Effect of Sulfosulfuron or Byspyribac-sodium on Seedling Rough Bluegrass and Creeping Bentgrass.

Controlling mature rough bluegrass (Poa trivialis L.) using bispyribac-sodium (bispyribac) and sulfosulfuron often yields inconsistent results.  Attempting to control rough bluegrass shortly after emergence may eliminate it with fewer inputs and potentially greater safety to creeping bentgrass (Agrostis palustris L.).  The objective of these studies was to evaluate control of rough bluegrass and safety on creeping bentgrass of bispyribac and sulfosulfuron applied at various rates and dates shortly after emergence.  The studies were initiated in spring of 2007 and will be repeated in 2008.  Adjacent studies with creeping bentgrass or rough bluegrass were conducted, each a 2 x 4 x 4 factorial including two herbicides (bispyribac and sulfosulfuron), four herbicide rates (bispyribac: 18.5, 37, 55.5, and 74 g a.i. ha^-1) (sulfosulfuron: 6.5, 13, 19.5, and 26 g a.i. ha^-1), four application timings (1, 2, 3, and 4 weeks after emergence (WAE)) and an untreated control.  Plots were maintained at 1.3 cm and emergence was defined as >50% of the stand had germinated.  Four weeks after initial treatment, bispyribac applied at 37, 55.5, or 74 g a.i. ha^-1 resulted in <20% rough bluegrass cover while the same treatments had no effect on creeping bentgrass cover.  Although sulfosulfuron applied one to three WAE provided excellent rough bluegrass control, it also reduced creeping bentgrass cover.  Sulfosulfuron applied four WAE was safe on creeping bentgrass while reducing rough bluegrass cover.  Controlling rough bluegrass with bispyribac or sulfosulfuron shortly after emergence shows promise of providing excellent control while ultimately reducing herbicide inputs and minimizing creeping bentgrass injury.