Climatic differences between regions can affect the timing and severity of symptoms, but not the type of symptoms. Hot climates accelerate symptoms because moisture stress is more severe even with adequate soil moisture. In the following year, some canes or spurs may fail to bud out. From late April through summer infected vines may grow at a normal rate, but the total new growth is less than that of healthy vines. In late summer leaf burning symptoms reappear.
Symptoms appear when a significant amount of xylem becomes blocked by the growth of the bacteria.
Other sucking insects, such as grape leafhoppers, are not vectors. A new Pierce's disease vector, the glassy-winged sharpshooter, has recently become established in California. This new vector is a serious new threat to California vineyards because it moves faster and greater distances into vineyards than the other species of sharpshooters. The glassy-winged sharpshooter occurs in unusually high numbers in citrus and avocado groves and on some woody ornamentals. Until now, these plants have not been sources of Pierce's disease vectors.