Bacterial Infection on Guarianthe aurantiaca?
 

....or Cattleya for those I may have offended. This brown spotting occured a few days after I sprayed my terrarium with Serenade brand fungicide/bateriacide; I spray this every few weeks as a preventative measure, and it has not caused problems. I have had issues with edema on this plant before, in fact you can see a small pimple in this photo. Watering has been regular(cut back slightly now that temp has dropped a bit) and humidity has dropped; point being, (I think) I have ruled that out. It is not raised at all, and it is not spreading.

The active "ingredient" in this brand is a patented strain of Bacillus subtilis. Are there instances of infection caused by typically-beneficial bacterium?

If anyone has any culture tips for this species I made need them.

According to the EPA profile for Bacillus subtilis, it is non-pathogenic to plants. I assumed this, as it is a widely used species. Although, you cannot place much confidence in assumptions.

I am still looking for any insight that one might offer.

Kilol. I don't know if you can get it in duh lann of duh fee, or not.
A 3 minute dip in 10% KMNO4( potassium permanganate) might whoop it too. No damage to the plant with either product.

spray the whole plant with hydrogen peroxide

it only evaporates and kills the bacteria in the process....

are you sure it is bacteria not fungi? because bacterial infestation is fast and can kill you plant in a couple of days

Bud: I am not at all sure. It has not spread much, if at all. It doesn't "ooze" as is typical either. I was thinking of doing a wash with some botanical household cleaner that contains thymol. I have read that it can combat a variety of bacterium and fungi. Might as well go for the kill.(?)

Can you tell anything from the looks of it. Its been in this state for about a week but onset QUICKLY; seemingly overnight.

Arenalbontanicalgarden: That Kilol sounds like a wonder extract. I have hunted around and have not found a distributor in the US.

I'd love to hear more thoughts from both of you.

I'd vote bacteria, brown spot, though not sure 100%.

I'd isolate, largely cut the part, treat with fongicide/bactericide, cinnamon on the cut.

Check Orchid Diseases
In the bacterial brown spot part, you have the link for a specific pdf of Sue Bottom with a Catt example.

Anyway, wade into the site and the pdfs, lots of informations available.

Ah yes, I have another .pdf she put together. The pictures on this one are much more informative;"slow growing" sounds like it, "rarely fatal"makes me smile. It is also on the oldest leaf which is typical according to her and her sources.

Whether fungal or bacterial, the treatment will be the same.

Thank you to you all.

best to eradicate the infestation early before it spreads to the whole plant....I would use the big guns on this.....home remedies might be too slow

Thank you for your your suggestion. What has worked best for you? I see quite a selection on Sue Bottom's pdf. Or are there others you prefer that are not listed?

We don't have the same products authorized this side of the Pond, so I won't be of much help… (not to mention the names… it gives headaches)

I forgot you were from France! I noticed that before and thought to myself how wonderful horticulture is to bring people together no matter what age or origin.

Bud? Anyone else?

My fungicide is myclobutanil based, in case (got to verify though, the manufacturer site is a nightmare so I had to make a guess).