Submitted to: Citrograph
Publication Type: Trade Journal
Publication Acceptance Date: 12/15/2012
Publication Date: 12/31/2012
Citation: Smilanick, J.L., Cerioni, L., Rapisarda, V., Doctor, J., Grech, N., Fikkert, S., Ruiz, T., Fassel, R. 2012. Use of phosphite salts in laboratory and semi-commercial tests to control citrus postharvest decay. Citrograph. 3(6):36-40. Interpretive Summary: A large portion of citrus fruit can be lost after harvest unless measures are taken, usually the application of fungicides, to control rot caused by several types of fungi. Both recently granted regulatory approval for use in California, calcium phosphite and potassium phosphite can control rot caused by some classes of fungi, and in this article we describe how these can best be used for this purpose under commercial conditions in citrus packinghouses. The impact of this work is to state some conclusions that clarify the effectiveness of these newly approved products, so managers of citrus packinghouses can make informed decisions about the materials they apply to control rot.
Technical Abstract: Many growers of citrus fruit and other crops often apply phosphite or phosphorous acid containing products before harvest. Phosphite fungicides include calcium or potassium phosphite salts, or the phosphite-generating fungicide fosetyl-aluminium (Aliette®, Bayer CropScience). Recently, two products were also approved for postharvest use in California (KPhosTM, Pace International, Seattle, WA and Fungi-PhiteR, Plant Protectants Inc., Visalia, CA). This article reviews some of our work, a comprehensive description was recently published in the journal (Plant Disease). Potassium or calcium phosphite (or phosphonates) salts contain a less oxidized form of phosphorous, and formulations are available as fungicides, fertilizers, or “defense stimulators”. Their spectrum of fungicidal activity to control other fungi is irregular and some characteristics are unusual or even mysterious, such as systemic mobility in both xylem and phloem, and their natural absence in higher organisms (although they are found in some microorganisms). Phosphites are generally believed not to be able to supply phosphorus directly to plants and require oxidation prior to metabolic incorporation. Phosphites occur in low oxygen and anaerobic environments as part of the phosphorus cycling systems in soils and marine environments. Recent studies have shown that the microbial communities of soils possess the ability to oxidize phosphite to phosphate due to the presence of inducible phosphite dehydrogenase. The widespread occurance of these oxidative mechanisms in soils that oxidize phosphite in agrichemical products to phosphate bestows on these products a relatively benign environmental fate profile compared to complex organic structures of synthetic pesticides.