Garlic Mustard (Alliaria petiolata) is a plant in the mustard family which has a strong smell of garlic when the leaves are bruised. It’s native to Europe, Asia and northern Africa, and was brought to North America as an herb to be used in cooking, probably in the late 1800s. It’s now considered an invasive species and a noxious weed in the eastern U.S. and Canada.
Flowering Garlic Mustard
It’s a biennial, so it grows only leaves the first year. The second year it blooms, makes seeds, and dies. My goal is to keep those second year plants from going to seed.
First year seedlings, just coming up
Second year plants showing above dead leaves in the spring. The leaves are evergreen, so they can be found all winter.
Second year plants starting to send up their flowering stalks – around here that happens in early-mid April.
Each plant can produce hundreds of seeds. The plants also produce chemicals that discourage other plants from growing, so the garlic mustard plants rapidly take over the forest floor and turn it into a monoculture.
A large patch of Garlic Mustard had taken over this part of our woods.
I found the first Garlic Mustard plants on our land in 2007, and now every year I find new patches.
At first I pulled all the plants I found, and removed them from the site so they wouldn’t spread seeds or propagate by their roots. When I pull the plants, I try to pull the whole plant. Some references say that if you leave pieces of roots they’ll resprout; some say that’s not a problem – so to be safe, I try to get as much out of the ground as I can. Unless the plants have ripening seeds, I don’t think there’s a problem leaving piles of pulled plants on the ground to dry out – I’ve never found those piles resprouting. Pulling works, but it’s very slow, and as I find plants in new places every year, and I still have to check all the old places, it just takes too much time.
I’ve discovered that spaying with herbicide in the spring – or fall – is much faster than pulling, so that’s what I do now. I still spend weeks every April and May on control. I walk as much of the woods as I can and spray all the plants I find. I prefer spraying early in the spring so there are fewer ‘good plants’ coming up, but now there’s so much GM that the spraying project lasts much longer than I’d like – until seeds start forming on the GM plants. I still think it’s helpful – even parts of the woods that I’ve sprayed multiple times have recovered well with fewer GM plants and lots of natives in the ground layer.
I use Garlon 4 because the sprayed plants start drooping within a day or two – it makes it much easier to see where I’ve been. (Roundup takes at least a week and sometimes longer to show its effects.) I use 4 Tbsp Garlon 4 + 1 tsp MSO in 1 gallon of water.
I try to go back to each place a second time to be sure I haven’t missed any plants. I concentrate on spraying second year plants, since they’re larger, and they produce the seeds. But if there are big patches of seedlings, with no ‘good’ plants in the way, I spray those too.
I mark big areas of GM with pink plastic tape so I can check that spot again the next year. Most of the places I’ve been treating for several years are getting better.
Many of the patches we have seem to start in the brushy edges of our prairie fields. The plants then follow deer paths and gullys where animals or water carry the seeds downhill.
I’m looking forward to having a biological control available – I think that’s the only way our native woodland species will survive. Work on a biological control was begun in 1998, and experimental releases of the potential insect controls are being tried. I can’t find any definite news of the current state of this project, but I have great hopes for it.
My latest find is several plants with Garlic Mustard Aphids – a European aphid that feeds exclusively on Garlic Mustard.
Garlic Mustard plant with aphids
Garlic Mustard aphids
This aphid species was first spotted in North America in Ohio in 2021, and has since been found in several other states including Wisconsin. It eats the leaves and developing flower stalks. The plants I’ve seen with aphids on them didn’t flower – so I’m very hopeful that they’ll help control GM.
More information about Garlic Mustard Aphids:
Prairie Haven
Bugguide
How to report aphid sightings
More information on Garlic Mustard:
Garlic Mustard – Wisconsin DNR
Garlic Mustard – Invasive Plants of the Eastern U.S.
Garlic Mustard – Wikipedia
PCA Alien Plant Working Group