Compiled by Sandy Garland
We asked WPP members to send us information and stories about what invasive plant species they are dealing with and how. Our aim was to exchange information, especially about best practices and techniques that work.
For this purpose, we defined invasive as any plant that spreads so quickly and extensively that it dominates a site at the expense of other vegetation.
Wild Parsnip (Pastinaca sativa)
Janet Mason has a 2-ha hay field, on an old farm in the rural west end of Ottawa. It includes a lot of Common Milkweed plants, which are used by many Monarch butterflies, as well as some non-native, but non-invasive flower species. The field is cut for hay after the bird nesting season, usually in late July/early August. About 5 years ago, Wild Parsnip started to move in. The plants are sporadically spread across the field and not in large clumps.
Starting when Wild Parsnip is just beginning to bloom, I cut the plants at the base using long-handled loppers. I walk the field about 3 times a week for a month to do this. Sometimes a plant grows back and tries to flower again so I lop it off again. I leave the plants lying on the long grass.
Long sleeves, long pants, gloves, and glasses protect me from the sap. Cutting at the base using a long-handled tool also helps.
It used to take 3-4 hours for the first cut 5 years ago. Now I’m down to about an hour, with follow-up forays of about 15 minutes each.
Parsnip has a hard time competing where the turf is dense and the grass grows high. It prefers disturbed areas, so it grows along my mowed pathways in the hay field.
I have also noticed what appears to be Parsnip Webworm attacking the plants and preventing them from flowering. Unfortunately there aren’t enough of them to make a big difference.
Although my control method is labour intensive, it works because Wild Parsnip is a biennial. That means flowering plants do not grow back the following year. If you can keep them from producing seeds, no new plants will grow the following year.
My neighbour’s field still has parsnip so I’m getting new seeds sprouting along our boundary.
Common Buckthorn, Purple Loosestrife, Poison Ivy, and Knapweed
Johanna Cutts owns about 4 ha of land in rural Carp. Significant invasives on her land are Common Buckthorn, Purple Loosestrife, Poison Ivy, and Knapweed. She is looking for effective techniques to control them.
Hundreds of buckthorn trees are located along a forest edge. Many have been cut down and burned, some trimmed, and small trees pulled out. These efforts have curbed berry production, but because of sheer numbers, nothing has been effective to eradicate its spread. Looking for suggestions.
Purple Loosestrife grows in areas along the edge of the pond and creek beds. Plants have been dug up using a backhoe and deposited in garbage bags for curbside pick up. New plants are regularly pulled up by the roots. This has helped in deterring its spread.
Poison Ivy plants occur along a trail by a creek. Many plants were dug up and put in garbage bags for curbside pick up. Others were eradicated using a Pine Sol spray; however, that does not kill the roots.
Knapweed plants are located in sandy areas or in disturbed soil. Currently, nothing has been done to eradicate or deter its spread.
Facts and best management practices from the Ontario Invasive Plant Council
Knotweed and Dog-strangling Vine
Sharon Boddy lives near Hampton Park Woods, an 11-ha urban forest that is connected to a city park. The woods consist of several habitats including uplands deciduous woods, wood-edge areas, open grass and meadow, and marshy areas that are part of an old creek bed and which still functions as stormwater control.
Two years ago, a flora and fauna inventory identified about 140 species, of which at least 20 were invasive flora. The most problematic plant species are Norway Maple, Japanese Lilac, Japanese Knotweed, Dog-strangling Vine, and buckthorn.
- Cut and cover. Volunteers chopped down a 100-m2 stand and covered it with landscape fabric. Monitored for regrowth around edges. Each year, take up tarp, dig out roots, re-lay tarp.
- Cut and covered as above but this was done by the National Capital Commission and more roots were dug out, heavier tarp was laid, and woodchips laid on top of that. Signage erected.
- Glyphosate. The NCC did a pilot chemical treatment on one knotweed colony (two rounds of spraying, June and September). Their plan is to regenerate in late 2022-2023.
- Cut, dig and/or pull. Depending on the time of year, DSV can be pulled relatively easily out by the roots. At other times, it is cut as close to the ground as possible to weaken the system.
Consistent monitoring is important. If you’re not using chemicals and you don’t want to have an area covered for too long (e.g., 5 or more years), continual digging every spring must be done or the plant quickly re-establishes.
Chemical treatments work but should be done by professionals and ensure that no other native vegetation will be harmed. The treatment process used by the NCC targets the knotweed directly.
A small amount of regular table salt poured directly into large canes that could not be dug out weakened plants and made it easier to dig them out a few weeks later. Salt must be used sparingly as it can be toxic to other plants and the soil.
The NCC wants to keep all areas covered for 5 years, but we believe we can slowly edge back the tarp, remove the knotweed roots, and immediately replant. We did a test of this in one area (on a slope in fact, which is more difficult) and the native plants are “holding the line.” We plan to beef up that area with more native species (asters, coneflower, goldenrods).
We find that pulling DSV out in spring and cutting it back in mid summer, before or right around the time plants are flowering, has helped to weaken the root systems. Note: We had a very small patch and it was discovered early so we’ve been able, for the most part, to keep on top of it.
In a meadow area, a large patch had invaded. Although few native species were being harmed by it, we are trying to increase biodiversity in this area. We cut and dug out as much DSV as we could and immediately planted Black-eyed Susans and New England Asters in its place. DSV has a chemical in its roots that can make the soil inhospitable for other plants, but these two species are holding their own.
