Generally the earlier in the spring the vine is infected by insect vectors, the more extensive and more severe the symptoms of PD in that vine will be by fall. In addition, the earlier the vine is infected the less chance that the vine will recover from PD during the next winter. This also depends on the age and variety of the vine.

The first symptoms are discoloration of leaves on infected stems. Yellowish or reddish discoloration may be evenly spread over the leaf when the first symptoms appear in a vine infected in mid- to late summer. A single leaf, but more often several leaves in row along the cane will discolor.

The photo below shows October symptoms of several dead canes with raisined fruit in September on a Chardonnay vine in the north coast that had been insect vector-inoculated at a single point on a cane the previous April. Note the single yellowed leaf on an adjacent cane has no marginal scalding, only a uniform yellowing.

file:///C:/Documents%20and%20Settings/Rodrigo%20Almeida/Desktop/Webpage/xylella/nonPD.html (Photo by Helene and Bill Feil)
October symptoms. Mendocino County, 2000.

The next photo shows the mid-September symptoms of a Cabernet Sauvignon vine infected at one point by insect vectors 2 months earlier (July). Note the lack of marginal discoloration or "scorching" (dead brown tissue) that is usually considered "typical" for Pierce's disease. (Yolo County 1997. Photo by Helene and Bill Feil)

(Photo by Helene and Bill Feil)
Non-typical mid-September symptoms. Vine was infected in July.

More frequently the discoloration begins at the margin of the leaf. Over days or weeks, the discolored area advances toward the center of the leaf, and the previously discolored parts of the leaf die, leaving in its place dead brown tissue.

Edge of a Merlot leaf with marginal leaf scorch caused by PD.		Fall symptoms of PD in Pinot noir.
(Photo by Jack Clark)		(Photo by A.H. Purcell)

This progressive discoloration and dying of leaf tissue continues until the leaf blade is completely brown and falls off, leaving only the petiole remaining. The petiole continues to die from its tip towards its base, much like a candle wick. Petioles on PD vines may remain attached to canes weeks after most leaves on healthy vines have fallen off in November.

(Photo by A.H. Purcell)
Temecula Valley, 1999

The symptoms on the young vine above may give some clues as to why GWSS is such an important PD vector. Note that the position of the first symptoms seemed to be reversed or "upside down". That is, the symptoms are worse on the base of the canes and progress upwards as if the infection spread uniformly from the trunk or cordons upward. This could occur if the vine was infected in the older branches or the trunk, where glassy-winged sharpshooter feeds in the winter on grapevines. Normally such symptoms spread to adjacent canes on the same cordon or arm as canes infected earlier.

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