Evaluation of Amicarbazone and Industry Standards for Annual Bluegrass Control and Perennial Ryegrass Response.

Amicarbazone is a photosystem II inhibiting herbicide being evaluated for annual bluegrass (Poa annua L.) control in cool season turfgrass. Annual bluegrass germination in conjunction with perennial ryegrass overseeding in the fall poses a challenge for turfgrass managers. A field study was conducted to evaluate P. annua control and perennial ryegrass response to single and sequential applications of amicarbazone and industry standards. Herbicide treatments consisted of December and March applications. December applications included: amicarbazone (0.13, 0.13 followed by (FB) 0.13, 0.26, and 0.26 FB 0.26 kg/ha) and ethofumesate (2.1 and 1.05 FB 1.05 kg/ha). March applications included: amicarbazone (0.13, 0.13 FB 0.13, 0.26, 0.26 FB 0.26, and 0.53 kg/ha) and bispyribac-sodium (0.074 and 0.074 FB 0.074 kg/ha). All sequential applications were made 3 weeks after initial application (3 WAIA). All herbicide treatments included 0.25% v/v non-ionic surfactant and were applied with a CO₂-pressurized backpack sprayer at 280 L/ha. Plots were assessed using visual ratings for P. annua control and perennial ryegrass injury (%), cover (%), and quality (0-9 scale; 0 = worst, 9 =best). Treatments were organized in a randomized complete block design with 4 replications. Data was analyzed using PROC GLM in SAS. Fisher’s least significant difference (α = 0.05) was provided as a general means of comparison. December-applied amicarbazone at 0.26 FB 0.26 kg/ha injured perennial ryegrass 45% 4 WAIA. Amicarbazone at 0.13 FB 0.13 kg/ha injured perennial ryegrass 25% 4 WAIA.  All other treatments injured perennial ryegrass < 10%. March applications did not injure perennial ryegrass nor reduce perennial ryegrass cover or quality 4 WAIA. Ethofumesate at 2.1 and 1.05 FB 1.05 kg/ha controlled P. annua 100 and 94% 18 WAIA, respectively. Bispyribac-sodium at 0.074 FB 0.074 kg/ha controlled P. annua 91%. Amicarbazone at 0.53 kg/ha controlled P. annua 73% 5 WAIA. All other treatments controlled P. annua < 35%. Based on the results of this field study, ethofumesate and bispyribac-sodium perform better than amicarbazone, and amicarbazone must be applied at high rates in the spring to achieve acceptable P. annua control and minimize perennial ryegrass injury.