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Dutch Elm Disease - Sexual: Ophiostoma ulmi   Gerald J. Lenhard, Louisiana State
University, Joseph O'Brien, USDA
Forest Service,
www.ipmimages.org www.ipmimages.org   Joseph O'Brien, USDA Forest Service, USDA Forest Service, Missoula Archives, www.ipmimages.org www.ipmimages.org  HOSTS: All species of
native and non-native elms.
Siberian and Chinese elms are much less susceptible. DESCRIPTION:
The
first evidence of fungal infection is wilting of the upper branches.
Leaves turn yellow, wilt, then brown, but remain on the branches.
Eventually the entire tree wilts and dies. Death can occur in several
weeks or several years. When bark on infected 1” diameter branches is
peeled back, light to dark brown streaks or discoloration in the wood
indicates a vascular infection. LIFE
CYCLE: This
fungus is spread from diseased elms via inset vectors or through root
grafts. European elm bark beetles and native elm bark beetles (Scolytus
spp.) are vectors of this disease. The beetles breed in trees or logs
infected with the fungus. Sticky fungal spores adhere to the insect's
body and are carried to healthy trees. Beetles then feed on and infect
healthy trees. The fungus invades the water-conducting vessels and can
infect the roots of a large tree in the first season. The fungus
proliferates in the roots and then ascends the trunk in a wave of
systemic infection that kills parts of or the whole tree. CONTROLS:Cultural: Do not prune in the spring! Spring pruning attracts the beetles that spread Dutch elm disease. There are now resistant cultivars available including: 'Dynasty', 'Groeneveld', 'Homestead', 'Jacan', 'Pioneer', 'Regal, 'Sapporo Autumn Gold', 'Thompson', and 'Urban'. The 'American Liberty' series are not as resistant as the above cultivars. Chemical: There are reports that tree injections of fungicide have prolonged the lives of infected trees. Fungicidal injections (propaconizole) are useless if the tree shows 10% or more dieback due to the disease. |
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