Switchgrass (Panicum virgatum L.) has tremendous potential as a biomass and stock crop for cellulosic ethanol production or combustion as a solid fuel. A three-year study was conducted to assess insect and weed diversity in a perennial switchgrass crop in Florence, SC. Insects were sampled from 2007 to 2009, using pitfall traps and sweep-nets. Collected specimens were identified to family and classified by trophic groups, and the predominant species were identified. The diversity and density of weeds in the field during the establishment year (2007) were greater than the following years. The ratio of dry weight of switchgrass to weeds increased from 2.4 in January 2008 to 15.3 in January 2009. Insect diversity at the family level varied significantly across sampling dates only for sweep-net samples, with diversity peaks in May of each year. Diversity at the trophic-group level showed significant differences for predators in pitfall traps and for predators and herbivores in sweep-net samples across dates. Diversity of herbivores in pitfall traps tended to decrease over time. Draeculacephala sp., Melanoplus sp., and a species of Tettigoniidae were the predominant herbivores, while Solenopsis invicta Buren was the predominant predator. Assessing arthropod diversity in switchgrass is a first step in identifying potential pest and beneficial insects in this crop.