Submitted to: Rangeland Ecology and Management
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/6/2007
Publication Date: 3/20/2008
Citation: Sheley, R.L., Bingham, B.S., Svejcar, A.J. 2008. Crested wheatgrass defoliation intensity and season on medusahead invasion. Rangeland Ecology and Management. Rangeland Ecol Manage 61:211-217 Interpretive Summary: Understanding how to graze desired plant communities in a manner that minimizes invasion by medusahead is critical to implementing effective prevention programs. Crested wheatgrass is an important grass in many western states. We defoliated created wheatgrass at ranges from 0 to 100% in the spring or fall at two sites with soils varying clay content. Then, we seeded each area with medusahead. In poor condition soils, medusahead established well regardless of treatment, but was less dense in stands that were defoliated after the growing season had ended. Medusahead initially established in low amounts in all plots on the less clayey soil. By the end of the experiment, medusahead was absent in areas where created wheatgrass was moderately defoliated. This suggests improper grazing can accelerate invasion by medushead, but proper grazing may actually help keep the grasses strong, vigorous, and competitive on good quality sites.
Technical Abstract: The objective of this study was to determine the effects of crested wheatgrass (Agropyron cristatum L. Gaertn.) defoliation intensity and timing on medusahead density and biomass. We hypothesized that crested wheatgrass defoliation greater than 60% during the spring would provide maximum medusahead (Taeniatherum caput-mudsae ssp. Asperum Simk Melderis) density and biomass. Eighteen treatments (6 defoliation levels, 3 seasons of defoliation) were applied to 2m2 plots in a randomized-complete-block design on two sites with varying clay content. Blocks were replicated 5 times at each site. Plants were clipped in 2004 and 2005. Crested wheatgrass was hand-clipped to defoliation levels of 0, 20, 40, 60, 80, and 100% in the spring, summer, or fall. Density of crested wheatgrass and medusahead was sampled in June 2005 and 2006, whereas their biomass was harvested only in 2006. Data were analyzed with least square means ANOVA. Over the two seasons, site had much more of an impact on medusahead invasion than either defoliation intensity or timing of defoliation. The results support previous suggestions that clayey soils favor medusahead and that perennial grasses with high biomass can resist this weed. On the clayey site where medusahead did persist, fall defoliation of crested wheatgrass reduced the density of this weed by 50% or more compared to spring defoliation. Given the developmental pattern of medusahead, the goal of any management program should be to maximize resource use by the desirable species during April to late-July.