What is ash dieback?

Find the answers to the most frequently asked questions about ash dieback.

Tree surgeon felling a tree with ash dieback

Facts about ash dieback

Ash dieback is a serious threat to ash trees of all ages and it will kill up to 95% of the ash trees it infects across the UK, with the effects of the disease impacting the landscape forever.

In this article, our Manchester tree surgeons provide the answers to our customers’ most frequently asked questions about ash dieback.

1. What is ash dieback?

Originating in Asia, ash dieback (Hymenoscyphus fraxineus) is a fungus that does not result in much damage to its native hosts, Manchurian ash (Fraxinus mandshurica) or Chinese ash (Fraxinus chinensis).

However, ash dieback has unfortunately destroyed the European ash (Fraxinus excelsior) following its introduction to Europe three decades ago. That was a result of native ash species not evolving with the fungus to create a natural defence against it.

2. How does ash dieback affect a tree?

Leaf litter covering the ground, and in particular, ash leaf stalks, is where the fungus winters. Between July and October, the fungus will produce small white fruiting bodies. These bodies release spores into the immediate area. With wind action, the spores can be sent as far as tens of miles away from where they were released. They stick to leaves and eventually penetrate the leaf and other parts of the tree they have attached to.

The fungus will grow inside of the host tree and over time, will cut off the water transport systems causing the tree to die. Trees will fight back but repeated annual infections will weaken and destroy the tree.

3. What does ash dieback look like?

Although this fungus can affect trees regardless of age, younger trees will die faster. The symptoms that commonly appear include the following:

Leaves – During the summer months, the trees leaves will develop dark patches. After that, the leaves will wilt and completely turn to black. In some cases, the leaves may fall from the tree a little earlier than normal.

Branches – Lesions develop in locations where the branches of the tree join the trunk. The lesions are dark brown and shaped similar to diamonds.

Trunk – The inner bark of the trunk will have a brownish-grey colour underneath the lesions. There will also be new growth coming from buds that were previously dormant further down the trunk. This is a common sight when trees are stressed. It is known as epicormic growth.

4. When and where did ash dieback first appear in the UK?

Although it was not formally described until 2006, the ash dieback fungus has been known to exist in the UK for at least 30 years. It has had the most impact to date in the south-east of England where the first recorded sighting of it was made in 2012.

As for how long the fungus had been in the area before symptoms were identified, it is not known. There has been evidence of ash dieback in several other parts of the UK but, unfortunately, experts believe that the epidemic to plant life is only just beginning.

5. How did ash dieback get to the UK?

The spores produced by the ash dieback fungus can become airborne and travel a fair distance. Although ash dieback possibly arrived in the UK naturally, it may have also been accidentally transported on ash saplings.

Before a ban being imposed in 2012, thousands of plants were being imported to the UK from infected parts of Europe. This may have contributed to a speeding up of the spread of ash dieback in the UK.

6. What can we do to manage and control ash dieback?

It is too early to tell whether natural tolerance to ash dieback will increase in the UK, but there are indications that some trees are tolerant of ash dieback. This could point to a recovery of ash trees over time. However, that could take upwards of 50 years to take hold. As for disease tolerance specifics, the variables are many and include such factors as the volume of spores in the air, the health of the tree, and the genetic traits of the tree.

With Ash dieback becoming such a serious concern, we all have to work together to keep this devastating fungus under control. We can stop the damage and slow down the spread by taking a few precautions. Here are a few things you can do to prevent the spread in your neighbourhood:

  • Clean your shoes before you visit the woods. Once you return home, clean your shoes once again. This will ensure that if you stepped on some spores, they don’t get transported into your garden from the bottoms of your footwear.
  • Do not take cuttings or plant material from the outdoors and beyond to your property. It may be tempting to take something from the woods and attempt to grow it at home. However, if that cutting or plant has been infected, or is carrying some form of ash dieback, you will have introduced it to your home and garden.
  • Wash your vehicle and bike wheels to remove mud, dirt, and plant material. Again, this stops the spread of anything should your wheels or tires have come in contact with the material that contains ash dieback spores.

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