Practice description
The control of non-native invasive plants, as well as the control of aggressive native generalist species that threaten otherwise highly specialized natural communities. This practice description focuses on herbicide application, which is the most effective approach in most situations.
Controlling non-native invasive species is vitally important for maintaining ecological integrity and conserving biodiversity. Though less commonly applied, the control of aggressive native generalist vegetation can be equally important in situations where generalist vegetation threatens the integrity and persistence of highly specialized natural communities and the vulnerable species that these communities often support. The need to control native generalist species typically arises when there is a disruption of important natural processes such as fire, ice scour, or an unnatural change in an environmental setting such as altered hydrology or excessive nutrient inputs resulting from eutrophication. Examples include incursions of cattails into sloping fen communities, the proliferation of clonal goldenrods in a sandplain grassland, or a growing dominance of red maple and aspen in barrens situations.
The use of herbicides is highly regulated in Massachusetts; both in terms of who can apply herbicides, and which herbicides may be used. The Massachusetts Department of Agricultural Resources (MDAR) is the governing body that regulates all herbicide use in Massachusetts and should be consulted directly with any questions related to herbicide regulations. In general, only licensed applicators may apply herbicides on land that is not their own, and only herbicides that have been approved by MDAR may be used in Massachusetts.
Associated practices
- Mowing and mulching: In certain situations, pretreating areas slated for herbicide application can greatly increase the efficacy and efficiency of an herbicide application. This is especially true in situations where the target species are tall and are capable of densely resprouting. Pre-application mowing in these situations will lower the height of the target vegetation, greatly reducing drift and non-target impacts. In aquatic habitats, hydro raking, hand pulling, mechanical harvesting and diver assisted suction harvesting (DASH) can be used to physically remove plants from waterbodies.
- Prescribed fire: Prescribed fire alone will not control invasive species. However, if used in combination with herbicide applications, the use of prescribed fire in fire-influenced natural communities can work to accelerate the control of certain invasives while building the integrity of the community, making the community more resilient to the impacts of invasive species. Properly timed prescribed fire can also be used to effectively control certain native generalist species in fire influenced communities. In some situations, especially as a post-herbicide treatment in dense stands of phragmites, the use of prescribed fire can be very beneficial in removing dense thatch (to release the native seed bank) and standing dead stalks (to facilitate access for future herbicide treatments).
- Preventative methods: In aquatic habitats, winter water level drawdowns denude nearshore littoral habitats exposing them to sub-freezing temperatures which can kill rooted aquatic vegetation in exposed areas. This practice requires 2 weeks of near continuous sub-freezing temperatures and is lethal to non-target plants and organisms unable to avoid desiccation and freezing conditions. Benthic barriers are gas perm-able membranes affixed to lake bottoms which prevent light from reaching the benthos restricting plant growth.
Methods
There are many herbicide application techniques used to control invasive and aggressive generalist species. Determining the proper technique is always situational, with elements such as the life history of the target species, the mode of action of various herbicide options, the size and density of the target species, the structure and condition of the natural community in which the herbicide will be applied, the scale of the infestation, the potential impacts on non-target species, and the efficiency of the delivery method all being important considerations. The following are basic considerations when evaluating a potential herbicide project:
Choosing an Herbicide:
There are several critical elements to be considered when choosing an herbicide:
- Status: Is the herbicide approved for use in Massachusetts. Is the herbicide approved to be used in aquatic systems.
- Selectivity: Is the herbicide a generalist or a specialist. Some herbicides, such as glyphosate, are generalist, meaning that they will impact a wide range of targets. Others are much more selective and will impact only a limited band of targets. For example, some herbicides impact only broad-leaved plants, while others target only select types of grasses. Therefore, it’s critical to understand your targets and the goals of your application prior to selecting an herbicide.
- Mode of action: How an herbicide impacts a plant. Many herbicides target specific enzymes and therefore understanding both the mode of action and the life history of the target species is critical to ensuring the efficacy of an herbicide application; both in terms of selecting the right herbicide for the target and applying it during the optimal season. In aquatic habitats, herbicides are considered contact or systemic with the former acting when coming into contact with the specific plant of interest and the latter by uptake through the plant at specific concentrations. The choice of contact or systemic herbicides will depend on the species of plant that is the target of management.
