Oklahoma State University Turfgrass Science

Is it too late to apply glyphosate herbicide for winter annual weed control in bermudagrass?

Is it too late to apply glyphosate herbicide for winter annual weed control in bermudagrass? Dennis Martin


Is it too late to apply glyphosate herbicide for winter annual weed control in bermudagrass?

Dennis Martin


Glyphosate, the active ingredient in the popular herbicide product Roundup Pro and certain similar product, can sometimes be used over completely dormant bermudagrass for winter-annual weedy grass control.  With a broadleaf post-emergent tank-mix partner, the tank-mix can often be used for both winter annual grassy and broadleaf weed control in dormant bermudagrass.  But, how do you know if it is too late in winter to effectively use a glyphosate containing herbicide for weed control without damaging your bermudagrass?  You have to scout the area to make sure conditions are still suitable for this application!!!  That’s the only sure way to know!


Excerpt from the Roundup Pro label – “Dormant Turfgrass – This product may be used to control or suppress many winter annual weeds and tall fescue for effective release of dormant bermudagrass turf.  Treat only when turf is dormant and prior to spring greenup.”


Here are some tips for successfully using the glyphosate application over dormant bermudagrass while minimizing risk of bermudagrass injury:


1)    First, walk over the bermudagrass stand and closely observe from just above the bermudagrass leaf canopy just minutes before you make the herbicide application to ensure the stand is totally dormant and that no live bermudagrass shoots are popping through the canopy!  Do you see any live green, red or purple bermudagrass leaves or shoots?  While you might part the tan canopy with your hands just to see if the bermudagrass is alive below, it is the solid tan canopy viewed from above that shields the live material below from intercepting spray droplets.  Hopefully you will always be able to see live bermudagrass tissue in the lower canopy (if you part the canopy) that is being shielded by the dead, tan leaf canopy.  Without live tissue being contacted by the spray solution, the plant will not take up and will not be injured by the application.  If you see openings in the canopy from above where the bermudagrass leaf canopy is not thick, dense and tan, and if it’s not providing 100% shielding, then there is risk of injury from the glyphosate spray solution.  BE THE SPRAY DROPLET!  When scouting is done properly, you are essentially pretending you are the spray droplet.  Are you contacting any bermudagrass tissue?  Yes or No?  If yes, then don’t spray that area with glyphosate!


2)    Remember, the application is really not labeled for high quality turfgrasses other than bermudagrass.  While some people may use this application over dormant zoysiagrass, it’s not labeled for that use, so don’t apply glyphosate over zoysiagrass.  Also, never use this application over any desirable cool-season turfgrasses!


3)    Not all glyphosate herbicide products are labeled for use in this application even though they might contain the same active ingredient.  This is called “product label use-site specificity.”  It is the applicators’ responsibility to read the label and ensure that the product is labeled for this specific use and that the label is followed to the letter and thereby following the letter of the law!


4)    Use only the correct product labeled for this application and use the correct use rate and the correct carrier rate!  I mentioned this in point number 3 above but it is worth mentioning again!


5)    Don’t over use either the use rate or the carrier rate.  Remember, if you over apply the spray volume and exceed the 10 to 40 gallon per acre carrier rate, the spray droplets may roll down the stem by gravity and contact the live green, red or purple stems below.


6)    The application is best made when temperatures are in the 60s but definitely prior to bermudagrass green-up.  By the time air temperatures are in the 60s, winter annual weeds are generally metabolically active and are more effectively controlled by this application.


Winter annual weeds, left untreated, are often responsible for up to five early-season lawn mowings that occur before the bermudagrass actually needs mowing.  The use of glyphosate for winter annual weed control in dormant bermudagrass is a very useful and reliable tool with manageable risk when the practice is executed responsibly.  Remember to read and observe all pesticide label directions.
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