Boxwood Dieback (Colletotrichum theobromicola Delacr.)
I recently sent boxwood samples to The Ohio State University Plant and Pest Diagnostic Clinic. The results came back with the following comments:
After incubation in moist chamber, we observed Volutella spores (Volutella bligh) under the microscope.
The dieback of the branches reminds a novel disease, caused by Colletotrichum, that is creating a lot of issues in landscape and boxwood production. We did not observe any spores of Colletotrichum, but I recommend keeping the plants monitored and look for canker or sunken areas of the bark, and black fruiting bodies of the fungus on the upper side of the leaves.
Sincerely,
Francesca Rotondo, PhD
College of Food, Agricultural and Environmental Sciences
Department of Plant Pathology
Boxwood dieback is a foliar disease that has been detected from boxwood liners (Figure 5). The disease is thought to be introduced to new locations via infected liners. The pathogen is known to produce spores on young, infected twigs in the landscape (Figures 6 and 7). Disease spread from plant to plant is accomplished by poor pruning practice, and by the dispersal of conidia via rain or irrigation water.
