Banksia Serrata - Phytophthora Root Rot?

[Dasein]

Hi Shibui and Grant,

Thanks for replying.

Is it normal for the foliage to turn yellow and die off in such a quick, uniform manner (all foliage on one branch changed within 3-7 days, during a week of heavy rain; moving from bottom-up)?
- You can see the photos of the plant before the yellowing took over a week or two prior, in one of my replies.

Whilst some sources say foliage die-back is slow with phytophthora, others state it can happen almost overnight, particualrly in vulnerable shrubs or plants.

I hypothesised phytophpthoria for several reasons:
1) Its in a banksia
2) Changes occurred quickly after a week or two of heavy rains.
3) the foliage yellowing/die off was too rapid and uniform to be normal loss of foliage
3) the base of the pot was waterlogged, with compacted fine rotten medium (coco coir/pine mulch, i believe).
4) many of the roots at the bottom were a dark brown colour, and soft texture (see pictures)
You're right, there is no reason to suggest the mycelium I saw is phytophthoria - that is just my confirmation bias.

Beginnings of root rot - Banksia 2.jpg

Beginnings of root rot - Banksia.jpg

Beginnings of root rot - Banksia 3.jpg

Phytophthora - Banksia Serrata.jpg

[shibui]

It is certainly normal for old leaves to turn and drop in a short period. It is a seasonal process, even in evergreen trees. Pines, junipers and other exotic evergreens go through the same process in a similar short time. It seems that when the trees decide it is time they just get on with it.

One of the reasons I have continued to challenge your assumptions is that much of the 'evidence' appears to be confirmation bias. Coincidences do happen. Rainy periods can coincide with annual leaf drop.

Given this is just a single example it will be very hard to judge cause and effect.
If this tree recovers will it be because of the treatment or simply that there was no infection present for a start?
If it dies will that be because it was infected or because of the repot and treatment this time of year?

I note you have no location in your profile but just checked the original post to see you are in Sydney. It is probably warm enough up there to repot banksia any time of year Down here, in my experience, repotting banksias now leads to poor health for at least 6 months if not death of the trees.

Hope you will keep showing us as this one progresses.

[Rory]

Is it normal for the foliage to turn yellow and die off in such a quick, uniform manner (all foliage on one branch changed within 3-7 days, during a week of heavy rain; moving from bottom-up)?
- You can see the photos of the plant before the yellowing took over a week or two prior, in one of my replies.

No that is not normal.

Repotting now in Sydney isn't ideal no, but shouldn't result in death if the tree was healthy. It would have to have something badly wrong like bad root rot to result in death on top of a repot at this time of year. If it was mid winter, that would be much worse on top of root rot.

[Dasein]

Thanks for everyone's responses.

Yes, if the tree survives, it will be hard to know what happenned.
Others reading this post, please consider the differing points of view from experienced people responding.

Fingers crossed the warm days continue for a while in sydney.
Many of my other native evergreens, including my banksia seedlings are still sprouting new growth. So hopefully it isn't too stressed come winter.

I will update as things develop over the coming months.