Banksia Serrata - Phytophthora Root Rot?

[Dasein]

Help please - Is this root rot?

Pictures below are of Banksia Serrata, Located Sydney.

The yellowing ont he bottom foliage came up very quickly (over few days to a week)
It has been raining a lot recently.

Ph tested = 5.5

Added iron chelate, and yellowing continued to grow.
Very minimal browing or dead leaves - although some present (looks like normal die off)

I will likely repot into new soil with a phosphoric acid treatment, but would love a second opinion, please.

Root rot - banksia 1.jpg

Root rot - banksia 2.jpg

[shibui]

Any chance this is simply older leaves dying off at the end of their lives? Looks like all the affected leaves are right at the base of the plant ie the oldest leaves.
Any phytopthera and most other root rot I've seen the first signs are wilted tips because the roots cannot supply enough water to the plant.

Next question is what fertiliser program have you followed with this tree?
Before you repot please just tip the whole root ball gently out of the pot - it should have plenty of roots to hold the soil together - and take some photos of the roots and potting mix for us.
Some good quality photos of the growing tips might also provide some good clues.

[Phil Rabl]

I'm with Shibui. The old leaves on B. serrata turn yellow and fall off. Until/unless other evidence arises, I would consider that to be what is going on with this tree. The upper (newer) leaves look fine.

[KIRKY]

Also is the plant new to you. And where are you based?
More info helps us work out what’s happening.
Cheers
Kirky

[Kevin]

Hello Dasein,

What rang alarm bells for me was your comment:

I will likely repot into new soil with a phosphoric acid treatment

While I'm not familiar with this product, what I do know is phosphorus and Banksia do not like each other and may / will have disastrous effects to the health of the Banksia.

Kevin

[Phil Rabl]

Banksias and phosphorus

This is my understanding, based on quite a lot of reading and talks with others.

Banksias are among the relatively small number of Australian native plants that sometimes grow cluster roots known as proteoid roots. The issue is that proteoid roots are known to increase the uptake of phosphorus, and other nutrients, and that applying a phosphate-rich fertiliser to a tree with proteoid roots can cause it to take up phosphorus at a toxic level.

The full picture with regard to proteoid roots is complex and incompletely understood but there is lots of information that can help the bonsai enthusiast with trying to understand how best to manage (or avoid) proteoid roots. Although no definitive advice is available on how to stop our susceptible bonsai from growing proteoid roots, it is known that proteoid root clusters are generally rare or absent when plants are supplied with adequate phosphorus. Further, in most species, the formation of proteoid roots declines as phosphorus availability to roots increases. This suggests that, rather than withholding fertiliser from our Australian natives, we should fertilise them regularly.

And remember: root pruning will remove any proteoid roots that exist. They form on the very outside of the rootball.

Here is a link to an article titled “Banksia and fertiliser” on Shibui Bonsai website. It includes a photograph of proteoid roots. https://shibuibonsai.com.au/?p=1019

[Rory]

I very highly doubt you have a fertilizer issue because looking at the photos you have on Facebook, it indicates this has been possibly heavily overwatered for a longtime and possibly heavily shaded in the lower areas. Usually a fertilizer issue will take out all the foliage at the same time and not be restricted to whole branches like you can see on the Facebook photos.

It certainly looks like it could be rot of some kind.

After taking a closer look at the photos you’ve got up on Facebook of this, it doesn’t look good.
For me, when I’ve had root rot for the Banksia serrata, it can often start low and spreads up and affects the lower branching first and then spreads upwards. When you zoom in on those Facebook pics you can tell it’s been kept very wet for presumably quite some time.

I agree that you’ll want to take a close look at the roots.
Make sure the mix isn’t sludgy or slushy and check to see if it’s not draining well.

Do the scratch test on the badly blackened branch areas that you can see on the Facebook photos. Root rot will be darkish brown / black and will spread up the trunk.
I’ve lost more serrata to that, than to any other problem.

But the fact that new growth on a lot of those branches is badly affected in the photos on facebook is not a good sign.

Another tip it’s these is not to allow branches to be continually shaded. Presumably this was kept amongst a raft of other stock and the lower branching as heavily shaded for a long time while the upper growth was exposed to sunnier and drier conditions.
It wouldn’t hurt to removal all the blackened and badly affected growth. But leave all the healthy leaves on it so it promotes new roots.

