It’s well known that pesticide use can cause the development
of chemical resistance in target insects and plants. Based on anecdotal
information and personal observations, non-chemical invasive plant control
efforts appear to be able to cause the development of “resistance-like”
adaptations in plants. When we engage in sustained management activity on an
invasive plant at a site, we can create selection pressure on the plant.
Unwittingly we may serve like plant breeders trying to create desirable new
varieties, but creating undesirable new varieties that could become more
challenging to manage.
Several examples. These are based on anecdotes and personal
observations, and I am hoping that perhaps some folks will be inspired to
gather data and study this more closely. When Japanese Stiltgrass invades a
frequently mowed area like a managed lawn, I have seen reports that it adapts
to flower and set seed even in the face of the mowing. I have noted that as we
have intensified efforts to control Garlic Mustard by hand pulling, it may be
adapting by flowering and developing viable seed earlier, in advance of when we
have tended to focus our pulling efforts. (I realize that a confounding factor
here is our increasing warming trend.) Also, I think I’m seeing signs that we
are selecting out the tallest, most robust plants, and seeing more “stunted”
plants that may be harder to spot, yet still produce seeds. Upper parts of
plants may detach more readily leaving viable roots behind, and un-pulled
plants may have a second bloom later in the season.
Finally, over twenty-plus years of pulling English
Ivy at Long Branch Nature Center in Arlington, Virginia, I have noticed
recently that more of the remaining ivy seems to have a new characteristic. The
vines seem to be more fragile. Before, most vines pulled up very cooperatively,
leaving few rooted stem fragments. Now I find more uncooperative vines that go
to pieces on me, creating more work to find and pull all the viable remnants. I
believe that we’ve inadvertently selected for this trait.
In closing, my key point is that we in the invasive
plants community should be conscious of the possibility that we are selecting
for resistant traits. We should monitor for signs and consider changing up our
practices occasionally to reduce the risk of developing non-chemical
resistance.
Cheers,
Steve Young, Volunteer, Arlington VA (past MAIPC
Treasurer)
