Oriental Lady’s Thumb – a kind of Smartweed – is a fairly new invasive here at the farm.  We have several other species of Smartweed, and this one looks similar to Pennsylvania Smartweed (Persicaria pensylvanica), which is common, and not invasive.  So we didn’t really notice Oriental Lady’s Thumb until it began to spread prolifically on two of our trails in 2017.  Folks at the Wisconsin DNR were also worried about it, so we decided to try some different control methods to see if we could find one that worked.

One of our trails – before mowing

Oriental Lady’s Thumb is a sprawling annual that produces many seeds and seems to prefer damp, shady, disturbed places.

The easiest way to tell it apart from other similar Smartweeds is to look at the sheath at the base of the flower stalk (the ocreola).  Several long bristles stick out from the edge of the sheath.

We tried several schemes to get rid of it.  Mowing to keep the plants from going to seed.  Pulling and removing plants.  Spraying with Milestone.  All those methods worked for a while, but more plants always grew back.

We finally decided that we just didn’t have the hours it would take to eliminate all the plants and seeds, and we weren’t even sure it would be possible.   Since then we’ve been letting them grow, and trying to ignore them.  Now, 8 years later, we still have many plants but they’re less dominant, and they still mostly grow in paths and other disturbed areas.   They don’t seem to invade undisturbed areas of natives.