Dutch elm disease (Ophiostoma novo-ulmi)

What does Dutch elm disease look like?

Symptoms include:

• Clusters of yellow leaves that wilt and fall.
• Shoots that die back from the tip.
• Twigs that bend down in a ‘shepherd’s crook’.
• Dark streaks underneath the bark of twigs, or dark spots and rings in the cross-section.

What is Dutch elm disease?

Dutch elm disease is caused by the fungus Ophiostoma novo-ulmi which is spread by elm bark beetles. It got its name from the team of Dutch pathologists who carried out research on the diseases in the 1920s.

Where has Dutch elm disease impacted?

Since its introduction to the UK, it has killed millions of our elm trees. It has devastated populations in mainland Europe and North America too.

How did Dutch elm disease get here?

Dutch elm disease was accidentally imported into the UK from Canada in the late 1960s. It spread quickly, reaching Scotland in just 10 years.

The movement of elm products caused the spread of the disease, particularly on logs with bark attached but also through saplings, crates and mulching bark.

Outlook

There has been work in universities across the world to develop resistant elms and these hybrids are subjected to inoculum trials to assess their resistance to Dutch elm disease.

While these resistant strains look similar to English varieties of elm, it’s important to realise that they are exotic species. They might not perform the same ecosystem function so replacing elms with them is not a complete solution.

The spread of the disease can also be slowed with sanitary felling of dead and dying trees which removes the habitat of the beetles which carry the fungus. This type of management has been very successful in East Sussex where there are now more elms than there were before the disease hit. Some elms have been replaced with plants propagated from trees that have resisted the disease so far.

What are we doing about it?

To the spread of pests and diseases like Dutch elm disease we have:

• Developed a UK and Ireland Sourced and Grown assurance scheme to make sure that all the trees we plant and sell are produced in the UK.
• Lobbied the government to improve biosecurity at border points to stop new pests and diseases entering the UK.
• Partnered with Observatree, a tree health citizen science project which trains volunteers to spot pests and diseases, thereby helping tree health authorities identify and manage outbreaks early.