Efficacy of systemic fungicides to control the pathogen Phytophthora austrocedrae in Austrocedrus chilensis forests of Patagonia, Argentina

SILVA, P.V.; HERNÁNDEZ OTAÑO, D.; VÉLEZ, M.L.; GRESLEBIN, A.G.

Congreso; IUFRO Forest Protection Joint Meeting; 2011

IUFRO, Universidad

Phytophthora austrocedrae is a soil pathogen that causes Austrocedrus chilensis (mountain cypress) mortality in Patagonia, Argentina. No strategies of management or control are known at the moment. The systemic fungicides Metalaxyl®, Fosetyl-Al®, as well as other phosphonate based fungicides (phosphite), have demonstrated to be effective to control some Phytophthora species and, especially phosphite, are used to control Phytophthora- caused forest disease. The feasibility of using systemic fungicides against P. austrocedrae was evaluated trough in vitro as well as in planta assays. The effects of different concentrations (0.01 to 1000 µg/ml) of the fungicides on the growth and the reproduction of P. austrocedrae were evaluated. Metalaxyl reduced the growth, even in the lowest concentration, while Fosetyl-Al reduced it only in the highest one. Sexual reproduction was totally inhibited by Metalaxyl in all concentrations assayed and decreased by Fosetyl-Al in the 3 highest concentrations.Both fungicides reduced or even inhibited asexual reproduction. In planta assays were performed trough artificial inoculation of the pathogen in 3- year- old saplings as well as in adult trees treated preventively with the fungicides. Both fungicides showed to be effective as preventive treatment in saplings, but in higher concentrations than the recommended by the manufacturer. In adult trees preventive treatment with Fosetyl-Al reduced the lesion size developed in the phloem but Metalaxyl treatment showed not effect on lesion size. It may be due to the inappropriate dose application of Metalaxyl. The differences in the performance of Fosetil-Al in vitro and in vivo could be due to the complex mode of action of phosphonate that inhibits the growth of Phytophthora and also enhances plant defense mechanisms.