Addition of Homalodisca coagulata to the EPPO Alert List
The xylem-limited bacterium Xylella fastidiosa (EPPO A1 quarantine pest) can cause different diseases on various host plants (e.g. alfalfa dwarf, grapevine Pierce's disease, citrus variegated chlorosis, peach phony disease, almond leaf scorch, plum leaf scald, oleander leaf scorch, leaf scorch on several forest tree species) and is transmitted by insect vectors. All sucking insects feeding on xylem sap may be potential vectors. In California (US), the recent establishment of Homalodisca coagulata (glassy-winged sharpshooter) resulted in an increase of grapevine Pierce's disease incidence and is perceived as a threat to the whole Californian grapevine industry and also to other plants such as alfalfa, almond, peach, plum and oleander. Until the introduction and establishment of H. coagulata in California, the most important vectors of grapevine Pierce's disease were Graphocephala atropunctata (blue-green sharpshooter), Draeculacephala minerva (green sharpshooter) and Carneocephala fulgida (red-headed sharpshooter). All three species are listed as quarantine pests in the EU Annexes. The EPPO Panel on Phytosanitary Measures considered that H. coagulata, as an efficient vector of X. fastidiosa, could present a risk to the EPPO region and therefore should be added to the EPPO Alert List
Homolodisca coagulata (Homoptera: Cicadellidae) – vector of Xylella fastidiosa
Why: In California (US), the recent establishment of Homalodisca coagulata (glassy-winged sharpshooter) resulted in an increase of incidence of grapevine Pierce's disease (caused by Xylella fastidiosa) and is perceived as a threat to the whole Californian grapevine industry and also to other plants such as alfalfa, almond, peach, plum and oleander. As H. coagulata seems to present a greater risk to the EPPO region than the listed vectors of X. fastidiosa, with respect to both grapevine and citrus, the EPPO Panel on Phytosanitary Measures felt that it should be added to the EPPO Alert List.
Where: Mexico (north, except in very arid areas), USA (southern states: Alabama, Arkansas, Florida, Louisiana, Mississippi, North Carolina, South Carolina, Texas). Recently established in southern California but it is expected that it will continue to spread towards the north. H. coagulata is thought to have been introduced from other parts of USA, most probably as egg masses on plant material. Since the early 1990s, H. coagulata has been seen in high numbers in citrus groves along the coast of southern California but until 1994 it was confused with a similar species Homalodisca lacerta.
On which plants: It has a very broad host range. It has been found on more than 70 plant species in 35 families including: avocado, citrus, macadamia, and many woody ornamentals (e.g. Fraxinus, Lagerstroemia, Rhus). A list of host plants can be viewed on Internet (California Department of Food and Agriculture).
Damage: Adults are 13-14 mm long, dark brown with small yellow dots on head and thorax. Membranous, translucent wings with reddish veins. Insects overwinter as adults and begin laying egg masses (10-12 eggs) in late February through May. Adults of this first generation appear in late May through late August. Second-generation egg masses are laid from mid-June though late September. H. coagulata feeds on stems rather than leaves, and excretes copious amounts of watery excrement.
In California, H. coagulata is an efficient vector of X. fastidiosa to grapevine, almond, and oleander. In southeastern USA, H. coagulata is considered as the most efficient vector of peach phony and plum leaf scald. The strain of X. fastidiosa causing citrus variegated chlorosis does not occur in California. While H. coagulata is not positively mentioned as a vector of this strain, it occurs abundantly on citrus and seems likely to facilitate spread of the citrus disease if it were ever introduced into California. Following the establishment of H. coagulata in California, an outbreak of grapevine Pierce's disease occurred in the Temecula Valley of Southern California. The outbreak started in 1997. In 1998, symptoms were visible in a few localized areas but when tests were done they revealed a disease incidence of 25% to 97% in vineyards. It is estimated that during the last 3 growing seasons, the disease has killed more than 120 ha of vineyards in the Temecula Valley and that it threatens the whole Californian grapevine industry. Phytosanitary measures are being taken in California to prevent the spread of H. coagulata.
Pathway: H. coagulata could be introduced via its many host plants into the EPPO region. Plants for plantings, cut flowers and branches, fruits?
Possible risks: X. fastidiosa does not occurs in Europe but it represents a very serious threat essentially to grapevine and citrus crops, but also to other host plants such as deciduous forest and amenity trees and oleander. Measures are already taken to present the entry of X. fastidiosa but it is also very important to prevent the entry of efficient vectors such as H. coagulata.
EPPO RS 2002/013
Panel review date - Entry date 2002-01
Sources
Blua, M.J.; Redak, R.A.; Morgan, J.W.; Costa, H.S. (2001) Seasonal flight activity of two Homalodisca species (Homoptera: Cicadellidae) that spread Xylella fastidiosa in Southern California. Journal of Economic Entomology, 94(6), 1506-1510.
Gould, A.B.; French, W.J.; Aldrich, J.H.; Brodbeck, B.V.; Mizell, R.F. III; Andersen, P.C. (1991) Rootstock influence on occurrence of Homalodisca coagulata, peach xylem fluid amino acids, and concentrations of Xylella fastidiosa. Plant Disease, 75(8), 767-770.
Purcell, A.H.; Saunders, S.R. (1999) Glassy-winged sharpshooters expected to increase plant disease. California Agriculture, 53(2), 26-27 (abst.).
Purcell, A.H.; Saunders, S.R.; Hendson, M. Grebus, M.E.; Henry M.J. (1999) Causal role of Xylella fastidiosa in oleander leaf scorch disease. Phytopathology, 89(1), 53-58.
INTERNET
Xylella Web Site. http://www.cnr.berkeley.edu/xylella/
California Department of Food and Agriculture.
Pierce disease control programme and list of host plants of H. coagulata. http://pi.cdfa.ca.gov/pqm/manual/454.htm
GWSS/PD Home page. http://plant.cdfa.ca.gov/gwss/gwpics.htm
University of California. Agriculture and Natural Resources. Report of the Pierce's Disease research and emergency response task force. http://danr.ucop.edu/news/speeches/glassywinged.html
California Farm Bureau Federation. Glassy-winged sharpshooter news and information service. http://www.cfbf.com/issues/gwss/