Dutch Elm Disease Rears Its Ugly Head

By [http://ezinearticles.com/?expert=Saffra_Hall]Saffra Hall
Dutch Elm Disease has had a dramatic affect on the British elm population over the past century. The disease first reached north west Europe in 1910 and has had two notable pandemics in Britain since that time. The first reached its peak in the 1930s where it has been estimated that up to 40% of British elms were killed. The second pandemic, where a more aggressive form of the fungus (Ophiostoma novo-ulmi), began in th1960's and is still continuing today! It is estimated that in excess of 25,000,000 elms have been lost across Britain during this second pandemic.
Part of the reason the disease has been so wide spreading is due to its symbiotic relationship with the elm bark beetle (Scolytus scolytus). The beetle, which can travel up to eight miles in search of a suitable host tree, carries the fungus with it. The beetles feed on the tree, infecting it. As the tree dies back, the beetles bore under the bark laying their eggs. The eggs hatch and the larvae feed under the bark forming noticeable galleries and emerge to find new host trees.
An infected tree will react to the disease by blocking the xylem vessels to prevent the infection spreading. It does this through a process called tylosis. This not only prevents the fungus spreading through the cells, but also prevents water too. Without water reaching the foliage, the process of transpiration cannot occur and branches will die, eventually killing the tree. When a beetle has found a dying tree, it releases chemicals into the air that attract other beetles to its location.
Once infected, there is no cure for the tree. It should be removed and the wood disposed of correctly. Elm logs can still support the beetle even when cut up and stacked on the ground. Even uninfected elm logs can support the beetle and should therefore be disposed of appropriately. Burning is the most efficient method of disposal, though de-barking the logs will prevent beetles from breeding. When an infected tree is felled, the stump should either be ground out or de-barked.
Identification of an infected tree can be relatively simple. The sudden death of an infected branch can be a sign. Removing a shoot from the predicted area of infection and tearing back the thin bark may reveal staining. The tissue inside should be white, however if it is brown, it is likely that the tree is infected. Another obvious method of   rel=nofollow [http://www.pjcconsultancy.com]identification is on elms in an advanced stage of decline (or even dead trees) where the thick bark is removed to reveal the larval galleries. These form regular patterns and are easily identifiable when you have seen them before.
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