Wisconsin woodlands are being taken over by alien invaders! Alien invasive plants, that is. Among the worst interlopers are garlic mustard, buckthorn, wild grape vine and honeysuckle.
Garlic mustard spreads the fastest and many people fail to recognize it on their property until it’s way too late. Here’s one of the reasons: whoever came up with the name “garlic mustard” for Alliaria petiolata made a serious marketing error. People unfamiliar with the plant assume because “mustard” is part of its name, that the flowers are yellow, but they are not. If you remember nothing else from reading this article, remember this: GARLIC MUSTARD FLOWERS ARE WHITE.
This invader isn’t new here (here being the United States). European settlers brought it to the new world as a cooking herb and it has been spreading slowly northward and westward ever since. The problem is that the insect pests that control garlic mustard populations in the old country didn’t make the crossing.
The days of slowly spreading are over. In the past fifteen years, the garlic mustard population has exploded across the Midwest. It is impossible to predict or explain when a particular invasive species will suddenly go on a rampage. Perhaps environmental conditions have changed (ya think??) and the plants have jumped on the opportunity to invade, or maybe over 250 years the plants themselves have adapted slightly so they can take advantage of existing conditions.
So what’s so bad about garlic mustard? It’s a rather pretty plant with small white flowers and lacy-edged leaves, but evil lurks within. It has the potential to totally dominate a forest floor in a few years, shading or crowding out native wildflowers and tree seedlings before they have a chance to grow. This has a disastrous effect on birds and other forest wildlife as their food sources disappear.
The roots of garlic mustard emit a chemical that kills the fungi in the soil that should have been food for many tiny insects. When the smaller insects die, the larger insects that eat them die, then the birds that eat the insects starve and the effects move on up the food chain.
Even sneakier, garlic mustard attracts butterflies to lay eggs, but a chemical in the plant poisons the eggs or the larvae so butterflies never form.
Garlic mustard is a biennial plant. It grows a rosette of leaves its first year and in the second year a taller stalk appears with many small white flowers. It blooms from late April through May. Seed pods begin to form soon after flowering begins. Each plant produces hundreds of seeds that are viable for five to seven years.
In the United States, garlic mustard has no natural enemies, although the University of Minnesota is experimenting with a weevil that may be a method of biocontrol available in a few years. (But they’ve been saying “in a few years” for a lot of years now.)
For now, the best way to control garlic mustard is to pull it. It lifts easily from the ground just before and during its flowering period, in late April and early May. But it is a tricky plant. If you pull it and lay it on the ground, the plant itself will wither but the flower stalk will turn at a 90 degree angle and grow straight upward, produce flowers and set seed. This can happen even on a hot driveway or parking lot. It does everything it can to ensure its own survival! Therefore, when garlic mustard is pulled, it should be bagged and removed from the site.
With the passing of Wisconsin’s Invasive Species Identification, Classification and Control Rule, NR40, is it legal for homeowners to place bagged invasive plants such as garlic mustard out for garbage pickup to be taken to landfills.
If you like to play with fire, another control method is to use a propane torch to scorch first year seedlings, or melt the tops of the second year plants just before they bloom. All the control methods require re-checking a couple weeks later to search for plants that were missed.
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