Switchgrass (Panicum virgatum L.) biomass response to simulated insect defoliation

Grasshopper (Orthoptera: Acrididae) defoliation is a common biotic stress for perennial grasses. Switchgrass (Panicum virgatum L.) is a perennial warm-season (C4) grass being investigated for bioenergy production.  Biomass losses for two switchgrass cultivars, Shawnee and Kanlow, were examined for response to mechanical defoliation that simulated grasshopper feeding.  Defoliation was completed during a 10-day period at the vegetative stage of switchgrass development. The impact of 0, 40, 60 and 80% defoliation treatments was determined by measuring percent light interception and leaf area index (LAI) on every odd numbered day during the experiment. The percent light interception and LAI values for both cultivars declined significantly during the experiment. However, no significant yield reduction under any defoliation level was observed at the end of the experiment. Further studies will investigate injury levels between 80 and 100% defoliation to determine potential economic loss associated with grasshopper feeding.  Preliminary results indicate simulated insect defoliation at the vegetative stage of development does not appear to affect annual switchgrass biomass.