Phosphorous Acid and Phosphoric Acid: When all P Sources are not Equal
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Brunings, Asha M., Lawrence E. Datnoff, and Eric H. Simonne. 2005. “Phosphorous Acid and Phosphoric Acid: When All P Sources Are Not Equal: HS1010/HS254, 4/2005”. EDIS 2005 (4). Gainesville, FL.


While growers are familiar with phosphorus-containing fertilizer, the abundance of terms, apparently similar (such as phosphoric acid and phosphorous acid), may create some confusion on the actual content and efficacy of these products. Some common phosphorus-containing compounds are listed in Table 1. Some claims found in commercial literature and product descriptions refer to phosphorous acid as a “supplemental fertilizer,” while others present it as a fungicide (Table 2). The purpose of this article is to explain what phosphorous acid is and to examine both the fungicidal activity and nutritional value of phosphorous acid. This document is HS1010, one of a series of the Horticultural Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Publication date: April 2005.

HS1010/HS254: Are Phosphorous and Phosphoric Acids Equal Phosphorous Sources for Plant Growth? (
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Bashan, B., Y. Levy, and Y. Cohen. 1990. Variation in Sensitivity of Phytophthora infestans to Fosetyl-Al. Plant Pathol. 39:134-140.

Bayer Cropscience. 2004. Aliette Product Information. Bayer Cropscience. Last accessed: January 27, 2005

Biagro Western Sales, Inc. 2003. Nutri-Phite Fertilizer. Biagro Western Sales, Inc. Last accessed: January 27, 2005

Brown, S., S.T. Koike, O.E. Ochoa, F. Laemmlen, and R.W. Michelmore. 2004. Insensitivity to the Fungicide Fosetyl-aluminum in California Isolates of the Lettuce Downy Mildew Pathogen, Bremia lactucae. Plant Dis. 88:502-508.

Coffey, M.D. and L.A. Bower. 1984. In vitro Variability Among Isolates of Eight Phytophtora Species in Response to Phosphorous Acid. Phytopathology 74:738-742.

Cohen, Y. and M.D. Coffey. 1986. Systemic Fungicides and the Control of Oomycetes. Annu. Rev. Phytopathol. 24:311-338.

Cooke, L.R. and G. Little. 2001. The Effect of Foliar Application of Phosphonate Formulations on the Susceptibility of Potato Tubers to Late Blight. Pest Manag. Sci. 58:17-25.

Datnoff, L., J. Cisar, B. Rutherford, K. Williams, and D. Park. 2003. Effect of Riverdale Magellan and Chipco Signature on Pythium Blight Development on Lolium perenne, 2001-2002. The American Phytopathological Society. Fungicide and Nematicide Tests Vol. 58:T041.

Datnoff, L., J. Cisar, B. Rutherford, K. Williams, and D. Park. 2005. Effect of Fungicides and Other Prophylactic Treatments on Pythium Blight Development on Poa trivialis, 2004. In press.

Dolan, T.E. and M.D. Coffey. 1988. Correlative In vitro and In vivo Behavior of Mutant Strains of Phytophthora palmivora Expressing Different Resistances to Phosphorous Acid and Fosetyl-Na. Phytopathology 78:974-978.

Fenn, M.E. and M.D. Coffey. 1984. Studies on the In vitro and In vivo Antifungal Activity of Fosetyl-Al and Phosphorous acid. Phytopathology 74:606-611.

Fenn, M.E. and M.D. Coffey. 1985. Further Evidence for the Direct Mode of Action of Fosetyl-Al and Phosphorous Acid. Phytopathology 75:1064-1068.

Fenn, M.E. and M.D. Coffey. 1989. Quantification of Phosphonate and Ethyl Phosphonate in Tobacco and Tomato Tissues and Significance for the Mode of Action of Two Phosphonate Fungicides. Phytopathology 79:76-82.

