There have been several questions about the possibility of failed preemergence herbicide applications and the likelihood of annual grass weed escapes, particularly more difficult to control weeds such as large crabgrass. Emerged large crabgrass is difficult to control in conventional systems with smooth crabgrass being even harder to control. An article in last year’s Field Crop CAT Alert noted the difference between the two crabgrass species (vol. 20. No. 8 – June 2, 2005).
Postemergence herbicides that suppress large crabgrass include: Accent Gold, Accent Gold WDG, Basis, Callisto and Steadfast. These herbicides give only fair control of this weed. Additionally, weeds must be very small to provide even fair control of this weed.
Fair control of large crabgrass and smooth crabgrass is also possible with Liberty (Liberty Resistant Corn only) or Lightning (Clearfield Corn only). The weeds should be no more than two inches tall. Glyphosate is the only postemergence herbicide that provides excellent control of large crabgrass and smooth crabgrass (Roundup Ready corn only).
Source : msu.edu