Effect of postinfection application of phosphorous (phosphonic) acid on the incidence and sporulation of Plasmopara viticola on grapevine

Phosphorous acid (H3P03) applied at 1.2 gIL up to 12 days after infection reduced the incidence and severity of Plasmopara vitieola. When applied up to 13 days after infection, H3P03 reduced sporulation. In some experiments, the postinfection activity of H3P03 was better than metalaxyl, while in other experiments it was less effective. Both fungicides applied after infection reduced the incidence and severity of disease on leaves and flower clusters, indicating that postinfection applications should reduce the production of inoculum and the consequent spread of disease within a vineyard. In most cases, the addition of copper oxychloride did not affect the efficacy of H3P03•