Research Report
PoaCure (Methiozolin) for Kentucky Bluegrass Fairways By Sandeep S. Rana, Doctorate Student, and Shawn D. Askew, Ph.D., Associate Professor and Extension Turfgrass Weed Specialist, Virginia Tech
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ethiozolin (PoaCure) is a new isoxazoline herbicide under development by Moghu Research Center (in Daejeon, South Korea) for use in turfgrass in the U.S. and other countries. Methiozolin is typically used at 26 fl. oz./A for selective postemergence control of annual bluegrass (Poa annua) on creeping bentgrass putting greens. Previous research at Virginia Tech and Moghu Research Center, however, suggests that methiozolin at higher rates (52 fl. oz./A applied twice at monthly intervals) can also be used for annual bluegrass control on fairways. Controlling annual bluegrass on Kentucky bluegrass fairways has always been challenging due to the physiological similarities in the genus Poa. Moreover, genetic diversity between Kentucky bluegrass cultivars can vary a great deal in response to the same herbicide, making selective annual bluegrass control with safety to Kentucky bluegrass challenging. This variability in response of different Kentucky bluegrass varieties to the same herbicide is attributed in part to variable ploidy levels and the unique apomictic breeding behavior of Kentucky bluegrass species. Since most previous work with methiozolin has been focused around the use on putting greens or green surrounds, more research is needed to elucidate methiozolin use on fairways.
Our research
Field trials were conducted from fall 2011 through spring 2012 and from fall 2013 through spring 2014 at the Virginia Tech Turfgrass Research Center (TRC) in Blacksburg. Permission was granted to use a five-year-old Kentucky bluegrass National Turfgrass Evaluation Program (NTEP) trial site for this study. The NTEP site had a total of 110 Kentucky bluegrass varieties belonging to different genetic groupings. These varieties reflect a broad range of diversity within Kentucky bluegrass varieties and within the major Kentucky bluegrass varietal classification types. Each of the 110 Kentucky bluegrass cultivar plots was subdivided into 4 subplots, which were treated twice at a 6-week interval with methiozolin at 0 (NTC), 104 (2X), 208 (4X) and 312 (6X) fl. oz./A, respectively. Methiozolin rates used in the study are two-, fourand six-times higher than needed to control annual bluegrass in Kentucky bluegrass fairways. The higher methiozolin rates were used to mimic accidental overspray in the field and to achieve maximum varietal differences, which may not be apparent at the recommended 1X rate. The applications for first-year treatments were applied on October 14, 2011, with sequential applications at 6 weeks after initial treatment (WAIT).
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The second-year applications were made on November 17, 2013, with sequential treatments applied at the same intervals mentioned above. Data were collected three times each in fall and spring following methiozolin applications. Data assessed included Kentucky bluegrass, annual bluegrass and broadleaf weed cover, as well as Kentucky bluegrass injury and quality.
Research results
When averaged over cultivars, methiozolin rates less than 6X did not injure Kentucky bluegrass more than commercially unacceptable levels (>30%) at 26 WAIT (Figure 1). At 6 WAIT, injury to Kentucky bluegrass from methiozolin was mainly in the form of stunting. However, at 26 WAIT, injury to Kentucky bluegrass was manifested as inability to grow into the voids created by dead annual bluegrass following methiozolin applications (Photo 1). At 6 WAIT, methiozolin reduced turf quality at all rates (Figure 1). Reduction in turf quality was primarily due to annual bluegrass control, as annual bluegrass comprised approximately 40% of the turf area (Figure 2). At 26 WAIT, methiozolin at 2X increased Kentucky bluegrass quality higher than methiozolin at 4X, 6X and the untreated check (Figure 1). The lower Kentucky