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1999, No. 4
Postemergence Control of Warm Season Annual Grassy Weeds
Some good things, like bacon and eggs or Lennon and McCartney,
just naturally go together. Some not-so-good things - high summer
temperatures and invasions of warm season annual grassy weeds
- also seem to be inseparable. Presently, hot weather has encouraged
the development of crabgrass, goosegrass, bamyardgrass, and foxtail
plants. Only postemergence herbicides will control these weeds
at this time.
In cool season turf, there are three mid-summer postemergence
chemical options for controlling these grassy weeds. Two of these
products, the organic arsenicals (DSMA and MSMA) and fenoxaprop,
have been used for many years to control annual grassy weeds following
emergence. The third (and most recently labeled) postemergence
control option is quinclorac. Registered in late 1998, quinclorac
offers a few features that can be useful to turfgrass managers.
Quinclorac can be applied as an early postemergence herbicide
to turfgrasses to control crabgrass; bamyardgrass; and giant,
green and yellow foxtails. Kentucky and annual bluegrasses, tall
fescue, and perennial ryegrass are all highly tolerant of quinclorac;
fairway height creeping bentgrass is moderately tolerant (do not
use Drive 75 DF on collar and putting green height creeping bentgrass).
In evaluations (1989 to 1992) conducted at the University of Illinois
Research Center, quinclorac-treated Kentucky bluegrass showed
no signs of reduction in turf quality. This experiment was repeated
in 1998, and postemergence control was quite successful, again
without turf injury.
Another attribute of this product is its ability to control
certain broadleaf weeds in turf. Weeds listed on the label include
field bindweed, black medic, red and white clover, common dandelion,
and speedwell. In 1998 trials at the U. of 1., quinclorac successfully
controlled dandelions and white clover in Kentucky bluegrass.
Creeping bentgrass, maintained at fairway heights, also showed
good tolerance for quinclorac applications.quinclorac, therefore,
might be an excellent material for white clover control in bentgrass
fairways.
Other recommendations include not mowing turf 2 days before or
after applying quinclorac to maximize weed control and minimize
potential turf injury. Clippings from the first three mowings
after application should be left on the treated area. If soil
moisture is insufficient prior to application of quinclorac, irrigation
may improve weed control. For best results, do not irrigate for
24 hours after application. Rainfall, watering or irrigation 2
to 7 days after application is recommended. Do not apply quinclorac
to fine fescue unless it is part of a seed blend, nor apply within
4 weeks after seedling emergence of Kentucky bluegrass and perennial
ryegrass.
Quinclorac provides the turfgrass manager with an option for
managing both annual grass and broadleaf weeds after they appear.
Since most cool season turfgrass species have excellent tolerance
of this herbicide, it can be used later in the season than many
other existing herbicides. (Remember, be sure to read, understand,
and follow the label directions for the safest, most effective
control when using any chemical pest control. Also, always check
the pesticide label to make sure an application of a product will
not interfere with turf management activities such as overseeding.)
(Luke Cella, Tom Voigt, Tom Fermanian, and Bruce
Branham)
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