Dutch Elm Disease

 Dutch Elm Disease.

Dutch Elm Disease (DED) is one of the few tree diseases that most people have heard of. The first clarification that is needed is to say it did not come from the Netherlands. The epithet Dutch comes from the fact that the causal fungal agent was first identified there in 1921. The first  European description of the disease was also in the Netherlands in 1905. It probably has an Asian origin.

Larval galleries on dead 6" diameter
trunk. Dead Elm provided fuel when I 
first got the field.

There are three species of ascomycete microfungi in the genus Ophiostoma recognised as causing DED. O. novo-ulmi being the most virulant. This was introduced to Britain in the 1960's from Canada via Rock Elm imported through Bristol docks. Most large Elms had died by the end of the 1970's. The fungus is spread by bark beetles whose larvae eat the nutritious cambium layer the area where stem width growth takes place. The Large Elm Bark Beetle is a strong flyer and spread was rapid. The trees try to contain the Fungus by blocking water conducting tissues. The larvae  also interfere with the movement of water and nutrients within the tree. A die back type disease is formed where the ends of shoots where the water has furthest to go deteriorate and die. Eventually  the trunk gets girdled so all the tree upstream of the girdling dies. The fungus can keep spreading down into the roots which eventually die.

An original stump, there were also several dead secondary trees.
There have also been trees lost since.

                                     When the Cairn Wood field was bought in late 2006 there were Elms along the stream side about half way along near where a ditch joins the stream forming a field boundary on  the other side. There was a long dead stump from a large Elm on which the larval galleries of the beetle were visible. The stump has  weathered and is much reduced but does illustrate the durability of Elm timber. There were smaller Elms for about 50yrds either side of the stump. These were presumably suckers and the dead tree an English Elm. See Elm Species

An Elm hedge beyond Weston. A hedge which has not 
been cut regularly. As the plants reverted to
 hedge row trees they have died.

 The English Elm was a common hedge forming species. It can be cut back hard and as it suckers naturally fills in gaps and provides planting material for other hedges. Elm hedges could be identified by the large dead hedgerow trees sticking out of them.  Parts of the the hedge between Normanton and Normanton crossing were like that when I came to Sutton. The dead trees have now gone, but the hedge remains. There are lots of Elms at the Carlton cross roads end of the road to Ossington. Some are dead but small diameter ones survive. There is a large (Wych?) Elm in Kneesall which has not been affected. 

The White Elm in Cairn Wood.
Photo start of November 2023.

There is a White Elm currently unaffected in Cairn Wood near the stream at the far end. It came from Esmond Harris and was planted about 2009. The same time as the Oaks near it. It is very much bigger than them. Part of the hedge on Carlton lane opposite the track to the Rhymes is Elm. It is regularly cut and though there have been dead hedgerow trees in it it is sound. It was also the first place I found signs of  Elm Zig Zag Sawfly.

The reason that hedges survive while trees fail is simple the beetles do not lay their eggs on small diameter wood. This may be because the burrowing larvae would girdle and kill a small branch before maturing. It takes several generations to kill a large tree. The fungus can also spread into the roots and infect conjoined trees.