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Fall is a good time to manage invasive species

Low-growing plants with bright green heart shaped leaves growing in a cluster near the base of a tree surrounded by sticks and fallen leaves.
Garlic mustard growing on the forest floor

Fall is a great time to patrol your woodlands for damaging invasive plants. Certain species are especially vulnerable at this time, and controlling them now can pay off next growing season. As an added bonus, fewer biting insects and cooler temperatures are always welcome when working outside.

Buckthorn

Fall is an important time for managing this invasive species. Our colleagues on the Extension crops team recently wrote an excellent and in-depth article about buckthorn identification and management, Controlling buckthorn: the who, what, where, when and how.

Garlic mustard

Garlic mustard  (Alliaria petiolata) can be devastating to Midwestern forests. Originally from Europe, humans have eaten garlic mustard for at least the past 6,000 years. In the 1800s, this species was introduced into North America by European immigrants. Despite its use as an edible herb, garlic mustard is a restricted noxious weed, meaning it cannot be transported, introduced, or sold in Minnesota.

Its seeds are not commonly spread by wind or animals, but rather through water or mud. These seeds can stay alive in the soil for a long time, causing issues every spring and fall.

While it may seem like a hassle, removing soil from your boots before and after you leave a forest is a great way to avoid introducing invasive species, including garlic mustard.

One challenging aspect of garlic mustard, aside from how it spreads, is its effects on other plants. Studies suggest garlic mustard is allelopathic, which means this plant sends out chemicals that hurt the growth of its neighbors.

The chemicals garlic mustard releases are called glucosinolates. These give it a spicy taste but also harm beneficial soil fungi called mycorrhizae. These fungi help provide important nutrients to plants in exchange for energy. However, like many members of its plant family Brassicaceae, garlic mustard does not have this fungal relationship.

Over time, a large garlic mustard patch can severely damage native plant populations that otherwise would thrive in the area.

How to identify garlic mustard

Photo comparison of leaves from creeping Charlie, garlic mustard and violet.
Creeping Charlie, garlic mustard and violet

Because garlic mustard is a biennial weed, the first year of its life is spent as a rosette low on the forest floor. Often, it is confused with either wild ginger (Asarum species), creeping charlie (Glechoma hederacea), or violets (Viola species) due to its kidney bean-shaped leaves.

One trick to find garlic mustard is to scout in the late fall, as it is one of the last green plants in the woods. Its first-year leaf edges are "scalloped," with blunt, shallow teeth on the sides. In the spring and early summer, garlic mustard’s second year leaves look more triangular further up the stem. However, they will still have scalloped edges.

It can also be identified by smell:

  • Crushing garlic mustard leaves can give off a mustardy, garlic odor.
  • Violets will not have a strong smell.
  • Creeping charlie will have a minty, herbal aroma. 
  • Wild ginger’s stems, if broken, will release a smell similar to ginger.

Unlike creeping charlie and wild ginger, garlic mustard does not spread as a vine. If you pull garlic mustard plants you will not find runners or rhizomes, but a single crown with an S-shaped root attached.

Controlling garlic mustard

Photo of garlic mustard root on wooden planks.
Garlic mustard root

If the area is small, hand removal of the plant and most of its root system could be an option.

For larger sites, herbicide applications are generally the favored technique. If you decide to go this route, a labeled herbicide that contains the active ingredient triclopyr (Garlon) or glyphosate (RoundUp) can be effective.

Be aware that glyphosate products are non-selective, and will harm most actively growing plants if sprayed. Triclopyr normally does not hurt grasses and sedges, as it is more targeted toward broadleaves.

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