Garlic Mustard

Conservation Corner

Conservation Corner is a weekly article produced by the Forest County Land &Water Conservation Department. For more information contact Steve Kircher, County Conservationist-Land Information/GIS Director at 715-478-1387 or by e-mail at .

Along with trilliums and trout lilies, invasive garlic mustard has become another harbinger of spring in Wisconsin. Right now, the pesky plant is popping up along roadsides, trails and streams, (at least, in Southern Wisconsin) carpeting forest floors and taking hold wherever it finds open ground or disturbed soils.

First-year plants, called basal rosettes, appear as serrated, round-leaved ground cover. Long, 1- to 4-foot stems bolt from second-year plants, sporting spring clusters of tiny, white, four-petaled flowers. Crushing the leaves or stem releases the plant’s telltale garlic odor.

A small patch of garlic mustard plants with serrated, heart shaped leaves and small, white flowers.  Anyone who has experience managing a garlic mustard infestation is familiar with its persistence. Hand-pulling is the most common method of control and can yield bags and bags of plant material each spring. Plants can produce hundreds of tiny seeds that spread easily to start new patches.

Garlic mustard exhibits habits common to successful invaders. It gets an early start and covers a lot of ground, ensuring it will outcompete most native plants. It’s not picky about where it puts down roots. Sun, shade, moist or dry soils – it seems anywhere is suitable for this widespread plant. Garlic mustard has one more tool in its toolbelt – allelopathy – the ability to release chemicals that can limit or prevent the growth of other plants.

Native to Europe, garlic mustard is an herb with both food and medicinal uses. It was brought to the United States intentionally by settlers in the 1800s. Without its native predators, garlic mustard thrives here relatively unchecked.

The plant is a favorite of “invasivores” – a term combining “invasive species” and “devour” to characterize one who eats invasive species, according to Invasivore.org. Its garlic flavor can season soups, meats and sauces, and its leaves and stems can be added to salads or used as a garnish.

Though the goal of using, instead of wasting, edible invasive species is worthy, unfortunately, it hasn’t made a dent in the invasive plant’s population, leaving invasive species managers looking for new solutions.

What if there was a creature out there that just loved to eat garlic mustard?  Thanks to Rebecah Troutman, a natural areas biologist at Holden Forests and Gardens in Ohio, we now know there is.   While pulling garlic mustard at Holden in 2021, Troutman noticed a plant covered with tiny insects.  “I did some Googling and made a preliminary identification of the garlic mustard aphid, Lipaphis alliarae,” said Troutman. “I then sent a sample to Doris Lagos-Kutz, research associate at the U.S. Department of Agriculture, who confirmed it was the first official sighting of the European aphid in the U.S.”

The garlic mustard aphid is a small, dark gray to green insect sometimes called the “grenade” aphid due to the pattern of raised blotches on its back. It sucks sap from garlic mustard plants, causing puckered, yellowed or wilting leaves and twisted seed pods.

Troutman communicated her find to the Midwest Invasive Plant Network, where coordinator Michelle Beloskur is helping spread the word in hopes of finding more places where the garlic mustard aphid is already at work.

“Since 2021, we’ve identified isolated populations in Connecticut, Massachusetts, Michigan, Minnesota, Ohio and Wisconsin,” said Beloskur. “We’re seeing impacts like shorter plants, fewer and twisted seed pods, and less overall biomass at these sites. It appears that even a small number of aphids can affect plant growth.”

This spring, Beloskur and Troutman hope to identify more garlic mustard aphid locations to better understand the aphid’s range and impact, and they’re asking for help.

If you see the aphid or notice its signs on garlic mustard plants, please contact me:  Steve Kircher, County Conservationist-Land Information/GIS Director at 715-478-1387 or by e-mail at .

A final reminder, when removing garlic mustard, be sure to double-bag all plant material and place bags in sunlight for a few days to allow plants to decompose before disposal. Composting is not recommended, as seeds can remain viable.