Science behind root rot

[Ujjawal Roy]

Hello everyone. I am unable to understand the science behind rotting roots, from what I understand it's usually that the roots die because of too much water (i. e. Lack of oxygen) and then fungal pathogens corrode away that root and it can spread into the healthier sections as well. I stay in a tropical country where the temps are quite high and my soil is quite coarse and each particle retains moisture but the substrate as a whole is quite well draining and still somehow I'm seeing signs of root rot perhaps on my plants. It'll be great If you all could shed some light on this...

 

[Bonsai Nut]

In my experience, when I think of root rot I think of a condition brought on by absence of oxygen, which kills the roots, followed by fungus that colonizes the dead roots and travels upwards. In this case it isn't the fungus that kills the trees, but rather the initial conditions which kill the roots.

However there are plenty of times that you can get fungal root infections that are not brought on by absence of oxygen - particularly if the roots are damaged (like during repotting, or if you prune the roots). Fungus thrives in humid, dark conditions, so it is more or less always present in your soil in minute quantities, looking for an opportunity to spread.

 

[sorce]

I call it impossible to get if your pot has drainage and your soil dries.

I've read 0 true stories of trees dying from root rot.

I've read at least 100 stories of trees dying because people feared root rot and didn't water.

Remember only stagnant, festering wet, rots.

You can water free draining soil constantly and it will never rot, because those pathogens are always being flushed away.

Root Rot smells like the silty mud 3 feet deep in a riverbank.

Sorce

 

[Wires_Guy_wires]

I remember you posting that you recently did some repots. Not every tree overcomes that damage in a few weeks. And even if they do, the effects on the foliage don't disappear if the foliage isn't replaced; once it's damaged, it'll stay damaged.

Open wounds can get infected no matter the climate or conditions.
It's not just fungi, but also bacteria and other micro organisms, and insect larvae.

The signs are all the same on the top of the tree, but on the bottom there are different things going on that we can't see. But we can smell it sometimes, with some deduction most issues can be traced back or related to certain events or conditions.

Usually a lack of oxygen is a jumpstart for all of the above; some root parts die, this attract insects, the insects poop harmful bacteria, yeasts and fungi from their gut microbiome, the cycle continues long after the lack of oxygen is resolved.

Fungi and bacteria can linger as long as the tissue bleeds and supplies them with nutrients and water.

For a good diagnosis, we have to take all those elements into account, and logically go forward combating or acknowledging all of those elements.

There are very few people in the bonsai world with enough knowledge about plants and gardening to fully understand how plant disease develops and progresses, or where the cause and effect can blend into each other. This is no accident or lazyness on their side, because it's not just knowledge of plants and substrate, but almost all biologically influential factors; viruses, bacteria, fungi, other micro organisms, insects, physics, (bio)chemistry, physiology and so on. I've been studying and working for 15 years on those things and I still learn new stuff every day and people correct me more than weekly.

Most issues can be resolved by adjusting your behavior and habits, and giving the tree time. That's enough for most people to know, really. You can do bonsai without issues for decades with just that practice of 'whoops, adapt, wait, overcome'.
A little peroxide fixes a lot of issues as well.

 

[Javaman4373]

I remember that when we lived in the midwest, people had a practice of aeration of their lawns. This consisted of a treatment that poked holes in the sod. Do you think it would help potted trees to poke holes in scattered areas into the soil to provide aeration (oxygen) as well as some escape of moisture if the soil doesn't drain well enough?

 

[Bonsai Nut]

I remember that when we lived in the midwest, people had a practice of aeration of their lawns. This consisted of a treatment that poked holes in the sod. Do you think it would help potted trees to poke holes in scattered areas into the soil to provide aeration (oxygen) as well as some escape of moisture if the soil doesn't drain well enough?

If you are using a good soil mix, it does not require aeration because the soil mix already has plenty of void space between the particles. Water flows freely between the particles and draws oxygen in behind it as it drains out the bottom of the pot. You are left with moist (not saturated) soil and plenty of gas exchange.

Yes, if you have bad soil, in an emergency situation you can improve things slightly by poking holes in your soil. However you are only partially addressing the symptoms of the problem - and not the cause. The cause is that your soil is bad and/or it has been too long since you repotted and your soil has either broken down, or your tree roots have grown aggressively and are occupying all the void space between the particles.

 

[Deep Sea Diver]

I echo the above comments. Overwatering causing water logging, poor media, a pot designed with minimal drainage that doesn’t allow water to drain well, all contribute to allow opportunistic soil microbes to thrive.

Technically some of the pathogens involved are water molds of Phytophthora or other bad actors like Pythium, Fusarium and Rhizoctonia. What happens is that the water logging causes the normal balance of different fungi, bacteria, protists etc in the rhizosphere to get shifted, allowing the pathogens to proliferate.

