A number of diseases and insects have been reported for switchgrass and some concerns have been raised regarding large scale planting for feedstock production in the future [54]. However, no diseases or insects have demonstrated economic concerns to date. The list of diseases reported in the literature includes: rust associated with Puccinia spp., anthracnose caused by Collectotrichum spp., smut caused by Tilletia maclaganii, sharp eye spot caused by Phyzotonia cerealis, helminthosporium spot blotch caused by Bipolaris sorokiniana, and viral disease caused by Panicum mosaic virus (PMV), Phoma leaf spot (Phoma spp.), and Fursarium root rot, Fusarium spp. [55-64]. Most of these diseases are reported from a few field observations, with some cultivars being more susceptible to specific diseases. Individual genotypes can have susceptibility to diseases, but released cultivars and germplasms have been selected for a range of resistance to many diseases [16]. Sanderson [56] indicated that higher anthracnose infection was observed in Trailblazer than in Cave-in-Rock. Cave-In-Rock is the cultivar most susceptible to smut [16]. Smut infection can significantly reduce switchgrass biomass and seed production. In Iowa, a smut-infected seed field did not produce seed for several years [60,65]. Thomsen et al. [66] reported that smut infection reduced Cave-in-Rock switchgrass biomass yield by as much as 40%. Consequently, smut seems to be the most serious disease at the present.

Few insects have been reported in switchgrass and, at present, generally appear to pose a limited threat. Grasshoppers (Orthoptera) are common herbage feeding insects that could affect switchgrass biomass productivity [16]. Recently, two other insects have been identified in switchgrass fields and natural populations in the US Midwest. Prasifka et al. [67] identified a stem-boring caterpillar (Blastobasis repartella Dietz) and its distribution and symptoms. Infestation of B. repartella can cause death of young tillers of switchgrass but its damage on biomass yield was not quantified. Reducing seed production is the primary concern with insects in switchgrass. Boe and Gagne [68] discovered a new species of gall midge [Chilophaga virgate Gagne (Diptera: Cecidomyiidae)]) in South Dakota. Infestation of the gall midge was observed in the peduncle inside the sheath of the flag leaf and the inflorescence never emerged. Depending on infestation rate, switchgrass seed production could be reduced by the gall midge. For example, the bluestem seed midge (Contarinia wattsi Gagne) was reported to reduce big bluestem (Andropogon gerardii Vitman) seed production by about 40% [69] and has been observed by the authors in heavy infestations in switchgrass.