A few years ago I visited Great Falls Park in Virginia, to look at a rocky, turbulent river to see what the shores of a river with little ice are like compared to our ice meadows. There are many rare plants in the rocky area that is scoured by flood waters every year, but above that level it should have been thick with native spring flowers. But guess what, almost all there was garlic mustard! Acres and acres of it, under the hardwoods.
This spring, the forest floor on the way to the tafoni was covered with acres of tiny yellow and fragrant white violets, trout lily, spring beauty, red and painted trillium, bell flower, even Dutchman's breeches. By now there will be foam flower, baneberry, Clintonia, miterwort, twisted stalk, jack-in-the-pulpit, and many ferns, and this in an area with no marble bedrock as we have around here. If garlic mustard, which besides crowding and shading out the natives gives off a toxin from the roots, gets loose in that woods, the beautiful flowers will mostly disappear.
I think the town of Johnsburg is fairly free of this noxious alien, but if you see it (Google it for excellent pictures, of course), please pull and bag it, then watch the area for a few years afterwards. Call or email me if you are not able to do it yourself, but it is thankfully quite easy to deal with if there is only a little.