|
Disease of the Month - Dutch Elm Disease | |
|
|
|
| Ophiostoma ulmi
Crops Affected: Elm species
Disease Cycle:
- Fungal pathogen is spread from tree to tree by 2 different beetles, native elm bark beetle (NEBB) and the smaller European elm bark beetle (SEEBB)
- Both beetles are declared pests under the Alberta Pest Act
- Emerging offspring are covered in the sticky spores, which are spread to healthy trees as they fly and burrow into new host trees
- Spores that have been introduced into the host tissues germinate
- The fungus grows and spreads, plugging the xylem tissues (tree's water conducting elements)
- Infected branches wilt and die
- Eventually the tree dies completely, usually within 1 or 2 seasons
Symptoms:
- Elm trees may exhibit the following symptoms
- In early summer (mid-June to mid-July), leaves on individual branches may wilt, droop, followed by curling and browning
- Brown wilted leaves remain on the tree
- Later in summer, leaves droop and turn yellow (flagging), with leaves may drop prematurely
- Late infections can be confused with normal, seasonal changes
- Branches with smaller leaves than rest of the tree
- Branches with no leaves
- The sapwood will be stained brown
- This is visible when the bark is removed from infected twigs
- Evidence of insect pest vector
- Beetle emergence holes, the size of the diameter of a pencil lead, and/or sawdust on the bark would be indicative of burrowing beetles
Management:
- Monitor conditions of elm trees
- Maintain healthy trees
- Ensure that they have adequate water, nutrients, light and are not stressed
- Prune trees to remove dead, dying or diseased wood
- Avoid pruning elm from April 1 to September 30, which is when the insect vector would be attracted to pruning wounds
- Completely remove dead or dying trees, including the stump
- Dispose of pruned material properly (burning or burial deeper than 25cm) – do not chip
- Avoid transport of elms or elm firewood from other areas (diseased areas)
- Chemical treatment of infected trees is not effective and is very costly
The Disease Vectors
Native Elm Bark Beetle
Hylurgopinus rufipes
Description:
- Native beetle
- Small beetle (~1/8 inch, 2-3mm)
- Adults bore galleries across grain; larvae bore perpendicular to adult galleries
- Overwinters mainly as adult in galleries beneath the bark of healthy trees - can overwinter in any stage, except egg
Smaller European Elm Bark Beetle (SEEBB)
Scolytus multistriatus
Description:
- Introduced pest
- Small beetle (~1/8 inch, 3-4mm)
- Adults bore galleries parallel to wood grain; larvae bore perpendicular to adult galleries
- Overwinters as a larva, pupates and emerges as an adult in spring
Differences in breeding galleries
- Characteristic pattern of the breeding galleries on the surface of the wood under the bark can be used to identify the two elm bark beetle species
- Galleries that run parallel to the grain are caused by SEEBB
- Galleries that run across the grain are caused by the NEBB
| | |
Native Elm Bark Beetle - adult | Smaller European Elm Bark Beetle – adult | Breeding Galleries – Left = SEEBB; Right = NEBB |
Photos by: Natural Resources Canada, Canadian Forest Service |
|
|
|
|
|
|
For more information about the content of this document, contact Robert Spencer.
This information published to the web on February 27, 2018.
|
|