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2008 West Central Florida Xylella Survey
 

By: Gary K. England, Sumter County Extension, Bushnell, FL, Dr. Phil F. Harmon, UF Plant Pathology Department, Gainesville, FL and Dr. J. Stacy Strickland, Hernando County Extension, Brooksville, FL

The acreage of blueberries harvested in Florida has increased from 1000 to 2,500 between 1993 and 2005 (Pollack and Perez, 2005).  In 2005, the value of the Florida blueberry crop was $32,760,000 or 8.6% of the figure for the entire United States, ranking the state 7^th in the nation in income from this crop (Florida Department of Agriculture and Consumer Services, 2007).  New plantings of this important crop continue in several key production regions. 

With the expansion of the blueberry industry in Florida over the past 15 years, there has been an increase in plant pathogens and other pest organisms found attacking the crop.  One plant disease that has been observed in cultivated blueberries (especially in the cultivars 'V1' and 'Star') in Georgia is bacterial leaf scorch (BLS) caused by the bacterium Xylella fastidiosa.  According to (Brannen et al., 2007), BLS has the potential to become a major threat to southern highbush blueberry production in Georgia and elsewhere.  The bacterium is believed to be spread from infected plants to others by insect vectors such as sharpshooters and spittlebugs. 

The initial symptom observed in susceptible plants infected with X.  fastidiosa is a marginal leaf scorch (burn) similar to drought stress or fertilizer burn (Brannen et al., 2007).  In the spring infected plants will have very thin twigs which will drop their leaves and take on a characteristic yellow appearance before eventually dying. 

Cultural controls such as roguing infected plant material, insuring clean propagation stock and maintaining optimum fertility and moisture levels in plantings known to have BLS present are recommended to combat this serious pest (Brannen et al., 2007).  Use of insecticides during periods of high populations of the disease vector may also assist in reducing BLS occurrence. 

Florida Situation

X. fastidiosa has been isolated from southern highbush blueberry plantings in Florida.  Since this pest has the potential to be of concern to Florida blueberry producers, Dr. Phil Harmon from the UF Plant Pathology department has been conducting surveys to determine if X.  fastidiosa and bacterial leaf scorch symptoms are present in the major blueberry production regions in Florida. 

In October, 2008 a survey of farms in the west central Florida blueberry production region to determine if X. fastidiosa was present was conducted in commercial blueberry plantings.  In the surveys, plants exhibiting symptoms similar to those of BLS were sampled.  The blueberry cultivar 'Star' was examined closely, since it was known to be severely affected by BLS in Georgia.  In the survey, seven cultivars were sampled from six different blueberry farms in Citrus, Hernando and Pasco Counties.  ELISA tests were utilized to determine if X. fastidiosa was present in the sample. 

After analysis with ELISA, 9 of 17 samples collected showed the presence of X. Fastidiosa (Table 1).  Only 2 of 7 samples of 'Star' were positive, while 4 of 4 samples from 'Windsor' were positive.  Other cultivars that had at least one sample test positive for X. fastidiosa were 'Emerald', 'Millenia' and 'Springwide'.  These data indicate the need for further surveys to determine the distribution of X. fastidiosa in the major blueberry production regions and cultivars which commonly serve as its host. 

'Star' is the only cultivar in this survey that is known to be severely affected by BLS.  It should be determined which cultivars will exhibit severe symptoms of BLS when infected with X. fastidiosa.  It is possible that some cultivars could tolerate an X. fastidiosa infection better than others.  This could become important information for future cultivar recommendations. 

Table1. Xylella fastidiosa presence in samples from 6 farms sampled in west central Florida.

References

Brannen, P.M., G. Krewer, B. Boland, D. Horton and C.J. Chang. 2007. Bacterial Leaf Scorch of Blueberry. Southern Region Small Fruit Consortium Website. 8pp.

Florida Department of Agriculture and Consumer Services. 2007. Florida Agriculture Statistical Directory. 151pp.

Pollack, S.L., and A.C. Perez. 2007. Fruit and Tree Nuts Situation and Outlook Yearbook 2007. United States Department of Agriculture. FTS-2007. 200pp.