Lettuce plants in several fields in south-eastern Queensland were affected by a black root rot resulting in slow growth, small head size and harvest reductions. Isolation and pathogenicity tests showed Chalara elegans was the causal fungus. The host range included bean and cucurbits but not capsicum, celery, cotton, eggplant, parsley, radish or tomato. The weed Sonchus oleraceus was a natural host. Lettuce cultivars ranged in susceptibility with Centenary, Kirralee and Monaro being tolerant and Classic, Yatesdale and Buffalo being susceptible. The fungicides benomyl and propiconazole were inhibitory to growth of C. elegans in culture, while root drench applications controlled the disease in a glasshouse experiment.