Invasive Species
Mendota Heights has several invasive plants and trees. These are non-native species that take light, water, and nutrients from native plants, making it hard for them to survive. Invasive species can harm the environment, economy, and even the health of people and wildlife. They often spread quickly because there are no local insects or animals to keep them in check.
The best way to control invasive species is to prevent the spread of new invasive species to un-infested areas. You can help prevent the spread of invasive species by:
- Ensuring belongings, clothing, tools, and supplies are free of dirt, mud, and plant debris before transporting them.
- Identifying and utilizing local sources of certified firewood and weed-free hay, compost, and mulch.
- Leaving unused firewood and plant material onsite or at home. Do not transport plant material or firewood!
If you think you have an invasive plant or tree on your property, you can contact City Staff (see contact info below) or a tree care or restoration expert for help identifying it and learning how to manage it. Below are some common invasive species you might find, along with ways to remove or control them. For a complete list of invasive species in Minnesota, visit the MN Department of Natural Resources website.
Early Detection Species are invasive plants or pests that are either not yet in Minnesota or are only found in small numbers. Reporting them helps stop their spread. If you spot one, call “Arrest the Pest” at 651-201-6684 (metro) or 1-888-545-6684 (toll-free). You can also contact Monika Chandler from the Weed Program at 651-201-6537 or by email.
Common Invasive Species: These are some of the invasive or harmful weed species often found in Mendota Heights and across Minnesota, along with ways to control them.
Important Note About Herbicides: Always follow the label instructions and wear safety gear like gloves and eye protection. Do not use herbicides near water, on windy days, or when it’s raining or about to rain.
Field bindweed (Convolvulus arvensis) is an invasive perennial in the morning glory family with an extensive rhizomatous and deep root system. It has alternate, arrowhead shaped leaves and simple trumpet-like white flowers. Bindweed has seeds that can remain viable in soil for several decades, and can invade gardens, prairies, and wet areas by growing rapidly and intertwining with, and chocking out, native species.
Visit the Gardening Know How website.
Control Methods:
- Hand pulling or tilling where small populations exist
- Using competitive species to shade out plants and mulching to control seed germination
- Selective herbicide use when not in close proximity to native or desirable species, using glyphosate or a 2, 4-D and glyphosate combination (2, 4-D alone is generally not effective)
Buckthorn is an invasive, non-native understory tree, that is often pruned as a shrub or hedge, but can reach a height of up to 20 feet or greater. It was brought to North America from Europe in the early 1800s and has long-since escaped yards and invaded our native forests. It outcompetes its native counterparts by growing rapidly and leafing out early, as well as holding its leaves later into the fall. Buckthorn also produces a large amount of dark-colored berries that germinate quickly when spread by birds or after falling to the ground. Even though birds will eat the berries (usually as a last resort), they are not a good food source and can even make some birds and animals ill. There are two species of Buckthorn: Glossy Buckthorn (Frangula alnus) and Common or European (Rhamnus cathartica) Buckthorn. It can often be confused with the native Black Cherry tree, so identify carefully before removal. Fall is a great time for removal, as Buckthorn is easily identified by its green leaves well into late fall, when other native deciduous trees and plants have gone dormant. If you are unsure if you have buckthorn on your property, please contact City Staff (contact information at the bottom of this section) for a site visit and proper identification, or contact a tree care professional.
Controlling buckthorn takes a lot of tenacity and patience. Depending on the amount of buckthorn on your property, the control methods may vary. If you have a few trees, it is a much more achievable goal when planning to do the work yourself. If you have a large stand of buckthorn, it may be best to hire a tree care or native restoration company. In most cases, buckthorn removal and control is a multi-year process. If you do have more than a few trees, make a long-term plan. Remove plants that are fruit-producing first, as well as addressing areas with fewer concentrations before tackling heavily-invaded areas.
Control Methods:
- Pulling: Best done when trees are small, or 1” in diameter or less.
- Herbicide: If pulling is impractical (for example, large and heavily infested areas of small seedlings) spray foliage under 12” with an herbicide, such as glyphosate (Round-Up). Fall is the best time to apply an herbicide treatment, when most native plants have gone dormant, but buckthorn is still green and active.
- Cutting and stump treatment: Best used on large trees in the fall, but can be done anytime, except for the spring months during heavy sap flow. Cut buckthorn close to the ground, and immediately treat the stump with herbicide. A concentration of at least 20% glyphosate is recommended for stump treatment. If you do not plan on treating or covering the cut stump (see method below), do not cut, as the stump will produce sprouts at a more rapid rate the following year.
