Biocontrol agents can significantly reduce the growth and performance of individual invasive plants but often have limited success in controlling invasions. Here, we suggest that some biocontrol failures may be understood by distinguishing between individual plant performance and the performance of groups growing in monoculture. The success of a group growing in monoculture can be maximised if individual plants limit their allocation of limited resources to competition. However, individual performance can be maximised by acquiring resources at the expense of neighbouring plants. Enemies such as herbivores can reduce the dominance of individual plants and limit resource allocation to competition. Thus, biocontrol could have the unexpected effect of increasing the performance of groups of invaders.