Ash trees are dying for a variety of reasons. In the USA, Emerald Ash Borer is killing many trees. In Europe, the fungus Chalara is spreading and killing trees.
More about the decline of the forests.
Emerald Ash Borer
The signs and symptoms of an EAB attack
The symptoms an ash tree shows when it is infested with emerald ash borer are similar to symptoms caused by other ash pests or diseases in Wisconsin.
For example, crown dieback can occur due to EAB damage, but can also be the result of drought stress, soil compaction or verticillium wilt, just to name a few.
Therefore, it is important to look for a combination of at least two symptoms or signs when trying to figure out if emerald ash borer is in your ash tree. If you see two or more from the lists below report your findings here.
Symptoms
Crown dieback: Dieback of the upper and outer crown begins after multiple years of EAB larval feeding. Trees start to show dead branches throughout the canopy, beginning at the top. Larval feeding disrupts nutrient and water flow to the upper canopy, resulting in leaf loss. Leaves at the top of the tree may be thin and discolored. An example of this is shown below.
Epicormic Sprouting: When trees are stressed or sick, they will try to grow new branches and leaves wherever they still can. Trees may have new growth at the base of the tree and on the trunk, often just below where the larvae are feeding. An example of this is shown in the picture above, where small branches are growing on the trunk, about 6 feet off the ground.
Bark splits: Vertical splits in the bark are caused due to callus tissue that develops around larval galleries. Larval galleries can often be seen beneath bark splits.
Woodpecker feeding: Woodpeckers eat emerald ash borer larvae that are under the bark. This usually happens higher in the tree where the emerald ash borer prefers to attack first. If there are large numbers of larvae under the bark the woodpecker damage can make it look like strips of bark have been pulled off of the tree. This is called “flecking.” An example of this is shown below.
Signs
D-shaped emergence holes: As adults emerge from under the bark they create a D-shaped emergence hole that is about 1/8 inch in diameter. An example of this is shown below.
S-shaped larval galleries: As larvae feed under the bark they wind back and forth, creating galleries that are packed with frass (larva poop) and sawdust and follow a serpentine pattern. An example of this is shown below.
Larvae: Larvae are cream-colored, slightly flattened (dorso-ventrally) and have pincher-like appendages (urogomphi) at the end of their abdomen. By the time larvae are done growing they are 1 1/2 inches long. Larvae are found feeding beneath the bark.
Adults: Adult beetles are metallic green and about the size of one grain of cooked rice (3/8 – 1/2 inch long and 1/16 inch wide). Adults are flat on the back and rounded on their underside.
Chalara
Description
Chalara dieback of ash is a serious disease of ash trees caused by a fungus called Chalara fraxinea (C. fraxinea), including its sexual stage, Hymenoscyphus pseudoalbidus (H. pseudoalbidus). The disease causes leaf loss and crown dieback in affected trees, and usually leads to tree death.
Threat
It is potentially a very serious threat. It has caused widespread damage to ash populations in continental Europe, including estimated losses of between 60 and 90 per cent of Denmark’s ash trees. We have no reason to believe that the consequences of its entering the natural environment in Britain would be any less serious. Experience on the Continent indicates that it kills young ash trees very quickly, while older trees tend to resist it for some time until prolonged exposure causes them to succumb as well.
Susceptible species
Chalara fraxinea is especially destructive of common ash (Fraxinus excelsior), including its ‘Pendula’ ornamental variety. Narrow-leaved ash (Fraxinus angustifolia) is also susceptible. Chalara dieback of ash is particularly destructive of young ash plants, killing them within one growing season of symptoms becoming visible. Older trees can survive initial attacks, but tend to succumb eventually after several seasons of infection.
Spread
Local spread, up to some tens of miles, may be by wind. Over longer distances the risk of disease spread is most likely to be through the movement of diseased ash plants. Movement of logs or unsawn wood from infected trees might also be a pathway for the disease, although this is considered to be a low risk.
Outbreak stage
Ash trees suffering with the infection have been found widely across Europe since trees believed to have been infected with this newly identified pathogen were reported dying in large numbers in Poland in 1992. These have included forest trees, trees in urban areas such as parks and gardens, and also young trees in nurseries.
In February 2012 it was found in a consignment of infected trees sent from a nursery in the Netherlands to a nursery in Buckinghamshire, England. Since then it has been found in young ash trees in a number and variety of locations in Great Britain, including urban landscaping schemes, newly planted woodland, and more nurseries.
In October 2012, Food & Environment Research Agency (FERA) scientists confirmed a small number of cases in Norfolk and Suffolk in ash trees at sites in the wider natural environment, including established woodland, which do not appear to have any association with recently supplied nursery stock. Further finds in trees in the wider environment have since been confirmed in a number of places, mostly on the eastern side of England and Scotland, and mostly concentrated in the south-eastern region of England. In May 2013 the first wider-environment case was found in south-west Wales, which is the farthest west site in Britain that a wider-environment case has been confirmed. (Map below)
C. fraxinea is now being treated as a quarantine pest under national emergency measures and any suspected sighting must be reported.
Hundreds of staff from government agencies checked ash trees across the UK for signs of the disease during early November 2012. It was one of several actions to emerge from a meeting of the Government’s emergency committee, COBR, chaired by Environment Secretary Owen Paterson.
Survey results
Plant health experts are also undertaking a survey of about a thousand sites which have received saplings from nurseries where Chalara dieback has been found.
National plans have been drawn up for Chalara.
