Mechanisms causing root death

[Ray]

Originally Posted by K-Sci

A healthy flourishing phalaenpisis will develop crown rot if water sits in the crown for more than a few hours.

No scientific proof either way, but I think you’re missing a step or two between the apparent cause and the result. My suspicion is that there must be something going on after the accumulation of water that “opens up” the plant to infection. After a decade of overhead watering that sometimes left my plants “pooled up” for a day or two without getting crown rot, I cannot accept the direct causation.

Originally Posted by K-Sci

Don't you think it is possible for infections to occur in healthy tissue..

Yes, but there is likely an underlying “pre-existing condition” that makes some plants more susceptible than others, and/or the pathogen must be pretty virulent.

It is possible to grow virused plants and never know it is diseased. Do anything that puts stress on the plant, and it can go downhill pretty quickly. Certainly, the virus killed the plant, but it was not “healthy” before hand.

[K-Sci]

Originally Posted by Ray

No scientific proof either way, but I think you’re missing a step or two between the apparent cause and the result. My suspicion is that there must be something going on after the accumulation of water that “opens up” the plant to infection.

I overhead water too and have never had a problem with it, except for the following mystery, which you may want to consider and comment on. I have so little trouble with orchid diseases that the only treatment I keep on hand is Bayer systemic insecticide for roses. I use it to kill the occasional chewing insect and treat my Bryan Wheeler 'Grandson', which starts to get scale every spring. Okay, the mystery.

In 40 years raising orchids I've lost healthy well-rooted phalaenosis in active growth only three times. All three occurred in the last three years after moving to Mississippi. In all three cases rot started in the crown or leaf axil turning leaves into bags of fluid and completely defoliating the plant in 7-10 days.



In the first case the plant was in an east living room window in dry mid-winter. The second case was a Phalaenopsis on my patio in early summer last year. The most recent was about 6 weeks ago in my greenhouse.In all three cases the plant was lively green and in active growth putting out new leaves. The roots were great.


My best guess is that there is some sort of local bacteria or fungus that really likes Phalaenosis. I didn't see this kind of rot problem anywhere else I've lived - even when living near Seattle.

It is possible to grow virused plants and never know it is diseased. Do anything that puts stress on the plant, and it can go downhill pretty quickly. Certainly, the virus killed the plant, but it was not “healthy” before hand.

Granted, but attributing crown rot problems to virus would be a bit "hand wavey". I religiously follow safe handling/cutting procedures (e.g. 1 cut per razor blade), but I assume I have at least some infected plants, especially the older clones. I just bought a 25-test virus test kit and plan to test all my more valuable orchids.

K-Sci

[niamul21]

Originally Posted by K-Sci

If orchid roots rotted because infections set in when roots remain wet too long, neither growing in sphagnum nor semi-hydroponics should be viable growing options. Obviously the mechanism causing death from over watering requires something more than prolonged exposure to moisture. Some of the candidate modes of action sometimes theorized include:

1. Suffocation when sodden potting media blocks oxygen availability.
2. Suffocation when aerobic organisms consume the available oxygen when breaking down media.
3. Extremely low local pH caused by carbonic and organic acids produced resulting from decay.
4. Hydrogen sulfide produced by decay occurring in the absence of oxygen.

The growing techniques orchid growers use to prevent root death from over watering address these in two ways.

• They eliminate or reduce the organisms of decay that could deplete oxygen, produce acids, or release hydrogen sulfide. Examples include potting in scoria, Stalite slate, charcoal, Styrofoam, sphagnum, or LECA.
• They assure high oxygen levels throughout the root zone. Common techniques include growing on mounts, in baskets, and the use of sphagnum and LECA.

Semi hydroponics and growing in sphagnum are special cases because they appear in both the preceding lists. Sphagnum resists decay and contains many tiny air spaces that assure oxygen availability to roots. This is true so long as the moss isn’t so saturated that the spaces are filled with water. The LECA used in semi hydroponics does not decay and is porous to oxygen.

K-Sci

I found this one really helpful to me. Thanks.

[Ray]

Originally Posted by K-Sci

In 40 years raising orchids I've lost healthy well-rooted phalaenosis in active growth only three times. All three occurred in the last three years after moving to Mississippi. In all three cases rot started in the crown or leaf axil turning leaves into bags of fluid and completely defoliating the plant in 7-10 days.

In the first case the plant was in an east living room window in dry mid-winter. The second case was a Phalaenopsis on my patio in early summer last year. The most recent was about 6 weeks ago in my greenhouse.In all three cases the plant was lively green and in active growth putting out new leaves. The roots were great.

My best guess is that there is some sort of local bacteria or fungus that really likes Phalaenosis. I didn't see this kind of rot problem anywhere else I've lived - even when living near Seattle.

Sounds like erwinia to me, a pectobacterium that can start in the tiniest spot on a leaf, expanding rapidly, just as you describe. It doesn’t necessarily start there, but it seems to “target” the crown tissues.

Again though, it is a particularly virulent bacterium, but the fact that it attacks specific plants and not the whole collection suggests there was something slightly amiss that made those few vulnerable.

Granted, but attributing crown rot problems to virus would be a bit "hand wavey". I religiously follow safe handling/cutting procedures (e.g. 1 cut per razor blade), but I assume I have at least some infected plants, especially the older clones. I just bought a 25-test virus test kit and plan to test all my more valuable orchids.

K-Sci

I neither stated or implied that viruses cause crown rot. I was merely using that as an example about how something could be carrying a pathogen and not necessarily succumb to it unless something stresses the plant.

