- Author: Jeannette E. Warnert
The glorious fall colors in California wine country aren't good news for the industry. Although they look beautiful in the muted autumn sunlight, red leaves on grapevines can be a symptom of serious plant diseases, such as grape leafroll associated viruses and red blotch.
In 2008, a disease characterized by red blotches along leaf margins and red veins under the leaf surfaces was seen in red grapes growing in Napa Valley. The symptoms resembled leafroll disease, however laboratory tests did not detect any leafroll and rugose wood viruses in the samples. Since then, red blotch disease has been observed in vineyards throughout North America.
The infected grapevines may produce clusters with reduced sugar content, causing...