From Roch Gaussoin, Extension Turfgrass Specialist, for the University of Nebraska-Lincoln’s blog, TurfiNfo:
We are nearing the first “official” day of fall. While
daytime temperatures are currently in the 80’s, nighttime temperatures are
starting to decline and day length is decreasing. Summer annual grasses such as
crabgrass, foxtails, and goosegrass, are still quite visible, herbicide
application is not recommended in the fall – these grasses will die with the
Keep mowing sites with high annual grass populations to
limit seedhead maturation and increase turf density. Winter annual broadleaf
weeds such as common chickweed and henbit will be germinating soon and the
window for both annual and perennial broadleaf weed control with herbicides is
Fall-applied herbicides are preferred for broadleaf weed
control because 1) winter annual weeds are smaller and more easy to control
than when they mature in spring, 2) perennial broadleaf weeds are translocating
stored energy (and properly applied herbicide) below ground, and 3) cooler
temperatures reduce the likelihood of injuring turf or ornamental plants. For
best control that will be noticeable this fall, herbicide should be applied by
late September to mid-October. Three to 4 weeks post application a second
treatment can be applied if the targeted weeds have not been effectively
controlled by the initial application.
Single applications applied later in fall can still be
effective if soil moisture isn’t limited at the time of application, but
control may not be evident until the following spring. Herbicides are most
effective when applied to actively growing weeds not stressed by extreme
temperatures, drought, etc. It is also recommended that turf is not mowed
within 3 days before or after broadleaf herbicide treatments. Premixed
herbicides containing 2,4-D, dicamba, and/or MCPP, are effective on most winter
annual and perennial broadleaf weeds.
For difficult to control weeds such as wild violets or
ground ivy, herbicides containing triclopyr or fluroxypyr are most effective.
Quinclorac is effective on field bindweed. If you are doing any fall
renovation, including overseeding, check herbicide labels for recommended rates
and intervals for applications before or after germination and establishment.