Overview of Invasives Committee
PLC’s Invasives Committee works to promote active participation in the identification and control of major invasive plants in the Piscataquog River Watershed through public education and community outreach activities. The committee is recognized state-wide as a knowledgeable resource for invasive plant identification and removal.
Why is the PLC concerned about invasive plants?
It’s a matter of balancing nature and its habitats. Plants that live peacefully with natural controls in many parts of the world can be aggressive and invasive here. Purple Loosestrife may take over a wetland pushing out native species, leaving little or no room for wildlife to live and breed; Japanese knotweed may uproot a driveway or road; Buckthorn, Burning Bush and Barberry may invade a forest replacing native plants that once were the comfortable native habitat for mammals, amphibians and reptiles; Birds, turtles, deer, mink, and other wildlife that once used wetlands and forests must move on to less desirable habitat where they struggle to exist. Ultimately this change in plant life reduces natural biodiversity.
A Brief History of the Invasives Committee
From 1998 until 2005 the PLC Invasives Committee concentrated on educating about and controlling the spread of Purple Loosestrife, an all-consuming menace to the watershed wetlands. Working closely with the NH Department of Agriculture, that effort expanded to target eighteen additional invasive plants.
Click here to view a complete list of New Hampshire Department of Agriculture invasive species.
How are non-native invasive plants different from native and less aggressive plants that live here?
Tolerate a wide variety of soils and temperature conditions
Spread rampantly by wind, animals, water and man to areas where they are free of natural checks and balances found in their native areas
Produce vast amounts of new plants each season
Grow very quickly, displacing slower growing native plants
Are extremely difficult to eradicate
What Should I Know About Controlling Invasives?
In maintaining a well-balance ecosystem we first must know how invasive plants reproduce and spread. They can reproduce from any of these methods:
Rhizomes and other roots
Once we determine the reproduction method, we can choose from any of the following methods to stem their reproduction.
Seeds: Remove flower heads and seeds by cutting. Place in/under plastic, preferably black plastic. Seal the plastic from wind and water and let plants rot. Place in trash sealed. If small enough, plants should be dug out of the ground and disposed of.
Plant Pieces: Given various conditions, several plants can reproduce by any section of the cut plant rooting into the soil. Therefore cut plant sections should be bagged and disposed of properly. This is ideal for Purple Loosestrife and Japanese Knotweed.
Rhizomes and Roots: Dig out the plant or pull out with a Weed Wrench® removing as much root material as possible. Watch for shoots near the removed plant and pull them out. Shoots may take years to appear.
See Identifying and Controlling Non-native Invasive Plants field guide for plant specific methods.
How do I control shrubs, trees, large areas of weeds, bamboo-type plants and rhizomatous grasses?
Shrubs: If the shrub is small enough, dig it out carefully and place in a plastic bag. Allow the cut pieces to rot in bag and dispose of responsibly. If the shrub is medium to large sized, use a Weed Wrench® to pull the plant out of ground and dispose of responsibly. In most cases the shrub will have to be cut down to about ten inches before the Weed Wrench® can be used properly.[ photo of weed wrench] If the shrub is too large to pull from the ground, saw off the branches to a few inches above ground level, and paint the cuts with an herbicide immediately. Watch yearly to be sure that small plants don’t come up along the root system. Remove and dispose of these. This method is ideal for Multiflora Rose, Honeysuckles, Bittersweet, Burning Bush, small Buckthorns and Maples, and Autumn Olive.
Trees: Cut the tree down before seeds appear and paint cuts with a glyphosate herbicide such as Round Up®. Burn wood responsibly (no seeds attached). This is ideal for Norway Maples, Buckthorns, Tree of Heaven and large Bittersweet.
Soft fleshy weeds: 1) If the area is conducive to covering large areas from the sun and rain, cover with black plastic or old carpeting sealed to the ground all around for at least two months. Otherwise 2) Pull or dig each plant, removing as much root as possible and dispose of all parts of the plant in plastic bags. Let rot and dispose of carefully. This is ideal for Garlic Mustard, Purple Loosestrife and Black Swallowort. Small Phragmites plants may be pulled. Phragmites reproduce by seeds, plant pieces, and roots. Remove and dispose of as much plant material as possible and remove new plants as often as needed in the affected area.
Bamboo-like plants with hollow stems are the most difficult to control. Repeatedly cut the plant during the growing season to a few inches above ground level. 1) Cover with a heavy carpet, sealing the edges to the ground with rocks or other heavy objects. Leave on for at least one season. 2) Pour a glyphosate-based herbicide down each cane. This may have to be done repeatedly during a season. For both methods keep a close eye out for new plants as these plants generally reproduce by rhizomes (horizontal root systems). Dispose of all plant material by burning, or bagging and letting it rot. This is a must for Japanese Knotweed.
Perennial rhizomatous grasses: Hand-pull small plants and dig larger plants. The targeted invasive plant here is Phragmites.
Other things to be mindful of
Learn the soil and sun needs of the plant you wish to control. An example of this is Garlic Mustard, which cannot tolerate dry, acid soil. You might want to try spreading with lime. See how that works and if it is too slow, try another method in addition to the lime. Website searches can help identify plant needs.
Biological controls have been successful in many areas of the watershed in controlling Purple Loosestrife. See [Link to Purple Loosestrife Eradication Program History]. To help “move” Galerucella beetles from one site loosestrife site to others, call the PLC office at 487-3331.
Leave it to the NH Department of Agriculture
Giant Hogweed, also called Giant Parsnip, can be extremely irritating to human skin and spreads very rapidly once it takes hold in an area. The NH DOA wants to know where this is growing and will remove it. It looks very similar to cow parsley. Be sure to check websites for clarification of the plants’ characteristics before calling.
What can you do?
Begin at home. Remove all targeted non-native invasive plants from your landscape.
Purchase new plants from reputable nurseries. Educate others by giving them literature to study and websites to visit.
Plant native plants in your landscape, especially if you are planting near a forest edge.
“Adopt” any size stretch of road and watch for signs of invasives. Let the Invasives Committee know what section you want to “watch”. They will help you with identification of any invasive plants. Following the methods discussed, do your part in controlling those invading plants.
Use systemic herbicides only as a last resort to remove invasive plants. Do not use near wetlands.
Help monitor Galerucella beetle activity in Purple Loosestrife areas. Collect and move to other areas.
Help the IC in finding other groups that would like to see the very entertaining and informative invasives slide show.
Be a town invasives contact. You would keep up stocks of invasives literature in public buildings and connect community members to the PLC. If your town has annual events such as old home days, environmental events, etc. plan for a table to be set up to reach out to the public.
If you would like to learn more about PLC’s Invasives Committee please contact us.