The chronology of Phomopsis ganjae conidia germination and infection of Cannabis sativa leaves was observed with the scanning electron microscope. A-conidia germination approached 100% after 24 h, appresoria initiation began after 36 h; B-conidia germinated by 52 h but were not infective. Four-week-old C. sativa seedlings were more susceptible than 16-week-old plants, males more than females. THC and CBD, extracted and separated via TLC, inhibited P. ganjae conidia germination and hyphal growth.