Use of ethephon and chlormequat chloride to manage plant height and lodging of irrigated barley (cv. Puma) when high rates of N-fertiliser are applied

The objective of this study was to evaluate the effects of the plant growth regulators (PGR's) chlormequat, ethephon and their combination on plant height, lodging, grain yield and yield components of ‘Puma’ barley with differing amounts of N (120, 150 & 180 kg N ha−1). The PGR treatments and a water control were applied at three times of application (TOA): the beginning of stem elongation, at the flag leaf stage, or as a split (double) application at elongation and the flag leaf stage at two localities (Bethlehem and Vaalharts). Field trials were planted as 4 × 32 factorials in RCBD's with 4 replications in the 2004 and 2005 seasons. Plant height, lodging (at Vaalharts) and grain yield (at both sites) were significantly reduced with applications of ethephon and the PGR combination at the flag leaf stage and as a split application. Chlormequat application alone did not produce a response. Yield reductions with ethephon and the PGR combination were attributed to reductions in grains spike−1 and mass grain−1. Higher N levels increased lodging and simultaneously reduced grain yields, however, applications of ethephon significantly controlled lodging at higher N levels. Ethephon and the PGR combination, applied at the flag leaf stage, can be utilized as lodging controlling tools with ‘Puma’ in environments conducive to lodging.