Evaluation of dogwood and birch species and cultivars for resistance to key insect pests and diseases.
Ten cultivars of dogwoods (Cornus spp.) were evaluated in multi-year trials in Kentucky, USA for relative resistance to the dogwood borer, Synanthedon scitula; cold injury; canker disease, Botryosphaeria dothidea; spot anthracnose, Elsinoe corni; and powdery mildew, Oidium sp., Microsphaera sp., and Phyllactinia sp. Similarly, eight cultivars of birch (Betula spp.) were evaluated for resistance to the birch leafminer, Fenusa pusilla; Japanese beetle, Popillia japonica; aphids, Hamamelistes spinosus; the bronze birch borer, Agrilus anxius; and leaf-spot, Cryptocline betularum. All cultivars of C. florida, C. kousa and C. kousa × C. florida were susceptible to dogwood borer, although the C. florida cultivars were surviving better than the others. Cornus mas and C. kousa cultivars were relatively resistant to powdery mildew while C. florida × C. kousa hybrids and C. florida 'Cherokee Brave' were intermediately resistant. Betula platyphylla szechuanica 'Purpurea' was highly susceptible to the bronze birch borer, whereas B. nigra and B. nigra 'Heritage' were the most susceptible birches to aphid damage. Betula jacquemontii was highly susceptible to Japanese beetle defoliation. Betula pendula, B. nigra, and B. nigra 'Heritage' were most susceptible to defoliation by birch leaf spot. This study suggests that dogwood and birch cultivars vary in susceptibility to key insect pests and diseases. Planting relatively resistant cultivars may be useful in managing perennial pests in urban landscapes.