Recorded sightings of honey fungus in the UK have surged by almost 200% compared with the same period last year, according to data from the iNaturalist platform. The dramatic increase is attributed to last year's record-breaking summer heat followed by a damp autumn, conditions that experts say are linked to the climate crisis.
Honey fungus, scientifically known as Armillaria, is not a single species but a group of closely related fungi. It is notorious among gardeners as the UK’s most reported plant disease, according to the Royal Horticultural Society (RHS). The fungus attacks tree roots, killing off water-conducting tissue and causing plants to die back above ground.
Dr Jassy Drakulic, an RHS plant pathologist, noted that the RHS began receiving inquiries about honey fungus mushrooms earlier than usual this year. She explained that while healthy plants can wall off infection, stressed plants are far more vulnerable. The hot, dry summer of 2025, the UK’s hottest on record, likely left trees stressed and susceptible to colonisation.
The warm, damp autumn that followed provided ideal conditions for the fungus to fruit and release spores, which may play a greater role in spreading the disease than previously thought. In addition, honey fungus spreads underground via rhizomorphs, root-like black ropes that act as conduits for nutrients and movement within the mycelial network.
Experts warn that the surge in honey fungus could be a sign of broader ecological changes. Dr Daniel Henk, a mycologist at the University of Bath, said climate change is altering fungal fruiting patterns. While the mushrooms themselves are a key part of habitats and food webs, the underlying concern is the drought stress that makes trees vulnerable, said Dr Drakulic, calling for research into sustainable management of Armillaria species.
