Management of Riparian Woodlands for Control of Pierce’s Disease in Coastal California
This continuing project seeks to evaluate a new way to reduce Pierce’s disease (PD) of grapevines by managing stream bank woodlands in north coastal California to reduce populations of the blue-green sharpshooter (BGSS) and their level of infectivity with the bacterium, Xylella fastidiosa. By replacing wild grape, blackberry, and other plants used by BGSS for breeding with plants that are not favored by the BGSS for reproduction or feeding, the numbers of BGSS that we detected in yellow sticky traps were again reduced to very low levels compared to undisturbed controls. Fir trees in the buffer remained too small to have any expected effects on BGSS movements. Winter flooding and a dry spring prevented planting along the Napa River site. Seed for replants was collected and sown and seedlings for bare-root transplants are being grown in a commercial nursery for transplanting in fall, 1997 and winter, 1998. We received provisional approval from the California Dept. of Fish and Game to conduct riparian woodland management experiments at a new site in Sonoma County along Maacama Creek. Data on the infectivity of BGSS with Xylellafastidiosa showed that in one site (Conn Creek) infectivity was about 50%, compared to a range of about 5-15% the previous year and in the two other sites this year. This high level of infectivity at one location may simply be within the range of annual fluctuations in vector infectivity.