Spraying glyphosate on dormant bermudagrass lawns 01-15-07

I get several calls each winter requesting information on applying Roundup, a nonselective herbicide, to dormant lawns. Glyphosate (Roundup) herbicide, applied at the labeled rate of up to 16 ounces per acre to dormant bermudagrass, can be an effective method of controlling many winter broadleaf and grassy weeds. The efficacy of the herbicide is much greater when temperatures rise above 60 degrees, so it becomes a challenge to the applicator to target the application when the turf is dormant, but yet have temperatures warm enough for the herbicide to be most effective.

The greatest fear of applying glyphosate to dormant turf here in Mississippi is determining if the turf is truly dormant or not. This winter has been a prime example of the fluctuating temperatures we experience and often times our turf never goes completely dormant. Research data indicates that common bermudagrass is slightly more tolerant to glyphosate than hybrid “Tifway” bermudagrass. At the labeled rates of 16 ounce per acre, or less, it will not kill semi-dormant bermudagrass, but may delay spring greenup.

Therefore, my suggestion to anyone planning to apply glyphosate to their lawn:

• Read the label completely to be certain it can be applied to the your turf species
• Carefully examine the turf for stage of dormancy
• Determine if you can accept the possibility of delay in spring greenup
• Assess other weed control options as well.

Published January 15, 2007

Dr. Wayne Wells is an Extension Professor and Turfgrass Specialist. His mailing address is Department of Plant and Soil Sciences, Mail Stop 9555, Mississippi State, MS 39762. wwells@ext.msstate.edu