Scattered pattern of Dilwynnia laxiflora death There have been many comments recently about widespread shrub death in Foxes Lair due to the exceptionally dry spring and summer.
Certainly, there is more death than usual, but this doesn't explain the scattered pattern in Foxes Lair with dead plants next to healthy ones.
Luckily my esteemed colleague Detective Doug volunteered to investigate this problem.
The great man randomly selected two each of dead and healthy Dilwynnia laxiflora (pea flower) plants for examination.
Live plants had normal root systems.
Certainly, there is more death than usual, but this doesn't explain the scattered pattern in Foxes Lair with dead plants next to healthy ones.
Luckily my esteemed colleague Detective Doug volunteered to investigate this problem.
The great man randomly selected two each of dead and healthy Dilwynnia laxiflora (pea flower) plants for examination.
Live plants had normal root systems.
Dead plants.
The roots were very bent and thickened, particularly the tap root that snaps easily. Borer channels were on both the outside and inside, including one that contained a jewel beetle emerging from its pupal case.
The roots were very bent and thickened, particularly the tap root that snaps easily. Borer channels were on both the outside and inside, including one that contained a jewel beetle emerging from its pupal case.
 Thickened fissured root crown |  Jewell beetle larva inside root crown |
Jewell beetle nearly ready to emerge from pupal shell
Problem solved?
No, being a true scientist, Detective Doug insisted on also examining the healthy specimens
Roots of both live plants had also been attacked, although to a lesser extent than dead plants.
The first plant had a few minor lesions but otherwise appeared normal. However when split in half lengthwise the root was hollowed out and contained a hibernating? jewell beetle. These beetles are common on pea flowers in October so presumably they hibernate until spring.
No, being a true scientist, Detective Doug insisted on also examining the healthy specimens
Roots of both live plants had also been attacked, although to a lesser extent than dead plants.
The first plant had a few minor lesions but otherwise appeared normal. However when split in half lengthwise the root was hollowed out and contained a hibernating? jewell beetle. These beetles are common on pea flowers in October so presumably they hibernate until spring.
The second healthy plant showed evidence of insect attack that appeared to be confined to the surface. However, when cut in half it was obvious that insects had entered and tunnelled up the centre of the root. While doing this they brought in spores of a canker fungus, shown by the blackened areas. This fungus invades healthy tissue, blocks water and nutrient transport and kills the plant.
Conclusion
These plants are routinely attacked by borers and may survive for more than a year until invading canker fungus kills them or they snap off. Increased water stress from extended dry weather hastens plant death.
Interestingly, a previous investigation on wandoo crown decline in Foxes Lair found a similar combination of factors.
Conclusion
These plants are routinely attacked by borers and may survive for more than a year until invading canker fungus kills them or they snap off. Increased water stress from extended dry weather hastens plant death.
Interestingly, a previous investigation on wandoo crown decline in Foxes Lair found a similar combination of factors.
 Healthy plant, minor external damage |  root interior showing borer channels infected by canker fungus |
Update April 2024
Affter the driest spring to autumn period on record, Dilwynnia laxiflora and Gastrolobium poisons are again dying off, but to a greater extent. This borer was found in the base of a dead poison.
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