Disease resistant elms

The Covid-19 lockdown has interrupted our plans for the five disease resistant elms donated to the park by Butterfly Conservation as part of their rescue plan for the white letter hairstreak butterfly.

In order to protect us from possible coronavirus infection, Wiltshire Council closed our volunteer programme two weeks ago. Unfortunately this also closed our access to the expertise of the Countryside Team, our Tree Officer and the Council’s extensive range of tools; and it has left 250 of the whips donated by the Woodland Trust and our five disease resistant elm saplings un-planted.

1 Disease resistant elms in the back of Ian Bushell’s car. 2 Elm bark beetle

Dutch elm disease

Dutch elm disease is one of the most serious tree diseases in the world. It was originally identified in the 1920s in an outbreak that killed perhaps a quarter of Britain’s elm trees. It returned in an even more aggressive form in the 1970s and killed almost all of our mature elms and continues to spread today.

It is caused by a fungus that is carried between trees by several species of beetle of the genus Scolytus that lay their eggs underneath the bark of elm trees. When the eggs hatch, the feeding larvae create distinctive fern-like patterns in the wood just under the bark.

By the late 1980s the bark beetles had infected most of the mature elms that they relied on for breeding sites, beetle populations declined as the trees died and the disease virtually disappeared from many southern and south-western areas.

The elm saplings, suckers and seedlings, too young to meet the elm bark beetle’s requirement as sites for egg-laying, survived. The beetle returned, though, to attack this new generation of elms once they were large enough to support their reproductive needs. Treatment seemed impossible, so the focus has been on developing disease resistant cultivars.

3 Marks left by elm bark beetle larvae 4 White letter hairstreak

White letter hairstreak

White letter hairstreak butterflies are entirely dependent on elm trees. They lay their eggs in the tops of elm trees, their larvae feed there and the adults live there in small colonies.

We hope that there is a colony of white letter hairstreaks in the young elm trees in the hedge at the bottom of Sleepers; they have been seen and reliably identified there. Our five disease resistant elms is an attempt to provide long term habitat for these rare butterflies before the Dutch elm disease catches up with and kills the young trees they are presently colonising.

At the moment our sapling disease resistant elms are safe in pots in an FoSCP garden, the 250 whips will be temporarily planted in a trench, probably in the same garden, and we will wait for the emergency to end.

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