Garlic mustard battle underway 2011.04.20

Written by David Green.

garlic.group_pickBy DAVID GREEN

Which came first to the woodlands of the Midwest, garlic mustard plants or European earthworms?

It’s a question that didn’t have much bearing on the task at hand—pulling up garlic mustard plants by the hundreds—but it is an interesting question, said Matt Schultz of the Michigan Nature Association.

At this time there’s not much that can be done about the invasion of the European earthworms to Michigan’s forests, but garlic mustard can be pulled—over and over and over again.

I’m a co-caretaker of the Robert Powell Nature Sanctuary located between Morenci and Hudson. I’ve been the caretaker since the 1980s, although I do little but let it take care of itself. That’s the way old Mrs. Jewell of Jackson once described her role as a sanctuary caretaker.

Matt says that isn’t enough anymore. A woods can’t take care of itself now as the invasive garlic mustard plant continues to spread.

And what is garlic mustard? I meant to check up on that before I left home Thursday morning, but I forgot. So when the six of us mustard pullers were in the sanctuary woods ready to look for the plant—and Matt asked if everyone was clear on what we were doing—I had to admit that I wasn’t. I was a rookie mustard puller and didn’t even know what it looked like.

It was a little embarrassing for the caretaker who had bypassed all the many previous pulling sessions.

Garlic mustard is a native of Europe that’s been on this continent since at least 1868. It’s now found in 30 states and is moving north through Michigan.

When it grows unchecked in the spring, it takes over the woods and crowds out other plants. Our common spring wildflowers—spring beauty, trillium, wild ginger, hepatica, bloodroot, Dutchman’s breeches, toothwort, trout lily, etc.—grow in the same habitat as the mustard and lose out in the competition for light, moisture, nutrients and space.

Matt gave us our orders: Look for garlic mustard on the higher ground along the edge of the sanctuary. Down below, seeds wash in when Bean Creeks floods its banks.

“This we have some control over,” he said. “The other we have no control over.”

garlic.heronA typical garlic mustard plant produces thousands of seeds annually. Certainly not all of those seeds germinate and among those that do, only a fraction survive. But that still leaves an enormous number of new plants coming up every spring.

We set out and I tried to adjust to the task. I’m not accustomed to entering the woods with a purpose. I go to the woods to look everywhere and at everything, not to focus on a small rosette of dull, heart-shaped leaves with serrated edges.

The five other pickers were putting a lot into their plastic bags. I must have been walking right past it. I still had only the plant Matt gave me for identification plus one that I found on my own.

Eventually we finished one area of the higher ground and drifted deeper into the woods near the Mound—a hilly feature of the sanctuary that always delights visitors in the spring due to the large number of wildflowers.

Apparently it’s delighting something else and the guess is that it’s turkeys. A large area of the Mound is thick with droppings. It looks like a livestock operation out in the middle of nowhere.

Matt saw some evidence that the turkeys are nibbling the mustard, so at least they’re helping out.

It’s such a good time to visit this woods. Cool, bug-less and a good variety of flowers starting to show. When I visit later in the season, I have to wear a net hat and rain gear to fight off the mosquitoes and the stinging nettles.

We had drifted away from the Mound when Matt threw the other element into the invasive picture. It’s what I mentioned at the start: the earthworm.

“Garlic mustard is what we see, but some scientists suspect the real damage might be done by earthworms,” he said. “Garlic mustard may be a sign of an earthworm invasion.”

That’s a relatively new theory, Matt said, and not at all mainstream science, at least not yet.

There are 16 species of earthworms in the Great Lakes area and none of them are native. The glaciers would have killed off any native species, if there ever was one. What we have now are European invaders.

Worms are great for the soil of gardens and farm fields, but the forest ecosystem developed without them. Earthworms quickly convert the leaf litter to nutrients, leaving the ground nearly bare. Many native plants need the leaf cover, while garlic mustard loves the bare soil.

Worms alter the soil chemistry. A slower, fungal-dominated system of decay is changing to a more rapid bacterial-dominated system. The vast majority of forest plants need the fungal relationship for the best nutrient uptake. Garlic mustard also interferes with this relationship. It paves the way for its own invasion.

By now I had developed the knack for the hunt, but it was easy to get distracted, especially the closer we got to the heron rookery. It’s so amazing to watch that many of my favorite bird taking off from their stick nests. The mustard hunters were out of sight by the time I finished taking photos.

garlic.bagsI caught up with the others and Matt pointed out a bleak sight: Dead garlic mustard stalks from the previous year. Beneath the stalks were dozens and dozens of mustard sprouts. There’s no reason to pull them now, Matt said, because most of them won’t survive anyway. But next year, volunteers will be at the site pulling up the second-year growth.

It all seemed a bit hopeless—especially with the sight of the countless mustard sprouts—but every effort reduces the population of the invader a little more. Control efforts are proving successful in areas of repeated picking.

We knew many developing plants were overlooked, but we had several bags of plucked mustard to show for our efforts.

“You can’t get them all,” Matt concluded as we left the woods, “but we’ll be back in May to look for plants we missed.”

Until a wide-scale eradication system is developed, there’s nothing to do but place attention on specific woods.

“We have to focus on the areas that are really nice and worth the time and effort,” Matt said.

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