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© 2009 Plant Management Network.
Accepted for publication 20 February 2009. Published 8 May 2009.

Annual Bluegrass Control in Perennial Ryegrass and Tall Fescue with Bispyribac-sodium

Patrick E. McCullough, Department of Crop and Soil Sciences, University of Georgia, Griffin, GA 30223-1797; and Stephen E. Hart, Department of Plant Biology and Pathology, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901-8520

Corresponding author: Patrick E. McCullough. pmccull@uga.edu

McCullough, P. E., and Hart, S. E. 2009. Annual bluegrass control in perennial ryegrass and tall fescue with bispyribac-sodium. Online. Applied Turfgrass Science doi:10.1094/ATS-2009-0508-01-RS.

Abstract

Bispyribac-sodium is an efficacious herbicide for annual bluegrass (Poa annua L.) control with potential for use in perennial ryegrass (Lolium perenne L.) and tall fescue [Festuca arundinaceae (L.) Shreb.]. Field experiments investigated bispyribac-sodium efficacy applied sequentially for annual bluegrass control in perennial ryegrass and tall fescue under home lawn maintenance. Bispyribac-sodium from 37 to 296 g a.i./ha injured perennial ryegrass and tall fescue no greater than 15% and 23%, respectively, while both grasses completely recovered from injury after two months. Bispyribac-sodium from 37 to 148 g a.i./ha provided inconsistent levels of annual bluegrass control over years but treatments at 222 and 296 g/ha provided ≥ 90% control in both years. Overall, sequential bispyribac-sodium applications appear to safely control annual bluegrass in perennial ryegrass and tall fescue.

Introduction

Annual bluegrass (Poa annua L.) is a major problematic weed in cool-season turfgrasses (3). Annual bluegrass reduces turfgrass aesthetics and functionality due to its lighter green color, unsightly seedheads, and shallow root system (9,22). Annual bluegrass tolerates close mowing, germinates rapidly, and has undesirable qualities including poor disease, drought, and wear tolerances that create unsightly patches in turfgrass stands (3,7,9). Consequently, turfgrasses infested with annual bluegrass require more water, fungicides, and intensive management, especially in the summer months, to maintain acceptable quality.

Bispyribac-sodium is a pyrimidinyloxybenzoate herbicide that controls weeds by inhibiting acetolactate synthase (ALS, EC 2.2.1.6), similar to sulfonylureas (21). Bispyribac-sodium has been used for selective postemergence control of barnyardgrass [Echinochloa crus-galli (L.) Beauv.] and other weeds in rice (Oryza sativa L.) (20,24,25) and is currently registered for use in creeping bentgrass and perennial ryegrass fairways (1). Field research indicates bispyribac-sodium from 60 to 148 g a.i./ha may selectively control annual bluegrass in cool-season turfgrasses, and thus, practitioners have a highly efficacious herbicide for use in registered species (2,5,11,19).

Bispyribac-sodium efficacy for annual bluegrass control and creeping bentgrass (Agrostis stolonifera L.) tolerance has been extensively investigated in the United States transition zone and cool-humid region (2,5,13,14,15,17,18). However, bispyribac-sodium use for annual bluegrass control in other turfgrass species has received limited investigation. Preliminary field experiments in New Jersey noted perennial ryegrass (Lolium perenne L.) and tall fescue (Festuca arundinaceae L.) exhibited less than 20% injury from bispyribac-sodium at 37 to 296 g/ha after one month (10). Perennial ryegrass and tall fescue are widely used for golf courses, lawns, and sports fields in the United States transition zone and annual bluegrass often presents significant challenges to long-term successful culture (3,4). Bispyribac-sodium is currently not registered for tall fescue and research is limited for use in perennial ryegrass (1). Furthermore, bispyribac-sodium is currently registered for use on golf courses and sod farms but is not labeled for residential turf (1). The objective of this research was to investigate bispyribac-sodium efficacy for annual bluegrass control in perennial ryegrass and tall fescue maintained as residential lawns.

