One front yard coming up—hold the mustard


Laura Phillips-Mao has an occupational hazard: She can’t help noticing garlic mustard.

Phillips-Mao, a doctoral student in conservation biology at the University of Minnesota and a St. Anthony Park resident, has become an expert on an invasive species that is becoming more of a problem in Minnesota.

“I’m always ‘botanizing.’ Walking, driving – I keep noticing things,” she said.

There’s more garlic mustard to notice these days than when Phillips-Mao started her graduate program seven years ago.

“I think I first saw it in Como Park, where it’s a big problem,” she said, “and I’ve seen it in Merriam Park. Until last year, I hadn’t seen it in St. Anthony Park, but I did spot some in a front yard on my walk to work.

So why should we be concerned about garlic mustard?

The answer turns out to be a bit complicated. Garlic mustard changes the composition of soil, potentially rendering it more hospitable to other invasives, and also reducing levels of arbuscular mycorrhizal fungi, which have a symbiotic relationship with many woodland plants and trees. Plus, it spreads very rapidly.

Garlic mustard (Alliaria petiolata) is a biennial flowering plant native to Europe, western and central Asia, and northwestern Africa. It was likely brought to North America in the mid-19th century as a garden herb.

“I’ve had it in a sandwich, and some people make pesto out of it,” said Phillips-Mao. “It’s not an entirely useless plant, but it does represent a threat to our woodlands.”

Garlic mustard produces seed pods that pop open in July. Individual seeds are about the size of a sesame seed. They can become attached to people and animals, and can spread by water during heavy rains.

The only good way to control the stuff is by hand pulling, Phillips-Mao said.

“Mowing can help control it, but only if an area is mowed frequently so that it doesn’t have a chance to form seeds,” she said. “And herbicides often affect nontarget plants.”

There is some hope for controlling garlic mustard with biocontrol agents. The task is to find an insect that eats garlic mustard but doesn’t harm desirable plants.

“It would be nice if deer liked garlic mustard,” Phillips-Mao said, “since we’re overpopulated with deer in Minnesota. But they leave it alone.”

She said the plant is not considered an invasive species in its native areas because “there are probably natural predators there that keep it under control.”

Phillips-Mao said she’s not ready to start a campaign of snooping in people’s yards and knocking on doors if she spots garlic mustard growing, but she is concerned about the threat the plant represents to our woodlands.

“Garlic mustard isn’t the worst invasive out there,” she said, “but it is potentially harmful. The good thing is that in the early stages of an infestation, it’s not hard to control. It’s very manageable at the yard level.”

Phillips-Mao realizes that by trying to raise the profile of garlic mustard, she runs the risk of increasing “invasives fatigue.” She acknowledged that other invasives, like buckthorn and the emerald ash borer, have received a lot of attention lately.

“I know there’s only so much that people can devote their attention to,” she said. “Right now, I don’t know how much of a problem it is in this neighborhood, but I would like people to become more aware of it so they can help keep it from gaining a foothold here. Being vigilant now can prevent an insurmountable problem in the future.”