Submitted to: Southern Nursery Association Research Conference
Publication Type: Proceedings
Publication Acceptance Date: 8/15/2006
Publication Date: 3/1/2007
Citation: Li, Y.H., Windham, M.T., Trigiano, R.N., Fare, D.C., Spiers, J.M., Copes, W.E. 2007. Epidemiology of Powdery Mildew on Resistant and Susceptible Flowering Dogwood Cultivars. Southern Nursery Association Research Conference 51:239-243. Interpretive Summary: Powdery mildew caused by Erysiphe pulchra has impeded dogwood production and growth in nurseries and landscapes in the eastern United States since 1995. Variation of resistance to E. pulchra among dogwood seedlings was identified. The objectives of this study were to describe disease progress and investigate effects of host resistance in field conditions. Among the flowering dogwood cultivars tested in the experiment, ‘Karen’s Appalachian Blush’ had the highest resistance to powdery mildew characterized as later disease onset, slower infection rate, and lower disease levels. More experiments are needed to understand the reason of different resistance expression for MW 94-60 and MW 95-25. The results will provide useful information to extension and research scientists that are evaluating dogwood resistance to powdery mildew and developing fungicide recommendations.
Technical Abstract: Powdery mildew, caused by Erysiphe pulchra (syn. Microsphaera pulchra) is an important disease on flowering dogwood (Cornus florida) in the Eastern United States. Temporal progress of powdery mildew on flowering dogwood cultivars with different levels of resistance was investigated in the field in 2004 and 2005. Disease onset was observed in late-May, followed by a rapid increase in disease severity until early- to mid-August. Thereafter, disease severity increased slowly. Using nonlinear regression analysis, disease progress curves were fitted to logistic models (R(^2) > 85%) and absolute rates and y(max) derived. Standard areas under disease progress curves (sAUDPC), absolute rates and y(max) were significantly different (P < 0.05) among dogwood cultivars in both years. Cultivar ‘Karen’s Appalachian Blush’ consistently expressed higher resistance with lower values of sAUDPC, y(max) and slower absolute rate in both years compared to a susceptible line of variety ‘Rubra’ and moderately susceptible cultivar ‘Cherokee Daybreak’.