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ARS Home » Northeast Area » Washington, D.C. » National Arboretum » Floral and Nursery Plants Research » Research » Publications at this Location » Publication #230274

Title: Effects of Shading on Cercospora Leaf Spot in Bigleaf Hydrangea

item Reed, Sandra
item Spiers, James
item Rinehart, Timothy - Tim

Submitted to: Southern Nursery Association Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/20/2008
Publication Date: 12/15/2008
Citation: Li, Y., M.T. Windham, R.N. Trigiano, S.M. Reed, J.M. Spiers, and T.A. Rinehart. 2008. Effects of shading on Cercospora leaf spot in bigleaf hydrangea. Proc. Southern Nursery. Assoc. Res. Conf. 53:379-380.

Interpretive Summary: Hydrangeas are among the most popular flowering shrubs, with annual U.S. sales of approximately $32 million. Cercospora leaf spot is a common disease of bigleaf hydrangea in ornamental nurseries and gardens in late summer and fall. This study evaluated the effect of shading on the severity of this disease problem. It was determined that Cercospora leaf spot is more severe in bigleaf hydrangea plants grown in full sun or under low levels of shade. This work defines the environmental conditions needed for evaluating plants for resistance to this disease. It also identifies a possible management tool for control of Cercospora leaf spot in bigleaf hydrangea.

Technical Abstract: Shading densities significantly affected severity of Cercospora leaf spot on bigleaf hydrangeas. In general, lower disease severities were associated with higher shading densities. However, significantly differences in disease severities among cultivars could not be detected in higher shading densities with 90% and 60% shade. These results suggest that planting bigleaf hydrangeas under shade could be an effective component in integrated management of the disease. Screening of bigleaf cultivars for leaf spot resistance should be conducted under full-sun or low shading density to avoid false conclusions.