Sources of infection and methods of control of Septoria oenotheraein evening primrose (Oenotheraspp.)

Septoria oenotheraeWest. can cause severe damage in overwintered crops of evening primrose (Oenothera spp.), including complete crop loss. Damage would be reduced if the sources of infection could be identified and removed. Examination of seed capsules inoculated with S. oenotheraeshowed that 96% of the pycnidia present were on the outside of the capsules, and seeds bearing pycnidia were only rarely found. However, internal infection of seeds from these capsules was demonstrated by both a blotter test and by culturing on agar media. Immersing seeds in 45°C water for 25 minutes destroyed viable fungal propagules located internally in seeds without reducing seed germination. The pathogen was also shown to overwinter in the pycnidial stage on stems left standing in the field. It is concluded that both internal seed-borne infection and overwintered crop debris are potential sources of infection in commercial seed stocks of evening primrose.