Erysiphe heraclei is an ascomycete fungus that causes powdery mildew on carrots and other plants. This fungus forms structures called cleistothecia in its sexual phase, which are spherical and contain asci with ascospores. During its asexual phase, E. heraclei produces conidia in chains that are dispersed by the wind. The conidia germinate on the leaf surface, where the fungus penetrates the epidermal cells and develops haustoria that extract nutrients from the plant. Primary infection may arise from hibernating spores that reactivate with the arrival of favorable conditions, generally moderate temperatures and high relative humidity. Once established, the mycelium of the fungus spreads over the surface of the plant, forming a characteristic whitish layer. The continuous production of conidia allows the infection to spread rapidly to other plants.