Invasives Have Come on a Mile a Minute
by Maxwell McCormack
Recently, I returned to a northern Maine forest area I have visited regularly since 1979. It was a watershed study harvested in 1981. Over the years, I’ve marveled at the staying power of the common red raspberry (Rubus idaeus L.), a ferocious competitor that excludes tree regeneration for long periods, over 20 years on good sites. In 2015 it continues to dominate full-tree delimbing yards used during the harvest. But now, after more than 30 years, the raspberry brambles are being suppressed by a new arrival, a dense mat of wild buckwheat (Polygonum convolvulus L.), a species introduced from Eurasia also known as black bindweed, knot bindweed, and climbing bindweed – though it doesn’t belong to the Bindweed Family.
It’s a member of the Knotweed Family that includes Japanese knotweed (Polygonum cuspidatum Sied. & Zucc.), also known as Japanese bamboo, introduced from Asia. If you reside in Maine, you’ve seen this one – thriving, especially along riparian areas and wet sites. It’s the epitome of an introduced invasive. Established populations are extremely difficult to eradicate. Another member of this family is Polygonum perfoliatum L., first noted in Pennsylvania in 1946, and has since moved into southern New England. Beware of this one, aptly named “mile-a-minute weed.”
In some cases, field bindweed (Convolvulus arvensis L.) or hedge bindweed (Convolvulus sepium L. or Calystegia sepium (L.) R. Br.) is confused with wild buckwheat. These two, introduced from Eurasia, are perennials that also twine up and across adjacent vegetation. They each have perfect flowers, having both male and female structures, resembling morning glories; hedge bindweed is often referred to as wild morning glory.
Wild buckwheat (First photo) is an annual with distinctly arrowhead or heart shaped leaves borne on tangles of wiry stems. It, alone, among these three twining vines has an ocrea, a papery sheath that surrounds each node where the leaf stalks attach to the stems. Flowers are small (Second photo), less than 1/4-inch across, perfect and self-pollinating, arranged in clusters along the stems or on elongated spike -like structures at the ends of vines. Each plant can produce thousands of seeds. Small quantities can germinate when shed, but most seeds remain viable in the soil up to five years. Therefore, wild buckwheat can accumulate a sizeable seed bank. It’s able to germinate throughout the summer and can emerge through layers of soil.
The species requires sunlight, so its growth habit is to move aggressively across openings and climb adjacent vegetation. It’s very competitive, readily absorbing moisture and nutrients, even during dry conditions. Wild buckwheat occurs in disturbed open areas and is becoming more common in Maine woodlots. At the recent field tour in Windsor, it went almost unnoticed as it twined across openings and through the area where white pines had been planted.
Several members of Maine Woodland Owners have expressed interest in more information about introduced invasive plants. There are numerous examples. Wild buckwheat is my “poster plant” at the moment. This late summer-early fall, you can observe an especially colorful display of brilliant red and orange berries on woody honeysuckle (Lonicera L. spp.) shrubs in farmland forest openings and along edges. Mark them for future reference and treatment.
The Cooperative Extension Service is a good source of information and numerous references on invasive plants are available on the Internet. The “Invasive Plant Atlas of New England” is a good starting point. There are good reference books on weeds such as “Weeds of the Northeast” by R. H. Uva, J. C. Neal, and J. M. DiTomaso. 1977. Cornell University Press, 396 pp.