AbstractNeotephritis finalis (Loew), a fly known as a minor pest of cultivated sunflowers (Helianthus annuus L.), has been observed to attack Silphium spp., which are being evaluated as new crops to produce biomass or edible oil. Infestations of Silphium integrifolium Michx., Silphium perfoliatum L. and their interspecific hybrids were assessed by securing bags over heads late in bloom and counting emerged adult flies ∼30 d later. Effects on seed production were assessed by examining the percent of achenes containing fully developed seeds (i.e., seed set). In 2017, more flies emerged from S. integrifolium and hybrids than from S. perfoliatum, but even high numbers of adult flies emerged per head appeared unrelated to seed set in S. integrifolium. In 2018, far fewer flies were found across Silphium spp., but seed set was similar to 2017. Combined, results indicate that N. finalis is unlikely to limit seed production of Silphium spp.