Clethodim Effects on Fine Fescue Inflorescence Height and YieldLofland, Joseph CRF: creeping red fescueMFF: mixed fine fescuePGR: plant growth regulatorEnvironmental Resource ManagementB SNaturalized fine fescue (Festuca ssp.) stands have become increasingly common on golf courses and other low-input utility turf settings. However, reducing inflorescence height and density is a primary management objective. Clethodim, a selective grass herbicide, is a potential alternative to existing plant growth regulators due to its suppression of fine fescue. Field experiments were conducted in 2022 and 2024 on a seven-year-old strong creeping red fescue (CRF) 'Garnet' stand, as well as a mixed fine fescue (MFF) stand at the Joseph Valentine Turfgrass Research Center in University Park, PA. Clethodim was applied at the boot stage (50.51, 101.9, 203.4, and 272 g ai ha⁻¹) alongside an untreated control, and inflorescence height, inflorescence yield, and visual foliar injury were evaluated. Clethodim applied at 203.4 and 272 g ai ha⁻¹ consistently reduced inflorescence height and yield across both years and stand types, with yield reductions ranging from 11%–51% in 2022 and 25%–98% in 2024, relative to the untreated control. Polynomial contrast analysis revealed that inflorescence yield followed a significant linear dose-response in both years, while height suppression was characterized by nonlinear quadratic and cubic components, indicating that height and yield do not respond equally to rate. The greatest foliar injuries were observed at the highest rate in the MFF stand in 2022 and 2024, but injury was transient. These results indicate that clethodim can effectively suppress inflorescence development in mature mixed fine fescue stands, offering turfgrass managers a practical alternative to conventional plant growth regulator programs.Benjamin A Mc Graw, Thesis SupervisorMichael Lee Hile, Thesis Honors Advisoropen_access2026-04-05T17:02:18Zhttps://honors.libraries.psu.edu/catalog/9980jel5890