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Prnum: 11277   Chemical/Commodity: PHOSPHOROUS ACID SALTS / APPLE
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RegionNameCommentsDate Entered
WSR Historical JJF (CA)
1. Phosphorous acid products are generally used for Oomycete (Phytophthora root rot, Pythium damping off, late blight of potato, downy mildew) diseases, not for diseases caused by Ascomycetes (like apple scab). Oomycetes and Ascomycetes are in different kingdoms of organisms.
2. Phosphorous acid products are currently applied either as a soil drench for root disease or as a foliar spray for downy mildew and late blight. There has been some work with trunk injections for trees but mostly ornamental trees. My experience is that phosphorous acid products have moderately low efficacy for root and foliar diseases caused by oomycetes. In a brief search I also found potential trade problems with accumulation of phosphorous acid in apple tissues (see attached).
3. If phosphorous acid injected into the trunks was effective, then the issue is application cost. A dwarf apple orchard on 8 X 14 spacing is nearly 400 trees per acre. Injecting phosphorous acid into that many tree would be prohibitively expensive especially since the alternative is an air blast sprayer that the growers already use multiple time per year for insect and disease control. AS an FYI, I imported a photo of hatchet cuts on an avocado trunk to allow absorption of fosetyl-Al for Phytophthora root rot. (RS 8/1/13)
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