Garlic mustard vs. spring flora … Part two: Solutions

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Last week, Illinoisans were again reminded not to plant several invasive alien species that “can cause serious harm to threatened and endangered plants and wildlife,” according to Natural Resources Director Joel Brunsvold.

Garlic mustard was not among the alien species. Not because it causes no harm, but because it’s as abundant and free as dandelions. Who would bother to purchase and plant it?

After existing in relative obscurity in North America for several centuries, the species’ population has suddenly exploded, threatening the exquisitely balanced diversity of native woodlands.

Garlic mustard is a biennial. The first year, seedlings become rosettes up to six inches in diameter that remain green all winter. The second year, plants produce seed, then die. Those seeds can sprout for the next seven years.

We’ve battled the weed in our woods. We have experimented with various techniques, learned new ones, tested them, and tentatively concluded which are effective.

Following are some techniques for dealing with garlic mustard:

Remove garlic mustard before it gains a foothold. It’s much easier to pull a few weeds than a carpet of them. When garlic mustard first appeared in Illinois woodlands, most landowners didn’t know how aggressive it would become and did nothing. The problem multiplied.

If the plot is less than two acres, the best management technique is simple weeding of second-year plants. But garlic mustard is not a benign garden weed. Even when its roots are exposed, if it’s tossed on the ground, it will continue to grow and set viable seed. Fresh garlic mustard has too much moisture to burn like a brush pile. Composting it often fails, since most compost bins don’t become warm enough to destroy the seeds. Place entire plants in black plastic bags and seal them securely until the plants decompose. Allow about two to four hours of pulling time per acre.

With sufficient fuel and dry conditions, fire will destroy garlic mustard. However, fire must be extremely hot to destroy dense patches. Enough dry fuel, including oak leaves, grasses and sedges, is necessary. A spring burn can set back second-year plants; a fall burn will destroy next year’s seed producers.

Caution: Be sure that a trained fire manager is present at a burn!

Weeds may also be cut at the crown as they begin to bloom, but remove all stems, or seeds will ripen.

Herbicides can be selectively applied. Weeds are destroyed, but so are other plants that unfortunately grow nearby. The best approach is applying herbicides to first-year growth after other plants have died back in fall.

A combination of burning, hand pulling isolated patches, and applying herbicide to dense growth has succeeded for us. Native populations have filled in the void, and our woodland now appears as diverse as before.

The weed has retreated in our woods. We won’t stop our efforts, but the task is manageable now. And when our friends comment that we don’t have just a carpet of wild flowers, we have a billowy ocean, we know it’s been worth the work.

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