The host-pathogen relationship of Elsinoe panici (Tiffany and Mathre, 1961) on Panicum virgatum L. is particularly interesting because the only other Elsinoe species in this loculoascomycetous order, Myriangiales, parasitic on a member of the Gramineae is E. sacchari Lo (1964) on Saccharum officinarum L. However, Elsinoe spp. parasitize many herbaceous and woody dicotyledonous plants throughout the world;Since its description, no work has been conducted with E. panici. This study was undertaken to learn more of its geographic distribution, persistence, disease cycle, and development;E. panici occurs on native P. virgatum throughout Iowa, and has been recorded from Kalsow Prairie periodically for over 20 yr;In June, Sphaceloma conidia develop from acervuli in over- wintered stromata on wind dispersed litter or on old culms. Germ tubes penetrate between epidermal cells of young leaves, and 2 wk later tiny yellowish, subepidermal stromata are visible. Secondary conidia developed from acervuli on these stromata within 2 wk, spread the fungus to adjacent leaves. Stromata mature and become black, raised, shiny, ovoid-elongate patches, composed of thick-walled pseudoparenchymatous cells. Chlorosis or necrosis do not develop around stromata, which are visible on all leaves throughout the season. Acervuli, now appearing as white spots and opening by irregular tears in the epidermis over stromata, are common. Ascostromata develop from late July into September, primarily on lower leaves. They are tan-bronze, raised, ovoid-elongate, softer and more loosely structured than stromata and eventually contain asci and ascospores. Formed infrequently, ascostromata are typically supra-cuticular, irregularly multiloculate and uniascal. With the exception of possible spermagonia, no structures involved in ascus initiation were observed. Asci mature at different times, and at maturity, ascospores are discharged from the bitunicate asci and germinate directly by budding or by germ tubes;E. panici is a discrete pathogen, compatible with its host. Hyphae are intercellular, absorbing and replacing host cells, becoming intra- cellular only in epidermal, mesophyll, and colorless cells. Photo- synthetic bundle sheath cells restrict invasion into the vascular bundle. Cells in close proximity to infected cells remain intact.