Dutch Elm Disease

This disease is caused by the fungus Ophiostoma novo-ulmi and is disseminated by various elm bark beetles within the genus Scolytus. The fungus blocks the water conduction system of trees resulting in wilting and death of the foliage. Symptoms of the disease first appear in early summer as clusters of wilting or yellowing leaves which then turn brown and fall. Affected shoots die back from the tip and the twigs sometimes turn down to form ‘shepherd’s crooks.’ Because the disease is progressive an affected tree may have a mixture of healthy foliage, yellow or brown foliage and defoliated shoots, showing infection in different branch systems.