufficient funding to ensure there would be no unexpected consequences. “Unfortunately,” says Professor Murphy “although the Canadian Food Inspection Agency, for instance, has some control at airports, there is no one stop organization for control of invasive weeds. Municipalities, however, do a reasonable job with the funding they have.”

Although there is no monitoring of invasive species at the regional level, most local municipalities usually have a weed inspector on staff. Some municipalities enlist volunteers to help track and monitor invasive species in natural areas or assist in labour intensive eradication programs. While vigilante groups can also be helpful, it is important that they be aware of property issues and have an expert on hand to aid in identification.

Meanwhile, homeowners need to be vigilant and persistent if they are to eliminate invasive plants from the garden, or avoid inadvertently introducing invasive plants. The Ontario Invasive Plants Council offers a useful “Grow Me Instead” guide at http://www.ontarioinvasiveplants.ca/ while Ontario’s Invading Species Awareness Program recommends the following strategies:

Learn how to properly identify Japanese Knotweed and how to effectively manage invasive plants on your property.

Avoid using invasive plants in gardens and landscaping.

Purchase non-invasive plants from reputable suppliers. When gardening, consider the use of native plants which provide habitat and food sources for wildlife.

Do not dispose of invasive plants in the compost pile – discard them in the regular garbage or check with your municipality for disposal information.

When hiking, prevent the spread of invasive plants and seeds by staying on trails and keeping pets on a leash.

But why care, you may ask, as long as natural areas look more or less greenish? Unfortunately, when the biodiversity of ecosystems is disrupted or destroyed by invasive species, there are long term effects and often unexpected consequences. Besides removing a food source for birds and animals, alien plants harbour pests and disease that threaten agricultural crops. Ontario Ministry of Resources estimates that every year, invasive plants cost the agriculture and forest industries in Canada about $7.3 billion.

And besides, this is our home and native plant land . . . so please stand on guard.