Identify and diagnose Dutch elm disease
Dutch elm disease is one of the most serious tree diseases in the world. It has killed over 60 million British elms in two epidemics and continues to spread today.
This page will help you to identify and diagnose Dutch elm disease and will tell you all that you need to know about its history and spread throughout Britain.
Details of the disease
- First epidemic caused by fungus Ophiostoma ulmi from the 1920s onwards
- Second and ongoing epidemic caused by the highly aggressive and related fungus O. novo-ulmi, first recognised in the 1970s
- Elm bark beetles in the genus Scolytus disseminate the fungus
- Infects all of Britain’s major elm species
- Fungus invades water conducting system of trees
Symptoms and diagnosis
- Symptoms first appear in early summer
- Clusters of leaves turn yellow and wilt
- Leaves then turn brown and fall
- Affected shoots die back from the tip
- Twigs sometimes turn down to form ‘shepherd’s crooks’
- Twigs have dark streaks in the outer wood beneath the bark, or spots or rings in cross section
Browse more pictures of disease symptoms and find out how to make a diagnosis
- We have shown that Ophiostoma ulmi and O. novo-ulmi have spread across Europe, North America and central Asia in two major migratory events.
- The two pathogens cannot coexist when their ranges overlap and O. ulmi is eliminated although transient hybrids are formed between the two species. This has allowed useful genes to be acquired by O. novo-ulmi from O. ulmi and been the driver for rapid evolutionary change.
- Ophiostoma novo-ulmi exists as two subspecies: subspecies americana and novo-ulmi. They are currently hybridising freely in Europe where they come into contact having invaded the continent in a ‘pincer movement’
- ds RNA viruses, known as d-factors, debilitate both Dutch elm disease pathogens. A recent collaboration with Scion, New Zealand, has explored the potential of these viruses to act as bio-control agents of O. novo-ulmi.
- The beetles that spread Dutch elm disease have distinct feeding preferences for certain species of elm, so even susceptible elms can sometimes escape the disease if they are not attractive to the beetles.
- The geographic origins of both elm pathogens are unknown. However, emerging evidence suggests that O. ulmi could be endemic to Japan.