Growth Regulation of Kentucky Bluegrass With Several Growth Retardants1

Growth retarding chemicals may be useful in maintaining attractive turf with less mowing. Six growth regulators were applied to an 8‐year‐old stand of ‘Pennstar’ and ‘Fylking’ Kentucky bluegrass (Poa pratensis L.) to evaluate turf growth suppression, phytotoxicity, total, nonstructural carbohydrates (TNC), and recovery from retardation stress. The materials were three experimentals with undisclosed formulas (EL‐509, Proxazolon, and MBR‐12325), chlorflurenol, Sustar (3‐trifluoromethyl‐sulfonamido‐p‐acetotoluidide), and maleic hydrazide. Proxazolon and MBR‐12325 retarded growth more than the other materials, but Proxazolon was slower acting than MBR‐12325. EL‐509 was the only material that did not significantly retard growth. Approximately 4 weeks after initial application, turf that had been significantly reduced in growth, grew faster than untreated. All materials caused an unacceptable discoloration lasting for 2 to 3 weeks. Lower rates tended to cause less discoloration, but growth suppression did not last as long as higher rates. Turf treated with MBR‐12325 had a significant accumulation of TNC, but this occurred only after discoloration subsided. Of the materials used in this experiment, only MBR‐12325 appeared to have potential for retardation of fine turf; however, discoloration was unacceptable at the rates used. The other materials could be of use on hazardous‐to‐mow, non‐use, or other areas where discoloration would not be objectionable.