Management of Riparian Woodlands for Control of Pierce’s Disease

This is a continuing project to develop new methods of managing Pierce’s disease (PD) of grapevines by managing the plant habitats of the principal insect vector of PD, the blue-green sharpshooter (BGSS). Populations of BGSS would be reduced by replacing plants such as wild grape, blackberry, and others with plants that are not favored by the BGSS for reproduction or feeding. We are also testing buffer strip plantings of redwood and Douglas fir between vineyards and riparian woodlands as a barrier to reduce the influx of BGSS into vineyards during spring. The second goal is to reduce the percentage of BGSSs that are infective with the Pierce’s disease bacterium {Xylella fastidiosa) by replacing plants that support the multiplication, within-plant movements, and year-round survival of A”. Fastidiosa with plants that do not. Managing riparian woodlands to reduce the threat of PD also must meet requirements to maintain good habitats for fish and wildlife, prevent water contamination, and not degrade other public uses or values of this ecosystem. During 1995-96 we monitored populations of BGSS before and after the management treatments. We also estimated that about 6%of BGSS in the study site were infected with Z Fastidiosa in September, 1995. Sticky trap catches of BGSS along both sides of the study site along Conn Creek, Napa County, verified that BGSS was common along the entire study site. Trap catches in vineyards were much lower than in adjacent riparian vegetation (10%or less of riparian catches). During the fall, selected plants were removed from treatment plots by cooperating growers using California Conservation Corps work crews. Replantings and buffer strip plantings were made during February-March. Additional plantings to replace trees that died will be made after September, 1996, depending on rainfall. As expected, trap catches of BGSS were drastically reduced in plots where riparian vegetation was removed. Two additional experimental sites should be added in 1996. Approval from California Dept. Of Fish and Game for these experiments was given for a Napa River site. Permission will be sought to establish a Sonoma County site on Maacama Creek if BGSS activity proves to be sufficient based on our sampling of BGSS populations. Future replications of this experiment on other sites will give more realistic short term estimates of the effectiveness of the vegetation management approach because not as many large trees will be removed. A mix of University and AVF funding is planned to support this complex, multi-year project. This year funding (>$20,000/year) for 2 or 3 years shared funding has been awarded through a competitive grant from the California Department of Pesticide Regulation.