'Replacement' elm identified
11 September 2010
An Italian-bred elm with proven resistance to Dutch elm disease has emerged as the most suitable candidate to return the much-missed elm tree to the British countryside following trials of resistant varieties by Butterfly Conservation.
Ulmus 'Morfeo' was bred in Florence in 2000 and is a cross between a Chinese elm known for its resistance to Dutch elm disease, U. chenmoui, and a hybrid of U. x hollandica and the field elm, U. minor.
Of the 13 disease-resistant cultivars trialled, it showed the best adaptation to UK growing conditions and had the closest similarity to U. minor, once the most commonly-seen elm tree along with the wych elm (U. glabra). Nearly all have now disappeared following the ravages of Dutch elm disease (Ophiostoma novo-ulmi) during the 1970s.
The Hampshire and Isle of Wight branch of Butterfly Conservation have been trialling disease-resistant cultivars as they have become available over the last 10 years, evaluating the trees as potential hosts for the endangered White-letter Hairstreak butterfly which depends on elm trees for its survival.
'The principal advantage of 'Morfeo' was its phenology, leafing at the ideal time for the butterfly,' said Andrew Brookes, who oversaw the trials. 'But we also wanted to identify trees which would tolerate the British environment. Many of the disease-resistant cultivars, owing to their Asiatic heritage, are unable to thrive on our winter-wet climate and clayey, waterlogged soils.'
Unfortunately U. 'Morfeo', released commercially for the first time earlier this year, is not yet available in Britain. However several other resistant cultivars did almost as well in the trials and are easily obtainable from UK nurseries. These include US-bred 'Valley Forge' and Dutch-bred 'Lutèce' and 'Vada'.
The Forestry Commission has now begun planting cultivars with proven resistance to Dutch elm disease and Butterfly Conservation has also sourced disease-resistant trees for other landowners, including the National Trust and several nature reserves.