Stephen Denis Garrett (1 November 1906 – 26 December 1989) was a British plant pathologist and mycologist who did pioneering work on soil-borne pathogens, root pathology and soil ecology. He was the first to apply ecological concepts to interactions in the soil. Much of his research used as a model system the fungus Gaeumannomyces graminis, which causes the important cereal disease take-all. He also studied Armillaria root rot of trees, among other plant diseases.
