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.
Unfortunately the insect introduces spores of rot fungi that spread through the stem.
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.
Wandoo Recovery Group report