Alfalfa seeded during late summer or fall is susceptible to the destructive disease Sclerotinia crown and stem rot. Fall-seeded stands are particularly vulnerable to this disease because the young seedlings have not had sufficient time to develop adequate resistance before infectious spores of the pathogen are produced in late October. In contrast, spring-seeded stands are able to develop larger, more resistant crowns prior to this infectious period. Thus, spring plantings are better able to withstand an attack, should these air-borne spores be present in the field.