Invasive Plant Removal Methods

Removing invasive species may include manual, mechanical, or chemical methods.

Manual and mechanical methods involve physically removing plants from the environment through cutting or pulling. Chemical methods use herbicides to kill plants and inhibit regrowth. The technique and chemical used varies with the species. Several techniques may be effective in controlling a single species.

Regardless of the method selected , it is very important to minimize the impact on non-target species and the environment.

When removing invasive plants, special consideration should be paid to their disposal. A collaboration of the Connecticut Department of Energy and Environmental Protection and the University of Connecticut produced a useful information sheet (listed below).

Guidelines for Disposal of Terrestrial Invasive Plants

Manual methods

• Pull seedlings and small or shallow-rooted plants when soil is moist as soon as they are large enough to grasp. Remove the entire root, since root fragments may re-sprout.
• Dig out larger plants (up to about three inches in diameter) with a Weed Wrench™, Root Jack, or Root Talon. These tools, are designed to remove the aboveground portion of the plant as well as the entire root system.
• If vines are growing up trees, cut the vine at the base of the tree and at shoulder height and remove the vines from that area. Then remove a swath around the base of the tree. The vines above the cut area on the tree will eventually die and fall off.
• Suffocate small seedlings and herbaceous plants – place a double or triple layer of thick UV-stabilized plastic sheeting over the infestation and secure the plastic with stakes or weights. Leave the plastic in place for at least one year.
• For trees, cut through the bark and growing layer (cambium) all around the trunk, about 6" above the ground. This technique is called girdling, and starves the tree of the water and nutrients that it needs to survive. Girdling is most effective in spring when the sap is rising, and from middle to late summer when the tree is sending down food to the roots. Remove suckers or new growth.

To prevent the spread of seeds, cut off flowers and/or seeds or fruits before they ripen, and dispose of them in heavy garbage bags.

Mechanical methods

• Mow or cut back the plants at least three times a season to deplete plants' store of nutrients, reduce seed formation, and kill or minimize the spread of plants. Each time you cut the plant back, the root system gets slightly larger, but must also rely on its energy reserves to push up new growth. Eventually, you will exhaust these reserves and the plants will die.
• For trees, cut down, grind out the stump, and remove suckers or new growth.

Chemical methods

Using a contact (non-systemic) herbicide will usually not kill well-established (deep-rooted) plants. A systemic herbicide is often necessary to achieve adequate control of troublesome invasive plants. Systemic herbicides absorb into the plant foliage and/or stems, then move and accumulate to toxic levels in the growing points or roots.

Herbicides should be used when the infestation cannot be controlled through other methods alone. Refer to [insert link to Herbicide Use – General Guidelines].

Controlled burning

Controlled burning may require a permit – check with your local fire department and Conservation Committee before you act. 

• Perform controlled burning during the spring, and repeat over several years. Burning allows native vegetation to compete more effectively with invasives.

Invasive plant disposal methods

Proper disposal of removed invasive plant material is critical to the control process. Leftover plant material can cause new infestations. In general, remove flowers, seeds, and fruits before they ripen, and place them in heavy black garbage bags 4 mil or thicker to prevent re-sprouting. On some plants, flowers can mature and set seed even after the plant has been pulled.

Some disposal methods include:

• Burn—Make a brush pile and burn the material following local safety regulations and restrictions, or haul it to your town’s landfill and place it in their burn pile.
• Burning should only be done with a burn permit from the fire department during the burning season.
• Pile—Make a pile of the woody debris. Cover the pile with a tarp held down with rocks. Periodically check the contents for signs of resprouting.
• Compost—Place all your herbaceous invasive plant debris in a pile reserved for invasive plants and process as compost. Monitor the pile for resprouts and remove as necessary. Do not use the resulting compost in your garden.
• Dry—Place woody debris on your driveway or any asphalt surface and let it dry out for a month. Place herbaceous material in a doubled-up black trash bag and let dry in the sun for one month. At the end of the month, the material should be non-viable and can be disposed of in the trash.

Note that the following plants can sprout vigorously from plant fragments:

• Oriental bittersweet
• Multiflora rose
• Japanese honeysuckle
• Phragmites
• Japanese knotweed

These plants should ideally be burned or dried prior to disposal.

