During the summer of 2023 there was a subtle but significant browning of the leaves on some of the Grey Willow, Salix cinerea, in the willow carr (wet woodland) at Penrose.
Although noticeable we were unable to get to the bottom of the issue then. However, this year the browning leaves have returned with a vengeance and almost all the willow trees in Loe Valley between Helston and Loe Pool have significant browning to their leaves. A similar impact has been noted across The Lizard and elsewhere in the South West.
Investigative volunteers noticed the presence of lots of small blue beetles whilst working in the woods. At the same time, we sent a foliage sample to the Forestry Commission’s TreeAlert tree health team, who then confirmed the beetles are to blame. The leaves have distinctive ‘window-panes’, a shape left behind by how they eat the leaf.
The Blue Willow Beetle, Phratora Vulgatissima, specialises on all willow species and can build up to significant numbers in very short spaces of time. They usually live in a ‘boom-bust’ pattern with their parasites and predators catching up with them often nearly wiping them out in an area after their numbers peak. It is extremely rare for them to be at very high densities for more than two years, so we are hopeful that next summer, 2025, the trees will be back to their usual green selves.
Words: Calum McIntosh, Area Ranger, Penrose
Images: David Davies
Published: September 2024