I’d probably take it out, and get off all the old mix and look at the roots. Remove anything that’s rotten if it has root rot, and spray with anti rot. Scratch a bit of that heavily dark area and see if the rot is inside the branches. (If it is rot).
I’ve also had serrata die off its branches when they’ve been heavily shaded and then they blacken and the leaves turn yellow as it dies off. But that is odd how heavily black certain branches are on your Facebook photos.

[Rory]

From your Facebook photos

6F1AD0EB-1DEA-418F-A5A2-304559211243.jpeg

E15125F2-27BE-42B9-BB7E-08DA54627175.jpeg

[Dasein]

Hi all,

I appreciate the feedback.

FERTILISER
I am aware of the need for low P environments in Natives, and I have not once fed this plant since I got it a few weeks ago.
The only fertilizer I have used: some iron chelate, which would have reversed any phosphorous toxicity - although I wouldn't see the effects for a while; and a nitrogen rich, phosphorous poor fertilizer (amino boost) once (similar to seasol).

Hi Phil,
I've never heard of proteiod root clusters before, so interesting to learn about that, thanks.

SYMPTOMS
I must emphasize the yellow leaves have emerged over 1 week, which is highly abnormal, and they are distributed only amongst the lowest foliage and moving upwards, which reflects the typical pattern of phytophoria.
- I will remember to post past photos to compare to, in future (attached below)

TREATMENT
Kevin,
Phosphorate (phosphoric acid) is Anti-Rot, the only available antifungal treatment for phyotphthoria I am aware of. Although many people seem to use hydrogen peroxide baths also.
There is likely a chance phosphorate will lead to an increase on phosphorous uptake as the acid reacts and forms phosphorous salts.
Unfotunately, it's now or never for the treatment/re-pot.
TBH, i feel it may already be too late for this one... but I'm gonna try my best to keep it alive.

Thanks Rory.
Those closer pictures from when I first bought it, and the advice on how to test it further, is helpful.

I'm going to move ahead with the full assessment for rot through a repot, then treatment if I find any fungus/algae/shitcunt material.
I will likely do a hydrogen peroxide bath, with some light anti-rot spray, with some iron chelate in the new soil. hopefully this will balance out any potential phosphorous toxicity.

banksia serrata - after buying.jpg

banksia serrata - after buying 2.jpg

[Dasein]

Hi all,

figured I will keep updating here, so others cann learn from my successes or failures.

TREATMENT SUMMARY

• I removed all the dead/dying foliage

• Removed all the old soil I could.

• Removed all roots which seemed either rotten or to have become dark and soft in texture

• There was eviodence ofa small amount of white mycelia in the base of the soil, which indicates phytophthora (root rot)

Phytophthora - Banksia Serrata.jpg

• Removed many of the proteoid roots, with as little damage to primary root system as possible.

• Bathed remaining root system in 1% Hydrogen Peroxide solution (diluted with distilled water) for about 15 minutes, until bubbles started to slow down.

• Prepared new soil and pot: base layer of charcoal; mix of perlite, vermiculite, 3-5mm red scoria, course sand; small amount of native soil mix; 3mm river pebbles.

PXL_20230415_053430287.jpg

• Added a light amount of water mixed with nitrogen rich/phosphorous poor liquid fertiliser (eco-amino grow) and iron chelate (leaving it moist, not wet).

• Added H2O2 treated banksia into new soil and tied it down, to prevent movement in new soil - did not water it

• Placed plant in where it will receive the most sun.

• Will aim to bring under cover during heavy rain

PXL_20230415_053418946.jpg

NOTES

• I saw some interesting root structures - seemed to be large amount of proteoid roots near the surface and in the root ball, which were almost completely dry.

Banksia Serrata - Root ball - Proteoid root cluster 2.jpg

Banksia Serrata - Root ball - Proteoid root cluster & Phytophthoria.jpg

• The mycelium and rotten roots were found mostly in the base of the soil, which seemed to be a layer of compacted coconut coir and/or pine/eucalytus wood chip - This was reatining a large amount of moisture.

