Dutch elm disease is one of the world’s most serious tree diseases. It is caused by the fungus Ophiostoma novo-ulmi, which invades and blocks the water conducting systems of trees. This results in the wilting and death of the tree.
- Symptoms first appear in early summer
- Clusters of leaves turn yellow and wilt
- Leaves later turn brown and fall
- Twigs sometimes turn down to form ‘shepherd's crooks
- Trees may display a mixture of healthy and diseased foliage and shoots Affected shoots die back from the tip
If you suspect that a Dutch Elm tree is diseased, select some live twigs that show symptoms. First peel back the bark of the twig: dark brown or purple longitudinal streaks in the outer wood indicate disease. You can also cut across a twig to examine the outer wood: a ring of dark brown staining indicates disease.
However, not all twigs will show brown streaking, especially in the branches of large trees.