By Wisconsin DNR

Rosettes on a garlic mustard plant. / Photo Credit: Wisconsin DNR

As temperatures begin to fall the leaves of many plants and trees have begun to change color. Some trees in the northern part of the state have already started to drop their leaves.

The Wisconsin Department of Natural Resources (DNR) reminds the public that fall is more than a great time to enjoy the changing hues in the woods. It also presents a good opportunity to spot the invasive plants persisting among the native plants and trees.

As you walk through your woods this month, look for leaves that stay green into late fall, even after all other trees have shed their leaves. Those green leaves are likely evidence of an invasive plant species.

Invasive plants can hold on to their leaves much longer than native plants, taking advantage of late fall sunshine to continue to grow and spread throughout the forest, taking resources away from the native plant life that has already died out or gone dormant for the winter and affecting the biodiversity that native animals need to thrive.

Late autumn and early winter can be great times to identify and treat invasive plants. With most native plants dormant, treating invasives with chemical herbicides is likely to cause much less collateral damage.

Fall treatment is ideal for woody invasives, as the plants are busy directing resources to their roots to store nutrients for overwintering, and the natural flow carries the herbicide down to the roots. Spring treatments such as cut-and-swipe — a common treatment for buckthorn that involves snipping off stems and using a dabber to apply herbicide directly to the cut—are often ineffective because the opposite is true: plants are continually pushing resources up and out toward new buds.

Common invasive plants that can be treated in the fall include garlic mustard, nonnative honeysuckles and common and glossy buckthorns. Here are some basic identification characteristics and methods of treatment.

Garlic Mustard

Though not a woody plant, the basal rosettes (a cluster of leaves at ground level) remain green through fall and winter and are easy to spot. Due to its kidney-bean-shaped leaves, garlic mustard looks somewhat like wild ginger or violets. To check, crush a leaf — the leaves of garlic mustard should release a garlicky scent when crushed.

If only a few plants are present, they can be hand-pulled and should be destroyed by burning or sending them to a landfill in bags clearly labeled as “Invasive Plants — Approved by Wisconsin DNR for Landfill.” For larger infestations, plants may be cut or torched, or herbicide may be used as recommended in the Control Methods section of the Garlic Mustard Fact Sheet.

Photo of a non-native honeysuckle plant. / Photo Credit: Wisconsin DNR

Nonnative Honeysuckles

Non-native honeysuckles can hold their leaves well into winter. They often have a thick canopy of leaves, which can shade out native plants. When other plants are bare and the honeysuckle still has its thick canopy, it’s a great time to attack and treat it.

There are several types of invasive honeysuckles in Wisconsin. Learn more about each variety as well as control methods on the Management of Bush Honeysuckles fact sheet from the University of Wisconsin-Madison Extension.

A glossy buckthorn shrub covered in berries. Control berry-producing plants first to prevent further spreading. / Photo Credit: Wisconsin DNR.

Common And Glossy Buckthorn

A common sight in Wisconsin forests, common and glossy buckthorn is also best treated in late fall and early winter. Buckthorn is a multistemmed large shrub or small tree that can form an impenetrable understory layer, displacing native vegetation.

Small buckthorn seedlings can be removed by hand. Larger plants should be cut or girdled at the base. Buckthorn can easily resprout from cut stumps, so herbicide treatments are often best. Find more information on control methods in the Buckthorn Management fact sheet.

After treating any invasive plants in the fall, make sure to follow up in spring to check for new growth and seedlings. Controlling invasive plant species almost always is a long-term effort requiring multiple treatments and monitoring over several seasons.