Spitzer T. author Matušinský P. author Klemová Z. author Kazda J. author text journal article 2011 Influence of growth regulators chlormequat chloride, ethephon, trinexapac-ethyl, and a combination of chlormequat chloride and ethephon on decreasing sunflower height was examined in the years 2006-2009. Height was reduced by as much as 63 cm by double application of chlormequat chloride (915 g/ha) + ethephon (465 g/ha) at early and later growth stage (BBCH 32 and 50). Trinexapac-ethyl (375 g/ha) did not affect the height. One-time application of chlormequat chloride (1440-2160 g/ha), chlormequat chloride (458 g/ha) + ethephon (233 g/ha) (BBCH 30 or 50), or ethephon (480 g/ha) (BBCH 30) was sufficient for a ca 30 cm reduction during flowering, but this effect did not last until harvest. With double application (BBCH 30 and 50), reduction lasted until harvest. For ethephon (480 g/ha), application at BBCH 50 reduced height by as much as 35 cm and lasted until harvest. Combining a lower rate of ethephon with ammonium sulfate was effectively equivalent to using a full rate. Flower head diameter at maturity showed no significant negative influence compared to the control. In 2008 and 2009, a delay in flowering onset was observed after applying growth regulators. growth inhibition; chlormequat chloride; ethephon; trinexapac-ethyl 10.17221/75/2011-PSE https://pse.agriculturejournals.cz/artkey/pse-201108-0002.php https://pse.agriculturejournals.cz/artkey/pse-201108-0002.php continuing 57 8 357 363 2011 12141178 periodical academic journal