Studies on the Cherry Leaf Spot Disease in Flowering Cherries (Prunus species)

The Cherry Leaf spot (CLS) disease caused by Blumeriella jaapii affects flowering cherry and most Prunus species; it has increasingly become a significant constraint in nursery production of flowering cherries in the Southeastern United States. The objectives of this study were to (i) evaluate winter survival of the causal agent, (ii) assess the timing of infection establishment, (iii) evaluate several commercial cultivars for host resistance to CLS and (iv) evaluate fungicides for controlling CLS disease. The evaluation of B. jaapii winter survival in previously infested leaf debris showed that previously infected plants that were maintained in a greenhouse environment, protected from airborne inoculums, developed CLS indicating that overwintering structures of the pathogen in dormant buds are a significant source of primary inoculum in Tennessee. Assessment of the timing of spore release that were performed by trapping spores from the air in a field of previously infected cherry trees showed that initial inoculum were ascospores and conidiospores. These spores were trapped beginning in early March through June. The conidiospores were morphologically similar to those produced by B. jaapii and Cylindrosporium padi (anamorph). The number of spores trapped peaked in mid-May coinciding with frequent rain showers. This observation suggested that CLS pathogen survived on leaf debris from previous infection and that infested leaf debris provided significant amounts of primary inoculum that began in early March peaking in mid-May. Both ascospores and conidiospores were trapped before infection was observed in the field. This observation suggests that in early April primary inoculum was available when leaves unfolded during bud break. The efficacy of fungicide applications depend on the correct timing of spray programs. Results from this study should guide growers to manage this disease efficiently. Results also showed that plant propagation by cuttings or budding with infected plant material may play a significant role in the perpetuation of CLS. Spray programs with fungicides such as Captan™ (Captan) and Orius20Q™ (tebuconazole), and Flint 50WG™ (trifloxystrobin) and Captan in rotation beginning at petal fall, were most effective