Ornamental Plants as Hosts of the Blue-Green Sharpshooter and Xylella fastidiosa

Ornamental plants within landscapes around wineries and residential areas of Napa Valley near vineyards with incidence of Pierce’s disease were monitored for the presence of the blue-green sharpshooter (BGSS) for two consecutive years. A list of the most commonly used plant species was established and the important hosts for BGSS were identified from the list . For this study, the presence BGSS was determined by using yellow sticky traps while sweep net sampling was used to detect the BGSS within the plant canopy. We found that on the plants that were sampled around wineries, five out of 35 plant species sampled had adults or nymphs of blue-green sharpshooters (BGSS). Liquidambar and basil were found to be breeding host, while rose, butterfly bush, and xylosma were found to be feeding hosts. Twelve plants within residential landscapes were recognized as hosts for the BGSS. The breeding hosts were oak leaf hydrangea, bush sage, liquidambar, and Japanese snowball. Feeding hosts are rose, butterfly bush, oak leaf hydrangea, crape myrtle, bush sage, lilac, African lily, liquidambar, myrtle, Japanese snowball, xylosma, and dogwood. In late May, 1999, mock orange {Philadelphus sp.) and Spirea sp. were determined to be breeding hosts. Plants found to be breeding hosts as well as other plant species from the list of common plants will be used to determine important hosts of the Pierce’s disease bacterium, Xylella fastidiosa (Xf). Plants will be inoculated with either infected BGSS or by using the needle inoculation technique. Basil, one of the identified breeding hosts, was inoculated using infected BGSS and found to not be a host of ^/”according to culture plate isolation. Rose, the most commonly planted ornamental in the study, is currently being evaluated as ^/”host after needle inoculation. Analysis of plant abundance are being determined using measurements of plant coverage along a transect. Transects were made at 20 foot intervals. This survey will allow us to establish a correlation between cover-abundance of landscape species and the activity of BGSS. In conclusion, landscapes have been determined to be important habitats for the BGSS. Residential landscapes appeared to harbor higher BGSS populations than landscapes surrounding wineries. In general, partly shaded landscapes with lush plants are more suitable for the BGSS. During the spring when the weather is cooler, BGSS adults and nymphs can be found on plants in full sun, however. Finally, while a large number of ornamentals were determined to be feeding hosts for the BGSS, fewer plants were found to be breeding hosts.