[MAIPC] Invasive Management as a Selection Pressure

[frazmo]

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)
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