What is Dutch Elm Disease?

Dutch Elm Disease or  (DED) is a serious disease of elm trees which is caused by the fungus Ophiostoma novo-ulmi. It is a type of disease known as a vascular wilt because the fungus blocks the vascular (water transport) system, causing the branches to wilt and die. It is spread by elm bark beetles. You will normally begin to notice the damage in summer and early autumn.

Symptoms of Dutch Elm Disease

During the summer months, all or part of the em trees foliage suddenly turns yellow, then wilts shrivels and dies.

To check, Peel off the bark from the affected branches and you will see brown streaks in the outer wood, which appear as a broken or continuous brown ring in the outer growth ring if the branch is cut across

Dutch elm disease has over the years ravaged the Word’ Elm tree population.  There are in fact only a few places in the world that remain untouched by the disease.

Controlling Dutch Elm Disease

Non-chemical control

The disease has proved almost impossible to stamp out and apart from a few areas (the Isle of Man and Brighton and Hove) all attempts to prevent the spread of the disease have been abandoned. When the trees die or are dying it is sensible to have them felled immediately rather than run the risk of dead branches falling onto people or damaging property.

The RHS advise that native elms should not be planted, as it’s most likely that they will get DED.

It is possible to buy resistant hybrid elms, but these trees are not exact replacements,

The Conservation Foundation has a Native Elm Programme for propagating elms from the survivors of the last disease outbreak. Anyone who knows of a healthy mature elm (at least 190cms circumference at breast height) or would like an elm to plant as part of the experimental programme is encouraged to contact the Conservation Foundation.

Chemical control
Today there is no chemical control operation being employed to tackle the beetles. Initially, Protectant fungicides were injected into trunks of elm trees, but these treatments were required annually and were not considered to be feasible or cost-effective. Control of the beetle is also virtually impossible too.

More about the Fungus

One interesting face about DED is that the disease is known as ‘Dutch’ because important early research on it was carried out in the Netherlands. the disease did not originate there.

It is caused by the fungus Ophiostoma novo-ulmi which was accidentally introduced to the UK from the USA in the late 1960s on imported elm logs.

Before the introduction of Ophiostoma novo-ulmi, northern Europe already had a form of DED caused by another related fungus, Ophiostoma ulmi. and for some time it was not realised that the fungus in the UK was different. O. novo-ulmi is not native to the USA and its true origin is unknown.

The fungus is spread by elm bark beetles, particularly Scolytus scolytus.

Elm bark beetle

The elm bark beetles breed in dead and dying elm trees.  Their larvae dig tunnels in the bark and surface wood, forming galleries. The fungus produces sticky spores in these galleries which contaminate the beetle eggs and larvae.

As the newly hatched adult beetles emerge. They fly to healthy trees, feed on young bark and introduce the fungus into the tree

Have Hands on Tree Care had Experience with Dutch Elm Disease?

Yes, the last instance was in fact in June 2018

We were called to “The Elm Tree” Pub at Heath, Derbyshire. Sadly the Elm Tree which has stood there for 20 years has succumbed to the Dutch Elm Beetle.

Elm Tree with Dutch Elm Disease
Note the withered leaves.

Unfortunately, this is inevitable as an Elm reaches maturity. The landlord realised the tree was starting to lose its leaves and called us in to investigate. After a site assessment, the disease was confirmed, the tree was clearly showing signs of die back.

The Landlord was concerned if the tree was left standing it could pose a risk to patrons of the pub.  Naturally, he was concerned about the possibility of falling branches.  We decided that felling to ground level was the safe option.

 

Elm Tree felled
Felled by sectional dismantling

All works were completed within the day.

Related Links
The Conservation Foundation
resistantelms.co.uk.
Elm Beetle