Fall is a beloved time of year for many Minnesotans, and for good reason! We get to enjoy the vibrant colors of maples, oaks, sumac, dogwoods, and other native trees and shrubs as they transition with the weather. But as the leaves drop, you might notice something out of place in your woods or along the trails: patches of persistent, incongruous green foliage.
While other native plants have changed colors or dropped their leaves, this contrasting green should raise a red flag. Many invasive trees and shrubs hold onto their leaves later into the fall than our native species. This gives them a significant competitive advantage as they’re taking in the extra sunlight. Fortunately, this makes them easy to spot and manage.
As a bonus, fall is also the ideal time to treat and manage woody invasive species, as nutrients, along with any treatments, are carried down to their root systems for the winter. Herbicides applied at this time will move down with the sugars and nutrients, becoming more effective as a result.
Our native plants are going dormant as the temperature drops, so this means there will be less non-targeted damage when herbicides are applied to invasive plants.
Common culprits
In Minnesota, two of the most problematic woody plants are buckthorn and non-native bush honeysuckles. Their late-season green foliage easily identifies both and should be the primary targets of your fall management efforts.
Buckthorn
Many people are familiar with Common buckthorn (Rhamnus cathartica) and Glossy buckthorn (Frangula alnus), as they’re managing them themselves.
Buckthorn forms dense stands that crowd out native plants, prevent forest regeneration, and lead to less accessible and enjoyable land. Additionally, it serves as an alternative host for problematic pests, including oat crown rust, alfalfa mosaic virus, and soybean aphid, which significantly impact agricultural productivity.
Non-native bush honeysuckles
Non-native honeysuckle (Lonicera spp.) rapidly invades disturbed areas, creating dense thickets like buckthorn. It shades out native woodland plants, reducing biodiversity and suppressing regeneration. It also results in an unnavigable understory layer.
After removing invasives
For anyone looking to restore or rewild their land or help the local ecosystem, fall is a great time to scout for invasive species due to the visible contrast in the landscape. It’s also an ideal time to put on your gloves and get to work removing and treating them.
After the removal of invasive species, especially those such as buckthorn and non-native honeysuckles, revegetation is crucial to achieve a healthier plant community. Without it, invasive species will quickly regain control.
To suppress unwanted new growth, it’s recommended to revegetate as soon as possible after the initial removal. This usually means dormant seeding in the winter or planting in the spring. To learn more about forest understory revegetation to help manage invasive plants, as well as recommended native species to plant, visit the Cover It Up project page.
Buckthorn and non-native honeysuckle will be the first woody plants to leaf out in the spring, so remember these plants in a couple of months for early-season follow-up work.
More on removing and treating woody plants
- Controlling unwanted trees and shrubs
- Buckthorn managementMinnesota Department of Natural Resources
- Invasive Plant Control DatabaseMidwest Invasive Plant Network, University of Wisconsin