Herbicide Use – General Guidelines

Herbicides are chemical treatments designed to kill or inhibit the growth of certain plants. The decision to use herbicides should only be made after the benefits and the problems have both been considered. Some herbicides may damage the environment.

Herbicides are available as either selective or nonselective. Selective herbicides kill only certain types of greenery. Nonselective herbicides indiscriminately kill whatever plant they contact.

Two of the more widely used systemic herbicides are glyphosate and triclopyr. Systemic herbicides are absorbed by plant tissues and carried to the roots causing the entire plant to die usually within about a week.

Glyphosate

Active Ingredient (a.i.): N-(phosphonomethyl) glycine, as the isopropylamine salt

Glyphosate is a non-selective systemic herbicide applied directly to plant foliage. Glyphosate inhibits the synthesis of three amino acids necessary for plant growth.

Nearly all herbaceous plants and most woody plants are susceptible to glyphosate. Woody plants are more susceptible to glyphosate when treated in late summer or fall. Damage may not be apparent until the following spring as leaves either fail to emerge from buds or are dwarfed, misshapen, and yellow.

Glyphosate is a slow-acting herbicide; symptoms often appear within a week of the application, and include yellowing and stunting of the youngest leaves and growing point. Two weeks or longer maybe required for the plant to die.

General notes

• Controls invasive grasses such as Phragmites.
• No soil activity - will not injure desirable plants via root uptake, rapidly deactivated and biodegraded in soil.
• When used properly, glyphosate poses minimal risk to human health or to the environment.

Brand-name products

• Roundup Ready-to-Use Spray
• Roundup Concentrate 18% a.i.
• Roundup Super Concentrate 41% a.i.
• Roundup Pro, Roundup Ultra 41% a.i.
• Accord, Glyfos 41% a.i.
• Rodeo 53.8% a.i.

Both Roundup Pro and Roundup Ultra contain a surfactant that enhances glyphosate absorption into treated leaves. If using a glyphosate formulation other than these two, the addition of a non-ionic surfactant (0.5 fl. oz. per gallon) to the spray tank will increase the herbicidal activity of glyphosate.

Wetland consideration

A permit from the Massachusetts Department of Environmental Protection (DEP) is required to apply any pesticide to a body of water or to plants in a wetland. Contact your local Conservation Commission for permit information.

For control of emergent or floating aquatic plants or plants growing along a shoreline (where spray will contact the water), use the Rodeo formulation of glyphosate or the Accord concentrate. Rodeo does not contain surfactants included in Roundup products. The half-life of glyphosate in water is approximately 2 weeks, but it does not significantly affect submerged plants. Glyphosate toxicity to fish and other aquatic organisms is very low.

Triclopyr

Triclopyr is a systemic herbicide used to control herbaceous and woody broadleaf plants. It is especially useful in brush control and for use on freshly cut stumps to prevent re-sprouting. The herbicidal activity of triclopyr is more rapid than that of glyphosate. Herbaceous plants may show injury symptoms within 24 hours and usually die in a few days.

Triclopyr has low to moderate toxicity to humans and wildlife.

A non-ionic surfactant [0.5 fl. oz. per gallon] added to the spray tank enhances the herbicidal activity of triclopyr.

General notes

• Does not kill grasses, rushes, or sedges, nor other monocots such as lilies and orchids.
• More effective than glyphosate on some woody species (such as Oriental bittersweet and Black locust).
• Often provides better early-season control of perennial weeds.

Brand-name Products

Active Ingredient (a.i.): 3,5,6-trichloro-2-pyridinyloxyacetic acid, as the triethylamine salt

• Brush-B-Gon Poison Ivy, Poison Oak & Brush Killer(Ready-to-Use Spray) 0.7% a.i.
• Brush-B-Gon Poison Ivy, Poison Oak & Brush Killer(Concentrate) 8.0% a.i.
• Garlon 3A 44.4% a.i.
• Pathfinder II 13.6% a.i.
• Garlon 4 61.6% a.i.
• Crossbow: 2,4-D + Triclopyr (low volatile ester formulation)

Wetland consideration

Triclopyr herbicides are generally not approved for aquatic or wetland use with the exception of Garlon 3A, which is formulated for wetland applications.

A permit from the Massachusetts Department of Environmental Protection (DEP) is required to apply any pesticide to plants in a wetland.

