Odd stain on Oncidium leaf - Orchid Board

Karen00 · #1 08-13-2018, 02:39 PM

Hello folks,

I'm looking for a little help in trying to identify what looks like a stain on one of the older leaves on my Oncidium. This is a mini Twinkle. I purchased it in February. Currently it's growing outside.

Characteristics:
- The tip of this leaf was broken and dried when I got it. I'm not sure if a virus, bacteria or pest had already infected the leaf. I don't recall whether this stain/spot had already started. If it was there it was tiny.
- I think I first noticed this a couple months ago and thought maybe it was sunburn when I first put my orchids outside.
- This is on one of the older leaves. All new growth is fine.
- Colour: I can't tell if this is brown in colour. It looks kind of red or orange but that could be the colour mixing with the green of the leaf.
- It looks exactly the same on both sides of the leaf. Unfortunately I don't know if it started on one side or the other or both.
- It's not appearing on any any of the other leaves (so far) and the pseudobulb is fine (so far).
- The leaf feels perfectly fine and it looks healthy otherwise. It's not like it's dried or mushy or pitted.
- When I was feeling the leaf I thought I felt something hard on the underside but I couldn't see anything. I wiped the leaf down with isopropyl alcohol and whatever it was wiped off. Not sure if it was a bug or anything like that.
- It's spreading very slowly but is spreading.

I have never seen anything like this before. I couldn't find anything in any of the searches I did.

As mentioned I wiped the leaf down with isopropyl alcohol. I'm not sure if I should continue this or just cut the leaf off or just leave it if this is the normal demise of the leaf.

If more information is needed or more pics let me know.

Thanks in advance for any help!

Roberta · #2 08-13-2018, 03:14 PM

That looks to me consistent with sunburn - it is one spot, at the highest part of the leaf (where it curves). When moving it outside, it might have gotten a short term blast of sun (that happens easily, and takes seconds though the damage may not show up immediately) If that is what it is, no harm done (other than aesthetic) If it bothers you, you could trim the leaf below the discolored part with a sterile shears or razor blade. (When trimming damaged leaves, I try to cut to a point in the middle, to make it look more natural

Karen00 · #3 08-13-2018, 04:25 PM

Quote:

Originally Posted by Roberta

That looks to me consistent with sunburn - it is one spot, at the highest part of the leaf (where it curves). When moving it outside, it might have gotten a short term blast of sun (that happens easily, and takes seconds though the damage may not show up immediately) If that is what it is, no harm done (other than aesthetic) If it bothers you, you could trim the leaf below the discolored part with a sterile shears or razor blade. (When trimming damaged leaves, I try to cut to a point in the middle, to make it look more natural

Thanks so much for the speedy reply Roberta!! It doesn't bother me as far as looks go and I rather keep the leaf than cut it.

So is it possible with sunburn for the damage to spread out the way it has over the course of a couple months? The darker center part is of course the initial spot that appeared a couple months ago but the fainter part around it is what has been spreading.

I hope it is just sunburn. I rather that be the problem rather than anything else that can affect orchids. :-)

I forgot to mention I fertilize with a dilute 20-20-20 almost weekly because this has started to bloom. I didn't think the cause was from too much fertilizer given it's only on that one leaf but I guess you never know.

Thanks again!

Ray · #4 08-13-2018, 04:45 PM

I'm going to disagree with Roberta on this one. I think there was some mechanical damage (insect?) on that left leaf margin, and an infection started there and spread. See my red vectors in the attached image.

I recommend cutting off the leaf below any trace of infection, such as where I indicated with the yellow line. Dust the wound with cinnamon powder immediately after cutting and that should be the last of it.

Ray · #5 08-13-2018, 04:48 PM

Switching to general culture... define "dilute" 20-20-20, applied weekly. Orchids are quite undemanding of fertilizer, and too much can be as bad-, if not worse than not enough.

Roberta · #6 08-13-2018, 04:48 PM

Ray, I'll certainly defer to your expertise on this one. At any rate, we agree that clipping the leaf should do the job, and it'll look better besides.

Karen00 · #7 08-13-2018, 09:57 PM

Quote:

Originally Posted by Ray

I'm going to disagree with Roberta on this one. I think there was some mechanical damage (insect?) on that left leaf margin, and an infection started there and spread. See my red vectors in the attached image.

I recommend cutting off the leaf below any trace of infection, such as where I indicated with the yellow line. Dust the wound with cinnamon powder immediately after cutting and that should be the last of it.

Thanks for taking the time to do up that image Ray. It helps a lot! I'm assuming then that it's possible to have an infection yet the leaf still feels perfectly healthy? When I rub both sides I can't feel any cellular damage at all. It still feels smooth and supple. Even at the initial spot you indicated.

Thanks again!

Karen00 · #8 08-14-2018, 12:56 PM

I thought I would give an update to this. I decided to perform surgery on the affected leaf. I woke up today to find it had spread further so I figured it was better to sacrifice the leaf than potentially the entire plant. I had to make a cinnamon paste in order to get it to stick to the tip. Hopefully this is the last of it.

I've never had an infection before in any of my plants so lesson learned. I should've posted this when I first noticed it because I could've salvaged more of the leaf or I should've just assumed there was something wrong and cut the leaf.

Does anyone know of any systemics I could've watered the plant with to try and kill the infection and save the leaf or are systemics hit and miss or possibly more harmful to the whole plant making them a better option if the entire plant is infected vs one leaf?

Thanks again!

Karen

Ray · #9 08-14-2018, 01:27 PM

Systemics may stop the progression of an infection, but that damaged tissue will not be repaired.

Karen00 · #10 08-15-2018, 12:29 PM

Quote:

Originally Posted by Ray

Systemics may stop the progression of an infection, but that damaged tissue will not be repaired.

Yep, I know that. Had this leaf started to turn brown and wither or maybe had started to turn mushy then it wouldn't have been worth saving but, other than whatever damage happened internally, the leaf felt fine and would've been worth saving if a systemic could have done this.

If you have any recommendations that would be great.

You also asked about how much I diluted the fertilizer. I'd say I probably dose at just 15% (maybe less) of what the general dosage instructions say. Having said that I'm using a general fertilizer not one specifically for orchids. I've been dosing this way for three years and haven't had issues but of course every plant is different.

Thanks!