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suppressing native grasses

     How many of us over the years in the midwest, at some point, have
planted native warm-season grasses (C4) too thick.  I for one certainly
have, especially in the beginning of my native grassland restoration
efforts in south-central Michigan.  After examining 100's of tallgrass
prairie restoration/reconstruction projects in the midwest, it is clear
that the answer to the above question is "many, if not most individuals
have."
    I am now spending time in developing strategies in which to "thin" such
stands of native grasses.  Some thoughts on this subject follows.
1.  The ability to appropriately "thin" such grasses is not as easy as it
might seem.  I have experimented with the glyphosate family of herbicides,
almost exclusively Roundup Ultra.  The ability of this herbicide to "thin"
these grasses is a function of herbicide dose, climatic conditions at time
of herbicide application, type of grass species (e.g. which species, which
cultivar, etc.), grass age (extent of the root system), etc.  Let me give
you a couple of examples from such activities of mine in Michigan.  I have
completely "wiped-out" Indian Grass in a one-acre plot of mixed C4 native
grasses (5 species), effectively "thining" 2 grass species (Big Bluestem,
Little Bluestem) in this plot, while not,in this plot, affecting 2 grass
species (Switchgrass and Side-oats Grama).  I used a relatively low dose of
the above herbicide (1 qt/acre), administered once in mid-June.  In another
one-acre plot of only Switchgrass, to effectively fully kill this grass, it
required 3 consecutive high doses of this herbicide (3
qts/acre)(administered once in June, July and August). [Parenthetically, I
have spent considerable time in killing very thick monocultures of
Switchgrass (usually Cave-in Rock cultivar) plots, a function of
mis-informed Pheasants Forever activities in our state.]  I should point
out that all of these grass "thining" projects involve plots with only
planted native grasses, no native forbs. So, be careful, start with a very
low dose of glyphosate (1% or less) and work your way up in concentration.
2. I am intrigued with James Trager's suggestion (Shaw Nature Preserve,
Missouri), i.e., late fall burning of native grass stands followed by hand
scattering of native forb seeds (then mowing the following 1 or 2 years).
Most native forb seeds germinate best when scattered in fall, especially
after a burn. I would like to know, in his studies, which native forbs can
best compete with the thick stands of native grasses.
3. Lightly disking or tilling soil prior to scattering of native forb seeds
in native grass stands can have a very substantial negative effect, so be
cautious!  I have disturbed the soil in this manner, the result was an
"explosion" of seedlings of un-wanted aggressive and persistent
non-natives, e.g., Yellow and White Sweet Clovers, Queen Ann's Lace, Bull
Thistle, etc.  I do not disturb the soil in any native grass plot if
historically that site has had a substantial amount of these non-native
plants.  Indeed, I will not plant native forbs in native grass sites until
I have eliminated, via broad-leaf herbicides, the presence of the above
named non-natives.
  Thick stands of native grasses can be a substantial problem when the
objective is (or at least should be) to have a native prairie with a
balance of grasses and forbs.   Especially, as in my state of Michigan,
where we are just now getting sufficient quantities of native grass seeds,
with Michigan genotype, for our restoration activities. Thus, in the past,
our only source of native grass seeds have been native grass cultivars.
These cultivars are often very aggressive and have varying sensitivities to
herbicides (often more resistant then native genotypes). So again, I view
our current problem of excessively thick native grasses a relevant problem,
one that needs to be addressed, a problem that one must approach, when
using herbicides, with substantial caution.
Cliff Welsch

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