By this time of year many trees are showing signs of fungal attack. This strange growth on a developing alder cone is caused by a gall-forming fungus called Taphrina alni and is commonly known as alder tongue gall. An uninfected cone is illustrated below, for comparison. When the gall is mature it resembles a crimson tongue and occasionally you find several protruding from a single cone. Taphrina alni first arrived in Britain from France in the 1940s but didn't reach North East England, where it's becomong increasingly common, until the 1990s.
Turn over an aspen leaf like the one above and you may find its underside covered with clusters of golden spores, belonging to aspen rust fungus Melampsora larici-tremulae. Rust fungi have complicated life cycles, infecting different hosts at different times of the year.
When these leaves blacken, wither and fall to the ground they'll release spores that will infect next spring's new growth of larch needles, and the spores that form on those will then reinfect aspen foliage. This leaf came from an aspen growing near a larch plantation.
Aspen, whose leaf stalks are flattened along their sides, so that they flutter sideways in the wind and seem to tremble in the slightest breeze, normally turn an intense shade of lemon yellow in autumn, but the rust infected leaves simply wither and fall without changing colour.
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