Mesotrione as An Herbicide for Sping-Seeded, Cool-Season Turf.

This study was conducted in 2007 and 2008 at the Iowa State University Horticulture Research Station.  The objectives of this study were to determine if mesotrione was safe for use on perennial ryegrass (Lolium perenne L.) and Kentucky bluegrass (Poa pratensis L.) when applied at the time of spring seeding and if mesotrione was safe when applied following the first mowing of the seeded turf.  The secondary objective was to determine the efficacy of weed control.  Treatments included mesotrione at 175, 210, and 280 g ai/ha at the time of seeding, and 175 and 210 g ai/ha at the time of seeding and following the first mowing.  Also included was siduron at 6,700 g ai/h.  In 2007, perennial ryegrass and Kentucky bluegrass plots receiving herbicide treatments had an average of 18 and 24% higher cover, respectively, than the untreated control at the end of the season.  Plots treated with the highest rate (210 g ai/ha) of mesotrione, both as a single application and repeat application, exhibited the best weed control throughout the growing season for plots receiving mesotrione applications.  In 2008, perennial ryegrass and Kentucky bluegrass plots receiving herbicide treatments had an average of 25 and 65% higher cover, respectively, than the untreated control at the end of the season.  Following the second application of mesotrione, after the first mowing, there was some slight phytotoxicity to the perennial ryegrass.  All plots receiving herbicide treatments had an average of 58% less crabgrass cover than the untreated control.