Once the ecological balance is shifted and the bad actors come out in full force this situation is hard to stop. It can be, but a plethora of drastic measures need to be taken i.e. repotting in clean soil, root washing and trimming with clean tools and the appropriate use of the correct chemicals in proper concentrations. (Don’t forget about properly segregating and disposing of the waste). With luck a tree can be saved if the normal soil microbial balance can be restored.

That’s an iffy proposition. Best to ward the situation off from the start with proper watering, media and pot design.

One simple practical thing you can do to help if you suspect or are concerned waterlogging conditions is to “chock up one side of the pot about 30ish degrees or more with a stone or wood wedge... also during wet seasons. This has the effect of lowering the perched water table inside the pot, improving drainage. (Switch the chock around every once in awhile for best effect.

Good luck!
DSD sends

 

[leatherback]

it's usually that the roots die because of too much water (i. e. Lack of oxygen) and then fungal pathogens corrode away that root and it can spread into the healthier sections as well. I stay in a tropical country where the temps are quite high and my soil is quite coarse and each particle retains moisture but the substrate as a whole is quite well draining and still somehow I'm seeing signs of root rot perhaps on my plants

Maybe the one thing that gets missed often is.. When roots die, they start rotting, and can result in massive damage. The WAY these roots die, is irrelevant. Yet, overwatering in bad substrate can be an issue. But also letting roots dry out too much can be a cause.

Rarely do healthy roots die without any clear cause. Yes, pathogens exist. But something neds to happen for them to get the overhand, in most cases.

 

[LittleDingus]

I found this an interesting and somewhat relevant to the thread...

I recently did some work on my baobabs. They are succulent and very susceptible to root rot. They are not "woody" like trees we're used to so, once the tissue starts collapsing, they don't have the same sorts of compartmentalization that woody plants have...they can die off in a matter of days from root rot!

Here are the roots of a plant that was very healthy this past growing season.



You can see the black fungusy looking root next to lots of otherwise healthy roots. That root was laying on the bottom of a grow bag. Grow bags are permeable...much better than plastic pots, but maybe not as good as collandars...they drain very well. These babs were all in DE which drains very well. This part of the root was staying too wet for too long and suffocated. The tree was strong enough and the conditions higher up the pot good enough that nothing bad happened.

This case was a little more drastic!



Another baobab. This one was in a grow bag with DE sitting in a 3" deep drip tray. My guess to what happened is this: Back in the spring, we had a lot of rains. I wasn't always diligent in draining the drip trays frequently. The bulk of the root on this guy should have been well above the standing water, but the bottom 1" or so was likely in cool standing water for hours at a time. It started to rot from the bottom up. At some point, the conditions changed enough fast enough that the top of the tree was able to fend off the situation. The bulbous root was mostly just much by this point. The remaining healthy tissue sprouted new tap roots which then grew down through the dead root! My guess is this was entirely suffocation and fungus hadn't taken hold before the overly wet conditions dried up, otherwise, I think the entire tree would have died. Instead, the tree recovered and grew fine for the rest of the season until it naturally went dormant about a month or two ago.

By contrast, I grow my banana tree (herb) in Miracle grow which holds way to much water in our wet springs but is needed most the rest of the year. I do need to repot it every year for other reasons, but I can tell by the smell whether the soil went anaerobic or not. If it had gone anaerobic, it smells strongly of sulfur! Even when the soil is a wet mucky mass that reeks, I rarely find root rot on that plant. The peat may be rotting like mad, but the banana roots are often still white and plump as can be!

So, yes, I believe the root's reaction to lack of oxygen is the primary concern. Even though we call it "rot", it may have little to do with pathogens...at least initially. But, once there is unprotected tissue, pathogens can move in quickly!

 

[Leo in N E Illinois]

I find the most frequent cause of root rots is damage to the roots, most often by allowing the roots to get too dry between watering. Dry roots, the root tips die first. Then watering sets up a moist environment. Then opportunistic fungi and bacteria colonize the roots through the dead root tips. Best for most trees, is to never allow them to dry out.

 

[A. Gorilla]

Are maggots the cause of death in an animal?

 

[leatherback]

Are maggots the cause of death in an animal?

No. They are the cure.

Maggot therapy - Wikipedia

en.wikipedia.org

 

[Michael P]

"Root rot" is a symptom, and a very non-specific one at that. A wide variety of things can cause roots to die, and subsequently decompose. Most of what is called root rot in bonsai results from errors of cultivation: too wet, too dry followed by too wet, too cold, too hot, etc. Pathogens can cause root rot, but even then the roots are usually weakened by bad horticulture first.

 

[Alain BERTRAND]

I've read 0 true stories of trees dying from root rot.

Just a good recipe for root rot: let grow a pine in 100 % pumice or lavarock. Allow the root to clog the substrate, then remove most of the needles and go on watering like before. You'll got your own true story of root rot