- Herbicide alternatives: Cut stumps can also be covered using a Buckthorn Baggie, other dark-colored plastic bag, or similar alternative when herbicide use is not desirable. Please make sure your bag or alternative is tightly secured to the stump, and fanned out at the bottom to catch any new shoots. Leave the bag on the stump for a minimum of two years, and then remember to remove!
For more information visit the MN Department of Natural Resources or contact Krista Spreiter, Natural Resources Coordinator at 651-255-1123 or email Krista Spreiter.
Canada thistle (Cirsium arvense) is an herbaceous perennial with thorns along the edges of its oblong leaves. Purple flowers bloom on the terminal branched stems beginning in June. It grows to 2 to 5 feet in height and possesses both a taproot and horizontal spreading roots that can form new plants. Canada thistle invades prairies, savannas, and disturbed areas. It generally likes dry soil, but can also spread into intermittently wet areas.
Control Methods:
- Hand pulling or manual removal for small infestations
- Cutting prior to seed production combined with spot herbicide treatment
- Herbicide treatment using a chemical such as glyphosate
Common barberry (Berberis vulgaris) is a deciduous shrub native to Asia that invades several habitats, including woodland and prairie. It readily produces thousands of seeds per shrub with substantial longevity and a high germination rate. Common barberry can reach a height of approximately 8 to 10 feet and has 3-pronged spines or thorns that line its branches. It has pale yellow flowers, and blooms in May and June.
Minnesota Department of Agriculture
Control Methods:
- Manual removal by digging and removing the root system in small areas of infestation
- Cutting and treating stumps of large populations with herbicide
- After initial removal, regular mowing and herbicide treatment of seedlings should be used to maintain control
Common burdock (Arctium minus) Biennial plant that produces a basal rosette of large leaves in its first year, and a tall stalk with purples flowers and numerous hooked bracts that form burs. Burs stick easily to clothing and animal fur.
Control Methods:
- Hand-pulling or mowing prior to flowering.
Garlic Mustard (Alliaria petiolate) is a biennial plant that grows to a height of 2-3 feet in its second year, with heart-shaped leaves and small clusters of white flowers that bloom in late spring. Garlic mustard gets its name from a strong garlic odor that is produced when the plant is crushed. It can invade wooded sites in both upland and wet areas, and outcompete native species rapidly. You can find it in shady wooded or landscaped areas throughout Minnesota.
Control Methods:
- Hand pulling (is pulled relatively easy, especially if soil is loose/moist)
- Cutting at ground level
- Burning (permit required)
- Herbicide treatments in early spring or fall with a 2, 4-D or glyphosate (2% concentration) herbicide when non-chemical methods are infeasible.
Several species of Knapweed (Centaurea spp.) including Brown, Diffuse, Meadow, Russian, and spotted, are herbaceous perennials or biennials from Europe and Asia that invade dry native prairie, pastures, and disturbed areas. Most species have hoary branched stems and thistle-like pink or purple flowers at the terminal stem. Knapweed blooms from July through September and grows to an average height of 3 feet.
Control Methods:
- Hand-pulling if detected early
- Repeated mowing prior to seed formation
- Herbicide treatment during bud growth in early June
Leafy spurge (Euphorbia esula) is a perennial herbaceous plant with alternate, thin oblong leaves with small yellow-green bracted flower clusters that bloom in late May through fall. Seeds disperse explosively and have a high germination rate. This invasive rapidly invades disturbed areas, such as roadsides, and cropland, but can also quickly invade prairies and savanna areas. It is extremely hard to control once established.
Control Methods:
- Prescribed burn (done by a restoration professional), often combined with multiple herbicide treatments, using glyphosate and/or 2,4-D chemical
- Herbicide treatment in fall when leafy spurge has gone through a second growth period, and most native plants have gone dormant.
- Biological control: several beetles serve as biological control for leafy spurge, including a root-boring beetle, root-mining beetles, and shoot-tip gall midge.
OAK WILT
Oak wilt is a deadly disease that affects all species of oaks (Quercus) found in Minnesota. Oak wilt infection spreads in two ways: sap beetles that carry the disease from fungal spore mats of infected trees to healthy trees, and below ground through root grafts (roots that have grown together). Oak Wilt is caused by a non-native, invasive fungus called Bretziella fagacearum. The fungus infests the vessels of oaks that move water through the tree, eventually killing it. The oak wilt pathogen can infect all species of oak. However, those in the red oak group (leaves with pointed lobes) die at a more rapid rate, about two months after infection. Bur oaks die one to seven years after infection, while white oaks die from one to over 20 years after infection.
