Photographer: Jonas Janner Hamann Affiliation: Universidade Federal de Santa Maria, Bugwood.org Copyright: (CC BY 3.0)
Photographers: Florida Division of Plant Industry Affiliation: FL Dept. of Ag. and Consumer Services, Bugwood.org Copyright: (CC BY 3.0)
This bacterium is known to create lesions on leaves, stems, and fruit; all of which are aboveground parts of the Citrus host plant. Leaf Lesions: Will have concentric circles on leaf underside. Yellow halo will surround the lesion and become dark brown/black. Lesion midpoint becomes corky with a volcano-like point and the lesions will eventually penetrate both sides of the leaf. Fruit Lesions: Also consist of concentric circles that have a yellow halo surrounding the lesion that becomes dark brown/black. However, the halo will be hard to see on ripened fruit. Lesion midpoint becomes corky with a volcano-like point, and the center of the lesion may crack to show a crusty “brown sugar” looking material inside.
While the bacterium does not pose a threat to human or animal health it makes fruit unmarketable because it covers them in unsightly cankers. It poses a significant risk to commercial production because it can spread easily through wind, rains, infected soil and can be spread by re-using contaminated pruning tools or boots with infected soil present.
Unlike Citrus Greening (Huanglongbing) this bacterium is not spread by insects but from contaminated soil, equipment, and infected plant parts or fruits. Unfortunately, wind and rain can also spread this disease which is what led it to be impossible to eradicate in Florida. This is why it is vitally important to adhere to Citrus Canker quarantines within Texas, report any signs of infection, destroy any infected trees on your property and clean any equipment that comes into contact with an infected tree.
It was first found in Florida back in 1910 and was considered eradicated by 1933 but unfortunately it returned in 1995. Hurricanes and large storms quickly spread the disease which made eradication impossible by 2006. A similar history exists for Texas in which the disease was found and eradicated within the state by 1947. Subsequently, the disease was reported in lemon and lime trees in Cameron County back in 2015. Then in 2016 it was found in residential areas in the cities of Houston and Richmond. From 2016-2022 more positive locations were found in similar areas within Brazoria, Fort Bend, Galveston, and Harris Counties. The spread of this disease within residential Citrus plants led to a quarantine issued within those four counties by the USDA-APHIS and the Texas Department of Agriculture (TDA) on February 2, 2022.
The most severe strain of this bacteria is from southeast Asia. Strains can be identified by molecular tests and host range.
Habitat: Citrus Canker thrives in warm, moist conditions with disease development being optimal from 68-86o F, but cold winters will not cause the disease to stop. Grapefruits and Lemons are most susceptible to Citrus Canker, but Mandarins, Kumquats and Tangerines show significant resistance to infection. If you have a tree suffering from this bacterium it will persist, but it will quickly die on inanimate objects (tools, tarps, etc.) within 72 hrs.
U.S. Present: AL, FL, LA, SC & TX (2015)
Citrus Canker can be confused with other citrus issues and diseases.
Symptoms on the fruit can be confused for Alternaria, Citrus Scab and Leprosis. However, it is important to note on those diseases the cankers do not have concentric circles or are not raised and/or there are no halos present. With Alernaria, it is found on tangerines and Citrus Canker is most infective on grapefruits and lemons, very rarely on tangerines.
Symptoms on the leaves can be confused with Citrus Bacterial Spot, Citrus Scab, Greasy Spot, and Leprosis. However, with Bacterial and Greasy Spots and Leprosis the lesions are flat and never raised; and Citrus Scab produces pustules that are cone-shaped without concentric circles or halos.
There is no cure for this bacterial disease, so it is very important to practice preventative measures and adhere to quarantines to stop the disease from spreading farther throughout the state.
DO NOT transport sickly Citrus trees, stems, leaves, fruit, or the soil the trees were residing in; in fact, Texas Dept of Ag. (TDA) regulations require the destruction and disposal of the infected tree. Proper procedure would be to cutdown the infected tree and burn it on site or bag all parts of the tree and directly transport it to a landfill where it should be buried at least 2 feet deep. Once the infected tree is removed the bacterium does not last long in the soil, but you should ensure all roots, leaves and fruit that could be buried within the soil are removed; leaving any remnants of the infected tree can allow Citrus Canker to persist in the soil.
Preventative: Use good sanitation practices to reduce potential disease spread. Practice general cleanliness and use alcohol-based sanitizers, bleach solution, and antibacterial soap solutions to decontaminate equipment and tools and reduce the risks associated with human and mechanical transmission of the disease.
Chemical: Plant protection chemicals that contain copper can help prevent infection. These products reduce risks but do not stop the disease from occurring or cure infected trees. New growth areas on Citrus plants are most vulnerable to infection. Applying these products as soon is possible is needed to help with protection, and multiple applications might be necessary. Always read all directions and labels before using any chemical control.
REPORT IT: If you suspect that a citrus plant has citrus canker, report the tree to TISI through invasives@shsu.edu with a picture and location information for future sampling. TISI currently has funding to provide these services with no cost to the citizen. We also encourage you to contact TDA at (800) 835-5832 or online at http://www.citrusalert.com/report-a-tree for further assistance.
Text References
Dewdney, M.M., P.D. Roberts, J.H. Graham, K.R. Chung, and M. Zekri. 2013. Homeowner Fact Sheet: Citrus Canker University of Florida, Institute of Food and Agricultural Sciences Extension. Electronic Data Information Source Publication #PP194.
Gochez, A.M., Behlau, F., Singh, R., Ong, K., Whilby, L. and Jones, J.B., 2020. Panorama of citrus canker in the United States. Tropical Plant Pathology, 45(3), pp.192-199.
Perez, E., Kunta, M., Ancona, V., da Graça, J.V., Ayin, C., Santillana, G. and Mavrodieva, V., 2021. The Return of Asiatic Citrus Canker to Texas: Surveys and Eradication Efforts. Plant Health Progress, 22(2), pp.143-148.
Polek, M., G. Vidalakis, and K. Godfrey. 2007. Citrus Bacterial Canker Disease and Huanglongbing (Citrus Greening). University of California, Division of Agriculture and Natural Resources. Publication 8218.
Schubert, T.S., Rizvi, S.A., Sun, X., Gottwald, T.R., Graham, J.H. and Dixon, W.N., 2001. Meeting the challenge of eradicating citrus canker in Florida—again. Plant disease, 85(4), pp.340-356.
Internet Sources
https://agrilifeextension.tamu.edu/library/gardening/citrus-canker/
https://www.citrusalert.com/report-a-tree/
https://idtools.org/id/citrus/diseases/
https://www.aphis.usda.gov/plant_health/plant_pest_info/citrus/citrus-downloads/spro/da-2022-03.pdf
https://edis.ifas.ufl.edu/publication/PP116
https://www.invasivespeciesinfo.gov/terrestrial/pathogens-and-diseases/citrus-canker
https://www.pesttracker.org/map?code=FDZAXAN
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