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What’s new for integrated management of citrus canker in Florida?

James H. Graham

University of Florida

Xanthomonas citri subsp. citri (Xcc), the causal agent of citrus canker, is disseminated by windblown rain associated with subtropical and tropical weather. Water droplets containing bacterial cells are forced through stomata into the substomatal chamber via water congestion at wind speeds in excess of 8m/sec. Bactericidal copper films no longer protect stomatal entry points when the droplets reach this wind speed.

Xanthomonas citri subsp. citri (Xcc), the causal agent of citrus canker, is disseminated by windblown rain associated with subtropical and tropical weather. Water droplets containing bacterial cells are forced through stomata into the substomatal chamber via water congestion at wind speeds in excess of 8m/sec. Bactericidal copper films no longer protect stomatal entry points when the droplets reach this wind speed. Hence, windbreaks are essential for reducing wind speed to improve the efficacy of copper bactericides for reduction of the incidence and severity of canker on fruit of the most susceptible citrus variety in Florida, grapefruit (Citrus paradisi). In an orchard with a perimeter windbreak of Corymbia torelliana, there is a linear relationship between canker incidence (% infected fruit) and wind speed (number of gusts recorded > 4.9 m/sec). An on-going goal is to reduce the rates of metallic copper for protecting fruit. Mixing fixed and soluble copper formulations or a program with fixed copper applied  early in the season followed by soluble copper achieves comparable control at 50% of the metallic copper per season. Firewall (streptomycin) is effective for canker control on grapefruit and reduces the risk of copper phytotoxicity to fruit, and may be useful for reducing risk of copper resistance in Xcc. To minimize development of streptomycin  resistance, Firewall is limited to two applications per season in late May-early June after applications of copper for control of fungal diseases on fruit, melanose and scab. Firewall reduces risk of fruit infection during tropical weather conditions because streptomycin is locally systemic. Soil drenches or trunk applications of neo-nicotinoid insecticides and Bion (acibenzolar-S-methyl) provide for systemic acquired resistance (SAR) control of canker. SAR reduction of canker on leaves lowers risk of fruit infection. Trunk or soil application of Bion and neonicotinoids at 60 day interval  provides comparable control on grapefruit to 21-day interval copper sprays. Integration of non-insecticidal Bion and/or neonicotinoid insecticides may be used to augment copper sprays for disease management.

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In accordance with the Organic Law on the Protection of Personal Data 15/1999, of 13 December, Promotora de Exportaciones Catalanas SA (hereinafter PRODECA), whose address is Gran Via de les Corts Catalanes, 620, principal, 08007 Barcelona, with tax reg. no. NIF A58241316, declares that the images contained on the website www.smartfruitcongress.cat are included in a file belonging to PRODECA. The purpose of this file is the promotion, via its website, of the activities conducted by PRODECA – SmartfFruit IPM International Congress.

PRODECA guarantees that you may, at any time, exercise your right to access, rectify, cancel or oppose by writing to the aforesaid postal address, using the reference "PROTECCIÓN DE DATOS - SMARTFRUIT", or to the email address smartfruitcongress@smartfruitcongress.cat.

Specifically, to correctly exercise these rights you must clearly provide the following items in that communication:
- Name, surname(s) and photocopy of National Identity Document or Passport.
- Statement of the purpose of the request.
- Address for notification purposes.
PRODECA also declares that it reserves the right to delete from its website any content that it considers violates current and applicable legislation.

D’acord amb l’article 17.1 de la Llei 19/2014, la ©Generalitat de Catalunya permet la reutilització dels continguts i de les dades sempre que se'n citi la font i la data d'actualització i que no es desnaturalitzi la informació (article 8 de la Llei 37/2007) i també que no es contradigui amb una llicència específica.