Ethephon [(2‐chloroethyl)phosphonic acid] used for lodging protection in barley (Hordeum vulgare L.) often increases spikes m−2. The degree to which such additional spikes contribute to yield has not been reported, and neither has the source of such spikes been determined. This study was undertaken to determine the effects of ethephon on tiller emergence and survival, as well as the contribution to yield of additional spikes appearing on ethephon treated barley plants. Ethephon was applied at Zadoks growth stage (GS) 35 and/or 45 at 240 g ha−1 to ‘Argyle’ conventional height and ‘Samson’ semidwarf barley grown at 100 and 300 plants m−2 at Winnipeg, MB. Ten plants per plot were observed at intervals through the growing seasons; tillers were tagged as they emerged and their contributions to spikes per plant and grain yield were determined at harvest. The two cultivars responded similarly to ethephon application. In all 3 yr and at both plant densities, ethephon application increased shoots per plant. Application at GS 45 increased shoots per plant more than at GS 35 in 1987 when moisture was adequate, but less in 1988 when some moisture stress may have affected barley at GS 45. Late appearing shoots contributed up to 32 and 15% of spikes per plant and grain yield per plant, respectively, for both plant densities in 1987 and for the low plant density in 1989. Increased spikes per plant due to ethephon application were attributable to late tiller production and survival rather than to prevention of senescence of early formed tillers. The increase of spikes per plant by ethephon should be a positive influence on grain yield, but total yield per plant was often decreased and was never increased by ethephon because ethephon also caused reductions in kernels per spike.
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Moes et al. (1991) studied this question.