Durham Field Office

Control of Nonnative Invasive Plants on Your Woodlot

Roger Monthey,
Forest Stewardship Program Representative
USDA Forest Service,
State and Private Forestry, Durham, NH

Chris Mattrick,
Senior Conservation Programs Manager,
New England Wild Flower Society, Framingham, MA

Like many landowners in the Northeast, you may be faced with nonnative invasive plants such as bush honeysuckles (Lonicera spp.), Japanese barberry (Berberis thunbergii), glossy buckthorn (Rhamnus frangula), and Oriental bittersweet (Celastrus orbiculatus) encroaching upon your woodlot. These and other invasive plants can reduce native biodiversity as well as restrict the regeneration of desirable species, primarily due to the dense shade they cast as well as their aggressive growth. Botanical groups such as the New England Wild Flower Society (NEWFS) host field workshops to teach landowners how to recognize and control these species, providing valuable hands-on experience. Chris Mattrick, Senior Conservation Programs Manager with NEWFS, conducted one such workshop in Groveland, Massachusetts in August 2000. This article summarizes Chris' presentation.

 
Photo 1. Some attendees at an invasive plant workshop.

Chris emphasized several critically important points in the control of invasive plants:
1. You must "pick your battles" in fighting the spread of these species. A "good" battle, for example, would be a landowner with relatively small acreage (as is the case for many nonindustrial landowners in the Northeast) who wants to retain his or her woodlot in as natural a condition as possible. Another "good" battle would be a small nature sanctuary attempting to hold off the threat of invasives. A "bad" battle would be trying to control invasive plants along roadsides or similar areas. Roadsides are vectors for transmission of invasive plants, which are often extremely plentiful in these areas.

2. Control of invasive plants is very labor intensive. You are likely to have a big job ahead of you, even on small acreage, so you will probably need help. You can often hire local students (possibly those with an interest in plant ecology) through nearby high schools or colleges. You may also be fortunate enough to get volunteers to assist you. Contact local offices of state and Federal agencies (e.g., USDA Natural Resources Conservation Service, U.S. Fish & Wildlife Service), or botanical groups for ideas on obtaining the help you need.

3. Know what you are controlling. Your woodlot is teeming with native plants, some resembling the invasive species you are trying to control. Proper identification is key. There are a number of educational articles and web sites to help you correctly identify invasive plants.

Biological and Natural Control

Biological control is the use of nonnative organisms to control nonnative plants and animals. Natural control is reliance on all biotic and abiotic factors that limit organisms. Several ongoing examples include the following: 1. Purple loosestrife (Lythrum salicaria), a native of Europe, is an aggressive invader of North American wetlands. It is being treated with two foliage-eating beetles (Galerucella spp.), which feed on bud, leaf, and stem tissue, and a root-boring weevil (Hylobius transversovittatus). The use of weevils is extremely labor intensive because each weevil must be inserted into the stem by hand. Studies at test sites in Rhode Island, Connecticut, and Vermont have shown significant dieback in purple loosestrife several years after release of these control agents.

2. Multiflora rose (Rosa multiflora), a native of Japan, Korea, and eastern China, was introduced to North America in the early 1800's. This plant is currently under attack by two control agents, both native to the western United States-a virus, Rose Rosette Disease (RRD), which is transmitted by a mite (Phyllocoptes fructiphilus), and the rose seed chalcid (Megastigmus aculeatus var. nigroflavus Hoffmeyer), a small wasp that lays eggs in and kills developing rose seeds. RRD began to spread eastward after millions of multiflora roses were planted across the Plains States as windbreaks. The rose seed chalcid is increasing in numbers in the eastern United States and is expected to eventually infest nearly 90 percent of the multiflora rose seeds of the plants that survive RRD (Amrine and Stasny 1993).

3. Tansy ragwort (Senecio jacobaea), a native of Europe and western Asia, has invaded North America and many other locations. It is toxic to cattle and horses, making it a serious rangeland pest. The cinnabar moth (Tyria jacobaeae) and the ragwort flea beetle (Longitarsus jacobaeae) have been introduced from ragwort's original range to help control this invader. The flea beetle damages ragwort primarily by larval feeding on the roots and crown of the plant. Cinnabar moth larvae feed on the flowers, buds, and leaves, often stripping the plant of everything but the main stem.

Mechanical Control

There are a variety of mechanical methods to control nonnative invasive plants. One of the simplest methods is the use of human power; however, devices such as weed whackers, clippers, loppers, brush saws, and chain saws help make the job much easier.

One of the more recent inventions is the Weed Wrench^TM, which has a set of jaws that clamp onto a stem, allowing you to lever the plant out of the ground. There are four models available (heavy, medium, light, and mini) based on the size of the plant you wish to remove. It works best on small-to medium-sized shrubs, but can also be used on some herbaceous species, such as purple loosestrife.
 
The Weed Wrench is available from New Tribe, c/o Tom Ness and Sophia Sparks, 5517 Riverbanks Road, Grants Pass, OR 97527, 541-476-9492. Prices in September 2000 ranged from about $90 to $120 for the medium to heavy models.

