We must breed new life into resistance to ash tree threat

Because our ash forests are young, it’s difficult to put a value on them, according to Dr Douglas, but he estimates that the State has invested more than €90 million to support the development of plantations over the past two decades.

“It’s a huge investment and a huge potential loss, because if the level of infection is very high not only will a proportion of the trees be killed, most of the other trees just won’t develop as they normally would.”

Because the fungus kills off a proportion of the leaves, it can stunt an individual tree’s ability to photosynthesise and grow. Younger trees are particularly vulnerable because they have less in reserve, explains Dr Douglas. And even when the diseased leaves fall off, the story isn’t always over – infected leaves can harbour the fungus and spores get released the following summer, when they can can re-infect the tree and even spread to others.

In addition, Ireland’s climate tends to be one that fungi generally like, he adds.

Halting the spread

One way to try and halt the fungus is to fell and burn infected trees, and to burn or bury the leaf litter that could be a source of spores.

Another positive step would be to implement a more rigorous tracking system for imported ash, according to Dr Douglas.

“So far any of the disease that has come in has been on imported plants,” he says. “At the moment there is documentation when you import plants to say where they come from, but plants are traded very extensively and it’s sometimes difficult to follow the paper trail. We really need a verifiable system using DNA technology so that we can trace where the trees come from if we import any plants. ”

And in the longer term, breeding programmes could offer a lifeline.

“Even if the outbreaks aren’t very bad in Ireland, we have to now consider breeding for resistance – we need to take this breathing space to gain a lead on the disease,” says Dr Douglas.

He is carrying out research to select and propagate trees with good “stem” qualities, and a small proportion of these trees may be resistant to ash dieback disease.

They could be identified and they could form the basis for new generations of high quality trees which also carry resistance, he explains: “That’s what we are planning at the moment.”