• Since the root rot was not systemic and located mostly in the base layer of the soil, I decided to avoid a systemic Anti-rot (Phosphoric acid) treatment, as I did not want the formation of phophorous salts, which could lead to toxicity in Banskias. This is a difficult choice to make, as if the phytophthoria survives, it will now grow within a vulnerable plant.

• If I had more H2O2, I probably would have used a 3% solution instead, as I know banksias like a more acidic soil, and such a concentration would be more effective at killing fungus and pests (3% H2O2 ~ pH 6.0).

• Since I removed the proteiod roots, i thought it best to feed the new soil - and will continue to do so intermittently.

[shibui]

Almost all fungi form hyphae, most of which are white in colour. Look at any pine to see healthy, beneficial mycorrhiza. In fact, I believe that mycorrhizal fungi are all symbiotic and therefore beneficial to the trees they associate with.
As far as I know it is extremely difficult to visually differentiate between different fungi at the hyphae stage. What makes you so sure the few small bits of white you found are Phytopthera and not some other benign fungi?
I just checked on P. cinnamomi and it is now shown to be a water mould, not that it makes a lot of difference because moulds also produce visible hyphae.

I have also not been able to find any reports of phytopthera affecting older leaves first or plants dying from the base up. All sources quote wilted shoots as one of the first signs as I mentioned in my earlier post.
Here's one description of symptoms:

Phytophthora species can invade the roots and crowns of woody trees but foliar symptoms may not become evident for months or even years.

Leaves are pale green, wilted and fall readily. Shoots die back from the tips so that eventually the tree is reduced to a bare framework of dying branches. Death of the tree may take from a few months to several years. Declining trees commonly set large crops of small fruit (avocado). Lack of foliage and dieback of small branches exposes fruit and major limbs to sunburn.

Feeder roots are black, decayed and few in number. As infected roots lose the ability to exclude salts, leaf margins in affected trees develop brown, necrotic symptoms typical of salt burn.

All the roots shown in the photos appear to be healthy. No sign of black, decayed roots or few in number.

You should also note that phytopthera grows inside the roots and trunks so a topical treatment such as H2O2 will only eliminate any parts outside the roots. By my reading, any infection inside the plant will not be treated by H2O2.

I still stand by my original diagnosis of natural senescence of older leaves.

[Rory]

Fair enough. But any time I've had root rot on my Banksias, it starts from the base and goes up. The top leaves don't appear to wilt at all, and only the major sections at the base that develop the rot first appear to have affected foliage. But it also depends on the severity of the rot. The branch that develops the rot, will have most of those leaves affected, but upper branches (not the ones with rot yet) can appear unaffected until the rot spreads heavily if left untreated.


Presumably this is because the rot often can be one-sided, and the water can travel up the other side of the trunk to support the upper structure. Very often the rot starts on one side and affects that area more so.
One Aemula in particular lose one complete side to root rot, and the other side was healthy as. I had to cut out and remove all the rot, and yet the other side continued to power on and was healthy throughout the entire treatment stage.

[Kevin]

Rory,

Or anyone else. I'm interested to know if the chemical Anti-rot treatment you have mentioned using is the same Anti-rot treatment that Dasein mentioned - Phosphoric Acid. If so, have you had positive results from using it. If not, what is the Anti-rot product you have had success with for your Banksia

Thanks,

Kevin

[Dasein]

Kevin,

See this link: https://www.dbca.wa.gov.au/parks-and-wi ... ra-dieback

"Phosphite, also known as phosphorous acid, or phosphonate, is a systemically-applied liquid fungicide developed for the control of Phytophthora diseases. Not to be confused, phosphite is a variation of phosphate - the plant-available form of phosphorous essential for plant growth... The only chemical treatment currently available for Phytophthora dieback (dieback) is phosphite, a systemic, non-hazardous and biodegradable fungicide. At the rates used for the treatment of dieback in native ecosystems phosphite does not kill or eradicate Phytophthora, rather it is believed to suppress the pathogen and boost the plant’s natural defence responses to infection"

[Grant Bowie]

Banksia will suffere root rot if soon is to compacted and waterlogged. It suffocates. I agree the yellow leaves were old and about to drop off. The tree should now settle in nicely/