Another Life: The noxious plant that costs Europe €4.5 billion a year

Ragweed, the bane of hay-fever victims, causes half the summer attacks of asthma. It also invades ploughed fields, waysides and wastelands. It’s still rare in Ireland – so root it up before it flowers more widely

Ragweed: one plant can generate up to a billion grains of pollen in a season, travelling hundreds of kilometres on the wind. Illustration: Michael Viney

Letting our lawn patches grow without mowing this year offered the pleasure, rare on a sheep-shorn hillside, of watching a sheet of wild grasses shoot up to full height and inflorescence, their flower heads shimmering in the wind. As May turned into June I tended polytunnel and rain gauge, and occasionally – in a dash ahead of rain – the clothesline, along narrow tracks between thigh-high, feathery plumes and panicles of foxtail, fescues, Yorkshire fog and the rest. It was only to help make the house look lived in that we finally bowed to persuasion by a more robust friend with an even more robust mower.

Close up, the flowers of grass can be intricately lovely (see John's Feehan's book for Teagasc, The Grasses of Ireland), but the mechanics of lodicule, glume and lemma – don't ask – are all about launching pollen into the wind. The flowers, says Feehan, usually open only once to release the pollen, all at once, often between 5am and 9am, when few people are around to see. They stay open for perhaps an hour or two, and then the lodicules shrivel again to close the lid.

Breathed in and settling on the moisture of nasal airways, the pollen grains break open, their molecules provoking the immune systems of vulnerable (often urban) people into the quite excessive symptoms of seasonal allergic rhinitis, otherwise hay fever. In our early years on this hillside the breezes of July could indeed bring a few days of thick-headed misery, but advancing decades of exposure seem to have taught my immune system that it already has enough to get worked up about.

Meanwhile, this happens to be International Ragweed Day for most of rural Europe. But by 2050 or even earlier the appeal to root up this noxious plant before it gets the chance to flower will register in these islands, too. Ragweed’s economic costs to Europe, in healthcare and crop losses, are already an estimated at €4.5 billion a year, to say nothing of the seasonal suffering of several million people, including half the summer attacks of asthma.


Ragweed is not the common yellow ragwort of Ireland's late-summer waysides and neglected pastures but a plant called Ambrosia artemisiifolia, although how the bane of hay-fever victims in its native North America – and now much of Europe – came to involve the Greek "food of the gods" seems obscure. It is one of nature's global opportunists, eagerly invading the disturbed soil of ploughed fields, waysides and wastelands and annually producing millions of long-lived seeds.

A paper by French scientists, published this spring in the Nature Climate Change journal, predicted from computer modelling that rising warmth and extra carbon dioxide could quadruple the production of ragweed pollen by 2050, much of it through the plant's northern spread to areas where it is now rare. One plant can generate up to a billion grains of pollen in a season, travelling hundreds of kilometres on the wind.

Last year researchers from the University of Leicester recorded airborne ragweed-pollen levels in the English east midlands high enough to cause rhinitis, and the UK is now one of 33 EU countries in a four-year research network to find biological means of control. One candidate now under trial is a ragweed leaf beetle, Ophraella communa, already successfully voracious in Asia and recently found unexpectedly in southern Switzerland and northern Italy.

So what has the Swiss-based International Ragweed Day to do with Ireland just this minute? It is the conclusion of one European research study after another that spilled birdseed contaminated with Ambrosia artemisiifolia has been a leading cause of the spread of ragweed in Europe.

Even in Ireland one of the half-dozen records of ragweed has been of plants growing from discarded birdseed in a Co Down garden. The others, mostly in southeastern counties, may well have grown from seed in imported grain or chickenfeed. One large plant, found growing on Alexandra Quay in Dublin docks in 2001, was given a special mention in Sylvia Reynolds's A Catalogue of Alien Plants in Ireland.

So, while we wait for a warming world to infiltrate ragweed into our landscape, some small alert for those bird-lovers who offer back-garden tubes of imported seed now seems appropriate. In my own experience, shoots of strange cereals and grasses may, indeed, appear in the flower bed beneath the feeders. What to look for now are the filigree leaves depicted in my drawing, on a plant with tight-packed flower heads that grow up into tall, slim green-yellow spires. Don’t let them stand, even out of curiosity.