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Chemical Growth Regulation of ‘Baron’ Kentucky Bluegrass¹

Effective chemical growth regulation is desirable in reducing mowing frequency of certain turf areas. The objectives of this field research were to study the influence of some promising growth regulators with and without repeated treatments during the 2nd year on ‘Baron’ Kentucky (Ky) bluegrass (Poa pratensis L.) and to determine the long term effects caused by persistent regulators. Mcfluidide, diethanolamine salt of N-[2.4 — dimethyl-5-[[(trifluoromehtyl) sulfonyl] amino]phenyl]acetamide; fluridamid, a diethanolamine salt of N-[4-methyl-3[[(1, l, 1,-trifluoro-methyl) sulfonyl]amino]phenyl]; metolachlot, [2.chloro-N-(2-ethyl-6-methylphenyl-N- (2-methoxymethyl-ethyl) acetamide]; chlorflurenol (methyl-2-chloro-9-hydroxyfluorene-9- carboxylate, methyl-9-hydroxylfluonene-9-carboxylate, methyl-2, 7 dichloro-9- hydroxyfluorene-9-carboxylate); CGA 17020, chemistry not released; and RO7-6145, (2, 3: 4, 6 Bis-0 ((l-methylethybidene)-(xxylo-2-Hexulofuranosonic acid), were applied twice in 1974 and once in 1975 to lawn turf grown on a Typic Hapludult clayey, kaolinitic, mesic soil. Treatments were randomized in a complete block design, and replicated three times.

All regulators and formulations evaluated caused some phytotoxicity, especially at higher dosages. Granular mefluidide did not reduce turf quality until after the 1975 application. No phytotoxicity was apparent for several weeks following each treatment of all regulators.

All regulators caused yield depressions the 1st month after each 1974 application. None caused a significant reduction in clipping weights after 2 months. Mefluidide EC and RO7-6145 caused the longest yield suppression.

Approximately 1 month after retreatment in the 2nd year, all regulators reduced clipping yields. There was no apparent suppression after 2 months.

All regulators, except metolachlor, had less root growth than the control after a year following the 1974 application. Fluridamid and mefluidide suppressed rooting the most. Roots were suppressed by all regulators applied the 2nd year.

Regulators applied in 1974 stimulated seedhead production in 1975. Reapplication of treatments in 1975 suppressed inflorescence except treatments with RO7-6145.

Mefluidide and fluridamid showed a reoccurance of phytotoxicity, and all regulators showed some yield suppression in 1976.

Regulators affected root growth for a longer period of time than they did foliage. Reapplication of regulators was required to continue suppression of shoot and inflorescence growth. Possibly, lower dosages should be used with subsequent treatments since regulator influence appears to persist for several years. Application of some regulators in late summer may enhance seed production by Ky bluegrass.

Key Words: Turfgrass • Root-suppression • Inflorescense suppression • Inflorescence stimulation • Poa pratensis L.

² Associate professor of agronomy and professor of plant physiology, respectively.

Received for publication January 27, 1977.