A Severe Outbreak of Fire Blight in Woody Ornamental Rosaceae Plants in North Florida and South Georgia

Woody ornamentals including ‘Bradford’ and ‘Aristocrat’ pears (Pyrus calleryana), Indian hawthorn (Rhaphiolepis sp.), and cotoneaster (Cotoneaster spp.) developed blossom and shoot blight symptoms suggestive of fire blight caused by Erwinia amylovora. Disease was observed in several counties in north Florida and south Georgia and samples were sent to Florida Extension Plant Diagnostic Clinic-Quincy (FEPDC-Q). The incidences in individual ‘Bradford’ pear were as high as 30 to 40 strikes per tree. This level of severe E. amylovora infections on ‘Bradford’ pear has not been seen in Florida for the last 10 years based on FEPDC-Q data. Symptomatic plants first appeared in the landscape and nurseries around the first week of April 2000 in the following counties: Bay, Holmes, Washington, Gadsden, Leon, Jefferson (north Florida), and Decatur (south Georgia). Severely infected ‘Bradford’ pear trees were also observed in Georgia cities of Cairo, Thomasville, Moultrie, and Tifton. The presence of E. amylovora in samples was verified by pEA29-polymerase chain reaction (PCR) (2,4), fatty acid methyl ester analysis (MIDI, Newark, DE), and colony type on semi-selective modified Miller-Schroth (MMS) medium (3). Of the 16 samples tested by PCR, E. amylovora was present in all. Actively growing shoots of Cotoneaster salicifolius (a susceptible host) were inoculated with a bacterium isolated from ‘Bradford’ pears that was identified as E. amylovora by PCR. Dark brown necrotic tissues with typical fire blight appearance developed within 10 days. E. amylovora was reisolated on MMS medium from inoculated shoot tissues of C. salicifolius and confirmed by PCR. The presence of E. amylovora from ornamental pears, Indian hawthorn, and cotoneasters was previously reported in Florida (1). Cool spring temperatures in the Florida panhandle and several rain events during the bloom period may have stimulated the severe outbreak of fire blight. This severe outbreak highlights the importance of using a forecasting model such as Maryblyt 4.3 to predict unexpected infection periods so that preventive control measures can be taken. References: (1) S. A. Alfieri, Jr. et al. Florida Department of Agriculture and Consumer Services, Bulletin No. 14, 1994. (2) S. Bereswill et al. Appl. Environ. Microbiol. 58:3522, 1992. (3) W. Brulez and W. Zeller. Acta Hortic. 117:37, 1981. (4) M. T. Momol et al. Plant Dis. 82:646, 1998.