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United States Department of Agriculture

Agricultural Research Service

Research Project: Mitigating Alternate Bearing of Pecan

Location: Fruit and Nut Research

Title: Research progress for integrated canker management

Authors
item Graham, James -
item Gruber, Barratt -
item Bock, Clive

Submitted to: Citrus Industry
Publication Type: Trade Journal
Publication Acceptance Date: February 28, 2014
Publication Date: April 1, 2014
Citation: Graham, J.H., Gruber, B., Bock, C.H. 2014. Research progress for integrated canker management. Citrus Industry. 95:20-24.

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 2013, crop losses in Hamlin from premature fruit drop, and in grapefruit from unacceptable levels of fruit lesions, were substantial. To protect fruit against losses from canker, disease management for the most susceptible cultivars of grapefruit includes windbreaks, stringent leafminer control, and copper sprays to protect fruit during the entire expansion period from April to October. In grapefruit orchards, 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 2013, 5 yr-old red grapefruit trees in an 11 acre trial block surrounded by a 20-30 ft tall Corymbia torelliana windbreak averaged 5% near the windbreak and 75% in the middle of the orchard. Reducing wind speed below 18 miles per hour greatly increases the efficacy of the copper film for protection of the fruit surface from infection through natural openings and rind wounds. The program that includes soluble Magna-Bon at 20 percent of the copper metal per application results in use of 50 percent less metallic per season, a substantial reduction in copper loading of the grove soils. Use of FireWall™ (AgroSource, Inc.) effective reduced canker 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. Four drenches of Actigard® at 60-day intervals between April and October produced better control of foliar and fruit disease than the copper program alone. For best management, the timing for the application of neonicotinoids should be determined by the potential for insecticide movement in the soil by rainfall. Certain other systemically acquired resistance inducers also reduced canker. Additional information regarding insect and disease management recommendations consult the Florida Citrus Pest Management Guide (http://www.crec.ifas.ufl.edu/extension/pest/.

Last Modified: 7/25/2014
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