Evaluating Bispyribac-sodium Control of Annual Bluegrass

Experiments were conducted from May to August 2006 and 2007 at the Rutgers Plant Science Research Center in Adelphia, NJ. Mature stands of ‘Gator 3’ perennial ryegrass and ‘Avenger’ tall fescue were grown on a Holmdel sandy-loam (fine-loamy, mixed, active, mesic Aquic Hapludult) with a pH of 6.4 and organic matter content of 23 g/kg (2.3%). Grasses were mowed at 6.3 cm with a rotary mower three days per week with clippings returned, fertilized at 24 kg N per ha/mo, and sufficiently irrigated to ensure optimal growth. Other nutrients were applied as needed to correct deficiencies. Annual bluegrass populations on the day of initial treatments (31 May 2006 and 30 May 2007) in tall fescue were 16% (± 1) in 2006 and 48% (± 2) in 2007. Initial annual bluegrass populations in perennial ryegrass were 20% (± 2) in 2006 and 23% (± 2) in 2007. From visual assessment, annual bluegrass was predominately the annual biotype.

Experimental design was a randomized complete block with four replications of 1 × 3-m plots on both fields. Bispyribac-sodium was applied at 0, 37, 74, 148, 222, or 296 g a.i./ha on 31 May and 20 June in 2006 and 30 May and 21 June in 2007. Rates were chosen based on personal observations in preliminary field experiments. Treatments were applied by making two passes per plot in opposite directions with a single nozzle CO₂ pressured sprayer calibrated to deliver a total 374 liter/ha. Nozzles used were 9504E and CO₂ regulators were set for 220 kPa.

Turf injury was visually rated one, three, six, and nine weeks after initial treatments (WAIT) on a percent scale where 0 equaled no injury and 100 equaled completely dead turf. Percent annual bluegrass cover was visually rated nine WAIT where 0 equaled no cover and 100 equaled complete plot cover. Annual bluegrass control was calculated with the following equation:

                   percent control = [ ( Poa_o – Poa_x ) / ( Poa_o ) ] × 100

                   where Poa_o = annual bluegrass cover of untreated plots;

                   and Poa_x = annual bluegrass cover of treated plots.

Data were subjected to analysis of variance and significance of main effects was analyzed at the 0.05 probability level. Year by treatment interactions were detected, and thus results are presented separately by year. Regression analysis was performed to predict bispyribac-sodium rates that would control annual bluegrass by 75% and injure turf by 20%.

Perennial Ryegrass Experiments

Perennial ryegrass injury was minimal (0 to 3%) by one WAIT in 2006 (data not shown) but injury increased with bispyribac-sodium rate from 2 to 14% by three WAIT (Fig. 1). Injury consisted of leaf chlorosis and stunted growth. Perennial ryegrass injury was not detected by six and nine WAIT (data not shown). Required rates of bispyribac-sodium to injure perennial ryegrass by 20% were > 296, > 296, and > 296 g/ha by one, three, and six WAIT (Table 1). In 2007, perennial ryegrass was injured less than 3% by one WAIT (data not shown) and injury ranged 0 to 4% from bispyribac-sodium by three WAIT (Fig. 1). Perennial ryegrass injury was not detected by six and nine WAIT (data not shown) while > 296 g/ha of bispyribac-sodium was required to injure perennial ryegrass on all dates in 2007 (Table 1).

Fig. 1. ‘Gator 3’ perennial ryegrass injury three weeks after initial bispyribac-sodium applications in field experiments, 2006-2007, Adlephia, NJ.

Table 1. Rates of bispyribac-sodium required to injure turf 20% and control annual bluegrass 75% calculated with regression analysis from data collected in field experiments, 2006-2007, Adelphia, NJ. WAIT = week after initial treatments.

In 2006, annual bluegrass control ranged 60 to 95% from bispyribac-sodium by nine WAIT (Fig. 2). Lower rates of bispyribac-sodium were less efficacious in 2007 and control ranged 0 to 94% by nine WAIT. Required rates of bispyribac-sodium to control annual bluegrass by 75% were 134 and 208 g/ha in 2006 and 2007, respectively (Table 1).

Fig. 2. Annual bluegrass control in ‘Gator 3’ perennial ryegrass by nine weeks after initial treatments of bispyribac-sodium in field experiments, 2006-2007, Adelphia, NJ. Sequential applications were made three weeks after initial treatments.

