Efficacy of Flazasulfuron for Control of Annual Bluegrass (Poa annua) and Perennial Ryegrass (Lolium perenne) as Influenced by Nitrogen

Abstract

Certain sulfonylurea (SU) herbicides are used to remove overseeded cool-season species from bermudagrass. The effects of nitrogen (N) on the efficacy of a new SU herbicide, flazasulfuron, have not been determined. Field and laboratory studies were conducted in 2008 and 2009 evaluating the efficacy of flazasulfuron for control of overseeded perennial ryegrass contaminated with annual bluegrass. Flazasulfuron was applied at rates of 4.4, 8.8, and 17.5 g ha−1alone, and in between sequential applications of N fertilizer at 73 kg N ha−1. N was granularly applied immediately prior to herbicide treatment and 4 wk later. In both years, the level of annual bluegrass control with flazasulfuron and two applications of N at 73 kg N ha−1was significantly greater than following treatment with flazasulfuron alone. This response was observed for all application rates of flazasulfuron on every rating date. The level of annual bluegrass control with flazasulfuron at 4.4 g ha−1and two applications of N at 73 kg ha−1was greater than flazasulfuron at 17.5 g ha−1alone each year. No significant differences in perennial ryegrass control were observed for flazasulfuron with and without N fertility. In laboratory studies with annual bluegrass, treatment with N fertilizer at 73 kg N ha−1increased translocation of14C flazasulfuron (and any potential metabolites) from treated annual bluegrass leaves to other shoot tissues by 18% at 1 h after treatment and 22% at 4 h after treatment compared to plants not treated with N fertilizer. This increase in translocation may explain the increased level of annual bluegrass control observed in the field.