Photo 2. Closeup view of Weed Wrench

Photo 3. Bush honeysuckle pulled from ground and
hung in adjacent small tree to dry out.

3. Repair the disturbed area that you create when removing plants. Tamp the soil down with your feet and cover it with leaves or brush. Monitor the disturbed areas at a later date to see if resprouting or seeding has occurred.
 
4. Woody brush with roots can be chipped to reduce its volume, and then disposed of (see #2).

5. Do not take invasive plants to a composting facility unless the facility specifically accepts them. Otherwise, you will likely spread the plants to other locations.

6. Invasive plants can be controlled by repeated cutting with loppers and clippers, but you may need to cut 3-4 times over a period of 3-4 years. If you miss a cutting, the root systems will get larger and resprout aggressively.

7. Some of the more difficult, woody nonnative invasives to control (e.g., Oriental bittersweet, Japanese honeysuckle, Japanese knotweed [Polygonum cuspidatum or Fallopia japonica]) have the capability to "run"-they have long horizontal root systems that will actively sucker, especially after some initial control has been applied. Some of the woody nonnative invasive shrubs that don't run include glossy (Frangula alnus) and common buckthorn (Rhamnus cathartica), bush honeysuckles (Lonicera spp.), and privets (Ligustrum spp.).

8. Glossy buckthorn is more of a widespread problem than common buckthorn because the common buckthorn typically grows only in upland sites, whereas the glossy grows in wetland and upland areas.

9. Ailanthus or Tree of Heaven (Ailanthus altissima) will shoot off roots from dormant buds even after cutting or girdling.

Another mechanical control method for herbaceous species, such as purple loosestrife, is to "dead-head" the seed head. This means to literally break off the immature seed heads or flowers with your hands. This must be done before the seeds are mature. The removed seed heads should be placed in black plastic bags to prevent the dispersion of seeds to new sites.

Chemical Control
 
Often the most effective method for removing invasive plants is chemical control; however, the use of herbicides is sometimes considered risky due to the potential for "collateral" damage to nearby desirable resources (e.g., plants, aquatic life, water quality). It is important to understand the laws that regulate herbicide applications in your state. Landowners applying over-the-counter herbicides (also known as general use or nonrestricted use herbicides) on their property generally do not need an applicator's license, but there are many mitigating circumstances. Herbicide application on or near wetlands normally requires approval from wetland protection agencies. Plant and animal species listed under the Federal Endangered Species Act must be protected as outlined in the act. Individual states may have additional legislation protecting plant or animal species, usually under a clause in the State Endangered Species Act (McLellan 1997). A pesticide applicator's license is generally required before herbicides may be used on properties that are not owned by the applicator, although the need for a license may vary from state to state depending on whether or not the applicator receives compensation.

Photo 4. Chris Mattrick shown providing some
advice on how to apply herbicides.

2. Follow label directions. Use up to only a 5 percent concentration for foliar sprays. Use stronger concentrations (up to 25 percent) on cut stems. Mix the herbicide with water in mixing bottles. When finished, the bottles should be treated as hazardous waste and disposed of properly. Do not recycle plastic bottles that contained herbicides.

3. Triclopyr works well on Oriental bittersweet when applied to the cut stem or leaves in autumn.

4. Kill ratios of 85-90 percent may be achieved on honeysuckles, privets, buckthorns, and multiflora rose if they are cut off and subsequently treated with herbicides on the cut surfaces using sponge applicators in autumn.

5. It is not necessary to apply herbicides immediately after cutting stems of invasive plants. They may be applied later in the same day. However, cutting in the spring followed by herbicide application in the fall will not be effective because the cut surfaces will callus over during the summer.

6. For multistemmed plants like Japanese barberry, all main stems should be cut and painted with herbicides.

7. For Japanese knotweed and phragmites (Phragmites australis), cut the stems just below the leaf nodes (where the leaf joins the stem) so you can expose the hollow stem. Then inject a 25 percent concentration of herbicides using a squirt bottle with an injector tube (available from biological supply companies). To keep track of what stems have been treated, use a water-soluble dye to color the herbicide solution.

Some additional methods for applying herbicides include the following:

Herbicide Wand -The herbicide wand is a homemade sponge-tip applicator that stores herbicides in a plastic or PVC pipe assembly. The wand is used to dab herbicides directly onto cut stems, eliminating the use of spray. Its design can be modified for your particular requirements. The wand can be assembled using about $20 worth of materials. For diagrams and instructions on building your own herbicide wand, see http://tncweeds.ucdavis.edu/tools/wand.html). The tool was developed by Jack McGowan-Stinski of The Nature Conservancy's Michigan Field Office.

E-Z-Ject® Lance -This metal lance includes a capsule injection system. Capsules containing herbicide can be injected directly into unwanted brush and trees. It is operated by placing the lance at the base of a tree or bush and using a short compression stroke to drive an herbicide capsule into the bark. Refer to forestry supply catalogs such as Forestry Supplies, Inc. (P.O. Box 8397, Jackson, MS 39284-8397) for additional information.