Tall Fescue Experiments

Tall fescue injury increased with bispyribac-sodium rate from 0 to 15% and 3 to 21% by one and three WAIT, respectively, in 2006 (Fig. 3). Tall fescue injury from bispyribac-sodium ranged 0 to 15% by six WAIT but turf recovered with no injury by nine WAIT (data not shown). Required rates of bispyribac-sodium to injure tall fescue by 20% were > 296, 257, and > 296 g/ha by one, three, and six WAIT (Table 1). In 2007, tall fescue injury was minimal (less than 5%) from bispyribac-sodium by one, three, and six WAIT in 2007 (data not shown) and turf required > 296 g/ha of bispyribac-sodium to induce 20% injury (Table 1).

Fig. 3. ‘Avenger’ tall fescue injury from bispyribac-sodium applications in a field experiments, 2006, Adelphia, NJ. WAIT = weeks after initial treatments.

Fig. 4. Annual bluegrass control in ‘Avenger’ tall fescue by nine weeks after initial treatments of bispyribac-sodium in field experiments, 2006-2007, Adelphia, NJ. Sequential applications were made three weeks after initial treatments.

In 2006, annual bluegrass control ranged 88 to 100% from bispyribac-sodium by nine WAIT. Lower rates of bispyribac-sodium were less efficacious in 2007 and control ranged 22 to 95% by nine WAIT. Required rates of bispyribac-sodium to control annual bluegrass by 75% were 71 and 168 g/ha in 2006 and 2007, respectively (Table 1).

Discussion

Bispyribac-sodium is currently registered for use in perennial ryegrass fairways and results support tolerance levels previously reported in field experiments (10,12,14). Bispyribac-sodium is currently not registered for use in tall fescue due to injury concerns and a lack of comprehensive investigations for end-users (1). However, tall fescue appears to have acceptable tolerance levels to the herbicide when applied in late spring. When tall fescue was injured, approximately 257 g/ha of bispyribac-sodium was required to induce 20% injury which is greater than twice the maximum labeled rate (111 g/ha) for annual bluegrass control (1). Similar injury from bispyribac-sodium was reported by one month after single applications from 37 to 296 g/ha suggesting the herbicide may have potential for use in tall fescue (10).

Bispyribac-sodium efficacy for annual bluegrass control in both turfgrasses was greater in 2006 than 2007. Bispyribac-sodium activity for annual bluegrass control is highly affected by application timing, temperature, and soil properties which may influence efficacy over years (6,8,11,12,23). Lower rates (37 to 148 g/ha) of bispyribac-sodium provided inconsistent levels of annual bluegrass control over years but higher rates (222 and 296 g/ha) provided ≥ 90% control in both years. Since predicted rates required to injure turf by 20% were significantly higher than rates required to control annual bluegrass by 75%, practitioners may safely increase bispyribac-sodium rates to improve efficacy in both turfgrasses.

Perennial ryegrass and tall fescue were mowed at 6.3 cm height to simulate residential turfgrass management which may have reduced herbicide efficacy relative to fairway height turf (16). Bispyribac-sodium at 74 to 111 g/ha applied sequentially to creeping bentgrass and perennial ryegrass mowed at 1 and 1.3 cm, respectively, effectively controlled annual bluegrass by 80 to 100% in Maryland, New Jersey, and South Carolina (11,12,14,18). In greenhouse experiments, creeping bentgrass injury from bispyribac-sodium was reduced with increased mowing height from 3 to 24 mm (16). Thus, higher mowed turf may have better tolerance to bispyribac-sodium but efficacy may be reduced for annual bluegrass control. Although tall fescue appeared to have minimal injury from bispyribac-sodium, turf-type tall fescue mowed at lower heights may have reduced herbicide tolerance and warrant further investigation for end-users.

Bispyribac-sodium effectively controlled annual bluegrass in tall fescue which has promising implications for future herbicide registration. Perennial ryegrass fairways are currently registered for bispyribac-sodium use and results support turf tolerance, annual bluegrass control, and use in higher mowed turf such as residential lawns. However, practitioners may need to apply bispyribac-sodium at rates higher than current registrations on fairways (> 74 to 111 g a.i./ha) for successful annual bluegrass control in turf mowed at 6.3 cm. Further research is needed to refine rates and application regimes to improve annual bluegrass control levels in these species. Overall, bispyribac-sodium appears to have potential for use in perennial ryegrass and tall fescue for selective annual bluegrass control.

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