Effects of secondary fungi on the epidemiology of western gall rust

Abstract

Results of rust gall (Peridermium harknessii) population studies, made in five coastal California stands, substantiate earlier reports of gall mortality. Evidence suggests that secondary fungi and insects were responsible for this mortality and not the rust alone. Nectria fuckeliana was the most aggressive secondary fungus encountered and was present on most of the dead and damaged galls in those locations where gall mortality was greatest. The results suggest that secondary organisms are important in controlling rust populations in these locations.