Saturday, June 7, 2008

Turf - Controlling Crabgrass Escapes

Now is the time of year that crabgrass (and goosegrass) escapes from preemergence program breakdown will be showing up. Fortunately, there are a number of good post-emergence product for crabgrass control. The following is some information.

Postemergence herbicides are used to kill weeds after they germinate and emerge from the soil. Crabgrass and goosegrass are easiest to control with postemergence herbicides when they are small, and in the 2- to 4-leaf stage of growth. This normally occurs in mid-late June in most areas of Delaware.

The most common postemergence herbicides used for annual grass control in turf are organic arsenicals, dithiopyr (early postemergence only), fenoxaprop, and quinclorac. Only fenoxaprop is effective for control of goosegrass.

Organic arsenicals are most effective on seedlings. Two or more treatments 7- to 10-days apart may be needed. Dithiopyr (Dimension) can be used on 1- to 4- leaf crabgrass. Dithiopyr will also provide pre-emergence activity, which can be good or bad depending on the potential need to re-seed or overseed. Fenoxaprop (Acclaim Extra) can be used up to the 4 tiller stage crabgrass. Fenoxaprop can discolor Kentucky bluegrass. Quinclorac (Drive) is best on untillered crabgrass.
Inconsistent control on 1- to 5-tillered plants should be expected. There is 20 to 30 days of soil activity, which could be helpful for some pre-emergence control. Later in the summer quinclorac can be used to treat (control) mature multi-tiller plants as a “rescue” strategy; if applied before seed set this can be helpful in reducing future weed pressure (reduced seed dispersal).

From "Clover and Crabgrass Management in Turf" by James Murphy, Ph.D., Specialist in Turf Management in the June 14, 2007 edition of the Plant and Pest Advisory, Lanscape, Nursery, and Turf Edition, Rutgers Cooperative Extension.

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