Harvest Date and Endophyte Status On the Yield and Nutritive Value of Tall Fescue Stockpiled for Summer Grazing.

Tall fescue is grown on more than 24 million acres in the east-central and southeastern United States.  It is the primary forage base for more than 9 million beef cows in this region.  Although stockpiling tall fescue for winter grazing has received much attention, little work has considered its potential to be stockpiled for deferred grazing during the summer months.  One reason for this lack of attention is that most tall fescue is infected with an endophyte that results in the production of alkaloids associated with lower animal performance.  The symptoms of tall fescue toxicosis are enhanced by high temperatures during the summer months, so recommendations have focused on grazing alternative forages during the summer.  However, with the development of cultivars infected with the friendly or novel endophyte, stockpiling tall fescue in late spring for summer grazing may be a viable option.  The objective of this study was to evaluate the yield and nutritive value of ‘Jesup’ tall fescue infected with no endophyte, toxic endophyte, or the novel endophyte.  Plots were seeded near Lexington, KY and Blackstone, VA in the fall of 2007 and allowed to establish in 2008.  In May, 2009, plots were harvested at the early head stage and then fertilized with 67 kg N ha^-1.  Regrowth was allowed to accumulate until July 1.  Starting on July 1, each plot was harvested one time during the summer months on a predetermined date.  Harvest dates were July 1 and 15, Aug 1 and 15, and Sep 1.  Yield was determined by clipping a strip through the center of each plot using a self-propelled forage harvester.  A subsample was collected from each plot for DM and nutritive value determinations.  At the Blackstone location, Jesup tall fescue infected with the toxic endophyte yielded more than the no endophyte, but not the novel endophyte (P = 0.06).  Averaged over harvest date, yields were 2426, 2383, 2174 kg DM ha^-1 for the toxic, novel, and no endophyte, respectively.  In 2009 at the Blackstone location, yield increased initially due to favorable growing conditions and then decreased after second harvest date (Jul 15).  Yields were 1851, 3103, 2425, 2484, and 1774 kg DM ha^-1 for the Jul1 and 15, Aug 1 and 15, and Sep 1 harvests, respectively.  Depending on the harvest date and utilization rate, tall fescue stockpiled for summer grazing could supply 115 to 200 grazing d ha^-1.  Although these initial data indicate that the novel endophyte tall fescue could be stockpiled to provide grazing during the summer months, more work is needed to determine the long-term persistence and productivity of tall fescue under this management regime.