DIEBACK OF EVENING PRIMROSE - CHARACTERISTICS OF SEPTORIA-OENOTHERAE,ITS INTERACTIONS WITH BOTRYTIS-CINEREA, AND USE OF FUNGICIDES TO MANAGE DISEASE

Septoria oenotherae is a little known and poorly characterized pathoge n of evening primrose (Oenothera biennis). Studies were carried out to assess certain cultural and taxonomic characteristics of S. oenothera e, interactions with Botrytis cinerea, and the use of fungicides to ma nage disease. Observations of conidiogenous cells showed that conidial ontogeny in S. oenotherae is similar to that in S. lactucae and S. ly copersici. Optimum temperatures for radial growth and germination of c onidia indicate that pathogen activity is likely to be greatest at tem peratures of 22-25C. Infection of plants by S. oenotherae and subseque ntly by B. cinerea results in greater disease severity than infection by S. oenotherae alone. Yield responses to chlorothalonil applications varied from year to year.