Methiozolin (MRC-01) is a new herbicide under development by Moghu Research Center of South Korea for use on golf putting greens in the US and other countries.  Previous research has shown that annual bluegrass control increased when methiozolin was applied in fall compared to spring or early summer treatments.  Fall treatments work well in southern climates where annual bluegrass populations are typically less than 15% coverage and perennial biotypes are most commonly encountered.  In the north, annual bluegrass populations on putting greens can exceed 70% and have a higher proportion of annual biotypes.  Annual biotypes are easier to kill and fall treatments in the north may result in rapid control of large annual bluegrass populations, resulting in thin turf or bare areas on the putting green the following spring.  In addition, creeping bentgrass does not have opportunity to fill voided areas of turf during the winter.  Since spring and early summer is the time when most golf revenue is generated in the Northeast, loss of putting green canopy is unacceptable during this time.  Since spring treatments are known to be less effective at controlling annual bluegrass, we hypothesized that repeated treatments in spring will result in a slower, smoother transition from annual bluegrass to creeping bentgrass.  Our objective was to evaluate several treatment programs that included 4 kg ai/ha methiozolin split into 4, 6, or 8 treatments during spring and early summer compared to a program that included two high-rate spring applications followed by an additional application in fall.

Two studies were conducted on golf courses in Blacksburg and Harrisonburg, VA.  Studies were arranged in randomized complete block designs with 3 replications.  Plots were 2 m by 2 m in Blacksburg and 2 m by 5 m in Harrisonburg.  The larger plots in Harrisonburg allowed for measurement of ball speed (stimp).  Treatments were initiated on March 4, 2011 at Harrisonburg and March 20, 2011 at Blacksburg.  Methiozolin was applied in 280 L/ha water using TeeJet 11004 TTI nozzles.  Treatments included 8 applications of 500 g/ha at 2 wk intervals, 6 applications of 667 g/ha at 2 wk intervals, 4 applications of 1000 g/ha at 4 wk intervals, and 3 applications of 1120 g/ha in March, April, and October.  On June 15, 2011, Methiozolin applied 8, 6, or 4 times in spring reduced annual bluegrass cover from 58% in nontreated plots to 2, 1, and 5%, respectively.  The spring + fall program had received two of three treatments at this time and reduced annual bluegrass cover to 15%.  Similar reduction in annual bluegrass cover was noted in Blacksburg.  On June 3, 2011 in Harrisonburg, stimp on nontreated plots was 8.4 feet and significantly higher (9.5 to 10.0 feet) in methiozolin treated plots.  Methiozolin did not injure creeping bentgrass at any assessment date.  Putting green turf quality and NDVI was significantly lower than nontreated turf in April but equivalent in March, May, June, July, and October.  The loss of NDVI and quality in April was attributed to loss of annual bluegrass vigor.  The greatest loss of turf quality from methiozolin treatment was on April 28 when nontreated plots had quality of 6.5 and the worst methiozolin treatment had quality of 5.83, where 6.0 is minimally acceptable.  Such transient loss of quality was actually deemed acceptable by golf course personnel due to the reduction in annual bluegrass.  Turf quality was significantly higher in methiozolin-treated plots from May through October.  NDVI was equivalent in all plots from June through October.  These data suggest spring programs can successfully control annual bluegrass while having minimal impact on putting green quality on golf putting greens having greater than 50% annual bluegrass infestation.