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The effects of the presence of fungal endophytes, treatment with a systemic fungicide, and simulated herbivory on growth and biomass allocation were investigated in 2 varieties of perennial ryegrass (Lolium perenne): 'Repell', an endophyte-bearing variety, and 'Pennfine', a low-endophyte variety. In the absence of herbivory or fungicide there were no significant differences in the growth or pattern of biomass allocation between varieties. Treatment with the systemic fungicide benomyl reduced growth of both varieties by approximately 50% and reduced root growth more than shoot growth; fungicide effects were similar in the 2 varieties. Simulated herbivory reduced root growth more in endophyte-bearing Repell plants than in endophyte-free Pennfine plants, and root:shoot ratios of Repell plants were significantly lower than those of Pennfine plants following either moderate or severe herbivory. Statistically significant interactions between fungicide treatment and simulated herbivory were frequent in Repell plants but absent in Pennfine plants, suggesting that the fungicide had both direct phytotoxic effects and indirect effects mediated through the loss of endophytes by the Repell plants. While the proximate cost to seedlings bearing endophyte seemed small, the presence of the endophytes altered the allocation pattern of biomass following herbivory in such a way as to increase the probability of mortality. This material was digitized as part of a cooperative project between the Society for Range Management and the University of Arizona Libraries. The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact lbry-journals@email.arizona.edu for further information. Migrated from OJS platform August 2020