The plant growth regulator ethephon has been used to reduce height and lodging of intensively managed corn (Zea mays L.). However, the impact of ethephon-induced changes in vegetative growth on water use and grain yield of corn grown at various densities under drought stress conditions has not been widely studied. Field studies were conducted for 2 yr in semiarid eastern Colorado to determine if foliar ethephon application can alter vegetative growth and water use and promote drought stress resistance of corn. In 1989, treatments consisted of a factorial combination of two irrigation levels (low and high), two plant densities (53 333 and 80 000 plants ha−1), and five ethephon treatments (0, 0.28, 0.56, and 0.84 kg ha−1, applied at the 6- or 8-leaf growth stage) at one site. In 1990, treatments consisted of a factorial combination of four plant densities (24 700,37 045, 49 390, and 61 735 plants ha−1) and three ethephon rates (0, 0.28, and 0.56 kg ha−1 applied at the 6-leaf stage) at two sites. Plant height, leaf area index (LAI), dry matter yield, cumulative evapotranspiration (ET), and grain yield were measured. In both seasons, ethephon application reduced plant height and LAI by 10 to 40%, relative to the control, and this resulted in early season ET reductions. Ethephon application either had no effect or decreased yields in 1989 under all irrigation and plant density treatments, because of a lack of significant drought stress. However, when drought occurred in 1990, ethephon application decreased yields at low plant densities but enhanced yields at high plant densities at both locations, with a maximum 37% yield increase for the intermediate ethephon rate. Our data indicate that ethephon application has the potential for improving resistance to drought in corn.
Supported in part by the Colorado Agric. Exp. Stn. Project 218.