Leaf-kicking, conker-bashing schoolboys beware
ANOTHER LIFE:IN THE VASTLY DISPARATE world of nature’s fungi, moist autumn is the time for growth and propagation, not only of colourful mushrooms in the woods, hoisted up to spread the spores of underground mycelia, but also of moulds and mildews, rusts and rots.
Furry white botrytis stalks the lettuce in the polytunnel; dark smudges of mould begin to shade the tunnel’s skin. “Mellow fruitfulness” attends the sweet scent of ripening apples, but also the musky perfumes of decay.
A lot of fungal action renews the nourishment of plant life, season by season, pouring out enzymes to digest the cellulose and lignin of fallen leaves – part of the recycling of nutrients for the spring.
Fallen trees, too, soften and melt away as threads of fungal growth help to let in a legion of tunnelling, chewing insects, along with the rain.
Such sublime economy has to be admired. But the agenda of fungal species (200,000 of them, mostly microscopic) is far from uniformly benign. Many do not wait until plant life is dead or even dying before attacking its substance.
Farmers routinely spray with cereals with fungicides against mildews and rusts. And as climate changes, bathing Europe in new levels of wetness and humidity, fungi that flourish, often fatally, in living trees are spreading explosively across the temperate world.
The latest European eruption is of Chalara fraxinea, already blamed for the die-back of most of Denmark’s ash trees. It has spread across Europe from Poland, where it was first discovered in 1992. Infected trees have been discovered in several nurseries and planting sites in England and Scotland, and now in Co Leitrim. Other Irish sites may have been planted with young trees from the same European consignment.
EU rules on free trade frustrate any wholesale import ban, so the forest service of the Department of Agriculture is relying on voluntary action by the forestry trade and verifying the health of imports through the EU Plant Passport system. Quite as problematic is whether ash wood imported for hurley manufacture (mostly from Poland), and not live plants alone, could be spreading the die-back disease. (The email address for reports of sick ash is firstname.lastname@example.org.)
Imports of European ash plants have already been concerning Coford, the national forest research agency, as these have produced many poorly growing commercial plantations. These are now seeding, and the fear is that the wild native ash of Ireland’s countryside, Fraxinus excelsior, will eventually be crossed with the narrow-leaved continental species, Fraxinus angustifolia (which has brown winter buds, not black).
This could seem a lesser worry, compared with the new fungal disease.
It belongs to the same big group (the ascomycetes) as Dutch elm disease, Ceratocystis ulmi, and threatens a similar destruction. In the wholesale outbreak of the late 20th century, Britain lost about 25 million elms. Ireland’s countryside, too, lost these most stately wayside trees, as the fungus was carried from tree to tree by boring bark beetles.
But another important threat to Ireland’s trees belongs to the Phytophthora, a genus of fungi including many plant pathogens that spread by wind-blown spores.
Phytophthora infestans is the fungus we know as potato blight. Phytophthora ramorum is the “sudden oak death” that killed more than a million trees in western North America. Arriving in the wetter western forests of these islands, it seized on other host trees, notably Japanese larch, producing lethal stem cankers. The UK has felled several million larch prematurely, mostly in Northern Ireland.