and deposition into the soil profile ensures that annual bluegrass will
be a perennial problem on these fields. For example, researchers have
reported that annual bluegrass deposits nearly 2 million seeds per ft2
(185,000 seeds per m2) in the top inch of soil. In these instances,
climatic conditions usually favor annual bluegrass seed germination
and growth for large portions of a calendar year making permanent
control with herbicides difficult.
Many field managers have had success managing annual blue-
grass with applications of Tenacity (active ingredient is mesotrione).
Tenacity is a carotenoid inhibiting herbicide that turns susceptible
weeds white after application (Figure 3). Researchers have observed
that sequential applications of Tenacity in the fall can remove
annual bluegrass from Kentucky bluegrass (Poa pratensis); how-
ever, responses may vary with location, year, or annual bluegrass
biotype. Individuals managing fields with high percentages of
perennial ryegrass Lolium perenne) will need to reduce application
rates because this species is less tolerant of Tenacity than Kentucky
bluegrass.
In addition to having activity on annual bluegrass, Tenacity can
be used to control several winter annual broadleaf weeds, includ-
ing common chickweed, henbit, and lawn burweed (Soliva sessilis)
either pre- or postemergence. Label directions allow for Tenacity
to be applied for weed control on fields before being re-seeded
or sodded as well. However, applications after seeding should be
delayed a minimum of 4 weeks or until newly germinated turf has
been mowed twice.
Xonerate (active ingredient is amicarbazone) is a new herbicide
labeled for use on many mature warm- and cool-season turfgrasses
that has efficacy for annual bluegrass control on golf course turf
with sequential applications. Despite significant interest among
athletic field managers, Xonerate use on cool-season fields is lim-
ited because current labeling does not allow fall applications due
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Figure 3. Annual bluegrass bleaching after treatment with Tenacity
