Submitted to: American Forage and Grassland Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/20/2003
Publication Date: 4/24/2003
Citation: Sanderson, M.A., Schnabel, R.R., Curran, W., Stout, W.L., Genito, D., Tracy, B.F. 2003. Switchgrass and big bluestem response to spring burning and glyphosate application: hay, biomass, and seed yields. American Forage and Grassland Conference Proceedings. v. 12. p. 161-166. Interpretive Summary: Spring burning or glyphosate application may be useful in controlling cool-season weeds invading switchgrass and big bluestem in the northeast USA. We burned or applied glyphosate to these grasses in April, early-May, and mid-May at Rock Springs, PA. Generally, the timing of burning treatments did not have a large effect on hay or biomass yields of switchgrass and big bluestem. When yields were affected, the late burning treatment did not reduce yields as much as a late application of glyphosate. Delaying glyphosate application into May frequently reduced warm-season grass yields. Thus, mid to late April seems to be the threshold date for glyphosate application to switchgrass and big bluestem sods in climates similar to central Pennsylvania. Frequently, the herbicide effect on hay yields persisted into the later biomass harvest; however, burning effects on yield were most evident in the first (hay) harvest. Thus, burning or glyphosate application may be more flexible for warm-season grasses managed for a single late-season harvest, such as for biomass energy feedstock production.
Technical Abstract: Cool-season weeds frequently invade stands of warm-season grasses, such as switchgrass (Panicum virgatum L.) and big bluestem (Andropogon gerardii Vitman) in the northeast USA. Spring burning or glyphosate application may be useful in controlling cool-season weeds. Our objective was to determine when burning or glyphosate application in the spring affected forage or seed yield in switchgrass and big bluestem. We burned or applied glyphosate to switchgrass and big bluestem in April, early-May, and mid-May in 1998 and 1999 at Rock Springs, PA. Dry matter yield was measured in July (hay harvest) or September (bioenergy feedstock harvest). Seed yield was measured in September. Timing of burning had little effect on hay or biomass yields of switchgrass or big bluestem. Glyphosate reduced yields of both warm-season grasses when applied later than 21 April. Delaying glyphosate application until late May reduced hay yields by 80% and biomass feedstock yields by 30% in switchgrass. Late application of glyphosate to big bluestem reduced hay yields by 90% and biomass feedstock yields by 40%. A late burn reduced yields less than a late application of glyphosate. Seed yields generally were not affected by burning or glyphosate. Switchgrass and big bluestem can be burned any time through the first week of May in central Pennsylvania. Glyphosate application, however, should be done before mid to late April if switchgrass or big bluestem are to be cut for hay in summer or by the first of May if the grasses are to be harvested in September or later.