Abstract: The invention relates to materials and methods useful for controlling the unwanted spread of energy crop plants. The methods involve an F1 hybrid transgenic switchgrass plant containing a transgene that affects a developmental stage such as spikelet meristem identity, establishment of floral meristem identity, or floral organ initiation, development, or function. The methods also involve one or more transcription factors that activate expression of the transgene. Such F1 hybrid plants are incapable of forming viable seeds.