Statewide Citrus Research and Extension

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Florida lobortis vel | Brochure

Overview

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Canker was first introduced in Florida around 1912 from imported seedlings from Japan and was declared eradicated in 1933
Second discovery in Florida in Manatee County (1986) and thought to be eradicated in 1994
Third introduction in Florida in urban Miami in 1995
Canker spread from Miami in 1995 to twenty-five counties throughout central and south Florida today
A statewide mandatory eradication with the 1,900-foot (579m) rule was implemented in 2000 after determining the original 125-foot (38.1m) rule was not effective
Quarantine areas were established when citrus canker was detected, and decontamination was required upon entering and exiting within those areas
Mandatory statewide decontamination procedures became required in April 2000
By March 2002, over 1.56 million commercial trees and almost 600,000 infected and exposed dooryard trees were removed or cut back
Tree removal of infected and exposed trees was delayed due to lawsuits in 2002 by homeowners in Broward County
The hurricanes of 2004-2005 increased the spread of canker
The first nursery with canker was found in May 2005
The mandatory eradication ended January 11, 2006. The impact of the eradication program was an excess of 5 million nursery trees were destroyed, an excess of 11 million residential and commercial citrus trees were destroyed, and 100% of the Division of Plant Industry Dundee Budwood Foundation was lost.
Currently, the removal of infected trees is voluntary
Decontamination procedures are still in effect statewide to prevent the spread of canker
The state of Florida is under quarantine, and the movement of citrus fruit is prohibited to any citrus producing region

Citrus Canker is caused by Xanthomonas citri citri
- Gram-negative bacterium (Gm-)
Small (cannot be seen by the naked eye)
Size and shape: 1 by 3 microns, rod, covered with slime, single polar flagellum
Reproduction: divide every 20-30 minutes at optimum temperatures (28°-30°C/82.4°-86°F) . In 6 to 8 hours, the population can reach 1 million cells
Have a flagellum (a tail-like structure used for movement)
Survive in moist conditions; when they dry, they die
Must have a host to survive in the natural environment

Citrus canker is highly contagious
Citrus canker is NOT harmful to humans or animals
Can be spread by natural means (uncontrollable) and by humans (controllable)
Natural spread by wind-driven rain, overhead irrigation, flooding, incidental spread by insects and birds, animals
Human spread responsible for moving canker over long distances around state
Human transport of infected/exposed plant material is primary means of spreading the canker pathogen over long distance

Symptoms appear on fruit, leaves and twigs
Causes necrotic lesions

Leaf Symptoms

Small, round (often raised) blister-like lesions with water-soaked margins and yellow
halos; lesions often appear on both sides of leaf surface
Heavy or severe infection causes defoliation
Raised lesions on fruit (oranges & grapefruit) create a water-soaked margin with
yellow halo
Fruit drop

Twig Symptoms

Twig lesions are similar in appearance to fruit lesions; lesions on stems cause recurring infection

Decontamination

Decontamination has been found to be effective for preventing the spread of citrus canker by human activity
Decontamination solutions kill the bacteria; therefore, reduces the spread of the bacteria
Decontaminant solutions are like a mild antibacterial soap for personnel
Equipment solutions are quaternary ammonia and should not contact skin or fruit
Decontamination is required by law upon exiting a citrus grove, but most growers require personnel and equipment to be decontaminated upon entering and exiting
It is required by the Citrus Health Response Program that employees have annual decontamination training and growers provide adequate quantities of approved decontaminant solutions that are premixed and maintained at appropriate dilutions

Tree Removal

Tree removal is voluntary and is no longer enforced by the state of Florida.
In areas previously free of canker, the removal of infected citrus trees is recommended to slow disease establishment

Defoliation and Pruning

Defoliants can reduce the inoculum levels in severely affected groves, but there are no approved defoliants for citrus. High rates of legal copper fungicides or fertilizers can be used.
Pruning is generally ineffective to control canker and should only be done under dry conditions in a selective manner.
Pruning can cause wounds that allow the bacterium to enter the tree

Windbreaks

Windbreaks have been proven to slow wind to below 18 mph (8 m/s) and to be highly effective in reducing the spread and severity of citrus canker.
They are more effective than copper alone as was demonstrated by Gottwald and Timmer (1995).

Copper Sprays

Copper is the only registered product for the prevention of citrus canker.
Use rates indicated on the label

Leafminer control

Leafminer galleries create wounds that allow the bacterium to enter the leaf and cause many times more infections than without leafminer.

Ozgur Batuman
Associate Professor, Citrus Pathology
239-658-3408
obatuman@ufl.edu

Megan Dewdney
Professor, Extension Specialist
863-956-8651
mmdewdney@ufl.edu

Nian Wang
Professor
863-956-8828
nianwang@ufl.edu