"Podosphaera plantaginis" is a powdery mildew fungus that infects "P. lanceolata". All of the "P. lanceolata" populations are infected by several strains of this powdery mildew fungus. Once the populations are infected, the symptoms are minimal at first. Then, after a few weeks or months lesions start to appear covering the entire surface of the leaves and the stem, making it very noticeable. Another species that infects "P. lanceolata" is "Golovinomyces sordidus". Both of these mildews are obligate biotrophs, meaning that they can only infect living tissue. They cover the surface of the leaves and extend hyphae into the cell matrix in order to extract nutrients.