- Environmental factors: Characteristics such as toxicity to various taxa, half-life, bioaccumulation and soil activity are important considerations when choosing an herbicide. Much of this information can be found on an herbicide’s label, as well as any special safety and environmental considerations to be employed when using the herbicide. In aquatic habitats, oxygen and temperature at depth must be closely measured and monitored before, during and after treatment as vegetation die off and resulting plant decomposition can result in lethal oxygen deficits depending one temperatures and depth.
- Herbicide delivery method: The following are the most commonly used herbicide application methods used in Massachusetts. Finding the balance between control and efficiency is very important. Generally, foliar spray applications are used when the target is dense, and more discrete delivery methods are used around sensitive resources.
- Mist-blower: A mist-blower is a motorized applicator that forces a stream of herbicide through a blast of air that atomizes the herbicide into fine droplets. Typical mist-blowers resemble (and function somewhat like) back-pack style leaf-blowers. The primary advantage of mist-blowers is that a large area can be treated in a short amount of time while using less herbicide than more conventional applications. Mist-blowers are often used in large, dense patches of target vegetation where there is not a lot of desirable vegetation to be retained. Mist-blowers are important tools in treating large monocultures, and when used by experienced applicators, drift to non-target plants is minimal.
- Hydraulic backpack-sprayer: A hydraulic backpack sprayer is a tank and pump worn on the back of an applicator. Hydraulic backpack sprayers can treat much less area than a mist-blower and use a higher volume of herbicide. The advantage of a hydraulic back-pack sprayer is greater control of herbicide drift. The primary use of a hydraulic back-pack sprayer is for spot-treatments, especially in areas with interstitial patches of desirable non-target vegetation. The hydraulic backpack sprayer is the most common tool used in herbicide applications.
- Wick: Wicks come in many forms, but they are essentially a rope attached to a reservoir of herbicide. When in operation, the wick becomes saturated with herbicide and is then wiped on the target vegetation. Two of the more common types of wicks used are a weed-wand and a boom. A weed-wand is a wick at the end of a handle; the applicator stands and wipes the wick against the vegetation. A boom is a long wick mounted on a horizontal bar and moved over the vegetation at a desired height. This can be done either by mounting the boom to a tractor, or by tying a rope to each end of the bar and dragging the boom through the vegetation. Wicks enable the applicator to precisely treat an area while minimizing herbicide volumes. The primary use of the wick is to treat target species with structural height differences compared to the non-target species. Allows you to treat overstory target species while protecting the understory species.
- Glove: The glove technique is essentially a variation of a weed-wand, but the wick is a glove worn on the hand. The applicator simply wears a wooly glove with a protective rubber glove beneath, dips the hand in glove into herbicide until it is saturated, and then wipes their hand in glove against the target vegetation. This method is typically used in highly sensitive areas on herbaceous species.
- Cut-stem: The cut-stem technique consists of an applicator cutting stalks/stems and dripping herbicide into/onto the hollow stem/cut stump of the plant. Cut-stem treatments are the most precise of all listed treatments but are also by far the most labor intensive. This method is typically used in highly sensitive areas on woody species and may also be used on taller herbaceous species with hollow stems such as Japanese knotweed or common reed.
- Boom sprayers: Using a boom sprayer mounted to a tractor, UTV or boat which allows a manager to deliver a highly calibrated, evenly distributed foliar application over a large area. A boom sprayer is especially effective in open situations, such as fields, grasslands and recently mowed shrublands.
- Low-pressure amphibious vehicles: The use of low-pressure amphibious vehicles has become an important tool in treating invasive species in open marsh situations. These are relatively light-weight tracked vehicles that are capable of moving over open water and traversing wetland vegetation while causing very little impact to wetland resources. Many of these vehicles apply only about 1 pound of pressure per square foot (a standing adult applies about 7 pounds). For herbicide application, most of these vehicles are equipped with an elevated deck where an applicator applies herbicide with a wand. Low pressure amphibious vehicles provide easy access to otherwise difficult situations, resulting in a more complete and accurate treatment in significantly less time.
