Fungal endophytes, which naturally grow in some plant leaves and stems, can act as a defense against herbivory and may or may not be advantageous to plants, depending on their exposure to herbivores and the effects of the endophyte on plant growth. Boerner et al. compare the effects of moderate and severe simulated grazing among perennial ryegrass (Lolium perenne) plants, with and without fungal endophytes, and plants whose fungal endophytes had been removed with fungicide. Increasing the level of herbivory decreased shoot and root mass, and total plant yield of all plants. Plants with endophytes decreased biomass allocation to roots when recovering from grazing, causing their root growth and mass to be lower than naturally endophyte-free plants. Plants whose endophytes were removed with fungicide had limited recovery after grazing. Although endophytes may offer some protection from herbivores, they can alter the recovery of plants from grazing events compared to endophyte-free varieties of the same plant. This implies that if herbivores become resistant to the negative effects of fungal endophytes, and are able to graze the plant, then endophytes actually become detrimental, and not advantageous, to the plant. Fungicides are not a reasonable method for removing the endophytes because of their negative effects on plant growth.
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