Tall Fescue Sward Dynamics: II. Influence of Four Plant Growth Regulators

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Very little is known about the influence of plant growth regulators (PGRs) on turfgrass sward dynamics (including shoot development and mortality) and reproductive development. PGR‐induced growth suppression might increase assimilate supply to axillary buds, resulting in their release. A 2‐yr study was conducted to determine the impact of four PGRs applied in late March on the sward dynamics of ‘Kentucky 31’ tall fescue (Festuca arundinacea Schreb.). Maleic hydrazide [1,2‐dihydro‐3,6‐pyridazinedione] and mefluidide N‐(2,4‐dimethyl‐5‐[([trifluoromethyl]‐sulfonyl)amino]phenyl)acetamide], two PGRs that suppress vegetative and reproductive growth, were applied at 4.48 and 0.56 kg ha−1, respectively. Flurprimidol [α‐(1‐methylethyl)‐α‐[4‐(trifluoromethoxy)phenyl]‐5‐pyrimidinemethanol] and paclobutrazol [(R*,R*)‐(±)‐β‐[(4‐chlorophenyl)methyl]‐α‐,(1,1dimethylethyl)‐1H‐1,2,4‐triazole‐1‐ethanol], two PGRs that suppress vegetative growth only, were each applied at 1.12 kg ha−1. Twenty shoots were labeled at random in each plot and observed 3, 6, 10, 14, 19, and 31 weeks after treatment (WAT). Maleic hydrazide and mefluidide treatments caused 75% shoot mortality (55% greater than the control) by 10 WAT; however, stand density was unaffected by maleic hydrazide and mefluidide, due to the release of axillary buds beginning 2 WAT. Maleic hydrazide and mefluidide induced a postinhibition growth response, with proliferation of new shoots and rapid growth of shoots surviving chemical treatment. Leaf and crown total nonstructural carbohydrates (TNC) declined during the postinhibition response from 4 to 6 WAT. Flurprimidol and paclobutrazol, despite effective foliar growth suppression, failed to influence shoot mortality, axillary bud release, or TNC levels. Patterns of TNC partitioning in response to PGRs, though different, did not appear to be the result of the effectiveness of seedhead suppression.