DISEASE
 
   NAME
     Dieback (General)
     Various Dieback Causes

Description of the Problem
This is a problem that affects Eucalyptus and Corymbia species in Australia and is rarely the result of an individual organism with the one exception of Phytophthora cinnamomi. It also affects many ornamental trees such as Populus species.  It is difficult to identify the exact cause of dieback but there are certain factors that contribute. 

Trees that remain in cleared areas for pastures which are fertilised with superphosphate or treated with insecticide are most at risk. Insects repetitively attack such isolated trees reducing there vigour and with less trees there are less predatory birds or lizards. 
The clearing of the land damages the overall ecology of the area and this imbalance results in excessive insects, salinity of the soil and changes to the water table.  Certain fungus has been named ‘Die Back’, infecting stressed trees and killing them from the top down, commonly during periods of drought.

 Die-back (Phytophthora cactorum) initially causes the buds and leaves turn brown and die. This is followed by cankers that form on the branches, girdling and causing ringbark. All parts above the canker die and infection is found on Rhododendron species.
 
Appearance and Distribution of the Pest
Dieback has been a natural occurrence for hundreds of years but has increased significantly since clearing and cultivation of the land started during colonisation of the country
.
Period of Activity
Dieback occurs throughout the year but is assisted by drought, fire and flooding. The trees are exposed to adverse climatic conditions putting them under greater stress. Dieback has also been attributed to heavy acidic soils.

Damage Caused
When a tree is suffering from dieback it normally has sparse foliage with suckering growth from the main branches or trunk. The leaves eventually shrivel and fall leading to the death of the branch and the tree will linger for a period of time but then suddenly die.

Susceptible Plants
There are many Australian native species and ornamental trees affected including Eucalyptus, Corymbia, Callitris, Lophostemon, Syncarpia and Casuarina species. Trees that are isolated singularly or in small groups as in pastures or along road sides are most at risk.

Alectryon excelsus is susceptible to an unknown Die Back that has recently infected trees. The symptoms include the new growth shedding leaves and the stems die. New growth occurs on live wood but once again it suddenly dies off. This repetitive defoliation reduces the trees vigour. Currently there is no current control methods.

Betula species are susceptible to the Die-Back (Melanconium betulinum) which kills the upper branches and eventually the tree.

Nothofagus antarctica has had occurrences of Die-back in southern Chile causing the crown and eventually the tree to die. There is no current control method.

Pseudotsuga menziesii Douglas Fir is infected by the fungal Die Back (Dermea pseudotsugae). Symptoms include the foliage and branches turning brown and dieing from the apex and normally attacks young plants. There is no current control method.

Taxus species are also affected by dieback.

Cultural Control
It is very complex problem and individual trees may be saves by dealing with the insect problem but generally the ecology of the region needs to be addressed. This is very difficult to do as new plantings are also attacked or affected by saline soils.

Chemical Control
There is no chemical control for this problem.