Epicormic shoot (left), dead shoot (right) Greetings fellow Foxies,
Have you noticed large numbers of dead leaves on local wandoos, particularly where a whole twig or small branch has died?
This condition where wandoos die back and leave dead branches projecting though the leaf canopy is called Wandoo Crown Decline. This is a cyclical problem that caused huge damage in the 1990’s when the Wandoo Recovery Group was formed.
Research showed that boring insects and associated pathogenic fungi, are the principal agents disrupting stem nutrient and water conducting channels. Symptoms are worse in dry autumns, but underlying factors driving the long term cycle are unresolved.
This autumn I couldn’t find any pattern of areas affected. There are a couple of monitoring sites in Foxes Lair that don’t appear to have a lot of very recent damage. Affected trees in Foxes Lair seem to be randomly distributed, but badly affected ones have obviously been repeatedly attacked.
Being a loyal citizen scientist, I nipped out and sampled a couple of branches from a badly affected tree for close analysis.
My first observation was that the branches were distorted and gangly with lots of dead lower shoots, stems with dark cankers (sunken dead lesions) and resprouting shoots. Clearly not a single year problem.
Looking closely, it was amazing to see so many things attacking the tree. I found stem and leaf galls, and leaf damage from a range of chewing insects, but the real cause of branch death is inside the stems.
Have you noticed large numbers of dead leaves on local wandoos, particularly where a whole twig or small branch has died?
This condition where wandoos die back and leave dead branches projecting though the leaf canopy is called Wandoo Crown Decline. This is a cyclical problem that caused huge damage in the 1990’s when the Wandoo Recovery Group was formed.
Research showed that boring insects and associated pathogenic fungi, are the principal agents disrupting stem nutrient and water conducting channels. Symptoms are worse in dry autumns, but underlying factors driving the long term cycle are unresolved.
This autumn I couldn’t find any pattern of areas affected. There are a couple of monitoring sites in Foxes Lair that don’t appear to have a lot of very recent damage. Affected trees in Foxes Lair seem to be randomly distributed, but badly affected ones have obviously been repeatedly attacked.
Being a loyal citizen scientist, I nipped out and sampled a couple of branches from a badly affected tree for close analysis.
My first observation was that the branches were distorted and gangly with lots of dead lower shoots, stems with dark cankers (sunken dead lesions) and resprouting shoots. Clearly not a single year problem.
Looking closely, it was amazing to see so many things attacking the tree. I found stem and leaf galls, and leaf damage from a range of chewing insects, but the real cause of branch death is inside the stems.
The insect involved is a jewel beetle Cisseis fascigera). Beetles emerge from November to February, mate and lay eggs on stems. The larva that looks like a witchetty grub chews tissue and wood inside and along the stems (longitudinal galleries), before pupating in its gallery and emerging a year later.
Unfortunately the insect introduces spores of rot fungi that spread through the stem.
Unfortunately the insect introduces spores of rot fungi that spread through the stem.
 Intact branch showing exterior hole |  split branch showing the larva in its gallery |  Intact and split stem (frass is entomologist name for poo) |
 | I split the sections of stem down each branch and was shocked by the extent of fungal invasion that is easily seen as dark stained tissue. On these branches fungus is doing more damage than the insects. Tissue is often infected with few external symptoms The branch1 stem on the far left shows fungal staining only around a gallery between the bark and the wood. In the split section you can see that the fungus is more extensive in the wood. In branch 2 infection has spread down the stem from a dead part. |
The following images shows how the fungus symptoms progress with age
 No external symptoms. Longitudinal spindle shaped lesions in the sapwood and cambium layer |  Healthy epicormic shoot on a diseased stem being invaded by fungus |
 Sunken fungal canker lesion on stem surface |  External disease that has spread from a canker then exposed internal dead wood. |
Other borers like this large longicorn beetle larva could also be involved
References
Wandoo Recovery Group report
References
Wandoo Recovery Group report