Förster, H., J.E. Adaskaveg, D.H. Kim, and M.E. Stanghellini. 1998. Effect of Phosphite on Tomato and Pepper Plants and on Susceptibility of Pepper to Phytophthora Root and Crown Rot in Hydroponic Culture. Plant Dis. 82:1165-1170.

Griffith, J.M., M.D. Coffey, and B.R. Grant. 1993. Phosphonate Inhibition as a Function of Phosphate Concentration in Isolates of Phytophthora palmivora. J. Gen. Microbiol. 139:2109-2116.

Heffer, V., M.L. Powelson, and K.B. Johnson. 2002. Oomycetes. The Plant Health Instructor. doi:10.1094/PHI-I-2002-0225-01. ©2002 The American Phytopathological Society. Last accessed: January 28, 2005

Helena Chemical Company. 2001. Introduction to Helenas Latest Products. Helena Chemical Company. Last accessed: January 27, 2005

Helena Chemical Company. 2002. Helena ProPhyt. A Systemic Fungicide Containing Potassium and Phosphate. (promotional brochure). Helena Chemical Company.

Johnson, D.A., D.A. Inglis, and J.S. Miller. 2004. Control of Potato Tuber Rots Caused by Oomycetes with Foliar Applications of Phosphorous Acid. Plant Dis. 88:1153-1159.

McDonald, A.E., B.R. Grant, and W.C. Plaxton. 2001. Phosphite (phosphorous acid): Its Relevance in the Environment and Agriculture and Influence on Plant Phosphate Starvation Response. J. Plant Nutr. 24:1505-1519.

McGrath, M.T. 2004. What are Fungicides? The Plant Health Instructor. doi: 10.1094/PHI-I-2004-0825-01. ©2004 The American Phytopathological Society. Last accessed: January 28, 2005

Nelson, M.E., K.C. Eastwell, G.G. Grove, J.D. Barbour, C.M. Ocamb, and J.R. Aldredge. 2004. Sensitivity of Pseudoperonospora humuli (the causal agent of hop downy mildew) from Washington, Idaho, and Orgeon to Fosetyl-Al (Aliette). Plant Health Progress doi:10.1094/PHP-2004-0811-01-RS. ©2004 Plant Management Network. Last accessed: January 28, 2005

Nufarm USA. Phostrol®. Nufarm Ltd. Last accessed: January 27, 2005

Ouimette, D.G. and M.D. Coffey. 1989a. Comparative Antifungal Activity of Four Phosphonate Compounds Against Isolates of Nine Phytophthora Species. Phytopathology 79:761-767.

Ouimette, D.G. and M.D. Coffey. 1989b. Phosphonate Levels in Avocado (Persea americana) Seedlings and Soil Following Treatment with Fosethyl-Al or Potassion Phosphonate. Plant Dis. 73:212-215.

Pesticide Action Network. 2004. PAN Pesticide Database. Pesticide Action Network North America. Last accessed: January 27, 2005

Rebollar-Alviter, A., L.V. Madden, and M.A. Ellis. 2005. Efficacy of Azoxystrobin, Pyraclostrobin, Potassium Phosohite, and Mefenoxam for Control of Strawberry Leather Rot Caused by Phytophthora cactorum. Plant Health Progress doi:10.1094/PHP-2005-0107-01-RS. ©2005 Plant Management Network. Last accessed: January 28, 2005

Smillie, R., B.R. Grant, and D. Guest. 1989. The Mode of Action of Phosphite: Evidence for Both Direct and Indirect Action Modes of Action on Three Phytophthora spp. in Plants. Phytopathology 79:921-926.

Street, J.J. and G. Kidder. 1989. Soils and plant nutrition. UF/IFAS, Fla. Coop. Ext. Serv. Fact Sheet SL-8.

Waggoner, B.M. and B.R. Speer. 1995. Introduction to the Oomycota. University of California at Berkeley. ©1994-2004 Regents of University of California. Last accessed: January 26, 2005

Wilcox, W. ProPhyt, Aliette, and Phosphorous Acid. The Lake Erie Regional Grape Program. Last accessed: January 27, 2005

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