by William Bennett in Environment and Open Space, Wildlife sightings
Posted on July 17, 2010 at 10:29 pm
Last Modified on July 24, 2010 at 9:11 am
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Somerville’s chainlink fences have become the breeding ground of a weed that threatens the monarch butterfly. It is black swallowwort, also known as dog-strangling vine (Cynanchum louisiae). You will strike a blow for the monarch butterfly if you pluck the seedpods off vines growing up fences, poking out of hedges, or just growing in clumps from the ground as you pass by. Put them in a plastic bag, tie up the bag, and toss it in the trash. The risk of putting the pods in yard waste is that they will open, even after they are pulled off the vine, and release their airborne seeds on the way to the municipal compost heap.
You can see this plant almost everywhere. It is easy to recognize at this time of year, because its seedpods look like small chili peppers hanging off the vine. The more sun-exposed the plant, the more numerous the seedpods will be, which is why they are so visible on fences. The leaves of this plant are a glossy green and oval-shaped with a pointed tip.
It is believed that Ground Zero for black swallowwort was a garden in Cambridge, Massachusetts, where it was planted early in the nineteenth century, either for academic study or as an ornamental. By 1850 it had escaped and was noted as far away as Ipswich. After that it invaded eastern New England slowly. In the last ten years or so, perhaps because of a recent adaptation, the weed, which originated in Europe, is proliferating explosively in New England and threatening natural ecologies as well as home gardens and commercial agriculture. Black swallowwort is a member of the milkweed family. Unfortunately, the monarch butterfly mistakes this related plant for a true milkweed and lays eggs on it, but the larvae cannot use the plant to develop. Thus, the higher the ratio of black swallowwort to other milkweeds, the more threatened are the monarchs.
Black swallowwort is very efficient at seeding itself, so it can make a real difference to remove the pods before they open and send out their little parachutes. Meanwhile, back in your own yard, there probably is no way to eradicate them that isn’t labor intensive. Digging them out requires care to remove the root and the underground shoots, which are poised to come up if the vine is just pulled away. (Also, the nascent shoots act like little grappling hooks, holding the root system in place.) Black swallowwort sends out rhizomes, so nearby plants are likely to be connected to the first one you see. You can just keep shearing off the above-ground growth, thus eventually starving and killing the root system. This requires both vigilance and diligence, but I’m told that it has worked in Somerville, and it avoids chemical treatments. Some authorities think that glyphosate (Roundup Pro) or triclopyr ester (Garlon 4) can work if sprayed on the plant or, better, is carefully painted, undiluted, on the stem immediately after the vine is cut. This should not be done before June, when the plant is growing and flowering, because that is when it will be most vulnerable to herbicides. Once seedpods form, however, viable seeds may survive this treatment.
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Thanks for the warning, but, geez, Bill, you could have left off the pesticide bit, Round Up Pro and triclopyr ester! Check out the toxicity (and the manufacturer and the Round Up friendly genetically modified seeds, etc.) and the animal studies would make you cringe. No need to go there, just stick with the sweat equity.
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LOL. Sure, Alex, sure. I’ll not use roundup in my yard. LOL.
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Good luck with that sweat equity when the roots are behind a porch lattice, or wedged in the 6″ between a chainlink fence and a building (and growing from a crack in concrete). I dealt with the latter case myself – and after breaking off the tops multiple times, resorted to Roundup. (It wasn’t this weed, it was another that I think I ID’d as bittersweet nightshade, Solanum dulcamara.) There’s just NO WAY to pull the roots in such cases.
Joe’s got a good point about the chain link – I was trying to figure out why a street beyond Davis looked “classier” than mine, and finally figured it was the complete lack of chain link!
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I say the real cuprit here is chain link. Take down the chain link fences of Somerville and deprive these villains of their upward mobility!
Seriously, Jon, thanks for the tips. And I’m only half joking about the chain link eradication. I had this stuff growing on the fence for a few seasons. After the fence came down and the concrete and poles removed, I must have destroyed the root system sufficiently to prevent regrowth. Would have been much easier to use the RoundUp, but I like not having the old rusting chain link surrounding the property.
Haven’t seen hide nor hair of the invasive weed since.
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At last I have a name for my foe! Blasted Black Swallowwort! I have been doing battle with that nasty weed in my yard for years now. I suppose I must have composted the pods. Barnacles! Also, I can report that they are happy to grow all over my hydrangeas and roses and tiger lilies; so chain link or no, this weed is a great invader! I’ll bet it would strangle a dog if you let it sleep outside!
By the way, Bill, thanks for this and, in general, for some of the greatest writing Somerville has to offer.
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