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Weeds - let’s get ’em next year

published: October 29th 2010
by: Edder Funderburg
source: Noble Foundation

All sports fans know that when the team didn't do as well as expected this year, there's always next year. Weed control can work like that too. If you didn't get the sandburs this year, make plans now to get 'em next year.
    Noble Foundation conducted a study in 2010 on how well four products controlled sandbur in bermudagrass and how much the three post-emergent products injured the bermudagrass crop. Fol-lowing is a list of the different products we used, how well they controlled sandbur and how much crop injury they caused.
    Prowl H2O® (pendimethalin)-This is a pre-emergent product that must be applied before the sandbur emerge. This is usually in March or very early April. Rainfall must occur within two weeks of application or efficacy will be reduced dramatically. We used 2.1 and 3.2 quarts of product per acre in our study. Sandbur control was rated at 63 and 70 percent, respectively. This was statistically the same as that provided by the post-emergent products. Prowl H2O® was not evaluated for crop injury.
    Roundup Weather-Max® (glyphosate) -Roundup WeatherMax® is labeled for sandbur control only after the first cutting of hay on bermudagrass. Application must be made very soon after hay cutting or crop injury may occur. There is a 28-day grazing and haying restriction after the herbicide has been applied.
    We used two rates of Roundup Weathermax®, 6.5 and 11 ounces per acre. Sandbur control was rated at 100 percent for each rate. Crop injury in the form of discoloration and reduced plant height was observed 14 days after treatment, but the bermudagrass outgrew the injury within 30 days after treatment. We harvested the plots, and there was no yield difference between the Roundup WeatherMax® plots and the plots that did not receive herbicide.
    Pastora® (metsulfuron methyl and nicosulfuron)-Pastora® is a relatively new product that is a mixture of herbicides trade-named Cimarron® and Accent®. The label re-quires using the product when sandbur are less than 2 inches tall and bermudagrass is less than 4 inches tall. There are no grazing or haying restrictions with Pastora®.
    We applied Pastora® at rates of 1 and 1.5 ounces per acre. We achieved sandbur control ratings of 97 and 100 percent, respectively. We saw visual crop injury soon after treatment, but the bermudagrass largely outgrew the injury after 30 days. When we harvested the crop 35 days after application, there was no statistically significant yield difference between the Pastora® treatments and the plots that did not receive herbicide.
    Panoramic® (imazapic)-Panoramic® is a ge-neric version of a product that was previously sold as Plateau®. It has both pre-emergent and post-emergent activity, but is usually more effective when used post-emergent. The label states to not use Panoramic® on drought-stressed bermudagrass, when bermudagrass is in the transition stage between dormancy and full green-up, on newly aerated fields, in the establishment year for bermudagrass or on the variety World Feeder.
    We applied Panora-mic® at rates of 6 and 12 ounces per acre. Sandbur control was rated at 100 percent for each rate. However, crop injury was very severe. Panoramic® caused the worst visual injury symptoms of the herbicides tested, and the injury carried over into yield. The 6 and 12 ounce rates of Panoramic® caused yield reductions of 41 and 78 percent, respectively, when harvested 35 days after treatment.
    Summary-All the herbicides we tested controlled sandbur. Visual crop injury symptoms were noted in all the post-emergent treatments 14 days after treatment, but the visual crop injury symptoms decreased dramatically when ob-served 30 days after treatment. Neither Roundup WeatherMax® nor Pas-tora® decreased ber-mudagrass yield when harvested 35 days after treatment, but Panoramic® applications caused severe yield reductions. In general, we feel that Prowl H2O® is a good pre-emergent product if rainfall occurs in a timely fashion after application and that Pastora® and Roundup WeatherMax® are good post-emergent products if applied in a timely manner. Although it controls sandbur well, we have difficulties recommending Pano-ramic® due to crop injury concerns.
    If you have sandburs, now's your chance to plan to get' em next year.