Garlic mustard, an invasive weed spreading into Iowa

Garlic mustard, an invasive weed spreading into Iowa

May 27, 2015

Spring morel hunters would be doing their favorite woodland a favor by packing along a big garbage bag, too…to load up with garlic mustard plants before they set their seeds. Morels are being found now; and should really be popping with the string of 60+ degree days ahead. In an ideal spring—and who has those anymore—a string of days in the 70s is sufficient to warm soil temperatures, to spur morel development. Last week’s cool down probably slowed things a little; but warm air hitting afternoon sun-facing slopes—especially near dead elms and other trees– should prod the fabulous fungi to pop from the soil.

It’s also good for garlic mustard. Which isn’t good for Iowa’s woods and the critters that live there. “It is a really noxious, invasive species. It overtakes the native flora; so it really outcompetes everything else on the forest floor, for sunlight”, explains Lake Macbride State Park manger Ron Puettmann. “We’ve been battling garlic mustard here for the better part of 15 years.”

Puettmann went through a short introduction to garlic mustard with a group of Solon ninth graders a few days ago. The primary lesson, though; how to remove it. “Wiggle it a little. A lot of times the root will go off at an angle. If you just pull it off, it will break off. Kind of wiggle them out of the ground.”

Rain over the past couple weeks had loosened the soil in the park, so that the dark green plants came out rather easily, as the students slowly moved along the wooded slope. And the seeds had not developed yet. The window of time to ‘de-mustard’ an area is narrow. Once the seeds are set—thousands per plant—you would just be planting the next generation, as you pulled the parent stem out of the ground.

“It’s an invasive species. None of the wildlife wants to eat it, so it just spreads through the park and then nothing else can grow”, observed freshman Brianna Smith, as she shoved some more mustard into the big garbage bag. This group and several others, picking up litter, were in the park as a community service. Classmates had spread throughout the community, getting yard work and other services done for neighbors.

It is important get to the plants before those seeds are mature. An animal walking through a patch, a bird flitting through, will knock seeds to the ground…or carry a few along on its fur or feathers. As it eventually falls out—a few feet or a couple hundred yards away—it has just planted another patch. “You want to avoid the plant, once the plant goes to seed; which is usually in June”, cautions Puettmann.

We are still trying to sort out its impact. Some entomologists worry that it is displacing toothworts’, a native woodland flower. That could affect, for instance, the West Virginia white butterfly. It deposits eggs on the plant, but they do not hatch, even though garlic mustard is in the same family as toothwort. The impact on other species is up in the air, too.