It has been proposed that host castration is a parasite strategy to reallocate host resources from reproductive to vegetative functions to increase parasite fitness. Since resource partitioning between reproduction and vegetative growth can affect host life-history traits, parasite effects on resource allocation can affect both plant fitness and host-parasite coevolution. Field and greenhouse experiments were used to investigate the effects of host castration by the fungus Atkinsonella hypoxylon on the resource allocation and architecture of the grass Danthonia spicata. The results indicate that noninfected D. spicata can reallocate resources from reproduction to vegetative growth when resource allocation to reproduction is prevented. However, I found no evidence that fungal castration causes reallocation of resources From host reproduction to vegetative growth. Instead, infection reduces host biomass and the fungus directly utilizes resources that would have been used for host reproduction for its own reproduction.