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Sweet Clover/biennial aliens

     Just a short note to share with you a small experiment that I
conducted on my 20 acre prairie reconstruction/restoration site in
south-central Michigan.
A number of by botanical colleagues indicated that certain biennials would
live and flower the 3rd year if, in the 2nd year, they were not allowed to
complete the flowering process.  I am particularily interested in certain
very troublesome biennial non-native species in my 20 acre site, i.e.,
Yellow/White Sweet clovers (Melilotus officinalis/alba), Queen Anne's Lace
(Daucus carota) and Bull Thistle (Cirsium vulgaris); whether or not these
species would flower in the 3rd year, if the flowering components were
continuously removed in the 2nd year, was unknown to me and my colleagues.
Thus, during summer of 2000, I continuously removed the flowering
components (immediately after the onset of flowering and right below the
inflorescence) of 20 plants of each of the above species throughout the
growing season and carefully marked each plant so that I would be able to
identify such the following year (this year, 2001). Results: not one plant,
a total of 80 plants, grew back in the 3rd year!!!  Thus, the prevention of
energy expenditure for flower and seed production in the above biennials
did not stimulate regrowth of these species in year # 3!
Interestingly, of the above species, it was only necessary to remove the
flowering components once in the genus Melilotus; these species did not
develop any new flowers when the flowers were excised immediately below the
inflorescence.  However, if one cuts this plant during flowering well below
the inflorescence (much further down the stem, such as in mowing), this
species will develop new stems and these new stems will form flowering
components, albeit quantitatively greatly reduced.  For the other 2 genera,
flowers had to be continuously removed throughout the entire growing
season.
    Thus, in the control of these noxious biennials, I will continue to
carefully, but aggressively, spot spray (with a 2,4-D type of herbicide) or
hand dig, when native forbs are present, or field spray (with a 2,4-D type
of herbicide) when only native grasses are present.  The Melilotus species
(officinalis or alba), under most conditions, and in my opinion, are the
most tenacious of our problamatic non-natives in my area; these species
must be vigorously controlled.
Cliff
(Clifford W. Welsch)


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