Reinfestation of Endophtye-Infected Tall Fescue in Renovated Endophyte-Free Pastures under Rotational Stocking

Received for publication December 8, 2004. Endophyte-infected (E+) tall fescue [Lolium arundinaceum (Schreb.) S.J. Darbyshire] is problematic in pastures because it produces alkaloids that can be toxic to cattle (Bos taurus). Replacement of E+ tall fescue pasture with endophyte-free (E-) fescue may effectively eliminate this problem. Endophyte-free cultivars, however, are less competitive than E+ fescue and are usually displaced over time. The main objective of this study was to determine whether E+ fescue would reinfest pastures planted with mixtures of E- fescue and other species and grazed under rotational stocking. In 2001, nine tall fescue pastures in western Illinois were renovated and planted with mixtures that contained E- fescue (Barcel) and two, four, or seven additional species. Pastures were grazed by beef cattle over 3 yr. Tall fescue tillers were collected each September and subjected to microscopic analysis for endophyte presence. After renovation, E+ still accounted for 18 to 38% of tall fescue. Relative to all other species, however, E+ fescue was <10% of pasture communities. The species mixtures sown with E- fescue had little influence on E+ fescue reinfestation (P = 0.70). Contrary to other studies, percentage of E+ fescue in E- pastures did not increase in the 3 yr of this study. Moderate grazing pressure under rotational stocking combined with relatively wet growing seasons likely favored Efescue and suppressed E+ reinfestation. We also suggest that if pasture renovation can reduce E+ fescue percentage to <10%, it is unlikely that E+ fescue will reinfest pastures to an extent that may cause fescue toxicosis in cattle.