British distribution: Widespread, locally common but under-recorded in some areas.
This is a powdery mildew, parasitic predominantly on labiates (Lamiaceae).
This is a powdery mildew occurring on numerous native and garden species of the family Lamiaceae (labiates), including Lamium (dead-nettles), Stachys (woundworts), Galeopsis (hemp-nettles) and Lamiastrum galeobdolon (Yellow Archangel). It also occurs on species of Acanthus (Acanthaceae) and Catalpa (Bignoniaceae). A few British records on plants of unrelated families can safely be dismissed as blunders, misunderstandings and transcription errors, though a single record from China on Althaea (Malvaceae) has been verified by molecular analysis (Braun & Cook, 2012).
Neoërysiphe is a small genus, close to Golovinomyces and principally differing in its lobed, not nipple-shaped, appressoria. The cleistothecia of N. galeopsidis contain numerous asci, each (2-)3-6(-8)-spored, the ascospores not maturing until the cleistothecium has over-wintered, cleistothecial appendages generally short, flexuous, unbranched, often dense. The conidia of the anamorph (asexual state) are hyaline, shortly cylindrical to slightly barrel-shaped, 25–45 × 12–22 µm, produced in chains, and lack fibrosin bodies. The fungus produces white patches on the surfaces of leaves, stems and inflorescences of the host, sometimes extensive and markedly affecting its vigour.
Descriptions and diagrams of the sexual and asexual stages are provided by Uwe Braun (1987, 1995) and Braun & Cook (2012). This is the predominant powdery mildew on labiates in the UK, but Golovinomyces biocellatus (Erysiphe biocellatus) also parasitises numerous members of the Lamiaceae and may be under-recorded. The generalist G. orontii is also recorded on labiates. Microscopic confirmation of identifications is recommended.
For an explanatory overview of the powdery mildews, go to the profile of the Erysiphales.