November 23, 2011

CVC enlists landowners to battle "super weeds"

As published in The Erin Advocate

Just because a species of plant is green and healthy does not mean it will be welcome when it moves into the neighbourhood, especially if it is an immigrant from Asia or Europe. An aggressive campaign has been mounted against invasive species, which can overwhelm native plants and take over large tracts of land.

Human activity has severely disrupted the slow, natural evolution of local ecosystems, creating opportunities for the invaders. Conservation authorities are now attempting to manage forests as one might tend a garden. It seems we must weed the wilderness if we want it to serve our needs.

Credit Valley Conservation (CVC) warns that aggressive new species can destroy the balance of ecosystems and reduce biodiversity, diminishing the goods and services we get from nature, including air and water regulation, recreation, crops, fish and wood products. The costs to Canada's agriculture and forestry sectors alone may be as high as $7.5 billion per year.

Teaching landowners about problem plants is a difficult task, so it is often presented as a war against intruders, or a hunt for criminals. The Ontario Invasive Plant Council publishes a series of "UN-WANTED" posters, with mug shots of plants like Dog-Strangling Vine, a member of the milkweed family that arrived from Europe about 120 years ago. It is currently invading backyards, altering natural areas "at an alarming rate" and has made it onto the CVC's Top Ten Troublemakers list.

The Town of Erin published a warning this year that Giant Hogweed (#1 on the CVC list) had been spotted in the area. This member of the carrot-parsley family, which grows 10-15 feet tall and looks like a giant Queen Anne's Lace, is a special public health hazard. Its watery sap has toxins that cause photo-dermatitis, meaning that skin contact followed by exposure to sunlight produces large, scar-causing blisters, and eye contact can cause blindness. Call County Weed Control if you encounter this plant.

Most of the aggressive newcomers, though, are not poisonous and are quite attractive on their own, with some available at your local nursery. CVC wants landowners to become aware of the most common ones, and to take action against them. That includes not planting them, digging them out (down to the root tips), trimming off seed pods before they open, mowing them down and attacking them with herbicides if necessary.

"People often don't care about this stuff until it actually affects them personally," said Rod Krick, a Natural Heritage Ecologist with CVC, at a recent seminar on invasive species. For example, a farmer would naturally be concerned about Dog-Strangling Vine if it threatened to make valuable pastureland unusable.

Often, these weeds don't simply grow among the native foliage, they obliterate it to create a monoculture. "These aren't just weeds, they are super weeds," said Krick.

While it may be necessary to battle these species, it is important to remember that the enemy is really our species. Humans have created the clear-cut and disturbed areas where invasives often thrive, and it is we who have transported most of them from their natural habitats, either accidentally or for ornamental and commercial purposes.

Sometimes, natural forces can help restore some balance. Do you remember Purple Loosestrife? It was a huge concern in the 1990s as it choked the life out of valuable wetlands under a sea of purple flowers. One of the reasons that invasives flourish is that they have been set free from their natural enemies. Severe infestations of purple loosestrife have been successfully controlled by introducing beetles that feed on it.

Others on the CVC hit list are Common Reed and Rough Manna Grass, which also invade wetlands, and Garlic Mustard, European Buckthorn and Non-Native Honeysuckles which take over forest floors, crowding out the native inhabitants.

CVC urges people who already have invasives to not let them "escape", and especially to not dump garden waste into or next to natural areas, where it could spread invasive seeds. CVC also suggests alternatives for gardeners and landscapers. For example, instead of aggressive ground covers like Periwinkle, English Ivy and Goutweed, consider Wild Ginger or Barren Strawberry.

Instead of Norway Maple, which grows so dense that it shades out all other native trees and shrubs, consider Freeman's Maple or Hackberry. Plant Joe-pye Weed instead of Japanese Knotweed, New England Aster instead of Himalayan Balsam, Blue Flag (Iris) instead of Flowering Rush, Switchgrass instead of Maiden Grass or Feather Grass, and Native Bush Honeysuckle or Witch-Hazel instead of Winged Euonymus (often sold as Burning Bush).

For more information, go to, and the Watershed Science / Invasive Species section of the CVC site,