Mitigation of Summer Stress of Roughstalk Bluegrass with Strobilurin Fungicides.

Rough bluegrass (RBG, Poa trivialis L.) is a problematic weed in tall fescue (Festuca arundinacea Schreb.) and Kentucky bluegrass (Poa pratensis L.) lawns and roughs, as well as creeping bentgrass (Agrostis stolonifera L.) fairways.� Rough bluegrass can be a contaminant included under the �other crop� category on seed labels, and is often unknowingly planted with desirable species as a result.� Rough bluegrass enters a stress-induced dormancy during summer months leaving behind brown patches that are easily mistaken for disease.� Recently, researchers observed the mitigation of summer decline of RBG with application of strobilurin fungicides and postulated that summer diseases may influence RBG decline.� Therefore, our objective was to determine the effects of several strobilurin products on measures of RBG health. Treatments on lawn-height �Laser' RBG included untreated, two formulations of azoxystrobin (Heritage and Heritage TL, HTL) at 610 g a.i. ha^‑1, and two formulations of pyraclostrobin (Insignia and Insignia SC, ISC) at 556 g a.i. ha^‑1 every two weeks from 21 May to 23 August in 2011.� Plots were sampled for pathogens twice in 2011.� Cover, quality, and gross photosynthesis (P_G) were monitored weekly.� A pathogen contributing to decline was not consistently detected in 2011.� No treatment resulted in acceptable RBG quality throughout the summer.� Compared to untreated, plots treated with HTL, Heritage, Insignia, and ISC averaged higher quality on 11, 4, 2, and 0 dates, respectively.� Plots treated with HTL, Heritage, Insignia, and ISC averaged greater cover than untreated plots on 12, 7, 2, and 1 dates in 2011.� Rough bluegrass treated with HTL or ISC averaged significantly greater P_G on 2 dates each from June through August in 2011.� While it is unclear if a pathogen is contributing to summer decline of RBG, strobilurin fungicide applications may increase summer quality, cover, and to a lesser extent, P_G.