SYMPTOMS
Oak wilt is not easily identified without a lab test, particularly on white and bur oaks, and can be easily mistaken for other diseases such as two-lined chestnut borer, bur oak blight, and anthracnose. Some of the symptoms of oak wilt include:
- Rapid leaf loss in mid-summer
- Leaf wilt starting at the edge of the canopy and moving inward
- Not all, but about half of infected red oaks produce fungal mats and pressure pads just under the bark of the tree, in many cases causing the bark to crack
PREVENTION & CONTROL
Do not prune, cut, or remove live oaks during the High-Risk Zone (April 1 through July 15). The High-Risk Zone may occur earlier in the year with unusually warm spring temperatures. Use caution and only cut or remove hazard oak trees during the Low-Risk Zone (July 16 through November 1). If cutting, removal, or pruning must occur outside of the Safe Zone (November 1 through April 15), immediately apply water-based paint or shellac to the cuts or outer sapwood of the stump.
Do not move logs or firewood from oak wilt areas to areas where oak wilt is not present.
Properly dispose of, or contain, infected wood. Options for on-site treatment include: debarking of the trunk, burying sections of the trunk or large branches, or cutting logs into firewood and stacking to allow for drying. During the High and Low-Risk Zones, firewood and cut branches should be covered with 4-6 millimeter clear plastic and sealed at the ground line.
For high-value trees, consider hiring a professional arborist to apply a fungicidal injection.
Means of control are highly site and situation dependent. Some methods of control include creating a barrier ring around diseased trees by trenching, or cutting roots to a depth of five feet or more (using a vibratory plow, trenching machine, or similar equipment).
For more information on the diagnosis, prevention, and treatment of Oak Wilt visit the Minnesota Department of Natural Resources website.
If you think you may have oak wilt in your area, please contact Krista Spreiter, Natural Resources Coordinator, at: 651-255-1123 or email Krista Spreiter.
Poison Hemlock (Conium maculatum) is a biennial plant that is highly poisonous when ingested, and can even be absorbed through skin contact. It has pinnately compound fern-like leaves, large clusters of small white flowers, and can grow to a height of 8 feet. It invades native wetland communities, stream banks, and roadsides.
MN Department of Natural Resources
Control Methods:
- Hand pull using protective gloves and clothing
- Remove the taproom 2 inches below ground level, and then remove the plant
- Cut or mow after flowers emerge, but before seeds evolve for multiple years
Purple Loosestrife (Lythrum salicara L.) is a noxious weed native to Europe and Asia. It is a semi-aquatic perennial species that invades wetland areas by forming a dense carpet of bushy growth, approximately 4 to 7 feet in height, and produces thousands of tiny seeds that are easily dispersed. It has bright pink to purple spikes of small flowers at the top of each stem, blooming from July through September.
MN Department of Agriculture
Control Methods:
- Hand-pulling and manual removal by digging are only recommended if there are just a few plants in an area
- Cutting is usually not practical in wetland environments, but effective if cut prior to flowering.
- Herbicide use is effective, but is not recommended near or in water, and in most cases a permit is required when using herbicide in or near water bodies.
- Biological control has been the most effective method in providing lasting treatment for large stands of Purple Loosestrife, using four different species of beetles. These beetles can be captured in early to mid-spring, and re-distributed to problem sites. Contact one the MN Department of Natural Resources’ Aquatic Invasive Species Specialists to learn more.
Vetches (Fabaceae Family) are spreading, perennial herbaceous legumes with a strong root system. They have pinnately compound leaflets and purple/pink flowers. They spread quickly both by seed and rhizomes, and are highly adaptable to several soil types.
Control Methods:
- Repetitive mowing or prescribed burn (permit required) for successive years, in most cases in conjunction with herbicide application
- Herbicide applications in areas of severe infestations
Wild parsnip (Pastinaca sativa) is a flowering perennial, native to Europe and Asia that reaches approximately 4 feet in height in the blooming stage, with alternate oval leaflets and a flat-topped cluster of yellow flowers. It blooms from June through late summer, and has a toxic sap that causes skin blisters when skin comes into contact with the plant and then is exposed to sunlight. The plant invades disturbed areas and spreads rapidly once established, posing a particular threat to native prairies.
Control Methods:
- Hand pulling (make sure to wear protective clothing, including gloves, long sleeves, and long pants)
- Herbicide use through spot application with glyphosate or similar chemical