Influence of Season and Intensity of Defoliation on Bluebunch Wheatgrass Survival and Vigor in Southern British Columbia

Abstract

Bluebunch wheatgrass (Agropyron spicatum Pursh) Scribn. & Smith) response to various clipping regimes which incorporated different times, frequencies, and intensities of defoliation was examined in southern British Columbia. The experiment was repeated for 3 consecutive years at a low (296 m) and a high (1,112 m) elevation site. Plant survival and vigor was evaluated the summer following defoliation. Greatest injury was incurred by treatments involving defoliation to a 5-cm stubble height from mid April to the end of May or from early May to mid June at the low and high elevation sites, respectively. Reduced injury occurred from treatments which left 10 or 15-cm stubble heights or which ceased defoliation earlier in the season. No appreciable damage was incurred by fall clipping to 5 cm or by season-long defoliation to 20 cm. Injury resulting from spring plus fall as compared to spring only defoliation was inconsistent. Greatly reduced injury for many treatments at the low elevation site in one year was attributed to unusually warm spring temperatures and attendant rapid spring growth.