Occurrence of Xyllela Fastidiosa and Its Vector, Glassy-Winged Sharpshooter, In Selected Alabama Orchards

A study to determine the occurrence of Xylella fastidiosa in five commercially grown fruit crops in Alabama and identify the vector species was initiated in 2008. Tissue samples from peach, plum, satsuma mandarin, muscadine grape and bunch grape were collected three times during the growing season. Sampling sites included commercial orchards in the Gulf Coast, Central, and North Alabama. An ELISA test was conducted to detect the presence of X. fastidiosa. Plum groves showed the highest incidence of X. fastidiosa when compared to the other crops in our study. At the end of the season (30 September), 100% of plum samples collected from the Gulf Coast and Central Alabama sites tested positive for the bacterium, whereas only 10% of the plum samples collected from the North Alabama site tested positive. Sharpshooter vector populations were monitored on a bi-weekly basis during the growing season. Four vector species were collected and shown to consist of Homalodisca vitripennis, H. insolita, Oncometopia orbona, and Graphocephala versuata. H. vitripennis appeared to be the most prevalent species. Peak trap capture of sharpshooters (98/trap) was observed on 16 June in the Gulf Coast location and on 30 July (20/trap) in Central Alabama. However, very few sharpshooters were captured at the North Alabama site with a peak trap capture of 1.5/trap on 30 July. As indicated by previous studies, sharpshooter populations and incidence of X. fastidiosa induced diseases in various fruit crops are likely restricted to warmer locations.