ARS | Publication request: Effects of Host Resistance and Shading Density on the Disease Severity of Hydrangea Leaf Spot

Submitted to: American Phytopathological Society Annual Meeting
Publication Type: Abstract
Publication Acceptance Date: July 26, 2008
Publication Date: July 26, 2008
Citation: Li, Y., Windham, M.T., Windham, A.S., Reed, S.M., Mmbaga, M.T., Spiers, J.M., Rinehart, T.A., Trigiano, R.N. 2008. Effects of Host Resistance and Shading Density on the Disease Severity of Hydrangea Leaf Spot. American Phytopathological Society Annual Meeting.

Technical Abstract: Leaf spot, caused by Cercospora hydrangeae Ellis & Everh., is a common disease of bigleaf hydrangea (Hydrangea macrophylla) in ornamental nurseries and gardens. Experiments were conducted to determine the effects of cultivars and shading density on the disease severity. Two year-old plants of six bigleaf hydrangea cultivars were purchased from Bell Family Nursery, Aurora, OR and transplanted in field plots. Shading treatments included 0% (full sun), 30%, 60% and 90% shade. Disease indices were assessed for leaf spot using a 0-5 index scale on September 17, 2007. Shading treatments significantly (P = 0.0003) affected the disease indices. In general, increasing shade decreased disease severity of leaf spot. Because of the significant (P = 0.0380) interaction between shading and cultivar treatments, comparisons of disease indices among cultivars were conducted in each shading treatment. The results showed that the disease indices were not significantly different among cultivars for the 60% (P = 0.2828) and 90% (P = 0.4348) shading treatments. However, significant differences in disease indices were detected among cultivars in 30% shading (P = 0.0053) and full-sun (P = 0.0001) treatments. `Fasan¿, `Blue Deckle¿, 'Lilacina¿ had significantly lower disease severities than `Miranda¿ and `Pretty Maiden¿, whereas `Sister Theresa¿ was intermediate in both 30% shading and full sun. The present results provide knowledge in the disease management and resistance screening for hydrangea leaf spot.