Blue sky, adorned with misty white splashes and ridges of thin high clouds; there is real heat still in the low sun. Hedges are laden with ripening blackberries and spotted with smoky blue sloes, as well as the reds of haws and hips. A standard oak is burdened with knopper galls, deformed shiny walnut kernels supplanting smooth acorns. When Andricus quercuscalicis, the gall crafting wasp, spread in the 1970s, oak procreation was thought to be in peril. Although oaks are still seeding successfully, the eventual effect of the wasp on the bounty of trees in the countryside remains unknown. On this particular oak we can’t find a single healthy acorn.
Further on, a horse chestnut is in a pitiful state: its curled and browned leaves exhibit the blotch mines of the horse chestnut leaf miner (Cameraria ohridella), a tiny moth that arrived 17 years ago, but the tree is in such a mess that I suspect it has also fallen victim to a 1935 import, the leaf spot fungus Guignardia aesculi. Adjacent ash trees appear healthy, although their prognosis is bad as ash dieback rampages across the country.
Of course, the first tree we lost from the British countryside to alien malady was the elm. It fell victim to Dutch elm disease (a fungus that we actually imported from America). The wych elm persists as a shrub, unable to grow a trunk due to the continued depredations of the fungus. Just outside Wadenhoe, some hedges are almost entirely elm, and it is there that I spot the most recent introduced hazard, the distinctive meandering incisions of the zigzag sawfly (Aproceros leucopoda). While affected leaves are still in a small minority here, it is just establishing, having been brought to the UK only two years ago. On the continent, where this Japanese insect has been resident since 2003, it has sometimes stripped more than 70% of the foliage of elms.
Just when we most desperately need our trees, as the Arctic and Amazon forests go up in soot and CO2, our woody companions are tormented by our seemingly uncontrollable addiction to importing live plants and their stowaways.
