Don’t worry. Dog-strangling vines aren’t actually strangling dogs.
But Derissa Vincentini, community science co-ordinator at the Invasive Species Centre in Sault Ste. Marie, Ont., said the invasive vine — which officials found in new locations in Norfolk County this past summer — is still concerning.
“They do invade a wide range of habitats, from forests to fields and all the way up to prairies. And in doing so, they can out-compete our native vegetation and our native plants,” Vincentini said.
The perennial vines, which belong to the milkweed family, also produce chemicals, which enter soil and inhibit native plant growth.
The Invasive Species Centre provides resources and education to help monitor and control invasive plants and animals throughout the province. Dog-strangling vine is just one of many such species in the Hamilton area. Others include a self-cloning crayfish, a tall reed and an insect that targets hemlock trees.
Norfolk County’s supervisor of forestry, Adam Biddle, told CBC Hamilton that dog-strangling vine has been known to exist in that region for several years. Around June, officials found it on a residential lot near Waterford, one of the county’s communities. The county then found it on five residential properties within the same block in Simcoe and on a rural woodlot in the area.
“It’s not well established here. It’s kind of just showing up,” Biddle said, adding the goal is to “eradicate it early” before it’s too late.
“It’s very possible it could snowball beyond our capabilities.”
According to the Ontario Ministry of Natural Resources’ website, the plant can produce up to 2,400 seeds per square metre. The seeds spread in the wind and new plants can grow from fragments of roots, “making it difficult to destroy.”
Vincentini said the name “dog-strangling vine” actually refers to two species: the black swallowwort and pale swallowwort — both are restricted under Ontario’s Invasive Species Act and Weed Control Act. The vine has been in the province for more than 100 years, Vincentini said, and continues to spread to new locations, aided by development and the transfer of soil and building products containing the plant’s seeds.
As a municipality, Biddle said, the county doesn’t typically control invasive species on private land. The county has some ability to compel landowners to remove regulated weeds, but in the case of dog-strangling vine, Biddle said it’s been simplest to get landowner permission for municipal crews to pull it out or use herbicide to kill it.
He said Norfolk County works with local conservation groups and land trusts to respond to species in the region, such as Japanese knotweed and wild parsnip.
Biddle added that county officials are talking with partners about how to deal with invasive species on private land, which is important given more than 80 per cent of the wood lots in his area are privately owned and uncontrolled species could spread from them.
To control one of the region’s worst invasive plants, scientists are releasing special caterpillars into wetlands around Ontario. The caterpillars eat phragmites, a reed which outcompetes and replaces invasive plants. At a release site in Binbrook, Ont., researcher Ian Jones explains the work and shares how it’s going.
Protecting hemlock in Burlington
At Royal Botanical Gardens (RBG) in Burlington, Ont., working with a range of partners is also key to managing invasive species, said the gardens’ director of science, David Galbraith.
“One of the things we can do is talk and share resources,” said Galbraith, whose job involves helping to co-ordinate the response to invasives, of which there are about 20 in the RBG’s nature sanctuaries.
The latest is an aphid-like insect called the hemlock woolly adelgid, which causes the destruction of hemlock trees. Galbraith said workers discovered the insect while assessing a forest. Now, the RBG has a grant from the Invasive Species Centre to help control the insect.
“For all invasive species, the most important thing you can do is prevent it from spreading,” he said, adding the RBG plans to take a census of its hemlock trees to learn what’s at risk so it can respond with some form of control.
Galbraith added that the RBG is home to several endangered species. One of them, the few-flowered club-rush, is a grass not known to exist in Canada outside the gardens, he said. It’s threatened by invasive grasses.
Generally, Galbraith said, there’s concern “many of these changes are driven by climate change,” as warmer temperatures mean more invasive species can survive winter.
Managing invasive Japanese knotweed can take years
In the Dundas Valley Conservation Area in southwest Hamilton, teams are working to control another invasive plant: Japanese knotweed.
The Hamilton Conservation Authority (HCA) manages knotweed on its lands and helps landowners in the watershed do the same, invasive species technician Ben Laing told CBC Hamilton in an email.
The plant can grow about three metres tall, Laing said, and grows in patches that can crowd out other plants and create poor environments for animals.
To control it, the HCA cuts knotweed, tarps it over and uses herbicide. Cutting can manage smaller less-established populations, but is time intensive, Laing said. Smothering the plant with a tarp works well in open areas that its taken over, and herbicides can be effective when targeting large populations.
“Like many invasive species, Japanese knotweed is very difficult to completely eradicate once it has established beyond the first few plants,” Laing said, adding that a project the team started on a site this month will likely continue over two years.
“If we determine eradication is unrealistic, either due to accessibility, size or costs, our goal becomes managing the species to prevent it spreading in size or taking over new natural areas we are protecting.”
How you can help stop invasive species
Organizations such as the Invasive Species Centre provide guidance on how communities can limit the spread of invasive species. One thing members of the public should always do is report sightings, Vincentini said, noting online tools such as the iNaturalist app or the Early Detection and Distribution Mapping System are good options.
Some plants such as dog-strangling vine are difficult to identify, she said, since it looks a lot like native milkweed. But the centre has fact sheets with photos to help.
She added that brushing off your boots, cleaning camping equipment, keeping pets on leash and staying on marked trails help too, especially this time of year when plants are seeding.
