# Ash Trees - there is a deadly fungus among us



## Planeman40 (Nov 3, 2010)

Will this come to the USA?

*Are Europe's ash trees finished?*

October 2012 by Andy Coghlan
http://www.newscientist.com/article/dn22449-are-europes-ash-trees-finished.html?full=true

A fungus deadly to ash trees has just reached Britain and Ireland, after emerging 20 years ago in Poland. Already it has devastated ash trees in mainland Europe, sweeping through more than 20 countries powerless to prevent its spread.

How did this fungus develop? And what, if anything, can be done to stop it in countries like the UK, where ashes account for around a fifth of all trees? By the sound of it, the outlook is not good. New Scientist investigates.

Just how many ash trees have been killed?
Although there are no official figures, ash trees have effectively been wiped out in Poland, where the disease first made its appearance in 1992. In Lithuania, 99 per cent of the ashes are gone; in Denmark, 90 per cent. Elsewhere, the impact has been mixed, with some but not all ashes succumbing.

And now it's reached the UK?
Yes, hence the current panic. Since February, the disease has been spotted in several English nurseries. The outbreaks were traced to trees and seeds imported from countries that are already affected, so the response has remained low-key, although 100,000 nursery trees and saplings have been destroyed.

The alarm bells really started ringing last month when the disease was spotted in wild ash trees in East Anglia, one of the regions of England that is closest to mainland Europe. The likelihood is that the fungus must have spread here naturally.

How did it do that?
It probably blew in from the European mainland; the fungal spores can travel great distances by wind. Alternatively, it may have been brought here by contaminated birds, or even vehicles and people.

How does the fungus kill ash trees?
Fungal spores land on leaves, germinate and begin invading tissue. It starts with the leaf, then moves into the leaf stalks. Ultimately the fungus spreads into the tree's trunk. As it spreads, the fungus chokes off all water channels in the tree, so in its wake tissues wither and die. Eventually, the tree succumbs.

Can it be stopped?
Apparently not. Most countries where it has taken hold simply gave up. Part of the problem is that the fungus does not spread from infected trees themselves, but from infected leaves shed in the autumn. The fungus grows on the leaves and leaf stalks as they decay, then produces copious spores in summer which spread to uninfected ash trees, completing the life cycle.

"There's very little you can do," says Ottmar Holdenrieder of the Swiss Federal Institute of Technology in Zurich, who in 2010 helped uncover the fungus's complete life cycle. "It's a waste of time to chop down trees." The infective material is all on the forest floor and cannot be removed or eradicated with fungicides without destroying countless other forms of forest life.

Which fungus causes the disease?
This is a long story. It begins in 2006, when Tadeusz Kowalski of the University of Agriculture in Krakow, Poland, identified a newly discovered fungus, Chalara fraxinea, as the cause of the disease (Forest Pathology, DOI: 10.1111/j.1439-0329.2006.00453.x).

This did not solve the puzzle. Fungal species often exist in two forms: one that reproduces itself asexually, and one that multiplies sexually by producing spores. It turned out that Chalara fraxinea is asexual, so the real killer remained at large.

By 2009, Kowalski had found what he thought was the sexual form of C. fraxinea: Hymenoscyphus albidus, which produces spores from tiny toadstool-like growths on ash leaf litter (Forest Pathology, DOI: 10.1111/j.1439-0239.2008.00589.x). But this was something of a red herring. H. albidus has been growing on the decaying leaves of Europe's ash trees for centuries, so was unlikely to be the culprit. It has been known in the UK, for example, since the mid-19th century.

The real killer was unmasked a year later, and produced toadstools identical to those of harmless old H. albidus. Using painstaking genetic analysis, Holdenrieder, Kowalski and others found that this doppelganger was actually a different, and lethal, species. They named it Hymenoscyphus pseudoalbidus (Forest Pathology, DOI: 10.111/j.1439-0329.2010.00645.x).

How did this killer emerge, apparently out of the blue?
Holdenrieder and his colleagues are still investigating that, and should reveal their results next year. For now, their hunch is that it came from Asia, either via the wind or accidentally brought in on imported ash trees. There is circumstantial evidence: ash trees in Asia are immune to the disease.

The ideas that H. pseudoalbidus evolved from its close European relative, or that climate change made European ashes more vulnerable to a pathogen that was already there, have both been ruled out. In short, the fungus is new to Europe, and the serious money is on it arriving from the east.

Does our identification of the culprit help in combating the disease?
Sort of. The most important thing is that it may now be possible to breed or develop ash trees that are immune to the fungus. These have already emerged in Lithuania, says Holdenrieder, where 99 per cent of the original ash population died out. He says that the offspring of survivors are proving resistant.

Alternatively, it might be possible to develop a vaccine, as was developed to protect elm trees against Dutch elm disease, but this is a distant goal.

Meanwhile, now that the fungus is in Europe, it is locked in an "arms race" with the ash trees. The fungus has the whip hand because it breeds far faster.

Can we do anything to stop the fungus evolving?
Newly published work by Holdenrieder's colleague Andrin Gross suggests that the key is to avoid importing any further variants of the fungus, as these help the fungus to continue evolving and overcoming resistance in the trees (Fungal Genetics and Biology, DOI: 10.1016/j.fgb.2012.08.008). "Ash trees will never be able to adapt if we constantly introduce new variants of the fungus," says Gross.

