I am not sure what “Normal Weather” is anymore.  This fall and winter have been so mild and wet that my lawn is turning green again.  However, this time it is less bermudagrass and more henbit.  These weather conditions have allowed a large number of winter annual broadleaf weeds to emerge in both cool and warm-season lawns around the county.  Weeds that I am seeing are the broadleaves: henbit, dandelion and common chickweed and the grasses: annual bluegrass, downy brome and cheat.

Home owners can achieve successful early post-emergent control of the broadleaf weeds in cool or warm-season turf in October through early December in “most years”.  The feature time periods that will still allow post-emergent broadleaf herbicides to be effective are spray applications made when daytime highs will be at least in the upper 50s or low 60s for a 4 to 5 hour consecutive period. Low temperatures reduce the effectiveness of broadleaf post-emergent herbicides. Appropriate broadleaf post-emergent herbicides for the home consumer include Weed-B-Gone or Trimec or generic products of the same formulation. These sprayable post-emergent herbicide products contain 2,4-D; MCPP and dicamba in an amine salt form. 

Use of broadleaf post-emergent herbicides in December over fall overseeded cool-season lawns like fescue and ryegrass can result in grass injury due the immature seedlings being less tolerant of herbicide. Therefore, a judgment call must be made as to the value of broadleaf weed control at this time versus the risk of injuring young fescue, bluegrass or ryegrass plants. Remember to read and follow all label directions when working with pesticides and be careful to use these products in a manner that keeps them off flower beds.

Neither of the two broadleaf post-emergent herbicides mentioned above control the winter

annual grasses. Winter annual grassy weeds can be controlled post-emergent in dormant

bermudagrass with a glyphosate product in late January through early March (depending upon

the environmental conditions in an individual year). Products containing glyphosate include

Kleen-up and Roundup products. Many different concentrations and formulations are available

and the consumer assumes responsibility for reading the product label to determine if the product

under consideration is appropriate for the job. Do not use glyphosate products for post-emergent

grassy weed control in any cool-season perennial grass or over centipedegrass, buffalograss,

St. Augustinegrass or zoysiagrass. Glyphosate applications for winter annual weedy grasses also

kill some winter annual broadleaves, but a more effective control program can be made by tank mixing glyphosate and a broadleaf weed killer. A word of caution here, as mild as it has recently been, there are still some areas in some lawns that still have green Bermuda grass crowns. Glyphosate only works on green plant material, so if your Bermuda is sprayed while it still has green growth on it, it can be damaged enough to slow next year’s growth so be sure that the entire lawn is dormant before making any glyphosate application to the lawn.

If you as a homeowner are uncomfortable with any aspect of the weed control program, they can be assured that Oklahoma has many capable commercial/professional lawn care applicators/operators ready to control weeds for a fair and competitive fee.

If you have any other questions about lawn spray programs please come by the OSU Extension Office 14001 Acme Rd Shawnee, call (405) 273-7683 or email kyle.robinson@okstate.edu

Have a wonderful New Year!