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Seasonal Application of Ethephon, Flurprimidol, Mefluidide, Paclobutrazol, and Amidochlor as they Affect Kentucky Bluegrass Shoot Morphogenesiscky

Dep. of Horticulture, Iowa State Univ., Ames, IA 50011.

^* Corresponding author.

Inconsistent efficacy has limited the use of turfgrass growth retardants. A 3-yr field study was conducted to determine if the spring reproductive, summer vegetative, and fall reproduction-inductive growth phases of Kentucky bluegrass (Poa pratensis L.) influence its response to turfgrass growth retardants. Amidochlor { N-[(acetylamino)-methyll-2-chloro-N-(2,6-diethylphenyl) acetamide} and mefluidide N-{2,4-dimethyl-S-[[(trifluoromethyl)sulfonyllamino] phenyl}acetamide were fast acting and most effective in spring with nearly complete growth restriction during the second and third weeks after application. Paclobutrazol [(2RS, 3RS)-I-(4- chlorophenyl-4,A-dimethyl-2-(1H-1,2,4-triazol-l-yl)pentan-3-ol] and flurprimidoi {-(l-methylethyl)-~-[4-(trifluoromethoxy)phenyl]-5- pyrimidine methanol} were slow acting, with an average of 16% growth reduction, which peaked 5 and 10 wk after treatment, respectively. Ethephon [(2-chloroethyl)phosphonic acid] effects were continuous throughout the 10-wk measurement periods, restricting growth an average of 30%. Flarprimidol was most effective in summer, whereas ethephon and paclobutrazol had similar effectiveness across seasons. Mefluidide prevented spring heading completely while amidochlor reduced heading by 79%. Mefiuidide was the only chemical to reduce turf quality severely. Ethephon was the only chemical to stimulate internode elongation. Measurement of individual phytomers within shoots from two sampling dates provided a continuous record of plant growth response to treatment over a 6-wk period. Blade growth was affected more strongly than sheath growth by all growth retardants except paclobutrazol. Consistent differences in seasonal plant response to treatments in spite of yearly climate variations support the hypothesis that unique combinations of season with growth phase influence the response of Kentucky bluegrass to turfgrass growth retardants.

Received for publication June 20, 1988.

This article has been cited by other articles:

				J.C. Stier, J.N. Rogers III, J.R. Crum, and P.E. Rieke Flurprimidol Effects on Kentucky Bluegrass under Reduced Irradiance Crop Sci., September 1, 1999; 39(5): 1423 - 1430. [Abstract] [Full Text]