Resisting Dutch Elm Disease with Ulmus 'New Horizon'
Image: An avenue of Ulmus ‘New Horizon’ in Cardiff Pontcanna Park
- July 2017
Ulmus ‘New Horizon’ is the perfect solution for virtually any design need. A proven winner that withstands pretty much everything you can throw at it – floods, sub-zero temperatures, inner city pollution, poor soils, central reservations and salt-laden coastal roadsides!
Unlike other new cultivars that have succumbed to Dutch Elm Disease, New Horizon is not affected and is great for wildlife too. It is 100% resistant to Dutch Elm Disease.
Every Ulmus ‘New Horizon’ supplied by Hillier Nurseries will come with a special Ulmus label and a Certificate of Authenticity. This proves they are fully tested elms, which are resistant to Dutch Elm Disease.
The Historic Spread of Dutch Elm Disease
Few of us can remain unmoved by the tragic fate of the elm tree during the last century. More than 70% of these glorious trees in Europe and North America have perished since the first outbreak of ‘Dutch Elm Disease’ in the 1920’s. Although it is still unknown how the pathogen, the fungus Ophiostoma ulmi, found its way into the elm population, its terrifying spread is due almost entirely to two types of beetle: the Large Elm Bark Beetle (Scolytus scolytus) and its lesser cousin the Small Elm Bark Beetle (Scolytus multistriatus).
These beetles live harmlessly under the bark of the elm, feeding on small new shoots. But in the spring, when the young emerge, they fly to another nearby elm carrying the deadly Ophiostoma spored with them. The fungus spreads through the tree, interrupting the liquid transportation system by blocking the xylem vessels. Deprived of water and nutrients, the tree begins to desiccate and starve, and most are dead within a year.
Development of Resistant Varieties
Since the 1950’s, scientists led initially by Professor Eugene B. Smalley of Wisconsin University began a series of experiments to hasten the progress of those already working on the problem. What began with simply selecting seemingly more resistant varieties was later tackled more aggressively by injecting dozens of varieties of elm with a strain of Ophiostoma fungus in their 3rd or 4th year of growth. This enabled breeders to select those trees better able to resist the fungus or to restore flow to blocked vessels and hence recover from the fungal attack. These trees were then crossed and re-crossed to strengthen their resistance.
This research led to a range of elm species known as ‘Resista’-elms. These are so far proving extremely effective at resisting this deadly disease and in fact come with a 10-year guarantee from the growers. As well as their resistance to Dutch Elm Disease, all have been selected as normal for fast growth, well-shaped crown, erect stem, leaf form and colour, resistance to stress, salt, drought and frost.
Ulmus ‘New Horizon’ thriving on the exposed coastal roads around Cardiff Bay
Ulmus ‘New Horizon’ is First of Resistant Elms
There are now a half dozen varieties of Resista-elm available for planting in Europe, and Hillier Nurseries are the exclusive partner for the UK and Ireland for the Resista-elm programme.
The first of these Resista-elms we feature is Ulmus ‘New Horizon’. This is a medium-sized tree with one straight central leader. A dense conical crown shows even branches and upright twigs. The leaves are a dark silky glossy green. It grows best in a sunny or part-shaded position, in neutral or slightly acid soil, well aerated and with a good water supply. It can tolerate compact soils and is resistant to stress from traffic, wind and frost. ‘New Horizon’ is particularly suitable for avenue or street planting because of its compact habit. Only small seeds are produced and the leaves decompose fast.