Summer and Fall Symptoms of Pierce's Disease

The type and extent of PD symptoms vary with the following factors:

1. Grape variety

    For most varieties we have not classified their relative susceptibility. Although there are large differences among varieties in their attractiveness to insect vectors, this does not match up with their relative susceptibility to PD. In general, more susceptible varieties seem to support faster movement of the bacterium (Xylella fastidiosa) that causes PD.

Highly susceptible varieties are Barbera, Chardonnay, Emperor, Fiesta, Pinot noir, and Red Globe.

Less susceptible varieties are Chenin blanc, Flame Seedless, Riesling, Sylvaner, Ruby cabernet, and Thompson Seedless,

Cabernet sauvignon, Merlot, and Sauvignon blanc are intermediate" in susceptibility.

2. Date when the vine was infected.

3. Vine age [no other link]

    The younger the vine, the faster severe symptoms will appear and the less chance that it will recover over the next winter. Young vines are smaller, morphologically simpler, and thus can be more completely colonized by Xylella fastidiosa bacteria in a few months than can older vines.

4. Climate

5. "Variability".

    For unknown reasons, different vines of the same age, location, and variety will develop somewhat different symptoms.

6.Other Diseases Mimicing Pierce's Disease

    Zinc deficiency, measles, salt burn...

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