Stack et al. (1996) notes that the observable symptoms and the progression of Dutch elm disease differs among trees that are inoculated through beetle feeding and those that are infected through root grafts. Trees infected by beetles first show wilting, curling and yellowing of leaves on one or more branches in the upper portion of the tree. Large trees may survive and show progressively more symptoms for one or more years. In addition, because of their position, the infections arising from native elm bark beetle inoculations have a head start in spreading through the tree. Frequently, by the time first symptoms are noted, the fungus has already reached scaffold branches or the main trunk of the tree. Once the fungus is established within a tree, it spreads rapidly via the water-conducting vessels. The tree forms gums within these vessels in response to the presence of the fungus, causing the tree to wilt and eventually die. Trees infected through root grafts wilt and die rapidly; this frequently occurs in the spring soon after the trees have leafed out and progresses from the base of the tree upward.
Location Specific Impacts:
Reduction in native biodiversity: Decline in Elm populations have been recorded in Austria, Belgium, the Czech Republic, the UK, France, Germany, Greece, Hungary, Italy, Poland, Portugal, Romania, Sweden, Switzerland and Spain.
Other: Decline in Elm tree numbers due to removal and destruction of infected trees.
United States (USA)
Other: Throughout North America, almost half the elm population has been destroyed (Stack et al 1996)