Influence of Application Volume and Post Application Irrigation on Annual Bluegrass Control By Methiozolin.

Methiozolin is an experimental post-emergent herbicide designed to selectively control annual bluegrass (Poa annua L.; ABG).  The objective of this study was to evaluate the herbicide’s efficacy to control ABG when applied at two rates and in four different water volumes. Additionally, the impact of post application irrigation was evaluated.  A field study was initiated on research putting green at the Valentine Turfgrass Research Facility in 2011 and repeated in 2012. Each site consisted of a mixed stand of creeping bentgrass (Agrostis stolonifera L.; CBG) and ABG at a ratio of approximately 55%/45% or 10%/90%.  Plots measured 0.9 x 1.8 m and were arranged as a randomized complete block design with four replications.  Treatments included methiozolin applied at two rates (1.0 kg a.i. ha^-1 and 2.0 kg a.i. ha^-1) in 407, 815, 1222, or 1630 L H₂O ha^-1.  Additionally, treatments applied in 407 or 815 L H₂O ha^-1 were foliar applied and left to dry on the surface or watered-in with 25,000 L H₂O ha^-1. Treatments were initiated on 2 Sept 2011 or 10 May 2012.  For the study initiated in 2011, plots treated with 2.0 kg a.i. ha^-1 generally had the lowest percent ABG (2% to 8%) when plots were rated in the spring of 2012. Methiozolin applied at 1.0 kg a.i. ha^-1 in 1222 L H₂O ha^-1 resulted in the lowest percent ABG. In the 2012 study, all treatments resulted in moderately lower ABG percentages (36% to 49%) when compared to the untreated control (61%), but few differences in percent ABG existed among methiozolin rates or application volumes. In both years, post application irrigation did not influence the efficacy of methiozolin. Based on the results of this study, application timing, herbicide rate and initial ABG populations likely all play an important role in herbicide efficacy. While post application irrigation did not affect ABG control, application volume appears to be an important factor especially when methiozolin is applied at lower rates.