Gray Leaf Spot

A rare disease of turf in the UK, first identified in 2020, caused by the fungal pathogen Pyricularia grisea or Pyricularia oryzae, with synonyms of Magnaporthe grisea and Magnaporthe oryzae respectively.

The actual pathogen would most likely be identified only by DNA analysis, so the disease pathogen might better be considered as a species group. It is more prevalent in hot (~27°C and over) and high relative humidity conditions.

The main grasses attacked are St. Augustine grass, Perennial ryegrass and Tall fescue, although other species can also be affected. Within the UK the most likely situation where this disease will strike is on perennial ryegrass sports pitches, which are in enclosed stadia environments during the mid to late summer.

References:
Zhang, H., Zheng, X. and Zhang, Z. (2016), The Magnaporthe grisea species complex and plant pathogenesis. Molecular Plant Pathology, 17: 796-804. https://doi.org/10.1111/mpp.12342, accessed 26th August 2025.
McCarty, L.B. (Bert), (2018), ‘Golf Turf Management’, CRC Press, 502-503.
Braithwaite, R. Wang, A. Kowalewski, J. F. Tabima, T. N. Temple, and H. M. Rivedal, (2023), First Report of Pyricularia oryzae Causing Gray Leaf Spot of Perennial Ryegrass (Lolium perenne) in Oregon, Plant Health Progress 24:3, 382-385, https://doi.org/10.1094/PHP-11-22-0119-BR, accessed 26th August 2025.
Dr Deborah Cox (2025), ‘Gray leaf spot update’, Grounds Management, Issue 32, Autumn 2025, 33-35.