January 30, 2012
University of Arkansas, Division of Agriculture
Turfgrass Science Program (http://turf.uark.edu) – Turf Tips
Warm winter weather – is it still safe to use Roundup?
Because it has been a warm winter so far, folks are going to be asking if it is all right to use Roundup in dormant bermudagrass for winter weed control. If there is any sign of green on the bermudagrass, don't do it. Do not just do a drive by - get down on your knees and look under the canopy for green stems or leaves. Be sure to check protected areas and south facing slopes first since they will green up first. The rate for dormant bermudagrass is 16 fl oz per acre of original Roundup and it is unwise to exceed this rate. Spot treatment with Roundup should be avoided (Photo 1) because the application volume (50 to 100 gpa) tends to be very high compared to broadcast spraying (20 to 30 gpa).
Photo 1. Injury caused by spot-spraying Roundup on a dormant zoysiagrass lawn
Winter use of Roundup should be confined to bermudagrass. Zoysiagrass, centipedegrass and St. Augustinegrass never go completely dormant during an Arkansas winter (Photo 2). Some zoysiagrass golf courses use Roundup safely but you have to really know what you are doing and have an accurately-calibrated boom-sprayer to pull it off. Dormant application of Roundup to zoysiagrass lawns is not recommended under any conditions.
Many people are using Roundup for annual bluegrass control. There are some non-Roundup options (Monument, Revolver, Katana and Certainty) that can be used safely on partially green bermudagrass or zoysiagrass. In centipedegrass and St. Augustinegrass, atrazine or simazine are decent for postemergence annual bluegrass control if the bluegrass is not well-tillered. If you want more options, contact me at 501-416-2480 or firstname.lastname@example.org.
Photo 2. Green tissue will almost always be present in dormant zoysiagrass, so injury from a dormant Roundup application is highly possible.
Dr. John Boyd