| This
disease occurs primarily in the southeastern United States and California.
It has not yet been found in the Great Lakes region. Initially, only a few
shoots start to show symptoms in mid- to late summer. Leaves show scorching
from the margin inwards and drop off, leaving the petiole attached to the
shoot. Flower clusters may set berries, but these tend to dry up.
In
fall, infected shoots mature in a patchy manner, leaving “islands”
of green tissue surrounded by dark brown mature wood. In spring, bud
break on infected vines may be delayed as much as two weeks, and new
shoots are stunted. An infected vine may die the first year after
infection or may live for five or more years, depending on the cultivar,
the vine’s age and climatic conditions. Pierce’s disease
is caused by a bacterium that lives in the xylem and is vectored by
sharpshooter leafhoppers and spittlebugs. The bacterium is present
in native plants such as grasses, sedges, bushes and trees. The range
of insect vectors determines the range of the disease. |
 |
Leaves
have dropped off, leaving the petiole.
Photo: A. Schilder |
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