Evaluation of plant growth regulators for managing fescue turf along highway rights-of-way

Plant growth regulators (PGR's) including metsulfuron plus mefluidide at 10 plus 140 g ha⁻¹, chlorsulfuron plus mefluidide at 20 plus 140 g ha⁻¹, imazethapyr plus imazapyr at 67.5 plus 2.5, 96.4 plus 3.6, and 115.7 plus 4.3 g ha⁻¹, ACP 2100 at 60, 120, and 180 g ha⁻¹, and DPX L5300 plus mefluidide at 10 plus 140, 20 plus 140, and 70 plus 140 g ha⁻¹ were applied to ‘KY 31’ tall fescue (Festuca arundinacea Schreb.). All rates of imazethapyr plus imazapyr, ACP 2100, and chlorsulfuron plus mefluidide afforded a significantly higher turf quality than metsulfuron plus mefluidide. ACP 2100 at 120 and 180 g ha⁻¹, imazethapyr plus imazapyr, DPX L5300 plus mefluidide at 70 plus 140 g ha⁻¹, and metsulfuron plus mefluidide gave the most consistent seedhead suppression. When treating seven month old tall fescue, DPX L5300 plus mefluidide did not adequately suppress seedhead elongation. Metsulfuron plus mefluidide, regardless of timing, caused excessive injury. All rates of imazethapyr plus imazapyr and the upper rates of ACP 2100 afforded the best turf quality followed by chlorsulfuron plus mefluidide in 1988 to ‘Rebel’ and both years to ‘KY 31’. Red fescue (Festuca rubra L.) quality was best with chlorsulfuron plus mefluidide and the high rate of DPX L5300 plus mefluidide. All other treatments resulted in a poorer quality turf. For all field studies on all turf types, in general, multiple applications were not practical and often caused excessive injury regardless of timing.

Root studies conducted in the greenhouse revealed that with one application, imazethapyr plus imazapyr, ACP 2100, and DPX L5300 plus mefluidide provided root dry weights ranging from 0.5 to 0.7 g, which was greater than metsulfuron plus mefluidide, chlorsulfuron plus mefluidide, and the mowed check which afforded root dry weights of 0.1, 0.3, and 0.2, respectively. With two applications ACP 2100 and DPX L5300 plus mefluidide afforded 350, 1100, 200 and 200% greater root volume than metsulfuron plus mefluidide and chlorsulfuron plus mefluidide and 200, 630, 600 and 600% greater root dry weights. Three applications are not recommended.

In laboratory studies using ‘KY 31’ tall fescue, mefluidide enhanced the uptake of ¹⁴C-DPX L5300 after 48 hours by as much as 11% and the translocation of ¹⁴C by 8.4% to the young leaves, 9.3% to the old leaves and 6.1% to the culm. Radioactive material concentrated in the tips of leaves. No significant accumulation of ¹⁴C occurred in the crown or roots.