Dutch elm disease is a fungal disease affecting elm trees. A particularly virulent form of the disease hit Britain in the mid nineteen sixties killing many English elms. A pandemic began affecting trees in Europe between the nineteen twenties and nineteen forties reaching Britain by the mid nineteen sixties. The disease was first noticed in the Netherlands and, therefore, called Dutch elm disease.
In the nineteen sixties, people did not realize, initially, quite what was wrong. English elm trees usually showed the first signs of infection by the Ophiostoma novo-ulmi on their upper branches, leaves began to yellow and wither in summer, much earlier than the usual autumnal leaf drop. Spreading to the rest of the tree causing branches to die, eventually because the roots are not getting nutrients from the leaves, the tree’s roots die too. Sometimes in English elms, not all the roots die immediately, but send up suckers, which appear healthy for around fifteen years but are infected and die after around fifteen years.
The elm bark beetle carries the disease and spreads it through elm trees very effectively. The disease cycle begins when young adult beetles emerging from the bark of dead elm trees, in spring, get fungal spores on their skin. They then fly to healthy elm trees where they feed on young bark, the disease spores enter the tree in this manner spreading quickly by growing into a yeast-like substance. This then rapidly kills branches or the whole tree. In the autumn, female beetles burrow into the dead bark, on such trees, and lay their eggs. The eggs hatch into larvae, which then eat the bark until they are large enough to pupate, and emerge as adults the following spring to begin the cycle anew.
It is likely that strains of Dutch elm disease have affected elm trees periodically since pre-historic times. In around 1967, a new and virulent strain of Dutch elm disease arrived, in England, in a timber shipment from the United States. It ravaged the United Kingdom, killing more than 25 million elm trees. The disease is still heading north through Scotland, it reached Edinburgh in the nineteen seventies and Inverness in 2006. By the nineteen nineties there were few mature elms left in the United Kingdom. It was terribly sad to see the gaps left by the necessary felling of diseased elms. Brighton and Hove, in East Sussex, is the only place in the Untied Kingdom to have a large concentration of mature elm trees now. There are around 15,000 mature elms in the city, some of which are more than four hundred years old. They owe their survival to the city’s isolation between the English Channel and the South Downs and the city’s aggressive disease management policies, requiring the immediate removal of diseased branches or trees showing symptoms. Local Authorities in the United Kingdom can, by law, order infected elm trees or timber, in their area, to be destroyed regardless of who owns them.
Although growers have developed disease-resistant foreign hybrid varieties these are not native to the United Kingdom and were not introduced. However, there is hope that English elms may once again grace the English countryside. It appears that some native English elms may have a genetic resistance to the disease. The Great British elm experiment is currently underway to discover whether this is indeed the case. If the experiment proves that some English elms have a genetic immunity to Dutch elm disease, it may lead to the English elm’s reintroduction to the United Kingdom, restoring one of Britain’s native tree species to its rightful home.