Examination of the impact of an organic fungicide program on disease severity in ‘Petite Pearl’ vineyards in Wisconsin

Demand for organic products continues to increase in the United States. For grape growers to meet this demand, they require data on organic disease management. Cold-climate grapes are a relatively new industry in the Midwestern region of the United States. In Wisconsin, the 'Petite Pearl' cultivar is valued due to its easy management and harvest quality. With natural disease resistance to most fungal pathogens, this cultivar presents an opportunity for organic disease management. However, there is a lack of data on the implementation of such a program. This study aimed to compare the performance of two fungicide treatments, an organic program and a common non-organic conventional program. Site 1, which was utilized in 2022 and 2023, displayed a treatment effect (P = 0.02) on average disease only in 2022. An additional Site, used only in 2023, did not show a treatment effect. Week was always an influential factor (P = <0.01) on average disease with an increase of foliar disease incidence commonly observed in the bloom window. At Site 1 during both years of the study, there was no effect of treatment on yield per vine. The study highlights an opportunity for organic fungal disease management of 'Petite Pearl'. Overall, the organic program had similar levels of disease to the non-organic except during the latter part of the 2022 season when disease pressure was the greatest. Future work should explore additional grape cultivars with low susceptibility to fungal pathogens and evaluate a more integrated vineyard approach that incorporates multiple cultivars.