Abstract Cassava cultivars were inoculated, under controlled conditions, with single‐conidium isolates of Elsinoë brasiliensis Bitancourt & Jenkins (Sphaceloma manihoticola Bitancourt & Jenkins) of diverse origins to study cassava resistance to superelongation disease. Disruption of the stem cuticle significantly increased the amount of stem disease on field resistant and field susceptible cultivars. In susceptible and resistant cultivars stem tissue developed a high level of resistance by the age of 10 days. Significant cultivar x isolate interactions indicating pathogenic specialisation were consistently observed. The interactions were weak, not always reproducible and none were characterised by a hypersensitive‐like component. Field resistant and field susceptible cultivars were treated with gibberellin A4 (the plant hormone responsible for shoot elongation) at 0 to 1 μg/μl and inoculated with a virulent isolate of the pathogen to test the possibility of using the hormone as a screening tool. No differences in response to the hormone were detected between resistant and susceptible cultivars. All cultivars showed increases in length at 103 μg/μl GA4 and all showed increases in the level of disease (% diseased area involved in lesion × length of affected area) with hormone application. Gibberellin A4 does not appear to have great potential as a screening tool for identifying field resistant cultivars. Notes Part of a thesis submitted to Cornell University by the senior author in partial fulfilment of requirements for the Ph.D. Technical assistant and plant pathologist (Cassava Program), respectively, Centro Internacional de Agricultura Tropical (CIAT), Apartado Aéreo 6713, Cali, Colombia.