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Field guide to exotic pests and diseases: Dutch elm disease
Ophiostoma ulmi(Buism.) Nannf., Ophiostoma novo-ulmi
Wilting, yellowing, browning and dieback
Cross-section of diseased branch showing discoloured streaks as brown dots in xylem
Distribution: Europe, North America, India, Iran, Turkey, Russia, New Zealand.
Hosts: species of Ulmus.
Signs: primary signs of infection - loss of water conducting ability and browning of infected sapwood in narrow streaks that follow grain. Cross-sections of infected branches show dark spots in outer annual ring, often forming a definite ring. Secondary signs of infection include shoot wilting followed by yellowing and browning of leaves. Branches die back from tip and severe attack can kill entire tree. Bark beetles belonging to the genus Scolytus or Hylurgopinus are vectors of the disease.
Likely pathway: seeds, nursery stock, bark, lumber, wood packaging material including dunnage and insects.
Potential impact: estimated to have killed >17 million of 23 million elms in southern England; lost 119,000 of 300,000 American elms over three years.