Integrated Management of Citrus Canker

Authors: GRAHAM, JAMES - University Of Florida; GRUBER, BARRATT - University Of Florida; Bock, Clive

Submitted to: Citrus Industry
Publication Type: Trade Journal
Publication Acceptance Date: 2/25/2013
Publication Date: 4/1/2013
Citation: Graham, J.H., Gruber, B., Bock, C.H. 2013. Integrated Management of Citrus Canker. Citrus Industry. 92: 12-17.

Interpretive Summary: Fruit losses due to citrus canker, caused by Xanthomonas citri subsp. citri (Xcc), vary each crop season depending on citrus variety, tree age, flushing condition, leafminer control, and coincidence of weather events with occurrence of susceptible fruit and foliage. Research results have demonstrated the following options for canker management: Windbreaks reduce wind speed and fruit infection experienced during typical Florida rain storms. Consistent with previous trials in Florida as well as in Brazil and Argentina, a protective film of copper on fruit reduced canker. Stringent leafminer control was essential to reduce canker severity on leaves and to minimize subsequent fruit infection. Some elicitors of systemically acquired resistance reduce canker effectively. Using these approaches in an integrated way will minimize the incidence and severity of citrus canker in orchards of susceptible citrus.

Technical Abstract: Fruit losses due to citrus canker, caused by Xanthomonas citri subsp. citri (Xcc), vary each crop season depending on citrus variety, tree age, flushing condition, leafminer control, and coincidence of weather events with occurrence of susceptible fruit and foliage. In 2012, crop losses in Hamlin from premature fruit drop, and in grapefruit from unacceptable levels of fruit lesions, were far lower compared to the 2011 season. This difference between 2011 and 2012 was due to the prevalence of April and May rains in 2011 that occurred when fruit were at the most susceptible stage of expansion. In grapefruit groves, where the goal is to minimize canker incidence and severity to ensure an economically viable pack-out, windbreaks reduced wind speed and fruit infection experienced during typical Florida rain storms in 2011. In 2012, 5 yr-old red grapefruit trees in an 11 acre trial block surrounded by a 20-30 ft tall Corymbia torelliana windbreak averaged 50 % less canker infected fruit in copper sprayed trees than in the non-sprayed trees. Consistent with previous trials in Florida as well as in Brazil and Argentina, the effectiveness of the protective film of copper on fruit did not vary greatly among standard copper formulations applied at 2 to 4 lb/acre of product (0.75 to 1.4 lb/acre of metallic copper). Because fruit grow more slowly than leaves, the copper film can protect for 14-21 days after which time fruit expansion exposes unprotected fruit surfaces. Recently completed studies identified the potential for development of copper resistance in Xcc after long-term use in citrus groves. Use of FireWall™ (AgroSource, Inc.) is effective for canker control on grapefruit and reduces the risk of copper phytotoxicity to fruit, and possibly for development of copper resistance in Xcc. Leafminer galleries are very susceptible to invasion by the canker bacterium. Extensive infection of leafminer galleries by Xcc greatly increases inoculum, making the disease explosive, particularly on flush from July to the end of the season. Stringent leafminer control is essential to reduce canker severity on leaves and to minimize fruit infection. Results documented a consistent reduction in foliar infection and canker-induced defoliation on young non-bearing trees after soil applications with the neonicoinoids, Admire Pro™ (imidacloprid) and Platinum™ (thiamethoxam) and certain other systemically acquired resistance inducers. Additional information regarding insect and disease management recommendations consults the Florida Citrus Pest Management Guide (http://www.crec.ifas.ufl.edu/extension/pest/.