Just when you are making progress beating back one invasive plant, another arrives. For years I have been battling goutweed, also known as bishop's weed, religiously plucking out the plant and all of its white, spidery roots. I'm happy to report that I am winning that battle.
I now have another plant popping up, a dainty, purple-flowered, hairy-stemmed plant started growing by the tool shed a few years ago. I thought it was nice so I left it in place. I should have known better and identified it right away! Plants then turned up near the wood rack; next, they were in a plant bed; and, now, they are growing along the sidewalk. This was not a good sign. I initially thought that the plant was an out-of-control mint, but it turns out that it is brittle-stemmed hemp nettle. Thankfully, hemp nettle is just another weedy nuisance for landowners, not a true invasive plant that escapes gardens and causes harm to natural areas.
Gardeners constantly battle weeds, and natural resource managers do, too. The Adirondack Park Invasive Plant Program (APIPP) and partners are eliminating infestations of common reed grass (Phragmites australis), one of the world's worst wetland invaders, Japanese knotweed (Fallopia japonica), an aggressive plant spreading along river and stream banks; and many other species. We are tipping the scale in nature's favor, but other plants are making inroads.
Cup plant is a perennial invasive plant that is spreading along the Ausable River.
n be distinguished from noninvasive look-alikes by its fused leaves that form a cup around its thick, square stem.
One of these plants is Indian cup plant, or cup rosinweed (Silphium perfoliatum). It is hard to believe that such a pretty plant is an unwelcomed arrival, but, similar to purple loosestrife (another beauty), cup plant doesn't stay put. Introduced to a private garden in Keene 30 years ago, it has spread more than 30 miles along the Au Sable River. Abundant seed production, expanding roots and continued garden introductions contribute to its swift spread. Cup plant is still available for sale in some local nurseries and is shared among unsuspecting gardeners.
This summer seems to be a bumper-crop year for cup plants. Landowners are contacting the Au Sable River Association (ASRA) concerned about its spread. Residents also stopped by APIPP to inquireabout control methods. Staff members of both organizations have seen new infestations in locations where they were not intentionally planted along a roadside anda stream. Flood events in recent years may be the culprit by washing its large seeds to new areas.
Indian cup plant is a perennial that grows to heights of 9 feet. It has a thick, square stem, oppositely arranged leaves and yellow disc flowers that bloom July through September. It will grow anywhere with wet to average soil moisture and full to medium light.
Don't be fooled by look-alikes. Cup plant can be confused with native plants such as sunflower (helianthus) and false sunflower (heliopsis). The telltale characteristic of cup plant is that its leaves completely envelope its stem, forming a cup.
Another twist in cup plant's story is that it is native to Mid-western prairies of the U.S. There, the plant is desired and does not invade natural areas. In New York, however, the New York Flora Atlas lists cup plant as non-native, and evidence of the plant's aggressive spread along the Au Sable River is reason for concern. The Plant Atlas of New England also notes the spread of cup plant outside of cultivation in several Northeastern states.
So what is a gardener to do? First, be mindful of your ornamental plantings; learn which species to avoid. Check plant identification guides before you buy or if an "uninvited guest" pops up in your yard. The big and beautiful may be misleading. Second, avoid picking or transplanting roadside flowers, which may be invasive. Third, if nurseries are selling invasive plants, ask them to carry noninvasive alternatives instead. Lastly, report sightings of cup plant or other invasive plants to the Adirondack Park Invasive Plant Program at 518-576-2082.
Eye on Invasives is a seasonal biweekly column that spotlights a top invader when it is easiest to identify. Hilary Smith directs the Adirondack Park Invasive Plant Program, a partnership program housed at the Adirondack Chapter of The Nature Conservancy in Keene Valley. Find out more about this award-winning program online at www.adkinvasives.com.