The number of golden mushrooms, which grow in clusters and can attack and kill trees, has increased by 200% in the UK this year due to a hot summer and wet autumn.
According to iNaturalist, the number of reported cases of honey mushrooms has increased by almost 200% compared to the same period last year.
Armillaria, or honey mushrooms, is not one species, but a group of closely related species. “As the name suggests, they are honey-brown in color, often with a greenish tint when young,” said David Gibbs, a field mycologist. “Large clumps often take on a frosty appearance and are covered in white spores.”
The clusters that appear in gardens and forests are temporary fruiting bodies of the main part of the fungus – the mycelium.
Dr Daniel Henk, a mycologist at the University of Bath, said the mycelium was underground or in wood, “doing the hard work of finding nutrients, fending off competitors, growing and persisting for a long time.”
Honey mushrooms can also form root-like black ropes called rhizomorphs. “They form these physically robust channels for transport and mass movement within the mycelial network—they're like superhighways,” Henk said. This makes them very effective at penetrating tree roots and bark.
Honey mushrooms are notorious among gardeners and are the most reported plant disease in the UK, according to the Royal Horticultural Society (RHS).
“This year we started receiving emails with photographs of honey mushrooms that we could identify much earlier than usual,” said RHS plant pathologist Dr Jassi Drakulic. According to her, the damage was caused Armillaria Melleawhich “kills the water-conducting tissue in the roots, preventing plants from absorbing water and dying above ground.”
Drakulich said that while healthy plants may be affected, they have ways to protect themselves from infection, so “it's much more likely that it will cause problems in plants that are already stressed.” The hot and dry summer of 2025 could be the cause of such stress.
The hottest summer on record in the UK may have left trees vulnerable to colonization by honey fungus mycelium. “We typically see more cases of honey mushroom root rot after dry years,” Drakulic said.
This was followed by a warm, wet autumn, ideal for mushrooms to bear fruit. The role of fungi is to release spores and spread to new territories.
“Early evidence from ongoing RHS research suggests that fungal spores Armillaria Mellea are more important for the spread of the fungus than previously thought,” Drakulic said, in addition to underground spread by rhizomorphs or root-to-root contact.
Should people worry? In gardens, honey mushrooms can destroy trees and shrubs, but a productive year of honey mushrooms may reflect broader environmental changes.
“Over the past two decades, climate has changed the fruiting patterns of mushrooms,” Henk said, adding that mushrooms “are a key part of the habitat for invertebrates and food for larger animals.”
“The concern is related to the drought itself,” Drakulich said, “because the volume of fungi is a sign of the stress that trees are under due to climate change and poor management practices that prevent dead wood from being recycled back into the soil.”
“Research in Biology, Ecology and Sustainable Management Armillaria species are needed to figure out how we can limit their potential harm to the climate now and in the future,” Drakulic said.
