Black rot or sunburn
 

So I just received two orchids from a large seller in Western NC. One of the leaves has a large black spot on the upside, but looks otherwise unmolested and green on the downside. What do you guys think, sunburn or rot? How shall I proceed?

Sunburn (which I am having some bothersome issues with right now) will be a more desiccated lesion than rot.

Thus when you touch the area, rot will be kind of soft and the sunburn will be firm and just atrophy over time.

Both types of lesions can extend as sunburn lesions can look small at first and become more extensive as the full damage is shown.

I have two plants I am still not sure about but are most likely sunburn.

I would watch it and have a "flexible" plan of action.

I love the terminology, "Flexible."

I would notify the seller right away. That way if it ends up being serious they will have been told the plants came this way.

Photo of the damage

http://www.orchidboard.com/community...tley_Leafe.jpg

That looks like fungal spots to me, possibly had some water standing on the leaf.
Joann

Sunburn or Rot
 

The black areas on the leaf are not indicative of normal sunburn. It may well have been caused by sun on water on the leaf and it looks that way due to the number of separate areas. If it is sunburn the affected area will go very dry but will not cause the plant any harm, it will just look a bit unsightly. I would treat the plant with a systemic fungacide as a precaution and check to see if the area grows in size, if it does then it will confirm it is not sunburn. cattmad.

"Flexible" means:

#1. Observe
#2. Choose:
a. continued observation and then repeat step #2
b. treatment with copper based fungicide (Phyton 27 or other) and then #2.a.
c. cutting off the leaf well into healthy tissue and then #2.a.

So at any point you can change your diagnosis and then react how you see fit to treat the current condition.
The information you get from observing is very valuable.
Fast moving soft or edematous lesions that leave behind brown atrophic spots are bacterial and possible fungal.
Slow moving are more likely fungal but can also be bacterial.
Spots that don't really increase much in size and simply become atrophic without any soft areas are likely sunburn.
This could also be a previously treated condition/infection :twocents:

This still looks a lot like sunburn to me.
Standing water on a cattleya plant on a bright day will certainly burn it.
However, the injured leaf can get a secondary infection! Thus you must be on guard..."flexible" :evil:

PS. I like Phyton 27 because it treats bacterial AND fungal disease with the exception of just a few fungal culprits left out :biggrin:
However, I recently learned it takes about a week for a copper based fungicide to become effective and was recommended to also concurrently treat with Physan which is broad spectrum

Can you give me a short lesson in Physan vs. Phyton?

I'll do better!

http://www.houstonorchidsociety.org/...ySueBottom.pdf

Physan and Phyton 27 can both be purchased online from many different orchid suppliers.

Ms. Bottom's presentation of what and when to use stuff is the best I've run across to date :goodluck: