Leaf-kicking, conker-bashing schoolboys beware

Sat, Oct 20, 2012, 01:00

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 forestprotection@agriculture.gov.ie.)

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.

Bleeding cankers have recently disfigured and probably doomed many of Ireland’s horse chestnut trees. These, too, can be caused by Phytophthora fungi, but the new, extreme pathogen is actually a bacterium called Pseudomonas syringae pathovar aesculi, only previously known from native horse chestnuts of the Himalayan region. Its damage was spotted first in the Phoenix Park, in Dublin, in 2010, and although some trees were felled and buried, others seem to have responded this year to anti-bacterial sprays (including garlic).

The spores of fungi, multiplied by climate change, can make humans sicker, too. Asthma is increasing across the world, even where smoking and air pollution have fallen dramatically.

In North America, the blame for seasonal peaks is put on floating, allergenic pollen from plants that flourish on extra carbon dioxide. In these islands, local thunderstorms are credited with triggering attacks, from rain and high humidity that concentrate both grass pollen and fungal spores released from crops. (The UK Met Office even has a fact sheet on it.)

Management guidelines for schools from the Irish Asthma Society urge shutting the windows during thunderstorms and ensuring that “piles of autumn leaves are regularly removed from school grounds”.

As a former leaf-kicking, conker-bashing, lightning-loving (and, now I think of it, quite asthmatic) schoolboy, I’m beginning to lose track of the changes in the world.

Eye on nature

Over the weeks from mid-September into October, I noticed that mosquitoes entering the house showed no interest in biting and just perched on ceilings and walls. - John Mullins, Wilton, Cork

The mosquito biting (breeding) season lasts from June to September. When the female lays her eggs she retires and slowly dies. Yours are at that stage.

When I was playing golf in Rosepenna, in Co Donegal, a crow took my golf ball smartly in his beak, off the fairway, and flew off with it towards the beach. - Kathleen Fagan, Clontarf, Dublin

The bird thought it was an egg.

In the car park at Parliament Buildings, Stormont, I saw a resident buzzard threaten and drive out a passing peregrine. A nearby group of civil servants discussing political administration were oblivious to the drama above their heads. An interesting metaphor. - Paula Campbell, Malone Road, Belfast

Spotted from the Dart between the lagoon at Booterstown and the Merrion Gates, a kingfisher perched on a timber post, resplendent in his vivid cloak of orange and blue. - Greg Carley, Killiney, Co Dublin

In early October I saw four buzzards, in the sky above Finglas. Is it usual to see them in groups like this? - Pat Murray, Finglas East, Dublin

They would have been a family.

* Michael Viney welcomes observations at Thallabawn, Carrowniskey PO, Westport, Co Mayo, or email viney@anu.ie. Please include a postal address

Sign In

Forgot Password?

Sign Up

The name that will appear beside your comments.

Have an account? Sign In

Forgot Password?

Please enter your email address so we can send you a link to reset your password.

Sign In or Sign Up

Thank you

You should receive instructions for resetting your password. When you have reset your password, you can Sign In.

Hello, .

Please choose a screen name. This name will appear beside any comments you post. Your screen name should follow the standards set out in our community standards.

Thank you for registering. Please check your email to verify your account.

We reserve the right to remove any content at any time from this Community, including without limitation if it violates the Community Standards. We ask that you report content that you in good faith believe violates the above rules by clicking the Flag link next to the offending comment or by filling out this form. New comments are only accepted for 3 days from the date of publication.