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Last Update 06/03/08

Florida Citrus Canker

What it is and what you can do to stop it...

Citrus Canker

Citrus Canker Lesions

Of all of the agricultural pests and diseases that threaten citrus crops, citrus canker may be one of the most devastating.

Citrus canker is a highly contagious disease caused by the bacterium Xanthomonas axonopodis pathovar citri. An infestation can destroy entire crops, but the disease poses no health risk to humans or animals.

Severe infection may produce a variety of effects, including defoliation, dieback, severely blemished fruit, reduced fruit quality, and premature fruit drop.

Appearance and Strains

Citrus canker symptoms appear on the fruit, leaves, and twigs of infected plants, and typically consist of small, round, blister-like formations called lesions. Lesions usually become apparent about 7 to 14 days after infection. As the lesions mature, the epidermis or outer layer of tissue ruptures, producing a craterlike spot lined with tan-colored tissue that is usually surrounded by an oily, water-soaked margin and a yellow ring that looks like a halo. On fruit, the lesions appear scab-like or corky. On leaves, old lesions sometimes fall out, leaving behind a scattering of round holes.

There are at least three distinct strains or types of citrus canker, as determined by serological tests and DNA analysis. The "A" strain affects members of the plant family Rutaceae, including most citrus species and hybrids, especially grapefruit, lime, sweet lime, and trifoliate orange. The "B" strain of citrus canker affects lemons in Argentina, Uruguay, and Paraguay. However, Mexican or key lime, sour orange, Rangpur lime, sweet lime, citron, and occasionally sweet orange and mandarin orange can also be affected. The "C" strain affects only Mexican lime growing in Brazil. Other, unrecognized strains may also exist. The current and all previous U.S. infestations have been associated with the "A" strain.


Like most bacterial plant diseases, citrus canker is greatly influenced by temperature and moisture conditions. The disease is most likely to develop when heavy rains occur during a period when the mean temperature is greater than 68 degrees F. (20 degrees C.).


Citrus canker spreads swiftly over short distances by wind driven rain, flooding, air currents, insects, birds, and human movement within groves. Overhead irrigation may also play a role in spreading the bacteria.

Movement of infected plants, seedlings, propagative material, and fruit is the primary means of spreading the canker pathogen over larger distances. Contaminated clothing, tools, packing boxes, and other items associated with harvesting and post harvest handling of fruit are also potential sources of infection.

Canker bacteria survive and multiply primarily in naturally occurring lesions. Bacteria may also survive in crevices in the bark tissues of citrus trees. Bacterial populations appear to decline rapidly in soil. It has been suggested that the bacterium may survive at low population levels on citrus hosts without symptoms developing, and it may also survive for short periods of time on some weeds and grasses. Neither of these survival mechanisms has been proven, however.

Citrus inspector's tag -- Front. Yes, a FloridaGardener citrus tree is being monitored.

Citrus inspector's tag -- Back. This tree is about 7 miles from infected trees found in Wellington, FL.

Identification and Control

When an area is suspected of being infested with citrus canker, fruit or leaf samples are sent for testing by State and Federal laboratories.

In countries where citrus canker is an established, ongoing problem, control of the disease is primarily achieved through a combination of tactics, including the production and use of disease-resistant plant varieties, use of protective sprays, and phytosanitary measures (use of certified nursery stock). Outbreaks of citrus canker may also be reduced when windbreaks are constructed in windy areas.

When environmental conditions are favorable for the spread of the disease, chemical control measures are not entirely effective. However, materials containing copper (bordeaux mixture, copper hydroxide, basic copper chloride, copper oxychloride, and tribasic copper sulfate) are the most effective bacterial sprays for protecting leaves and fruit. These materials can reduce the incidence of disease, but they will not eliminate established infections. Extensive use of copper may also cause phytotoxicity problems in treated groves.

Pruning infected shoots or plant parts during late summer and autumn can reduce the risk of infection the following spring. Defoliation of canker-affected trees can also further reduce infection risk.

In the United States, quarantining areas affected by citrus canker is still practical. Eradication of infected and adjacent trees is the most effective means of protecting commercial citrus from the disease. Once positively identified, diseased trees in commercial groves are uprooted, placed in a pile, and burned. Surrounding, disease-free trees are destroyed as well, as an added precaution. In residential areas, diseased trees and surrounding, exposed trees are cut down or removed.

Areas where trees have been destroyed must be kept free of citrus sprouts and seedlings. Movement of citrus fruit budwood and other plant parts is prohibited from property on or adjacent to sites where infected plants are located. All clothing, tools, and equipment used in infested areas must be properly disinfected.

For More Information

If you have questions about citrus canker, call the central office of APHIS' Plant Protection and Quarantine (PPQ) unit at (301) 734-8645, or contact the nearest regional office of PPQ:
Central Region (210) 548-2750
Northeastern Region (609) 757-5070
Southeastern Region (601) 863-1813
Western Region (916) 857-6241
Source: USDA Animal and Plant Health Inspection Service (APHIS)
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