Dutch Elm Disease - Tree Canada

lumber infected with the fungus arrived in North America about 1930
the disease reached Eastern Canada in the 1940’s
it arrived in Manitoba in 1975 and Saskatchewan in 1981
the disease does not occur in Alberta or British Columbia where American Elms were planted beyond their natural range (Saskatchewan to Nova Scotia)
the majority of elms in Eastern Canada died of the disease in the 1970’s and 1980’s
scattered healthy trees, generally young, do still occur in the east

Dutch elm disease is a fungal disease of elms
the fungus is spread by both a native and an introduced bark beetle whose larvae tunnel under the outer bark and create distinctive feeding ‘galleries’
the adult beetles are very small (2-3 mm or 1/8 in)
the first signs of the disease are upper branches dying and leaves turning yellow in mid-summer
gradually, the damage spreads to the rest of the tree which eventually dies
some trees will resprout from the base and the sprouts may live for a number of years

there are three native species of elm in Canada and all have been affected to varying degrees by Dutch elm disease
the greatest impact has been on American Elm (Ulmus americana) and Rock Elm (Ulmus thomasii)
Red or Slippery Elm (Ulmus rubra) is least affected by the disease

There are fungicide treatments available for individual trees but they are costly,
must be repeated regularly, and may only prolong the life of the treated tree by 5-10 years
in the early stages of the disease, infected branches may be pruned and destroyed
selection programs are ongoing to find and distribute resistant trees and several cultivars are presently available
hybridization studies are also underway to find trees not susceptible to the fungus
it will be many years before most of these cultivars or hybrids reach maturity and prove their resistance to the disease

Tree Killers: Dutch Elm Disease