Wednesday, March 12, 2014
By Tom Atwell
(Continued from page 1)
Swallowwort flowers are purplish-brown. The weed, which is an invasive species, grows about 6 feet tall, wrapping around other plants and killing them.
Courtesy Minnesota Department of Agriculture
Monarch butterflies lay their eggs on milkweed, and have to eat milkweed to survive. Because swallowwort and native milkweed are so similar, butterflies will lay their eggs on swallowwort. In an experiment conducted by a student at the University of Rhode Island, all of the eggs laid on swallowwort died.
"They stopped eating after a single bite," said Dr. Richard Casagrande, the professor overseeing the research.
Mechanically pulling the swallowwort will set it back, but if one node of the root system remains underground, a new plant will sprout. And pulling the root system often disturbs the roots of the plants you want to keep.
Chemical weed killers such as Roundup will kill swallowwort, but it will have to be used several times. Ogunquit has banned the use of synthetic weed killers on town property, so Roundup could not be used on Marginal Way. And Roundup is especially dangerous if it gets into bodies of water, so it would be dangerous if used on swallowwort in the coastal areas where it is most common.
There is hope in controlling swallowwort, but it is a few years off.
The weed is not a problem in Europe, where it originates. That is because Europe has some insects that will eat swallowwort, insects that North America lacks.
Casagrande led some research into such insects, and found two moths that will eat swallowwort and leave other plants alone.
According to an article in the newsletter of URI's College of the Environment and Life Sciences, the two moths "passed the acid test" and test applications of the moths in two Rhode Island communities.
These test applications take time, but similar biocontrols have been used in Maine, including efforts to control winter moth, which just arrived in Maine last year, and lily leaf beetle, which have been going on for about eight years.
Until then, keep your fingers crossed, pull the vines when you see them and, most importantly, pull those green pods before they send out all of those floating white seeds.
Tom Atwell has been writing the Maine Gardener column since 2004. He is a freelance writer gardening in Cape Elizabeth and can be contacted at 767-2297 or at: