Cold you please advise if I should smother a patch of this weed now or in the spring. I feel like cardboard would disintegrate over the winter and have to be replaced in the spring? It’s at the back of a garden bed at my kids school, moving forward into the perennials. The soil is covered with river stones in that back area, so removing roots would be more tedious than usual.
Thank-you for contacting Toronto Master Gardeners with your question. As you are probably aware, dog-strangling vine (Vincetoxicum rossicum) is on the list of invasive species for Ontario. It is great that you are ready to tackle this weed infestation at the school!
The Ontario Invasive Plant Council provides good general information, Factsheets and Bulletins about dog-strangling vine and its identification and management, as well on their Invasive Species Centre Website. Most of the recommended strategies for dealing with it begin with digging it up carefully/thoroughly to ensure that root pieces do not remain in the ground where they will regrow. Where this is not feasible (due to size of the infested area), cutting off the stems at ground level is recommended. Pulling the vines up is not recommended because they tend to break off, leaving pieces in the ground to regrow (in even greater numbers!) Once the vines have been cut or dug, it is very important to carefully bag the plant material for disposal in the garbage, rather than compost. Ideally, the bags will be sealed and solarized in order to kill the plants and any seeds, prior to putting them out in the trash. Re-visiting the area for follow-up weeding will be required for at least a few years. Herbicides are sometimes indicated for large infestations.
You have suggested suffocating the area with cardboard because of the difficulty of digging amongst the river rocks. I am including a section from the Ontario Invasive Plant Council’s Invasive Dog-strangling Vine – Best Management Practices below because it specifically describes their recommended process for “tarping”. I strongly encourage you to follow the link and read this article. It will give you thorough answers and is directly relevant to the handling of this pernicious weed in Ontario.
Tarping refers to covering an invasive plant population with a dark material to block sunlight and “cook” the root system. Tarping is not recommended in low light areas. Tarping is
most effective when started in late spring and continued through the growing season and is
a viable control method for medium to larger infestations. This method is best for monocultures. To tarp an area, first cut dog-strangling vine stems, taking care not to spread seeds to new areas (this is best done in late spring/early summer before the plant has produced seed). Next, cover the infested area with a dark coloured tarp or heavy material. Weed barriers used by landscapers or blue poly tarps are good options. Take care to weigh down the tarp material so it doesn’t blow away, but be sure it is still receiving adequate sun exposure. Tent pegs work well
as long as the ground isn’t too rocky. The tarp may need to be left in place for more than one growing season to ensure effective control. Monitor for plants growing out from under the edges of the tarp. As with many of the control measures listed in this document, re-planting the area with native vegetation will help to suppress re-sprouting and assist in preventing new invaders from establishing. Since tarping essentially “cooks” the soil, mycorrhizae (beneficial soil fungi) may need to be added when re-planting.
You will note that they suggest cutting the vines prior to tarping, and also that they specify using a dark plastic. I am worried that cardboard will not provide the extra benefit of “cooking” the leftover stem and root material. In answer to your question about timing, this report recommends late spring so that the process begins before the season’s seeds are produced. It is too late this year to avoid the seeds spreading. With the cooler weather coming, there will not be any ability to “cook” the roots. You may as well wait until spring.
Best of luck with your project. It is so worthwhile to eradicate this pest!
Oct. 6, 2023