Citrus handout #1
Citrus canker
Dr. Mongi Zekri
Multi-County Citrus Extension Agent
University of Florida, IFAS
Phone: 863 674 4092
Citrus canker, caused by a bacterial pathogen Xanthomonas axonopodis, is a serious disease
of most citrus varieties. The disease causes necrotic lesions
on leaves, stems, and fruit. Severe infestation can cause
defoliation, premature fruit drop, twig dieback, general tree
decline, and very bad blemishes on fruit. The earliest
symptoms on leaves appear as slightly raised tiny blister-like
lesions. As the lesions age, they turn tan to brown and water
soaked margin appears surrounded by a yellow halo. The
center of the lesion becomes raised and corky. Lesions are
usually visible on both sides of the leaf. Defoliation becomes
a problem as the disease intensifies on the tree. Symptoms of
bacterial citrus canker on twigs and fruit are similar and
consisted of raised corky lesions surrounded by an oily or
water-soaked margin. As the lesions on the fruit mature, they
appear scablike or corky. The lesions on the leaves sometimes
fall out, leaving round holes.
Citrus canker was first introduced in Florida in 1910 through
citrus trees coming from Japan. It was eradicated in 1927.
In June 1986, citrus canker was detected in residential citrus
in Hillsborough, Pinellas, Sarasota and Manatee counties and was also found in commercial
citrus groves in Manatee County. This second eradication program concluded with the last
detection in January 1992. The official declaration of eradication was made 2 years later.
In late September 1995, citrus canker was discovered for the third time in Florida in a residential area
near Miami International Airport. Even with an extensive eradication effort, the disease has spread
northward from Dade into Broward County. In May 1997, citrus canker was rediscovered in
Manatee County in both commercial groves and residential areas. In June 1998, citrus canker was
discovered in a commercial grove in Collier County and in February 1999, it was found in a
commercial grove in Hendry County. In November 1999, canker was detected in residential areas in
Hillsborough and Palm Beach counties. In September and October 2001, citrus canker was found in
commercial groves in Martin and DeSoto counties, respectively. In January 2002, citrus canker was
found in a residential area in Brevard County and in May 2002, it was found in a commercial grove
in Highlands County. In July 2002, it was found in a residential area in Orange County and in
August 2002, it was found in a residential area in Lee County. In October 2004, it was found in a
commercial grove and a residential area in Charlotte County. In August 2005, it was found in Glades
County.
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Through the eradication program, about one million citrus trees have been destroyed in
residential areas and about 12 million trees have been destroyed in commercial nurseries and
groves. Although eradication efforts have been very extensive to eradicate the disease in
Florida from 1995 through 2005, citrus canker kept spreading due to many things including
the 2004 and 2005 hurricanes.
Citrus canker is highly contagious and can be spread rapidly by wind-driven rain, unusual
storm events such as tornadoes and tropical storms, flooding, equipment, insects, and human
movement within groves. Overhead irrigation may also play a role in spreading the bacteria.
Movement of infected or exposed trees, seedlings,
propagative material, and fruit is the primary means of
spreading the canker pathogen over long distances.
Contaminated clothing, tools, ladders, containers and fruit
boxes, and other items associated with harvesting and
postharvest handling of fruit are also potential sources of
infection.
Citrus canker is most severe on grapefruit, Key limes,
trifoliate orange and their hybrids. Calamondin, kumquat,
and citron are considered resistant. To reduce the spread
of citrus canker, it is essential that equipment and
personnel working near or contacting any citrus material
be decontaminated with an approved chemical such as
quaternary ammonium. To the present time,
there is no cure for citrus canker. However, the following
practices can reduce canker spread and severity:
●Frequent inspection
●Removal of diseased trees
●Selective elimination of infected leaves and branches
●Removal of exposed trees, chemical defoliation or buckhorning of exposed trees
●Copper sprays
●Windbreaks are necessary for susceptible varieties and essential for fresh fruit
production
●Leafminer control with systemic insecticides, spray oils and/or other insecticides,
especially on young trees (up to 4 years)
Sanitation is very important. Quaternary ammonium disinfectants are available for use on
equipment, clothing, and even bare skin.
For more information on citrus canker visit these Web Sites
http://doacs.state.fl.us/canker
http://doacs.state.fl.us/~pi/canker/index.htm
http://www.aphis.usda.gov/lpa/issues/ccanker/citruscanker.html
http://edis.ifas.ufl.edu//pdffiles/PP/PP11600.pdf
http://edis.ifas.ufl.edu/CG040
http://www.biotech.ufl.edu/PlantContainment/canker.htm
http://www.imok.ufl.edu/plant/diseases/cankerid.htm
