We have seen a proliferation of phos-acid fungicides in recent years. These are reduced risk products that have been very effective on certain diseases. The following is an article on the subject.
Another category of “safer” systemic materials are the phosphorous acids or phosphonates. The first of these was Aliette, fosetyl-Al, which was introduced decades ago. Now a large number of products including Avalon, Flanker, Phostrol, Alude, Fungi-Phite T&O, and K-Phite have been labeled in New York with the same mode of action as Aliette. These vary in their acidity, and in whether there is aluminum included in the formulation, but they all have similar modes of action. The phos acid materials offer some key uses: downy mildew control on roses, Pythium and Phytophthora management, as well as some suppression against certain bacterial diseases. Aluminum toxicity has been problematic with application of Aliette on some plants, such as azaleas. Precautions given on some of the phos acid labels indicate that they should not be applied to heat-stressed or drought-stressed plants, or within 14-20 days of a copper application. These materials should not be applied if the foliage will not dry promptly. Some of the phos acid products are not safe to tank-mix with spreader-stickers, or with flowable chlorothalonil or mancozeb products, so be careful to read the label of the particular material you are using.The phos acid materials may be used on ornamental and bedding plants in landscape, nursery and greenhouse. The ability of these materials to limit Phytophthora disease is unquestioned—this is their strongest suit. Results on other kinds of diseases will be variable. The leaf spot on English ivy caused by Xanthomonas campestris pv. Hederae is one of the bacterial diseases for which phos acids are labeled. Fire blight suppression is also listed for some ornamentals.
Reprinted from "Exploring alternatives for disease control on trees and shrubs" by Margery Daughtrey, Cornell University Department of Plant Pathology and Plant-Microbe Biology, in the May 23, 2008 edition of the Michigan State University Landscape Alert newsletter.
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