Maine Natural History Observatory

Censusing and Monitoring the Species and Habitats of Coastal Maine

Invasive Plants

Recent inventory work on several Maine Coastal Islands National Wildlife Refuge (MCINWR) islands focused on the early detection of invasive plant species. Invasive plant species documented during these inventories included 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), and Japanese knotweed (Fallopia japonica).  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. 
 
During the 2015 growing season, we 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.