Disease-resistant Elm Project
The field trials of native and non-native disease-resistant elm trees are continuing with promising results. Most of the elm species and hybrids planted appear to be very suited to the local soils and climate. The majority of the elms, which were mainly sourced from research centres in the Netherlands, Spain and Italy, were planted in 2012.
Clones of three disease-resistant Ulmus minor trees discovered in Spain have been planted at Trelusback more recently and are doing well. These are the same species as many of the elms which succumbed to Dutch Elm Disease in Britain. In Spain this species reproduces from seed and is therefore more varied in levels of disease resistance compared with the trees in Britain. A small number of the trees in Spain were found to have high levels of disease resistance and were tested by inoculating them with the disease.
The trees in Britain, when originally introduced from other countries probably by the Romans, were mostly cloned by using suckers or cuttings and unfortunately were cloned from trees with poor disease resistance. The Dutch Elm disease was unknown at that time and these trees thrived in Britain for hundreds of years. The elms were introduced for many purposes including water pipes (when hollowed out), vineyard posts, waterways and boats. Since the arrival of Dutch Elm disease these trees in Britain now typically grow for ten to fifteen years before becoming attractive to the beetles that carry the disease. The trees die back to the ground before producing suckers. The cycle of growth and die back is then repeated. Each time the trees die the caterpillars of butterflies and moths that use elm trees are also unlikely to survive.
Eleven of the hybrid trees obtained from Italy in 2012 are now flowering profusely each Spring. This makes them suitable for colonisation by the White-letter Hairstreak butterfly. It is believed that the elm trees will also be suitable for a future White-letter Hairstreak research project to study the butterfly's dependence upon elm flowers for the early stages of its life cycle. This butterfly has not been seen at Trelusback for over 20 years since the previously existing Cornish elm trees succumbed to Dutch Elm Disease. Some of the new trees have already been used by the Comma butterfly with their larvae typically being found on the South side of the trees. Purple Hairstreak butterflies have also been seen feeding on the honeydew left behind by aphids. Many moth species have also used the trees as larval food.
All of the elms planted at Trelusback were cloned from trees previously tested at the research centres in Europe and found to have high levels of resistance to Dutch Elm Disease. It is hoped that they will now be suitable to replace the many Cornish and English elm trees lost to disease over the last sixty years. To date the new trees have shown no evidence of damage by disease despite being near the native elms which continue to die back to ground level when attacked by the beetles that carry the disease. It is possible that the Dutch Elm Disease will mutate again and could kill some of the elms currently resistant to the disease. For this reason a wide variety of elm species and hybrids has been planted at Trelusback. There are also other diseases of elms such as Elm Yellows.
The photograph below (bottom left) shows two of the new trees covered in developing seeds and emerging leaves.
Clones of three disease-resistant Ulmus minor trees discovered in Spain have been planted at Trelusback more recently and are doing well. These are the same species as many of the elms which succumbed to Dutch Elm Disease in Britain. In Spain this species reproduces from seed and is therefore more varied in levels of disease resistance compared with the trees in Britain. A small number of the trees in Spain were found to have high levels of disease resistance and were tested by inoculating them with the disease.
The trees in Britain, when originally introduced from other countries probably by the Romans, were mostly cloned by using suckers or cuttings and unfortunately were cloned from trees with poor disease resistance. The Dutch Elm disease was unknown at that time and these trees thrived in Britain for hundreds of years. The elms were introduced for many purposes including water pipes (when hollowed out), vineyard posts, waterways and boats. Since the arrival of Dutch Elm disease these trees in Britain now typically grow for ten to fifteen years before becoming attractive to the beetles that carry the disease. The trees die back to the ground before producing suckers. The cycle of growth and die back is then repeated. Each time the trees die the caterpillars of butterflies and moths that use elm trees are also unlikely to survive.
Eleven of the hybrid trees obtained from Italy in 2012 are now flowering profusely each Spring. This makes them suitable for colonisation by the White-letter Hairstreak butterfly. It is believed that the elm trees will also be suitable for a future White-letter Hairstreak research project to study the butterfly's dependence upon elm flowers for the early stages of its life cycle. This butterfly has not been seen at Trelusback for over 20 years since the previously existing Cornish elm trees succumbed to Dutch Elm Disease. Some of the new trees have already been used by the Comma butterfly with their larvae typically being found on the South side of the trees. Purple Hairstreak butterflies have also been seen feeding on the honeydew left behind by aphids. Many moth species have also used the trees as larval food.
All of the elms planted at Trelusback were cloned from trees previously tested at the research centres in Europe and found to have high levels of resistance to Dutch Elm Disease. It is hoped that they will now be suitable to replace the many Cornish and English elm trees lost to disease over the last sixty years. To date the new trees have shown no evidence of damage by disease despite being near the native elms which continue to die back to ground level when attacked by the beetles that carry the disease. It is possible that the Dutch Elm Disease will mutate again and could kill some of the elms currently resistant to the disease. For this reason a wide variety of elm species and hybrids has been planted at Trelusback. There are also other diseases of elms such as Elm Yellows.
The photograph below (bottom left) shows two of the new trees covered in developing seeds and emerging leaves.