| Résumé | Late blight, caused by Phytophthora infestans (Mont.) de Bary, is a devastating disease of potatoes (Solanum tuberosum L.). Current disease management is strongly dependent on extensive use of protectant fungicides. A three year field trial was conducted in Prince Edward Island to evaluate the efficacy of phosphorous acid (Confineᵀᴹ), applied alone or in combination with chlorothalonil (Bravo®500) during the growing season, for control of foliar late blight. The trial consisted of two French fry processing varieties (‘Russet Burbank’ and ‘Shepody’) and four treatments (check plots treated with water, phosphorous acid, chlorothalonil and a combined treatment of phosphorous acid + chlorothalonil). The experimental design was a randomized complete block with each of the four treatments occurring in each block. Fresh leaves from each plot were collected and challenge-inoculated with a sporangial suspension of P. infestans. The leaves were incubated and then assessed for disease severity at one, four, five, six and seven days after inoculation. In addition to a significant variety effect, all three treatments achieved significant reduction in late blight severity on detached leaves compared with the check plot. The combined treatment of phosphorous acid and chlorothalonil resulted in the highest reduction in disease development, followed by the treatment with chlorothalonil. The ‘phosphorous acid alone’ treatment provided substantial control up to four days post infection, but the effect diminished after seven days post infection. These results will help us develop management strategies for late blight in potatoes and other solanaceous crops. |
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