Entomologic and Agronomic Evaluations of 18 Sweet Sorghum Cultivars for Biofuel in Florida

Sweet sorghum [(Sorghum bicolor L. Moench); Cyperales: Poaceae] is a summer annual crop suitable for use as a biofuel feedstock. The juice from harvested sweet sorghum stalks can be readily converted into ethanol. The purpose of this study was to identify potential arthropod pests of promising sweet sorghum cultivars grown for biofuel on Histosols (muck soil) in southern Florida. This field study was conducted at the Everglades Research and Education Center at Belle Glade, Florida in 2010. Eighteen sweet sorghum cultivars planted at 3 dates were evaluated for insect feeding. Foliar damage was measured during the whorl stage and boring within stalks was measured at harvest. Seedling damage caused by Elasmopalpus lignosellus Zeller (Lepidoptera: Pyralidae) and black cutworm Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae) reduced the stand of most of the cultivars tested. Foliar feeding by Spodoptera frugiperda L. (Lepidoptera: Noctuidae) larvae was significantly affected by cultivar and planting date. Whorl infestations above 90% were observed for all cultivars at 30- and 55-d after the early May and June planting dates. Percentage of stalks bored by sugarcane borer Diatraea saccharalis (F) (Lepidoptera: Crambidae) larvae varied significantly among cultivars and planting dates reaching 13.7% in cv ‘Sugar T’ planted in early May. Twelve species of stinkbugs (Heteroptera: Pentatomidae) and one leaf-footed bug [Leptoglossus phyllopus (L.) (Heteroptera: Coreidae)] fed extensively on developing seeds during the milk and soft dough stages. Days to harvest was cultivar dependent and ranged from 84 to 153 d. Fresh and dry weights, percentage juice extraction, brix value and potential ethanol yield varied significantly among cultivars and planting dates. Significantly lower yields were found for all cultivars when planted in Jun compared to late Mar and May.