Tall Fescue Response to Plant Growth Retardants and Fertilizer Sources 1

Plant growth retardant applications have been reported to reduce mowing requirements of tall fescue (Festuca arundinacea. Schreb.), but turf response to retardants under various fertility regimes has not been adequately explored. The objective of this study was to evaluate the effects of three spring-applied growth retardants {mefluidide, (N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl]amino] phenyl]acetamide), at 0.14 kg ha⁻¹; maleic hydrayide (MH) (1,2-dihydro-3,6-pyridazinedione), at 4.5 kg ha⁻¹; and a combination of mefluidide plus flurprimidol, (α-(l-methylethyl)-α-[4(trifluoromethoxy) phenyl]-5-pyrimidinemethanol), at 0.3 + 0.8 kg ha⁻¹} and fertilizer sources and rates on the color, height, seedhead suppression, root growth and stand density of ‘Kentucky 31’ tall fescue. The three fertilizer sources included: a) 2-1-1 ratio ammonium sulfate blend, 160 g N kg⁻¹, b) ammonium nitrate, 330 g N kg⁻¹, and c) an ammonium sulfate liquor, ASL, 70 g N kg⁻¹. Each fertilizer source was applied at 39 and 78 kg N ha⁻¹ in October 1981 and 1982. A single ASL treatment was also applied in 1981 at 78 kg N ha⁻¹. The field plot was a Typic Hapudalt Clayey, kaolinitic, thermic (Cecil gravely sandy loam) soil. Mefluidide + flurprimidol and MH treatments reduced cumulative turf height 40% and suppressed seedhead formation up to 95% for 6 to 8 weeks. Mefluidide alone reduced turf height by 20% during this period. Fall fertilization of tall fescue improved turf color following spring growth retardant application. Interactions were not observed between fertilizer sources and growth retardant treatments, except for cumulative turf height at 7 and 9 weeks after 1983 treatment. Turf responses to fertilizer sources were equivalent, but higher rates of application improved color and increased turf height and seedhead numbers.