VIEW ARTICLE

Disease Control and Pest Management

Studies on the In Vitro and In Vivo Antifungal Activity of Fosetyl-Al and Phosphorous Acid. M. E. Fenn, Graduate research assistant, Department of Plant Pathology, University of California, Riverside 92521; M. D. Coffey, associate professor, Department of Plant Pathology, University of California, Riverside 92521. Phytopathology 74:606-611. Accepted for publication 17 November 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-606.

In a low-phosphate medium fosetyl-Al showed a much higher activity in vitro against Phytophthora than previously reported in the literature. Both fosetyl-Al, and more particularly phosphorous acid (H₃PO₃), were highly inhibitory in vitro against several species of Phytophthora. Phosphorous acid was much less inhibitory in vitro against Pythium and had only low activity against a selection of non-oomycetous fungi. The EC₅₀ values for an isolate of Phytophthora cinnamomi, cultured on a low phosphate medium, were 0.05 PO₃ meq of H₃PO₃ (4 μg/ml) and 0.45 PO₃ meq of fosetyl-Al per liter (54 μg/ml). An increase in the level of phosphate reduced the inhibition of mycelial growth due to fosetyl-Na, but there was little or no effect of phosphate on the inhibition caused by H₃PO₃. In vivo, either 12.7 PO₃ meq of H₃PO₃ (1.0 g/L) or 12.7 PO₃ meq of fosetyl-Al per liter (1.5 g a.i./L), applied as a foliar spray or soil drench, gave equivalent control of root rot caused in seedlings of Persea indica by Phytophthora cinnamomi. Compared to fosetyl-Al, H₃PO₃ had a similar, though generally higher efficacy, in reducing stem infection of Persea indica seedlings by Phytophthora citricola. The EC₅₀ values for inhibition of stem infection were 0.09 PO₃ meq of H₃PO₃ (8 μg/ml) and 0.22 PO₃ meq of fosetyl-Al per liter (26 μg a.i./ml).