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 might display a mixture of healthy and diseased foliage and shoots
• Affected shoots die back from the tip

Diagnosis

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.

• Dutch elm disease resources page