The state of Michigan defines an invasive species as a species that is “not native and whose introduction causes harm, or is likely to cause harm to Michigan’s economy, environment, or human health.” Invasive plant species are a major threat to the habitat around Muskegon Lake, and their impacts are wide-ranging.
Invasive species cause harm in several ways:
- They are aggressive competitors, often dominating an ecosystem and dramatically reducing native diversity.
- Some invasive species grow significantly faster than natives, some produce seeds that remain viable in the soil for years, some create chemicals that inhibit growth of other plants around them, and some reproduce quickly from rhizomes or tiny stem fragments.
- Invasive species have various ecological strategies that enable them to disrupt native ecosystems, therefore different invasives will require different and unique treatments.
To effectively manage invasive species, it is critical to be able to identify the species and understand its biology, lifecycle, landscape context, and reproductive traits. A list of common invaders found around Muskegon Lake, and recommended treatment, has been developed to assist with identification and management.
Once an invasive plant has been identified, one must decide whether or not to treat it, and how. The decision to remove or leave a plant is typically based on:
- The traits of the given species (Is it likely to spread? How much harm is it causing, or likely to cause?)
- The quality of the habitat
- The size of the population
- Your resources (Do you have the time, skill, equipment, or funding to effectively treat?)
- Your values (What are you really trying to accomplish at the site?)
One thing to keep in mind is that it’s usually most effective to treat invasive species while populations are still small. Therefore, prioritizing treatment typically means starting with the smallest populations in the highest quality habitat.
Once you’ve decided to treat an invasive species population, you’ll need to select a control technique. There are a variety of control techniques available, and they are broadly grouped into Mechanical, Chemical, Biological, and Hydrological. The chosen technique is usually based on the plant, the site, your abilities, and your values. There is not always a “one-size-fits-all” for invasive species control techniques, and the most effective management programs typically use more than one technique (this is called Integrated Vegetation Management, or IVM).
Mechanical control includes hand pulling, mowing, and girdling. These methods do not require the use of chemicals and are generally more effective on smaller populations, when working in sensitive areas, or when working with people who are not authorized to apply herbicide.
Small patches or scattered individuals of invasive species may sometimes be removed by hand or with specialized hand tools (soil knife or weed wrench). This method is advantageous when managing invasive species in sensitive areas or species with small leaves (spotted knapweed, sweet clover) where chemical treatment would result in off-target damage. When using this technique, it is important to pull at the base of the plant and remove the entire root. Root fragments left behind can resprout and produce seed in the same season. Plant material should either be burned on site or disposed of at a local landfill. Composting invasive species is not recommended because plant material may contain viable seed, root fragments, or rhizomes that can reintroduce invasive species. Hand pulling removal efforts should occur before the plants flower and set seed.
Selective and precisely timed mowing can be used as a technique to reduce populations of invasive species. Repeated mowing over several years can be used to prevent seed production, deplete root reserves, and give native plants a competitive advantage. For example, sweet clover is an annual or biennial plant that can be reduced if selectively mowed in the spring before flowering. Mowing can also be an effective first step in a restoration process. Buckthorn infestations can often form thickets that are too dense to effectively treat with a cut stump method and too tall for a foliar application. It can be more effective to mow dense populations, wait until resprouts are at a manageable height, and apply herbicide to new growth the following year.
Girdling can be an effective technique to control mature woody species when chemical use is not an option. Girdling is carried out by removing a band of bark around the trunk of a tree, which in turn severs the cambium layer and interrupts the flow of sap from root to crown. For large trees this band should be six to eight inches wide, while on smaller trees or shrubs, one or two inches is adequate. Girdling can be carried out with a chainsaw or hatchet.
Herbicides can be a useful tool, and in some cases the only effective control method for invasive species. Large populations of invasives and species that are difficult to remove by hand are ideal candidates for herbicide use. Herbicides fall into two broad categories: selective meaning they are only effective on certain types of plants (ex. Triclopyr based solution), and non-selective meaning they are effective on any plant they come in contact with (ex. Glyphosate based solution). The choice of herbicide depends on the target population, stage of growth, presence of desirable species, and the proximity of water resources. Herbicide treatments should be performed by certified pesticide applicators and applied in accordance with the chemical manufacturer label instructions. Use of herbicides near standing water will also require aquatic approved herbicides (ex. Aquaneat) and an Aquatic Nuisance Control Permit from the Michigan Department of Environment, Great Lakes, and Energy. To learn more, visit the EGLE ANC website: mi.gov/anc
Foliar treatment involves selectively applying herbicide to the leaves of a target species. This method can be done with a variety of different tools and herbicides. For example, small patches of multiflora rose in a forested wetland can be selectively targeted using a back sprayer and a selective herbicide (ex. triclopyr). Triclopyr is an example of a broadleaf specific herbicide that would be advantageous in this situation because it won’t kill surrounding native grasses or sedges. Foliar treatment can also be used in situations where it is more appropriate to be less selective. Large monocultures of phragmites or reed canary grass would be more effectively treated by using a motorized tank sprayer and a non-selective herbicide (ex. Glyphosate).
While chemical control is commonly associated with large populations of invasive species, it can also be used in a very selective and sensitive manner. Hand wicking involves spraying an herbicide solution on an absorbent glove and carefully wiping the herbicide onto the surface of a leaf. It’s important to wear an herbicide resistant glove beneath the absorbent glove, to protect your hand from the herbicide. This method is appropriate when controlling small populations of invasive species that are growing in a high-quality area, or when controlling invasive species in close proximity of endangered or threatened native species.
Cut Stump Treatment
Invasive trees and shrubs that are too tall for foliar treatment can be controlled with the cut stump method. This method is carried out by cutting stems of target species within two to four inches of the ground (using handsaw, loppers, or chainsaw) followed by application of herbicide to the cut surface. When treating larger stumps (>2 in.) herbicide should be applied to the outer edge of the stump, while smaller stumps (<2 in.) should be treated across the entire top surface. Treatment should occur immediately following cutting to ensure proper absorption of herbicide. Cut stump treatments may occur any time throughout the year, except during spring sap flow (mid March through May).
Biological control uses insects, fungi, microbial pathogens, competing plants, or even wildlife like goats to target and control invasive species. Biological control organisms interfere with a plant’s growth and reproduction by eating and damaging invasive species, resulting in a decline in population. Control organisms usually come from the native range of the target species, and require a period of extensive study to ensure that they will remain specific to the target invasive species. Otherwise the introduced organism may cause even more damage than the original target. Biological control typically does not completely eradicate the target species and can take several years to show results. The most common example of successful biological control in Michigan is use of the Galerucella beetle to control purple loosestrife.
Although this technique can be difficult to implement, invasive plants can sometimes be controlled by altering water levels. This may include raising water levels to drown out plants like cattails or Phragmites, or lowering water levels to control submergent invasive plants like Eurasian watermilfoil. This technique can sometimes have negative effects on desirable native plant communities, and may also require permits from state or federal agencies.