Invasive Plants

The Observatory has worked on Maine Coastal Islands National Wildlife Refuge (MCINWR) islands for a number of years detecting invasive plant species. The invasive plant species documented during these inventories include:
  • Purple Loosestrife (Lythrum salicaria)
  • Garlic Mustard (Alliaria petiolata)
  • Canada Thistle (Cirsium arvense)
  • Bull Thistle (Cirsium vulgare)
  • Coltsfoot (Tussilago farfara)
  • Narrowleaf Bittercress (Cardamine impatiens)
  • Asiatic Bittersweet (Celastrus orbiculata)
  • Garden Valerian (Valeriana officinalis)
  • Bittersweet Nightshade (Solanum dulcamara)
  • Japanese Barberry (Berberis thunbergii)
  • Glossy False Buckthorn (Frangula alnus)
  • Morrow’s Honeysuckle (Lonicera morrowii)
  • Salt-spray Rose (Rosa rugosa)
  • Japanese Knotweed (Fallopia japonica
  • Wild Radish (Raphanus raphanistrum)


(Check out the Island Plants Map to see what islands these species are on.)


Some of the invasive plant populations we have documented are small and spatially confined on small islands with a good possibility that they can be controlled.  

Alliaria petiolata, Berberis thunbergii, Cardamine impatiens, Lythrum salicaria,
Cirsium vulgare, Tussilago farfara, Celastrus orbiculata, Lonicera morrowii,
Valeriana officinalis, Solanum dulcamara, Fallopia japonica, Frangula alnus
Controlling Invasive Plants
During the recent years, the Observatory has controlled invasive plant populations on eight islands (Inner Sand Island, Ship Island, Bar Island, Trumpet Island, Little Marshal Island, Upper Flag Island, Compass Island, Spectacle Island).  Our methods to control these invasive plants favored, when possible, removal of flowering stems and seed heads to prevent establishment of new plants, digging or pulling of whole plants, as well as, depending on site location, a combination of applying seawater, foliar spraying with vinegar-based solutions (20% vinegar with clove oil and citrus oil), and application of aluminum sulfate.  Application of herbicides were used to control some of the invasive species in certain locaitons as well, and methodologies were site and species specific.  We will continue the collaborate closely with Maine Coastal Islands NWR to control selected populations.
Glen on Inner Sand Island preparing to hand-cut a patch of Rugosa rose.
photo by C. Mittelhauser