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Invasive Plant Control Methods

Three broad categories cover most invasive plant control: mechanical, chemical, and biological. Mechanical control means physically removing plants from the environment through cutting or pulling. Chemical control uses herbicides to kill plants and inhibit regrowth. Techniques and chemicals used will vary depending on the species.

Biological Control Methods
Biological controls use plant diseases or insect predators, typically from the targeted species’ home range. Several techniques may be effective in controlling a single species, but there is usually one preferred method—the one that is most resource efficient with minimal impact on non-target species and the environment.

Mechanical Control Methods
Mechanical treatments are usually the first ones to look at when evaluating an invasive plant removal project. These procedures do not require special licensing or introduce chemicals into the environment. They do require permits in some situations, such as wetland zones. [See sidebar on page 23.] Mechanical removal is highly labor intensive and creates a significant amount of site disturbance, which can lead to rapid reinvasion if not handled properly.

Pulling and Digging
Many herbaceous plants and some woody species (up to about one inch in diameter), if present in limited quantities, can be pulled out or dug up. It’s important to remove as much of the root system as possible; even a small portion can restart the infestation. Pull plants by hand or use a digging fork, as shovels can shear off portions of the root system, allowing for regrowth. To remove larger woody stems (up to about three inches in diameter), use a Weed Wrench™, Root Jack, or Root Talon. These tools, available from several manufacturers, are designed to remove the aboveground portion of the plant as well as the entire root system. It’s easiest to undertake this type of control in the spring or early summer when soils are moist and plants come out more easily

Suffocation
Try suffocating small seedlings and herbaceous plants. Place double or triple layers of thick UV-stabilized plastic sheeting, either clear or black (personally I like clear), over the infestation and secure the plastic with stakes or weights. Make sure the plastic extends at least five feet past the edge of infestation on all sides. Leave the plastic in place for at least two years. This technique will kill everything beneath the plastic—invasive and non-invasive plants alike. Once the plastic is removed, sow a cover crop such as annual rye to prevent new invasions.

Cutting or Mowing
This technique is best suited for locations you can visit and treat often. To be effective, you will need to mow or cut infested areas three or four times a year for up to five years. The goal is to interrupt the plant’s ability to photosynthesize by removing as much leafy material as possible. Cut the plants at ground level and remove all resulting debris from the site. With this treatment, the infestation may actually appear to get worse at first, so you will need to be as persistent as the invasive plants themselves. Each time you cut the plants 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. This may take many years, so you have to remain committed to this process once you start; otherwise the treatment can backfire, making the problem worse.

Chemical Control Methods
Herbicides are among the most effective and resource-efficient tools to treat invasive species. Most of the commonly known invasive plants can be treated using only two herbicides—glyphosate (the active ingredient in Roundup™ and Rodeo™) and triclopyr (the active ingredient in Brush-BGone™ and Garlon™). Glyphosate is non-selective, meaning it kills everything it contacts. Triclopyr is selective and does not injure monocots (grasses, orchids, lilies, etc.).
Please read labels and follow directions precisely for both environmental and personal safety. These are relatively benign herbicides, but improperly used they can still cause both short- and long-term health and environmental problems. Special aquatic formulations are required when working in wetland zones. You are required to have a state issued pesticide applicator license when applying these chemicals on land you do not own. We do not authorize any Weed Warriors to use chemical controls for removal on invasives in the District.

To learn more about the pesticide regulations in your state, visit or call your state’s pesticide control division, usually part of the state’s Department of Agriculture. In wetland areas, additional permits are usually required by the Wetlands Protection Act.

Cultural Control Methods
Cultural control methods include several measures aimed at changing human behavior to address the issue spreading invasives. Some examples include: prevention through the use of signs and other means that can educate people about practices to decrease the spread of invasives.such as: (a) cleaning shoes when leaving an invaded area and

Integrated Pest Management
The DC CWMA practices integrated pest management. Chemical herbicides used to be seen as the best way to control invasive plants, but the effects these chemicals had on the environment led to the creation of Integrated Pest Management, or IPM. PM is the practice of applying a combination of management methods to the pest in question before resorting to chemicals. These methods are categorized as cultural, mechanical and biological controls. Read More about IPM