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• Effect of PGRs was in the wavelength range from 540 to 650 nm. • Gibberellic Acid resulted in lighter leaves with higher yellow hue. • Paclobutrazol and Trinexapac Ethyl had a beneficial influence on colour and turf quality. • Flurprimidol and Mefluidide did not change turfgrass colour and quality. Plant growth regulators (PGRs) are used on turfgrass to slow vertical growth and reduce mowing intensity. However, turfgrasses sometimes exhibit some leaf discolouration after PGR applications. The objective of this study was to determine the effect of different rates of PGRs on turfgrass quality with a special focus on colour characteristics. Three cultivars of perennial ryegrass (Lolium perenne L.) were used in an experiment. Six PGRs were used, namely, Trinexapac Ethyl, Paclobutrazol, Flurprimidol, Mefluidide, Ethephon and Gibberellic Acid, at five different rates. A control without the addition of PGRs was also tested simultaneously. The measurement of leaf colour was performed using a portable spectrophotometer and is presented in CIE Lab colour space. The turfgrass quality was assessed by a visual score. The results showed that the turfgrass quality was significantly different regarding the perennial ryegrass cultivar, treated with different PGRs rates. The changes owing to different PGRs rates appeared in the wavelengths ranging from 540 to 650 nm. PGRs application significantly affected L , b and a colour components. Gibberellic Acid application resulted lighter leaves with higher yellow hue and in a lower score of overall appearance and turf colour assessment. Paclobutrazol and Trinexapac Ethyl, had a beneficial influence on colour characteristics and turf quality. Flurprimidol and Melfuidide had no effect on turfgrass colour and quality after PGR treatment. The changes in colour of turf of perennial ryegrass correlated with PGR rates. Higher rates resulted in increased intensity of discolouration. The results of the spectrophotometric analysis of leaf colour corresponded with visual turf colour assessment. However, visually scored turfgrass did not show differences between PGR rates. [ABSTRACT FROM AUTHOR]