Application methods

Herbicides may be applied by the following methods to control invasive plants:

Foliar applications

This method involves spraying a properly diluted herbicide onto plant foliage.

When problems are on a small scale, this type of treatment is usually applied with a backpack sprayer or even a small handheld spray bottle. It is an excellent way to treat large monocultures of herbaceous plants, or to spot-treat individual plants that are difficult to remove mechanically, such as goutweed, swallowwort, or purple loosestrife. It is also an effective treatment for some woody species, such as Japanese barberry, multiflora rose, Japanese honeysuckle, and Oriental bittersweet that grow in dense masses or large numbers over many acres.

This treatment is most effective when the plants are actively growing, ideally when they are flowering or beginning to form fruit. Some plants, such as Japanese knotweed, are more susceptible to this type of treatment if the existing stems are cut off and the regrowth is treated.

Thoroughly wet the target plants with the herbicide on a dry day and no rain is forecast for the next 24 to 48 hours.

Cut stem or stump

Cut stems at or near ground level and immediately apply a 25% herbicide solution, such as triclopyr, mixed in water to the cut stump surface, making sure to cover the entire surface. As with basal bark, a dye added to the mix will help keep track of treated plants.

Consider this method along with and basal bark when treating individual plants or when target plants are mixed in with desirable species which would preclude foliar treatment. It is usually effective when the ground is not frozen.

Basal bark

Prepare a mixture of 25% herbicide such as triclopyr plus 75% horticultural oil and apply to the basal parts of the shrub to a height of about a foot from the ground. Spray until run-off is noticeable at the ground line. A dye added to the mixture will help keep track of treated plants. This method is effective when the ground is not frozen.

Hack and squirt (injection)

Herbicide applied to downward-angled cuts into the sapwood

The hack-and-squirt or injection method is very effective and minimizes sprouting and suckering when applied to trees during the summer. Root suckering will be an increasing problem in the fall, winter and spring.

This method requires first downward-angled cuts into the sapwood around the tree trunk at a comfortable height using a hand ax. With spray bottle or wand in the other hand, squirt a straight (100%) concentration of a water-soluble triclopyr product (such as Garlon® 3A) into the cuts within a minute or two, applying 1-2 milliliters into each cut (typically 1-2 squirts of a trigger squirt bottle) so that the bottom of the cut is covered, but liquid doesn't run out of it.

Application equipment

• Hand-held sprayers, backpack sprayers, paint brush or sprayer for stump and bark treatments

Addition of a non-ionic surfactant [@ 0.5 fluid ounce (1 tablespoon) per gallon of spray] will improve coverage of spray droplets on treated leaves and enhance absorption of the herbicide into the plant. Surfactants (sold under many trade names) can be purchased at fertilizer and pesticide dealerships. Some herbicide formulations already contain a surfactant – check the product label carefully.

Control of invasive plants in wetlands

Control of invasive plants in or around wetlands or bodies of water requires a unique set of considerations. Removal projects in wetland zones can be legal and effective if handled appropriately. In many cases, herbicides may be the least disruptive tools with which to remove invasive plants. You will need a state-issued pesticide license to apply herbicide on someone else’s property, but all projects in wetland or aquatic systems fall under the jurisdiction of the Wetlands Protection Act and therefore require a permit.

Specific recommendations

The following table contains excerpts from "1998 New England Guide To Chemical Control of Problem Weeds and Brush Around Homes and on Non-Cropland"

(http://www.ct.gov/caes/lib/caes/documents/special_features/1998_ne_guide_to_chemical_contol__of_problem_weeds_and_brush.pdf)

References

http://www.hort.uconn.edu/cipwg/art_pubs/GUIDE/consideration.htm

 http://www.npic.orst.edu/factsheets/triclogen.pdf

http://npic.orst.edu/factsheets/glyphotech.pdf

http://www.watershedactivities.com/projects/summer/invasive.html:

https://www.nysdot.gov/spec-repository/615.0305--04.pdf

http://www.gardenguides.com/100146-herbicide-use.html

http://www.ct.gov/caes/lib/caes/documents/special_features/1998_ne_guide_to_chemical_contol__of_problem_weeds_and_brush.pdf

http://www.dof.virginia.gov/mgt/index-herbicide.htm