Zowie, I'm going to vote for a fungal infection in the crease of the leaf. Doesn't really matter, the treatment I would suggest is the same. Get a disposable very sharp instrument such as a razor blade, exacto blade, etc. etc. Heat the blade over an open flame until it is red hot and let it cool. As I see your photo, there is a black area in the crease of the leaf, then a border of white, then an area where the leaf is looking kind of clear or watery. You are going to have to get between that watery looking area and the main part of the plant, but far enough away from the watery looking area that you are sure you are in uninfected tissue, and cut that leaf off. Try to make just one clean cut. If you have to make two cuts, I would resteralize the blade before the second cut. get some kind of powdered horticultural fungicide and apply a liberal coat to the entire cut area. Do not water the plant for a week, and see if you have stopped the spread of the problem. If the infection is still present, do the procedure again, cutting even further into healthy looking tissue the second time.

If you are dealing with a Cattleya type plant, you may have to remove the entire pseudobulb. If it is something like a Phalaenopsis (your photo looks like it may be), then you will get to the main part of the plant, and my be in trouble if you don't get it stopped before that.

Your second photo, the spots on the leaf tips, I would not worry too much about those unless they begin to get the watery area around them and it spreads. Then the same procedure as above.

I would begin to look for a cause of this problem. Insects could be carrying this around. I suspect you are growing in your home, and most insects that would carry something like this would be noticeable, and most unwelcome in someone's home, so with no complaint about that perhaps you don't have an insect problem.

I would look at high humidity and stagnant air, with water splashing around on watering days. With these wet stagnant conditions, another plant may have had a problem, and splashing water could spread it. After you get this infection stopped, pop that plant out of its pot and check the roots. Stagnant air and wet conditions can mean over watering, and a root rot problem. Root rot = weak plants = high probability of disease.

Orchids need their water, but at least as important is a drying period, and vigorous air motion. Tough items to supply in some home growing areas.

Good luck

Bill

Hi Bill,

Thank you so much for your detailed reply. I shall definitely follow all your instructions and keep a close eye on its progress. Also I'll give it a good dry spell for a bit.

Our new house has been recently replastered, and we were using heaters to help dry the walls out. I'm wondering if the high moisture content and warm air might have played a part in allowing disease to take hold. It never even occurred to me before that my orchid would have been affected by it.

Just one last question, sorry to pester...

I was thinking of taking my orchid to my mums for a little bit, hoping better air conditions will aid its recovery. My only worry is that mums house plants will catch the infection from mine through the air. Is this possible? Should I keep my plant away from them?

Thanks again, you've given me some very good pointers to help my poor, long-suffering Phalaenopsis!

Zowie

Zowie, I'm not sure what a "little bit" is....., so lets approach it this way. You obviously do have a sick plant, that is not going to be able to cope with the stress of moving from one climate to another as well as a healthy plant. If you are thinking about an extended stay, say a month or more, that's one thing, but for just a few days, I wouldn't.

If its going to stay at your mums for an extended length of time, and you have not succeeded in eliminating all the infection, this same condition is going to appear again, and its going to probably be capable of spreading what ever it has at that time. If it stays home with you, you at least know what to look for, and can take action much quicker than someone who is not familiar with what the problem looks like.

Its a tough call, but I think I would lean toward keeping it at home and working at improving its environment at home. That way, if one of your mums plants comes down with something that is completely unrelated to your plants problem, it won't get the blame for it.....☺

Bill

Does it come off? I remember one phal once that for whatever reason secreted some sap like substance that would then get some black mold. Completely harmless as far as I could tell.

Haha, that's true I don't want to be blamed for an outbreak!

No, unfortunately the black's not coming off. It's on the underside of the leaf, like a discolouration. I'm going to be brave and have a go at cutting it, wish me luck. Thank you for everyone's quick and detailed replies. :)

Zowie