- Other considerations:
- Avoidance: The easiest invasive species occurrences to deal with are the occurrences that have never occurred. Therefore, it should always be a priority to avoid introducing invasive species and their propagules into any area. Some considerations are: washing equipment (mowers, vehicles, boats etc.) when moving from one site to another; avoid moving earth and vegetation debris; and wash and quarantine livestock (until seeds have passed through their digestive systems) when moving them to new pastures. In aquatic habitats, boats and trailers should be picked clean of aquatic vegetation at the ramp and later cleaned with high pressure hot (>120 F) if possible, and allowed to fully dry in the sun.
- Early detection-rapid response: Invasives species occurrences are always easiest to deal with when they are small and only recently established. In these cases, there will be fewer plants over a smaller area, and the seed bank will be much less established. Early detection of invasive establishment requires the regular survey of a site, and rapid response means treating the new occurrences soon after detection; ideally before it sets seed. Practicing early detection-rapid response results in less ecological degradation, a higher rate of success, and a great reduction in effort and the amount of herbicide used.
- Commitment, effort, prioritization, and goals: Any established invasive species occurrence will likely require at least multiple years of treatment, and in many cases, invasive species control is an indefinite proposition. As a result, many invasive species treatment projects fail because an individual or an organization has only planned for an initial treatment and then becomes discouraged when the occurrence is present beyond the expected time of action. Therefore, it’s very important that any invasive species action is properly sized up, and an appropriate commitment of resources is allocated. Because invasive control can require large commitments, it's also important that invasive occurrences are prioritized for treatment. Priorities may reflect the protection of an important natural community or rare species, or may simply reflect an opportunity that is most likely to succeed. Finally, setting reasonable goals is also important. While eradication is always desirable, complete eradication is seldom achievable in established occurrences. Determining whether a project’s goal is containment, control or eradication will be important in determining a project’s path forward. In aquatic habitats, excessive vegetation growth is often a result of nutrient enrichment. Nutrients concentrate in lentic waters as a result of increased run-off from anthropogenically altered landscapes which contain greater concentrations of nutrients. As herbicides only temporarily treat the symptoms of the underlying problem they should be paired with watershed scale efforts to reduce nutrient runoff to better address current and future habitat conditions.
- Wetlands and other sensitive communities: Invasive and generalist species control should not be avoided in wetlands and other sensitive natural communities. In fact, these resources often rank as the highest priorities for vegetation control when considering the conservation of regional biodiversity. Left uncontrolled, invasive and generalist species will end up altering these communities to a point where they no longer support the resources that originally lead them to be protected. Thoughtful vegetation control should be a part of any conservation plan of these communities. Any vegetation control that occurs in a wetland or waterbody requires permitting under the Massachusetts Wetlands Protection Act, and any vegetation control in rare species Priority Habitat requires review and approval by the Massachusetts Natural Heritage and Endangered Species Program.
- Contractors: Hiring contractors is often necessary for larger scale projects, or projects that occur on conservation land. When hiring a contractor, always make sure that they are licensed, check their references, and require a contract that clearly states the objectives of the project (project area, target species, percent kill, expectations for protecting non-target species, and any special circumstances related to the property or project).
Frequency
Adaptive management: Vegetation control plans must be adaptative so that treatments can be adjusted to reflect changing circumstances and lessons learned over the course of a project. This requires regular monitoring and post treatment assessment of what is working and what is not.
Additional resources
Mattson, M.D., P.J. Godfrey, R.A. Barletta and A. Aiello. 2004. Eutrophication and Aquatic Plant Management in Massachusetts. Final Generic Environmental Impact Report. Edited by Kenneth J. Wagner. Department of Environmental Protection and Department of Conservation and Recreation, Executive Office of Environmental Affairs, Commonwealth of Massachusetts.