A dramatic rise in sightings of the Armillaria mellea group of fungi—commonly known as honey fungus—is being reported across the UK, with garden and woodland observers logging nearly a 200 % increase in just one year.
The spike is being linked to the UK’s hottest summer on record followed by a warm, damp autumn, creating ideal conditions for the fungus’s spread and fruiting. Field mycologists say the hot dry spell left trees stressed, making them vulnerable to infection, while the subsequent moist season enabled massive mushroom production and spore dispersal.
Honey fungus isn’t a single species but a group of closely related fungi. They typically appear as honey-brown, clustered mushrooms that later develop a frosty white spore dusting. But these visible mushrooms are only the tip of the threat. The main fungal body—the mycelium—lives underground or within wood, persistently invading root systems and killing trees by blocking their ability to draw up water.
One of the fungus’s key tools are black rope-like structures called rhizomorphs, which act as “super-highways” within the mycelial network, enabling it to spread effectively by connecting from tree to tree. According to pathologists at the Royal Horticultural Society (RHS), honey fungus is already the most reported plant disease in the UK.
Dr Jassy Drakulic of the RHS highlights that while strong, healthy trees can often resist infection, those weakened by drought or other stressors are much more likely to succumb. “We started getting emails with photographs of honey fungus mushrooms for us to identify much earlier this year than we usually do,” she said. Indeed, the unusual weather patterns of summer 2025 seem to have provided that weakening stress.
Moreover, the warm, damp conditions of the autumn were perfect for the fungus’s mushrooms to fruit and spread. Previous understanding held that the main spread was via underground root-to-root contact, but recent RHS research suggests spore dispersal from the mushrooms may play a larger role than previously thought.
This boom in honey fungus is not just a gardener’s challenge—it may also reflect broader ecological shifts. Mycologist Dr Daniel Henk from the University of Bath said mushrooms are important components of ecosystems—providing habitat for invertebrates and food for larger animals—but the surge in honey fungus also signals tree stress linked to climate change and woodland management issues. As Dr Drakulic put it: “The concern is about the drought itself … with the volume of mushrooms being a sign of the stress trees are under from climate change and from poor management practices that fail to recycle dead wood back into the soil.”
Experts now call for more research into how to manage and control Armillaria species in changing climates. They warn that if these fungi proliferate unchecked, the consequences for woodlands, urban trees and gardens could be significant. Responsibility falls on both improved tree health management and climate-resilient practices.
