Cankers on Orange Trees

Features

• Citrus canker, also called bacterial canker, affects grapefruit, lemon, lime and orange trees, entering through wounds and natural openings called stomata. Rain, overhead watering and flooding can spread the canker from one tree to another. People can also spread the disease on hands, tools and clothing. Symptoms appear on leaves, where they take the form of blister-like brownish lesions with oily margins; on fruit, where they resemble crusty scabs and are often haloed with yellow; and on branches, where they resemble gray bumps. The distinctive raised appearance of the lesions can help to distinguish them from damage caused by hail and cold temperatures, and can help to confirm a diagnosis of citrus canker. In addition to causing fruits to fall prematurely, severe infestations can cause tree defoliation. Mature fruit that have managed to remain on the tree are disfigured but still edible.

History

• Citrus canker first surfaced in the United States on the Gulf Coast in the early 1900s; it was declared eradicated in 1933. A later outbreak in 1986 in Tampa Bay was declared eradicated in 1994. In 1995, it resurfaced yet again on residential citrus trees in Miami-Dade County. In 2004 and 2005, hurricanes spread the disease to 25 different counties in Florida, where it is active today. By January 2006, the disease had became so widespread that eradication efforts were abandoned; the citrus industry now focuses on managing the disease.

Control

• If you have an orange tree infected with citrus canker, you should wash your hands with soap and water for at least 20 seconds, use an alcohol-based hand sanitizer and change your clothes before handling other citrus trees. You should also disinfect pruning tools after use with a solution of 1 ounce of household bleach to 1 gallon of water. The University of Florida Extension reports that citrus canker can be managed with copper-containing products, used at three-week intervals during the months of April through October. Consult your county extension office for guidance. Do not mail samples to county extension offices; ask an agent to visit you.

Prevention

• To help prevent the spread of citrus canker, don't attempt to propagate your own trees or to transport citrus plants, or parts of citrus plants, out of Florida. Buy orange trees only from certified nurseries. University of Florida Extension recommends asking to see the vendor's license, and adds that the tree should be tagged with the registration number of the nursery. Valencia, Hamlin, Navel and Pineapple oranges are the cultivars most frequently affected.
  Planting orange trees in areas that are sheltered from the wind may provide some protection against citrus canker.