Leaf spot, caused by Mycosphaerella fragariae, is a common foliar disease infectious to a broad variety of strawberry cultivars. In a search for alternative control methods, seaweed extract from Ascophyllum nodosum was applied to strawberry cultivars and evaluated for its effect on Mycosphaerella leaf spot symptoms: growth-curve models were fitted for the progress of disease incidence and severity over time. A 29% seaweed extract was sprayed on soil, on plants or on both at the dose of 2 L ha-1. Disease incidence and severity were measured biweekly on the cultivars Dover, Toyonoka, Albion, Camarosa, Ventana, Campinas, Tudla and Camino Real. We used a completely randomized split plot design with three replicates. Disease incidence and severity were calculated as the area under disease progress curves, and analysis of variance was used to assess the effect of the seaweed extract on the cultivars. The progress of disease incidence and severity over time for each cultivar was adjusted using monomolecular, logistic and Gompertz models. The seaweed extract had no effect or interaction on Mycosphaerella leaf spot control for the tested cultivars. There was a cultivar effect with lower disease intensity in Ventana and Albion, mainly due to reduced inoculum effectiveness delaying the rate of infection. The progress of disease incidence and severity over time was adjusted for all cultivars by logistic and monomolecular models, respectively.
Mycosphaerella fragariae; Ascophyllum nodosum; modeling
