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.

Methods of Assessing Bermudagrass [Cynodon dactylon] Responses to HPPD‐Inhibiting Herbicides

“…The values for VB, F v /F m , and total chlorophyll responses are plotted over DAA with standard error bars presented as a means of statistical comparison. Linear regression analyses were used to determine relationships between chlorophyll and carotenoid pigment concentrations and assessments VB and F v /F m using Prism (GraphPad Prism, La Jolla, CA) on each observation date (Brosnan et al, 2010; Molulsky and Christopoulos, 2004). Individual observations from all herbicide treatments were pooled and used in regression analyses on each respective date.…”

Interactions Between Herbicide Application and Timing of Nitrogen Fertilization in Maize Hybrids

“…Many studies on the effect of nitrogen fertilization on the diversity of weed species have been carried out with varying N doses (Cathcart, Chandler, & Swanton, 2004;Kim et al, 2006;Zanatta et al, 2007;Brosnan et al, 2010;Sønderskov, Swanton, & Kudsk, 2012). For example, Zanatta et al (2007) used nicosulfuron + atrazine (32 + 1200 g ha -1 ai) and analysed the effect of nitrogen (0, 50, 100, 150 and 200 kg ha -1 ) and the weed control time in maize (V2, V3, V4 and V5).…”

Evaluation of Adjuvants on Flumioxazin Efficacy for Postemergence Annual Bluegrass and Residual Smooth Crabgrass Control

“…In 2013, flumioxazin with urea or NIS plus urea were the only treatments that provided <80% control. Urea at 73 kg ha −1 has shown to enhance efficacy of sulfonylureas for POST control of annual bluegrass in bermudagrass (Brosnan et al, 2010), but such treatments appear to reduce control by flumioxazin. Increased annual bluegrass growth from nitrogen may have mitigated the phytotoxic effects of flumioxazin compared with those of flumioxazin alone.…”

“…Nitrogen may also enhance efficacy of herbicides used for annual bluegrass control (Dickson et al, 1990; Gallaher et al, 1999). For example, urea at 73 kg ha −1 has been shown to increase control of annual bluegrass from flazasulfuron by enhancing translocation (Brosnan et al, 2010). Therefore, the use of adjuvants may help overcome the limitations of low temperature and growth stage on the efficacy of flumioxazin for annual bluegrass control.…”