What's the best hope for UK trees?
Earlier this week, the UK government banned any further imports of ash trees. It also initiated a huge survey of forests in East Anglia to establish how far the disease may have spread. "Once we have a handle on how big or small this issue is, we can decide whether to go for eradication or containment," says a spokesman for the UK Forestry Commission.

The best hope is that any fungus is present only in small pockets that can be cleared to prevent further spread. The worst case is that it is everywhere, in which case it's probably goodbye to the English ash.

"If that's the case, there's nothing they can do about it," says Jim Briercliffe, business development manager of the Horticultural Trades Association (HTA) in Reading, UK, which represents suppliers of plants, seeds and gardening equipment. The only option will be to replace dead ash with other kinds of tree.

The HTA warned the government in 2009 that the disease was rife in Danish nurseries and could easily reach the UK. "It is annoying that our warning was ignored," he says.

How is mainland Europe coping?
"My gut feeling is that the whole of Europe will have to live with the disease in the long term," says Holdenrieder. "Ash tree populations will be reduced to less than 10 per cent what they were originally."

Meanwhile, researchers are pooling their resources to see what can be done. A pan-European group of Chalara specialists called FRAXBACK is meeting for the first time in November in Uppsala, Sweden.


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## Swyftfeet (Jun 15, 2012)

The mountain ash tree in my backyard died this year with large sections being debarked. I am no arborist but my pop who has about a billionty chainsaws said fungus killed it.


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## Arminius (Dec 27, 2007)

It is really sort of moot, the fungus is unlikely to get here in time

http://en.wikipedia.org/wiki/Emerald_ash_borer


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## dhazelton (Feb 11, 2012)

Yeah, the borer is a big deal in NY state. It mainly spread by people transporting firewood and non kiln-dried lumber (ie, pallets). On the plus side I have a lot of ash firewood right now.


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## fussy (Jan 18, 2010)

Also the Asian Long-Horned beetle is poised to devastate the Eastern Hardwood forests, the Wooley Adelgid is destroying the walnut tree by passing around a fungus that causes thousand cankers disease. Pretty soon, all we'll have left will be poplar and pine. Forest fires will get those. Plastic wood, anyone?

Steve


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## davidmicraig (Nov 21, 2009)

One could daydream that if we had the fungus, maybe the beetles could eat it, get sick, and die. Two menaces wiping each other off the face of the planet


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## mmh (Mar 17, 2008)

We just felled 5 trees on our wooded lot and several are red oak that just started dying for no apparent reason. They have been known to do that in this area (central Maryland). One tree looked to be dead for several years and center of the tree had large insect holes which must have killed it. The bottom of the tree was fine and healthy wood (although the tree was dead and had no limbs left on it).


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## Manitario (Jul 4, 2010)

As others have said, I'm not sure the fungus is our biggest worry, I don't think there'll be any trees left for it once the Ash Borer is done…


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## Magnum (Feb 5, 2010)

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## BigYin (Oct 14, 2011)

Dutch Elm was known about and nothing was done till too late.
M.A.F.F knew about ash fungus and did not stop imports of ash to UK till too late. 
Abu Hamza was known about and was allowed into the country where we fed and housed him and all his family, taking years to get him out (extradited to US)
And its my taxes paying for this level of incompetance …. Sheeeesh


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## Purrmaster (Sep 1, 2012)

Ah, crap. I really like ash wood. Are there any control measures for the ash borer?


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## Dennisgrosen (Nov 14, 2009)

Dammed planeman
its only a few years ago they talked about some black spots in ash trees and they cuoldn´t 
see if the tree was attacked before they cut it up to be used in the furniture industry 
I didn´t knew it already have been spread out so much that 90 % of our ashtrees 
is attacked :-((((((
no wonder why ashfloors has gone from the market

thanks for the information

Dennis


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## OggieOglethorpe (Aug 15, 2012)

I like ash, too… Lots! I think it looks great unstained, and is a pleasure to work.

In CT, and NY, I see major efforts to get people to not moving firewood, and commercial logs. All over the east, as I ride my bicycle on trails, I see cobalt blue ash borer traps trying to identify the presence of the bug.

The flying version of the bug is kind of pretty. It's too bad it's so destructive.


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## Arminius (Dec 27, 2007)

There are control measures for the ash borer, but at around $400 per tree, it is not practical on a large scale. You can save the one in your yard, but not the forest you look onto.


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## OggieOglethorpe (Aug 15, 2012)

$400? What does it entail?


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## roman (Sep 28, 2007)

Coming to a theatre near you, whether you like or not.

It came up through Southern Ontario Canada, via the USA. Despite great efforts in cutting huge swaths of mature ash trees down and every baby ash tree, the cancer is continuing a slow march north and is probably due to the transportation of cut trees for firewood, by unintentional ignorance and the need to keep warm.

Like the giant elms and giant american chestnuts, the ash tree will one day be small patches of forest totally isolated by zero access from roads and its true value will drive the price of a board foot of lumber, through the roof.

Stock up


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