This is one of those posts that most orchid growers won't have the courage to post. It shows that even the best of us have problems growing orchids, and I am certainly no exception. I have always had a love of Coelogyne species and hybrids, especially the warmer growing ones, and have gone out of my way to find out species that I think ought to do well under my conditions.
One of the species that got added to my collections was Coelogyne rochussenii which I obtained from Burnham Nurseries a couple of years ago. I have to say that C. rochussenii is an untidy species with long lengths of rhizome between pseudobulbs; quite a hard plant to accommodate in a pot although not, ostensibly, a difficult grower. This is a species that bloomed for me shortly after I got it, but sadly not since. It blooms directly from the rhizome (botanically it is said to be heteranthous), and the flower spikes do not come from the centre of a new growth. This is similar to the cooler growing species such as C. cristata.
Now the reason I'm telling you all this is that around a year ago on one of my bi-yearly pilgrimages to Burnham Nurseries I noticed that their quite substantial stock of C. rochussenii was looking......ill. Leaves were spotting and dropping and some plants had died altogether. When I got home I looked at my plant and thought it looked OK (it is a bit of a mucky grower so some spotting is almost inevitable). It has been fairly recently potted on and partially re-arranged so it can stay in its pot. The rhizome is stiff and difficult to arrange unless growth is quite young. Recently, my plant has put out a new growth which looks healthy enough but the older leaves are spotting and turning yellow. Alarm bells ringing?
Scary, huh? Notice the yellow margin and necrotic brown spot within (on the leaf at the back - the front one is too far gone). This looks like classic fungal infection to me. What I need to know is where the disease has come from because this looks exactly like the plants at Burnham Nurseries. Needless to say I have put this plant in isolation and it has been sprayed with a systemic fungicide (fingers crossed the fungicide doesn't damage the plant). Obviously, the damage already there is not going to get better so it all rests on whether I think the damage is getting worse. The easiest (and slowest) way to tell is to keep an eye on the new growth. If it stays clean, then the fungicide has worked. I expect the damaged leaves to drop eventually, and therein lies the danger with fungal attacks. They rarely kill the plant in their own right but they do weaken plants significantly and it can take years for plants to recover.
Meanwhile, in my semi regular check of all remaining plants, I notice that Coelogyne asperata x rochussenii is showing signs of damage....
You can see that the damage isn't so severe on this plant, but note the yellow spotting that is appearing. This plant has also been isolated and treated with systemic fungicide. Fingers crossed. The disease has also appeared on Coelogyne velutina and it looks awful but you will be thankful to learn that I haven't taken a photo of it. The rest of my collection looks clear. I grow a lot of Coelogyne and they are quite close together but disease is not appearing anywhere else. Let's hope it stays that way.
I'm afraid i'm placing the blame for this disease outbreak squarely at the door of Coelogyne rochussenii from Burnham Nurseries.
Interestingly, if you research Coelogyne rochussenii on the internet, there is no reference to it being a straggly, untidy species with long internodes. All the photos I have seen show a neatly clumping plant that will happily grow in a comparatively small pot. I have bought another plant of this species from eBay (same seller from whom I bought the two Angraecum before Christmas) and it seems nice and clumpy (some internode but nowhere near as much as on my existing plant) and very healthy indeed with no sign of any disease whatsoever.
My plan is to spray this with fungicide as a precaution. I haven't decided whether to put this into my main growroom as yet (though it will end up in there eventually), or whether to keep it in isolation for a bit as a double level of precaution. At any rate, the new plant looks very healthy so it has the very best chance of staving off any disease that might be in the air.