“Holes” in Dog-strangling Vine

by Sandy Garland / FWG

Several years ago, we noticed an odd phenomenon in the middle of a field that had pretty much been taken over by dog-strangling vine (DSV). A circle of mostly grass, about 4-5 feet in diameter had no DSV growing in it. I mentioned our “crop circle” to colleagues at the garden and one speculated that a walnut tree had been growing there and its roots were producing something that was inhibiting DSV.

This made sense, but then the circle grew and grew until this year, it’s a good 30 feet in diameter! If residual tree chemicals had created the circle, you would expect less effect as time went on. Nothing growing in the circle seemed to explain the lack of DSV – meadow foxtail grass and another common species, both of which grow abundantly at the FWG.

This year, I was amazed to find several more “crop circles” – this time in relatively shady areas. Two are on the north side of the woods (see photo at left) and one is along the first part of the Bill Holland Trail under sumacs (photo below). They’re all about 5 or 6 feet in diameter. Coincidentally, all three contain a small amount of virginia creeper, although virginia creeper is also growing happily among thick stands of DSV.

For me at least, this has become a true mystery. And I would love to solve it as it may provide some clues to keeping DSV under control. Meanwhile, we’ll keep an eye on those circles and hope they grow like the first one did.

This “hole” is under sumac tree in an otherwise uniform understory of DSV. In the hole is a bit of virginia creeper and sparse grass.

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2 thoughts on ““Holes” in Dog-strangling Vine

  1. I would love an answer as you can see from my recent report we are battling DSV at Huronia buffer in Barrie. Early Sunday morning a group of intrepid volunteers from the young to the to young at heart, gathered at Assikinack Public School. We arrived in good spirits to learn how to begin to tackle the dog strangling vine (DSV) that had decided without the City’s permission to invade and take up residence at Huronia Buffer.

    The DSV is now found in Ontario, Quebec and several American states.

    The dog strangling vine is a like the nasty ” bad guy” in B rated movies with his black hat and handle bar moustache, who wants to take over the world. The DSV want to take over the meadow.

    It has an unprecedented survival arsenal at its disposal. It has the ability to produce countless numbers of seeds that germinate like they have been cared by a master gardener! Would you believe that one single plant can produce over 2 000 seeds per square metre! Farmers would love a cash crop that can produce seeds like this nasty vine!

    Incredibly, over one night it can grow 5 cm and if Mother Nature decides to wet its roots, it will grow over 10 cm!

    Surreptitiously it stretches its inviting long neck to nearby plants. It then proceeds to wrap its tantalizing tentacles around the unsuspecting neighbour in a friendly hug. The innocent plant has no idea that the dog-strangling vine has no intention of ceasing its hug. Slowly, the friendly hugs turns into strangulation and the vine reigns supreme. The native and naturalized vegetation doesn’t stand a chance against this stealthy invader.

    One would think that this plant would be content in wiping out its competition with strangulation, but there is more. The DSV roots contain nasty phytochemicals whose job is to attack and destroy any other defenseless plants that have set roots down in the same meadow. Deer instinctively know about the toxins and avoid areas where it is rampant. Farmers believe that DSV is toxic to their livestock.

    That is not all! Monarch butterflies will mistake the vine for a milkweed plant and will lay their eggs on its leaves. When the Monarch caterpillars begin to devour the leaves for their sustenance they immediately die. Why? DSV coat their leaves with poisonous chemical! Unfortunately, our Monarch butterflies in Ontario, are a species at risk due to a myriad of environmental threats.

    And to make matters worse this plant will thrive anywhere from sun to shade, and in any type of soil! What a super bad plant!

    When these nasty vines were discovered in Huronia Buffer by Jean Wilson from Brereton’s Field Naturalists she immediately set to work contacting the City, Living Green, and LSRCA. The big concern for Living Green, LSRC A and the City was to protect the thousands of native tree saplings planted by volunteers in the last few years to improve the environmental health of Barrie Creeks and to mitigate the devastating effects of climate change. We were particularly concerned that the 1 000 tree sapling just planted on April 28 with funds donated by Barrie Chiropractic and LSRCA would be most vulnerable. If the DSV were left unchecked the forest regeneration that we had hoped for would be greatly hampered by this infestations.

    The volunteers worked tirelessly detecting, digging, bagging, and scything any DSV that caught their attention. When digging we were very careful to dig up the whole fibrous root system as we knew that a tiny root fragment would in no time produce a new plant. We were floored when we found colonies of matted interwoven plants that were too difficult to walk through. Since it was impossible to dig, we decided that if they were cut with a scythe, at least we prevented tens of thousands of seeds from spreading through the Huronia Buffer.

    We would like to report that we won the battle! DSV has been eradicated from Huromia Buffer, but alas, that is not the case. To completely eradicate DSV from this area will require more volunteers and many more attacks throughout the next few years.

    Jean Wilson, from the Brereton’s Field Naturalists and Gwen Petreman, chair of Living Green, would like to extend our heartfelt appreciation to the volunteers who made an earnest and concerted effort to help us wipe out this relentless invader form Huronia Buffer. We hope that the same volunteers and many others will come out time and time again until we reign victorious! Our native wildflowers and trees must be protected so that biodiversity will once again reign supreme in our wilderness.

  2. Hi Gwen, Sorry to take so long to reply. I’m afraid I did not notice the wonderful comments and feedback on our text blog until this minute. I just replied to Jean Wilson and mentioned that there is some hope of a biological control agent, although these things – justifiably – take a long time to get into use.

    We are also still waiting for results from soil samples that were taken from some of our “crop circles” in July. The thought is that some fungus or other micro-organism in the soil is inhibiting DSV growth in these areas. DSV plants around the circumference of the circles are small and wilted, which seems to corroborate this theory.

    If you would like to be added to our mailing list, I guarantee we will publicize widely any good news that comes out of this crop circle study. Send me your email address at fletcher@ofnc.ca

    WRT control methods: your idea of stopping seed release is best, of course. It will take a while to get rid of existing plants, but at least you can prevent them from spreading. In areas that seem to be solid DSV with no (or few) other plants, I’ve had good results by just covering the area with a tarpaulin. We have a source of free discarded boat tarpaulins, which are much better than the feeble ones you can buy for camping. The tarp has to be left in place for at least a year, preferably two.

    Obviously, you can’t cover a very large area, but as you seem to be admirably resigned to many years of followup, it can be heartening to be able to clear one area, then work outward from there. In areas of thick DSV, I also always take great delight in piling cut or pulled DSV plants on top of the masses of tangles ones – killing those with their relatives.

    Good luck with your efforts. I would love to hear more. One of our volunteers, an academic, has done extensive research, so I would like to put you in touch with him as well. And we have a small invasive species group here in Ottawa that gets together to compare notes every now and then. It all helps.

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