Methiozolin has potential for selective annual bluegrass control in cool-season grasses and practitioners may wish to reseed in treated areas after applications.  The objective of this field experiment was to evaluate reseeding intervals of three cool-season turfgrasses following methiozolin applications at four application timings before seeding.  Methiozolin (2.1 EC) was applied at 0, 0.56, 1.1, or 2.2 kg a.i./ha and compared to bispyribac-sodium (Velocity 17.6WG) at 45 g ai/acre.  Herbicide treatments were applied 0, 2, 4, or 6 weeks before seeding on April 13, 2011.  A broadcast glyphosate application was made 7 days before seeding to kill existing vegetation and facilitate visual assessment of creeping bentgrass, perennial ryegrass, and tall fescue seeded perpendicular to herbicide treatments.

All methiozolin applications on the day of seeding reduced turf cover by approximately 75 to 90% from the untreated for all grasses at 14 days after seeding and were more injurious than bispyribac-sodium by eight weeks after treatments.  Methiozolin at 1.1 and 2.2 kg/ha applied two weeks before seeding reduced cover of all three grasses by approximately 35 to 50% from the untreated after 14 days but 0.56 kg/ha at this timing did not reduce final ground cover. Grasses established in plots treated with 0.56 and 1.1 kg/ha two weeks before seeding had similar cover to the untreated after six weeks.  However, 2.2 kg/ha of methiozolin reduced establishment of all three grasses after eight weeks. Methiozolin at 2.2 kg/ha was the only rate that reduced creeping bentgrass and perennial ryegrass cover from the untreated when applied four weeks before seeding, but did not inhibit tall fescue establishment.  All herbicides applied six weeks before seeding did not reduce establishment of the three grasses on any other evaluation date.  Results suggest reseeding intervals after methiozolin applications vary depending on turf species and application rate.  Due to temporary stunting and potential turf cover reductions, it appears practitioners should wait two, four, and six weeks before seeding in areas treated with methiozolin at 0.56, 1.1, and 2.2 kg/ha, respectively.