Klipkleen Applicator -This device mounts on a set of shears to deliver herbicide with each cut. It includes a vial containing herbicide so the user can clip vegetation and place herbicide on the cut surface in the same motion. Chris Mattrick has used the tool on plants such as goutweed (Aegopodium podagraria), black swallowwort (Vincetoxicum nigrum), and purple loosestrife. Refer to tool supplier catalogs such as A.M. Leonard, Inc. (http://www.amleo.com). The tool is manufactured by P.I. Systems, 527A Yeopim Road, Edenton, NC 27932. This tool received unfavorable reviews, however, in a field test conducted by The Nature Conservancy's Wildland Invasive Species Program (http://tncweeds.ucdavis.edu/tools/klipklee.html).

Hypo-Hatchet® Tree Injector -This hatchet has a hose and a bottle filled with herbicide attached so that a measured dose of herbicide can be dispensed with each cut. Users are advised to hatchet at intervals around the circumference of the trunk rather than to completely girdle the tree. Refer to forestry supply catalogs such as Forestry Suppliers, Inc. for additional information. The same results could be achieved with a hand ax used in combination with a hand sprayer, but much less efficiently and conveniently than with the Hypo-Hatchet.

Backpack Sprayers -These familiar applicators should only be used when wind is not a factor. Keep spray on the intended target and avoid spreading herbicide onto adjacent vegetation. Refer to forestry supply catalogs such as Forestry Suppliers, Inc. for additional information.

Safety Precautions

Safety precautions are a necessity when using mechanical or chemical methods to control invasive species. Proper safety equipment includes safety goggles, a hard hat, gloves, boots, chaps (if using a chain saw), and an orange vest during hunting season. Additional items for herbicide application include a dusk mask, a long sleeve shirt (or white Tyvek suit), hat, pesticide gloves, and eye wash. Have a first aid kit with you at all times.

Applying herbicides can be dangerous work. People who work with herbicides on a regular basis should have toxin screenings performed periodically. Herbicide and pesticide use has been linked to Parkinson's disease. Work carefully and take all precautions necessary.

Timing of Treatment

Autumn is the best time of year to control woody shrubs, such as honeysuckle, barberry, and buckthorn, since most of the plant reserves are being transported to the roots and the plant is more vulnerable to control. You can apply control methods to woody nonnative invasives in spring and summer, but not as effectively as in autumn and winter.

Herbaceous species such as purple loosestrife should be controlled before seed set. Controlling plants before they produce seeds will greatly reduce the possibility of spread.

Invasives at Nurseries

The sale of nonnative invasive plants by nurseries has created controversy and some outright opposition from environmental groups. Conversely, the nursery industry faces proposed regulations that may affect their bottom line. In Massachusetts, for example, the nursery industry has challenged the state listing of certain plants as invasive. Nurseries seek out species that propagate easily, tolerate a wide range of growing conditions, and grow rapidly, allowing plants to be produced quickly and in large number. Unfortunately, these are the same characteristics of nonnative invasive plants (New England Wild Flower Society 1998). NEWFS reports that the nursery industry is making some progress educating their members about nonnative invasives. Some of the nonnative invasives (as classified by plant ecologists) currently sold by nurseries include Norway maple (Acer platanoides), Japanese barberry (Berberis thunbergii), and burning bush (Euonymus alatus).

Literature Cited

Amrine, James W., Jr.; Stasny, Terry A. 1993. Biocontrol of multiflora rose. In: McKnight, W.N., ed. Biological pollution-the control and impact of invasive exotic species: Proceedings of a symposium; 1991 October 25-26; Indianapolis, IN. Indianapolis, IN: Indiana Academy of Science: 9-21.

McLellan, Toni. 1997. Threatened & endangered species and the private landowner. NA-PR-03-97. Durham, NH: U.S. Department of Agriculture, Forest Service, Northeastern Area. 4 p.

New England Wild Flower Society. 1998. New England Wild Flower: Conservation Notes of the New England Wild Flower Society. Invaders. Vol. 2, No. 3. Framingham, MA. 30 p.

Additional Resources

Benoit, L.; Goettel, B. 1999. The Connecticut River Watershed/Long Island Sound. Invasive Plant Control Initiative. Strategic Plan. Funded by the National Fish and Wildlife Federation. Silvio O. Conte National Fish and Wildlife Refuge, Turners Falls, MA. 31 p. + app.

Gleason, Henry A.; Cronquist, Arthur. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. 2d ed. Bronx, NY: The New York Botanical Garden. 910 p.

Maine Natural Areas Program. Invasive Plant Fact Sheets. Augusta, ME: Maine Department of Conservation. (http://www.state.me.us/doc/nrimc/mnap/factsheets/invasivesfact.html)

Native Plant Conservation Initiative, Exotic Plant Working Group web site: http://www.nps.gov/plants/alien

New England Wild Flower Society, Sources of Invasive Plant Information web site: http://www.newfs.org/invasive/invasive.htm

Smith T.E., ed. 1997. Missouri vegetation management manual. Jefferson City, MO: Missouri Department of Conservation, Natural History Division. 158 p.

The Nature Conservancy, Wildland Invasive Species Program web site: http://tncweeds.ucdavis.edu

Formatted for the internet: July 2001