Preemergence Control of Crabgrass (Digitaria spp.) On Creeping Bentgrass (Agrostis stolonifera L.) Putting Greens With Methiozolin.

Crabgrass species (Digitaria spp.) are problematic summer annuals, and found widespread on creeping bentgrass (Agrostis stolonifera L.) golf course putting greens.  Pre-emergence herbicides are an effective technique for control of crabgrass, but tolerance of creeping bentgrass is a concern at putting green mowing heights.  Methiozolin is a newly developed herbicide that exhibits both post- and pre-emergence activities.  The objective of this study was to evaluate the efficacy and safety of methiozolin for control of crabgrass as a pre-emergence herbicide on creeping bentgrass maintained as a putting green.  Field plots were established on a creeping bentgrass putting green in Columbia, Missouri in 2012 and 2013.  Treatments included methiozolin at 0.5, 0.75 or 1.0 kg ai ha^-1 as a single application or sequential applications at 14 or 28 d intervals, where the initial applications were applied prior to the germination of crabgrass.  In addition, the pre-emergence herbicides bensulide at 14 kg ai ha^-1, dithiopyr at 0.56 kg ai ha^-1, indaziflam at 5 g ai ha^-1, pre-packaged bensulide + oxadiazon at 13.5 and 3.4 kg ai ha^-1, and siduron at 3.4 kg ai ha^-1 were included as single or sequential applications at 28 d intervals, in addition to an untreated control.  Experimental design was a randomized complete block with four replications with each plot measuring 1.5 by 3.0 m.  Data collected included turfgrass quality, normalized difference vegetation index (NDVI), phytotoxicity and percent crabgrass cover.  All treatments, with the exception of siduron, reduced crabgrass cover by 60% or greater at 8 weeks after initial treatment (WAIT) in 2012, compared to the untreated control.  At 21 WAIT, plots treated with bensulide, dithiopyr and two applications of methiozolin at 1.0 kg ai ha^-1 at 28 d intervals resulted in 93, 94, and 90% crabgrass control, respectively.  In 2013, a similar trend was observed, where 76% or greater crabgrass control resulted for all treatments at 8 WAIT except siduron.  During this experiment, the only treatment that caused significant phytotoxicity was the pre-packaged bensulide + oxadiazon, which caused yellowing and turf thinning on creeping bentgrass in both 2012 and 2013.  However, the phytotoxicity was at or above the tolerable level of 6 for the 1-9 scale.  Results from root biomass are currently being analyzed and will be presented.