[K-Sci]

Originally Posted by Ray

I neither stated or implied that viruses cause crown rot. I was merely using that as an example about how something could be carrying a pathogen and not necessarily succumb to it unless something stresses the plant.

I was saying that it would be a hand wave if I drew that conclusion. I wasn't saying you did.

K-Sci

[K-Sci]

Originally Posted by Ray

Sounds like erwinia to me, a pectobacterium that can start in the tiniest spot on a leaf, expanding rapidly, just as you describe. It doesn’t necessarily start there, but it seems to “target” the crown tissues.

Again though, it is a particularly virulent bacterium, but the fact that it attacks specific plants and not the whole collection suggests there was something slightly amiss that made those few vulnerable.

I did some searches. The photos I found for erwinia look just like the infection that killed my phalaenopsis. The only treatment I know of for Bacterial Soft Spot (erwinia) is amputation, which is pretty disruptive to a phalaenopsis crow. Fortunately, only one of the three I lost was one I miss (photo attached). Unfortunately it wasn’t a named clone. It had compact branched sprays with dozens of very long lasting heavy waxy red flowers on a very small plant. It was also my wife's fav. Photo attached.

Okay, about weakened/damaged plants getting diseased. This spring I though I had a crown rot on several of my C. dowiana seedlings. Looking close I noticed tiny bug poop pellets in the crowns. Using a loop, sure enough, there was a very tiny white maggot munching away on the new tissue in the crowns in every plant affected (photo attached). One squirt from a bottle of Seven took care of the problem. So what?

I have phalaenopsis with a leaf that was emerging at about that same time. I’ve attached a photo I just took showing an area of leaf that was also probably chewed by the same insect, but wasn't noticed. So, after giving this some thought, it is entirely possible that the plant that developed Bacterial Soft Spot was chewed by the same pest, then overhead watered resulting in the infection.
K-Sci

[Ray]

I have read that copper treatments are effective against erwinia, but it is such a fast-moving infection, it’s hard to control.

I once cured an erwinia infection in a phal by an overnight immersion in a probiotic solution.

[SouthPark]

Certainly ------- a treatment can be effective when it is a suitable treatment. There were two occasions - where a small brown patch just developed on some 'arbitrary' spot on a leaf of one of my Paph. vietnamense. Spread quickly. Wiped out one leaf. Then a second leaf got it too. Small patch to begin with. And ----- although at first it was relatively small ------ it spread relatively quickly. The patch became relatively large - and was still growing quickly.

For that particular organism ----- whatever it was --- maybe it was erwinia ----- I ended up spraying copper solution on the patch. And interestingly (as well as surprisingly) ------- stopped whatever it was ----- dead in its tracks. The big patch stopped growing - permanently. That was the first time.

And ----- it was only recently when the same condition occurred (this is like more than 6 months later or so) ------ a small brown patch appeared on a perfectly nice leaf ----- same plant. But ----- this time ----- I sprayed that brown patch right away with copper solution. Stopped it dead its tracks ----- once again.

Interestingly ----- the next door neighbour ----- also a Paph. vietnamense ----- had never been attacked by the same thing, even though it's right next door, and it is growing in the same medium, and watered in exactly the same way. Same growing conditions.

Here are pics of what I mean (attached) --------- the copper stopped it. And then the vietnamense recovered ------ grew new leaves after that. The new leaf is seen in the pics. The pics are from the first incidence. The most recent incident was much much much less severe. The copper killed whatever the organism is ------ so the most recent case only involves a patch ----- maybe 1 square mm in size only.

[K-Sci]

Originally Posted by SouthPark

For that particular organism ----- whatever it was --- maybe it was erwinia ----- I ended up spraying copper solution on the patch. And interestingly (as well as surprisingly) ------- stopped whatever it was ----- dead in its tracks. The big patch stopped growing - permanently.

I'm not an expert, not even close. You can't argue with success, but I don't see how a topical (non-systemic) treatment with copper can stop the spread of an internal infection.

I don't treat many orchid infections. Instead, I amputate the infected area and apply Thiomyl powder to the cuts with a Q-tip. That's usually enough, but once an infection is in the stem of a phalaenopsis, it has taken out the phalaenopsis. I imagine that a phaph, being another monopoial, would be just as hard to treat. So, good job saving your guys.
K-Sci

---------- Post added at 07:53 PM ---------- Previous post was at 07:47 PM ----------

Originally Posted by Ray

I have read that copper treatments are effective against erwinia, but it is such a fast-moving infection, it’s hard to control.

I once cured an erwinia infection in a phal by an overnight immersion in a probiotic solution.

How do you know the probiotic worked?

And for that matter, what the heck is a probiotic, and how to they work to stop infections?
-Keith

[SouthPark]

Originally Posted by K-Sci

I'm not an expert, not even close. You can't argue with success, but I don't see how a topical (non-systemic) treatment with copper can stop the spread of an internal infection.

Exactly right! I used phosphorous acid ------ which didn't stop it, and also used thiomyl. And the only thing that stopped this particular nasty whatever it is/was ----- was the copper spray. Both times ----- the activity just stopped pretty much right away. Quite interesting. Definitely surprised me. I think this particular vietnamense would have been history otherwise. Also interesting how its next door neighbour ----- also a vietnamense ----- grown the same way - didn't ever get that. Surprises me.

The new leaf grew after the treatment. The orchid sat there for a while, and then eventually the wonderful teeny little green development started up ------ the new leaf.