Invasive Plants and Insects

Minnesota invasive species are species that are not native to Minnesota and cause economic or environmental harm or harm to human health.  There are a number of species present in Minnesota at this time and they will vary from area to area.  For a comprehensive list, visit:

If you’re not sure if you have an invasive animal or plant on your property, a good preliminary resource on what may be ailing your trees and plants can be found on the UofM Extension website:  What’s wrong with my plant?

Invasive Insects

The Emerald Ash Borer (EAB) is a nonnative invasive insect that has already killed millions of trees in Minnesota. In its native Asia, resistant trees and numerous predators keep the EAB population under control. Suspected to have arrived in North America via shipping crates in the Great Lakes, the Emerald Ash Borer was first identified in Michigan in 2002, and on their own spread about 12 miles per year.

Through firewood, EAB has spread further than they ever could on their own. EAB has been located in St Louis County and is likely to spread throughout the region.

3 important things you can do to help slow and mitigate EAB’s damage:
1) Do not transport firewood. Not even within Minnesota. EAB larvae and pupae remain hidden beneath the bark of the tree getting chopped into firewood, and then emerges fully grown. If you’ve transported wood with EAB in it, you’ve now created a satellite population in a new location. The MN DNR is taking the EAB infestation seriously, so before you go camping, check out their guidelines on what firewood is safe.

2) Learn to identify Emerald Ash Borer and evidence of its presence. The Minnesota Extension has a step-by-step guide for identifying ash trees, the ash borer itself, and insect damage. Diseased trees may be treated or removed.

3) Begin planting replacement species. For black ash growing in moist forests, consider tamarack, white cedar, mountain ash, and yellow birch. For black ash in upland forests, consider basswood, quaking aspen, oak, white pine, and white spruce. For green ash along river floodplains, consider dogwood, juneberry, or some of our native willows.

The gypsy moth is an invasive forest pest from Europe that is one of the most damaging tree defoliators currently in the U.S. Aspen and oak top the list of over 500 preferred host species. Gypsy moth caterpillars feed on leaves of deciduous trees and are present in early to mid-summer.

Gypsy moths are problematic for a number of reasons. They are voracious eaters and can completely defoliate entire trees. Outdoor recreation might be reduced as a result of bare trees, caterpillar presence on trees and roads, and feces falling from trees. Repeated defoliation can lead to the death of many trees, changing the mix of tree species and affecting dependent wildlife. Tree losses can impact forest and related industries. Because gypsy moths are nonnative, there are few natural enemies to keep them in check.

Gypsy moth controls include cultural, mechanical, and chemical controls; natural predators; and silvicultural practices. Various practices are used at different stages of population development. There are state and federal programs available at each stage to provide technical and financial assistance.

More information on the gypsy moth can be found on the Minnesota DNR website:

Gypsy moth male (right) and female (left)

Gypsy moth caterpillars

Invasive Plants

Buckthorn is a non-native invasive shrub species that was brought over from Europe in the 1800’s as a hedge for landscaping. Two species of buckthorn are invasive in Minnesota and many neighboring states: Common Buckthorn (Rhamnus cathartica) and Glossy Buckthorn (Frangula alnus).

Buckthorn harms woodlands. It chokes out native plants and creates a near-monoculture. Displacement of native plants removes food that sustains native animals. Animals that eat the berries are afflicted with health issues caused by the toxic chemicals in the berries.

Once Buckthorn becomes well established, it is difficult to remove. There are a few options to deal with infestations, most involve cutting and treating large individuals and pulling seedlings and small saplings. More specific details about this can be found on the Minnesota DNR’s website:

Common Buckthorn

Glossy Buckthorn

Japanese knotweed is a non-native invasive species introduced to the U.S. in the late 1800s for ornamental purposes and erosion control.

Japanese knotweed spreads primarily vegetatively to form dense thickets that suppress native vegetation.  It can pose a significant threat to riparian areas, such as disturbed stream sides, lakeshores and other low lying areas, where it can rapidly colonize. It tolerates full shade, high temperatures, high salinity and drought.It is currently occurring from Maine to Minnesota and south to Louisiana and scattered in midwestern and western states.

Japanese knotweed can be challenging to control.  Mechanical methods include digging plants for small infestations and in sensitive areas as well as pulling of juvenile plants. Plants can resprout from small fragments.  Mowing may spread plants to new areas.  Chemical removal includes cut stem treatment with glyphosate or triclopyr and Foliar spray in large single species populations.

More information can be found on the Minnesota DNR’s website:

Japanese knotweed