These sexually produced spores have thicker, protective walls and allows them to survive adverse conditions. Oospores can live in soil, stems and tubers, which means they can survive during winter and infect the next season's crop. Sexual reproduction also creates a greater genetic diversity for the pathogen's population, making it more adaptable to changing conditions. As a result, strains of the fungus of both mating types are starting to show resistance to fungicides. Resistant strains have been detected in the Pacific Northwest, British Columbia, Texas, California, Pennsylvania, Florida, Maine and Wisconsin.
Growers have several options for managing blight.
The strains resist metalaxyl, but are sensitive to other fungicides. Those other fungicides include external chemical protectants, such as mancozeb or chlorothalonil. These protectants have been around for years and provide a fungicide layer on the outside of the plant. In the past it has been important to recommend sanitation to control the fungus from getting started by planting healthy seed tubers and destroying infected seed tubers. The long-term solution is the development of resistant potatoes.