Vinews

No. 14 — July 1, 2019

Rupestris Speckles Masquerades Ability to Diagnose Early Downy Mildew Symptoms

Valvin muscat expresses Rupestris speckles much more so than other cultivars that are impacted by this physiological disorder. In addition to Valvin muscat being susceptible to Rupestris speckles, the cultivar is also slightly susceptible to downy mildew. The initial symptomology of downy mildew is “oil spots” and these spots resemble Rupestris speckles. However since Valvin muscat is only slightly susceptible to downy mildew the oil spots can be overlooked as simply being Rupestris speckles. When environmental conditions are favorable for downy mildew infections do not overlook Valvin muscat as just having Rupestris speckles. Look closely at the leaves, since Valvin muscat is only slightly susceptible to downy mildew the symptoms may be masquerading as Rupestris speckling.

close-up of Rupestris speckle spots on valvin muscat leaf valvin muscat leaf with downy mildow symptoms of brown leaf edges and spots at veins
Valvin muscat leaf with Rupestris speckles (A) and Valvin muscat leaf with downy mildew symptomology (B). Photo credit: D. Volenberg.

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