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.