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What is an invasive plant?

The National Invasive Species Management Plan, develped in response to Executive Order 13112, defines an invasive species as “a species that is non-native to the ecosystem under consideration and whose introduction causes or is likely to cause economic or envoronmental harm or harm to human health.”

Only a small fraction of the hundreds of non-native plants that have evolved elsewhere and been brought to Michigan are invasive.  The few that are, however, can be very aggressive and spread rapidly once establised.  In our native forests, grasslands, wetlands and dunes, they pose a threat to management goals by displacing native species or altering ecosystem processes.  Taken from the MSUE Field Identification Guide to Invasive Plants in Michigan book.

Eurasian Phragmites—This plant typically grows in coastal and interior wetlands, lake margins, roadside ditches, and other low, wet areas, although it can also be found in dry areas.  It ranges from 6 to 15 feet in height, yet 80% of the plant is contained below ground in a dense mass of roots and rhizomes that can penetrate the soil to a depth greater than 6 feet.  The feathery plumes that form at the end of stalks are 6 to 20 inches long and up to 8 inches wide with many branches.  This invasive is threatening the ecological health of wetlands and the Great Lakes costal shoreline.  It crowds out native plants and animals, blocks shoreline views, and can create fire hazards from dry plant material.

Control Methods—Controlling the spread of phragmites is crucial to the restoration of native wetland plant communities and protection of vital fish and wildlife habitat.  It can easily spread if improper control methods are used.  Phragmites can be controlled using an initial herbicide treatment followed by mechanical removal (cutting, mowing) and annual maintenance.  For large areas with dense stands of phragmites, prescribed burning used after herbicide treatment can provide additional control and ecological benefits over mechanical removal.  However, phragmites burns very hot and fast, and prescribed burns should be performed only by trained personnel.

Purple Loosestrife—This plant is dense, and grows up to 7 feet tall.  With attractive purple flowers it has become a popular ornamental.  One plant can produce over 100,000 seeds.  The problem is Purple Loosestrife adapts readily to natural and disturbed wetlands.  As it establishes and expands, it out-competes and replaces native grasses, sedges, and other flowering plants that provide a higher quality source of nutrition for wildlife.  It restricts native wetland plant species and reduces habitat for waterfowl.  Seed production is as prolific as the vegetative growth.  Seeds are widely distributed by animals, machinery and people.

Control Methods—Mowing should not be used because it can increase the spread of the population by dispersing seeds.

  • Mechanical: Small infestations of loosestrife can be removed by hand.  The entire root system must be removed from the ground.  All plant material should be bagged and removed.  Larger populations are harder to control by this means.

  • Chemical: Herbicides can be used effectively on small populations.  Only herbicides permitted for wetland use may be used.  The most species specific way to apply is by cutting and treating the stems.

  • Biological: Several species of insects are being studied for their effectiveness in control of loosestrife.  Although this method will not eradicate the species, it may create a more tolerable population level that will stabilize over time.

Garlic Mustard—This invasive impacts our forests.  It out-competes many tree seedlings and other native vegetation.  It also adversely affects native insects and other wildlife.  It is a biennial herb that smells of garlic when crushed.  The first years plants are low rosettes with rounded leaves that remain green in winter and continue to grow when temperatures are above freezing.  Second year plants grow 6”-40” tall, have triangular shaped leaves with toothed edges and have clusters of small white flowers with 4 petals.

Control Methods—Any control method must be repeated for several years until the garlic mustard seed bank is depleted.

• Hand pulling—before budding begins, plants may be pulled and scattered about to dry.  Do not put pulled plants in piles where roots can stay moist and plant development continues.  Once flowering has begun, all plants must be bagged.  Do not compost garlic mustard

• Cutting—Results vary.  Some say cutting plants at ground level just after the flower stalks have elongated but before the flowers have opened can be effective in killing plants and preventing seed production without disturbing the soil, others say that garlic mustard re-sprouts with this technique.

• Herbicide—Do not use herbicides unless absolutely necessary.  Severe infestations can be controlled by applying Round-up to foliage of individual plants or dense patches in October or early spring when most native plants are dormant.

Japanese Knotweed—This is a perennial, herbaceous shrub that grows 3-10 ft in height.  It has a deep tap root and an extensive network of rhizomes that may extend laterally from 23-65 ft.  Its hollow stalks persist through winter and resemble bamboo.  The leaves are simple and typically grow up to 5 in. long and 5 in. wide.  Knotweed has numerous small, creamy white flowers arranged in spikes near the end of the plants arching stems.  In MI they bloom in August and Sept. It is found along roadsides, stream and river banks, wetlands, and woodland edges.  It can tolerate a wide array of soil and moisture conditions.

Control Methods—Control efforts must target knotweed’s massive underground system of rhizomes.  To date, a combination of chemical and mechanical techniques, in conjunction with on-going monitoring, provides the most effective control of this species.  In all cases, monitoring and follow-up treatment will be required for 4-10 years, depending on the size and age of the population being treated.  More information on control for knotweed and other invasive plants is available at our office.



A link to description pages of both of the above insects is below.  The Asian Longhorned Beetle has not been documented in this area as of yet but there are reports of it heading in this direction.

Asian Longhorned Beetle and Emerald Ash Borer

Here are some options on treatments and how we can help!

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