By N. K. Osterbauer and C. M. Ocamb
Cause The fungi, Cercospora cannabis and Pseudocercospora cannabina, which overwinter on infected crop residues on the soil surface. More commonly observed in field-grown hemp. In greenhouses, most commonly observed in plants near open greenhouse doors or near vents.
Symptoms Cercospora cannabis produces circular to elliptical spots, gray in the center with dark brown-black margins. Conidia are produced in the gray centers. Pseudocercospora cannabina can cause complete defoliation.
Cultural control
- Improve air circulation and minimize leaf wetness.
- Remove and destroy infected leaves.
Biological control
- LifeGard WG (Group P6) at 1 to 4.5 oz/A on 3- to 14-day intervals for activating plant resistance. Refer to label for appropriate rate per application volume. Preharvest interval is 0 days. 4-hr reentry. O
References Rodriguez, G., Kibler, A., Campbell, P., and Punja, Z.K. 2015. Fungal diseases of Cannabis sativa in British Columbia, Canada. American Phytopathological Society Annual Meeting, Poster 529-P.
Ward-Gauthier, N., Beale, J., Amsden, B., and Dixon, E. 2015. Greenhouse hemp in Kentucky exhibits many common diseases. American Phytopathological Society Annual Meeting, Poster 502-P.