Everything we’ve done has worked in some way, shape, or form. We always do our homework and try to learn from others’ mistakes.
Cities, provinces, and the federal government need to have an invasive plant strategy that includes better oversight of nurseries that continue to sell invasive species.
The City of Ottawa does not have a policy or strategy. Indeed, there is some evidence that councillors and city staff confuse “toxic” or “noxious” with “invasive.” Poison ivy is a native species but it’s toxic so the city sprays it. Dog-strangling vine is not toxic but the city has no control plan for it.
Like many other cities, Ottawa allows Japanese tree lilacs to be planted as part of their Commemorative Tree Programs. This is an invasive species and it can spread in natural areas, such as Hampton Park Woods, as happened when the city planted one tree.
Facts and best management practices from the Ontario Invasive Plant Council
A range of invasives
Iola Price takes care of urban natural area 176: the 2-ha Caldwell-Carver Conservation Area on the east side of McKay Lake. The east side of McKay Lake was once a marsh that was filled in to make a line of building lots. Public pressure and legal action stopped the filling.
|Invasive species removed||Native species planted|
|Yellow Flag||Iris versicolor||Black Walnut (nuts)||Juglans nigra|
|Glossy Buckthorn||Frangula alnus||Red Oak (acorns)||Quercus rubrum|
|Common Buckthorn||Rhamnus cathartica||Canada Anemone||Anemonastrum canadense|
|Norway Maple||Acer platanoides||Nannyberry (seeds)||Viburnum lentago|
|Dog-strangling Vine||Cynanchum rossicum||White Trillium (plants)||Trillium grandiflorum|
|Euonymus||Euonymus spp.||Grey Dogwood (seeds)||Cornus racemosa|
|Yellow Archangel||Lamium galeobdolon||Ostrich Fern (plants)||Matteucia struthiopteris|
|Oriental Bittersweet||Celastrus orbiculatus||Cardinal Flower (seeds)||Lobelia cardinalis|
|Poison Ivy (hand dug)||Toxicodendron radicans||Virginia Waterleaf (plants)||Hydrophyllum virginianum|
|Garlic Mustard||Alliaria petiola|
|Honeysuckle (to provide space for a memorial bench)||Lonicera spp.|
Manual (one Weed Wrench, one Pullerbear), hand pulling plus shovels, a hooked garden tool (works great for DSV and yellow iris), garden trowels, winch attached to a chainsaw motor, saws, DIY buckthorn baggies.
All methods listed above have worked to a degree. Buckthorn baggies didn’t work very well.
In about 1999, when we started trying to control invasives, there was very little info available and so we worked things out. We found that cutting buckthorn only made it sprout so then we had to pull. We didn’t have to worry about endangered or threated species because there was very little in the way of anything except buckthorn and the others. We didn’t know that glossy buckthorn was present until it started to take over where the common buckthorn was removed. The landfill soil gets very hard when dried so we need to work after a rainfall.
When the Ontario Invasive Plant Council (OIPC) was preparing its best management practices (BMPs), we could contribute info and also learn techniques from other people. That was useful for garlic mustard and advice from the FWG on Dog-strangling Vine was great.
We planted a few small trees (white spruce, burr oak and others) but most successful was broadcasting acorns, sugar and red maple seeds, seeds of other shrubs.
We have a management plan, agreed to by the Rockcliffe Park Village Council before amalgamation, and that was accepted by the new city forestry staff and, eventually, others in the bureaucracy.
- Developing good relations with city staff helps as well as being knowledgeable about the species to be removed (city staff respect expertise).
- Adjacent landowners used the site to pitch garden waste and that is a problem we are now tackling (yellow archangel and maybe someday Japanese knotweed).
- Tell people what you are doing, encourage volunteers, keep city staff and elected officials informed by means of annual reports and articles in community newsletters.
- Take good before and after photos and follow the techniques outlined in the OIPC BMPs – especially about tackling the outliers first.
- Some people want only to control one species so let them (i.e., develop specialists).
- Adjacent properties may also need control activities so don’t be afraid to ask if you can help them clear up their areas.
- Know the history of the area where you will control invasive plants; get a soil test done so any replanting will survive in the soil – bringing in new soil might help but is expensive. Mycorrhizal amendment via logs from the area might help – I am less sure about the material from a store to help amend the soil but it could be worth trying.
- You may need mulch – but be sure it is insect pest free.
A general approach
Jim usually focuses on small sites – a few square metres – in fields, woods, and waste places. They are usually rife with first-colonizer species and have unpredictable soil/moisture conditions. His main technique is to plant native species that will co-exist.
We’ve also adopted that method at the Fletcher Wildlife Garden. For many years, we spent considerable time cutting, pulling, and digging Dog-strangling Vine. Eventually we noticed that some native species were starting to compete with DSV. Goldenrods are one of them. We now try to keep DSV from setting seeds by cutting it with a scythe once or twice over the summer. Then we let the native species do their job.
In a shady area, White Snakeroot, Purple Flowering Raspberry, and Elderberry have replaced DSV. Walnuts seem to have a particularly significant effect, as we find DSV-clear areas near this tree species.
Use iNaturalist to identify plants you think might be invasive. There’s an invasive species project to add your sightings to, but it doesn’t include everything that you might think is invasive, as that varies with region and climate.
Ontario Invasive Plant Council – Lots of useful information, including best management practices.