Strange spotting on Cattleya leaves, please help

[escualida]

Hi all, I've noticed some dark spots on the new growths of some of my Cattleya leaves, can anyone help me identify what it is, and how to treat it? I've looked at the pdf on orchid diseases and it doesn't really look like anything there, the spots are small and black and don't seem to be spreading or getting worse, and they're only on the newest growths. I'm relatively new at this and would like a second opinion from people who have been doing this for much longer than me. Here are some pictures:





Any ideas? Thanks in advance!

[DavidCampen]

Last night my wife pointed out the exact same thing on a couple of my cattleyas. I grabbed my spray bottle of Physan-20, diluted to 200 ppm AI, and sprayed with that but I need to determine what it is causing this.

Edit:
Check out this paper by Sue Bottom:
http://www.houstonorchidsociety.org/...ySueBottom.pdf
There are many versions of this paper available; our link here for this to the St. Augustine website but this Houston link seems to be better. Bacterial and Fungal Spots and Rots starts on page 14.

I may spray with Cleary's 3336 and some other agent this weekend.

[tucker85]

Those spots are usually caused by leaf spotting fungus. The good news is that it usually doesn't harm the orchid it's just a little unsightly. Here, in Florida, orchids grown outdoors often have a lot of that type of fungus on the leaves.
Just out of curiosity, what fertilizer are you using?

---------- Post added at 10:55 AM ---------- Previous post was at 10:42 AM ----------

David's idea of using Physan 20 is probably a good one. The fungus lesions can sometimes get a secondary bacterial infection.
That's a great article from the St. Augustine Orchid Society, David. Thanks for sharing that. Their newsletter often has very good articles with lots of good information.

[escualida]

Thank you so much for your replies, I'm relieved that it's not something horrible, I will definitely be spraying them down with Physan 20.

DavidCampen - that's exactly the pdf I had been looking at before, it's really great.

I forgot to mention that I use First Ray's 13-3-15-8Ca-2Mg MSU fertilizer for pure water which does have calcium and magnesium added.

tucker85 - I saw you mention on another thread that I should also use a calcium and magnesium supplement, any suggestions as to which one?

Thanks again!

[tucker85]

Adriana, what fertilizer do you use?

[escualida]

Originally Posted by tucker85

Adriana, what fertilizer do you use?

I edited my post above just now with that information, would love to hear your take on which supplement to use.

[tucker85]

You're using a good fertilizer because it's low in phosphorous and contains calcium and magnesium. You may not need to use a supplement at all with that fertilizer. I use a cal/mag supplement called MagiCal from technaflora. Botanicare also makes one. They're available online or from hydroponics stores. My experience has been that after using a cal/mag supplement once or twice a month for a few months I no longer have fungus problems on any of my leaves. I'm not sure you need it because your fertilizer contains a decent amount of calcium, but if you decide to try one, start out using once a month, along with the fertilizer you use. That will increase the calcium a little bit. It's up to you.

[dounoharm]

to me, besides all the above wonderful information, I think maybe you could up your light a bit...your plant looks like the new growth is kinda puny....more light! good luck!

[james mickelso]

The color looks good. The size is perhaps from the orchid not being in as good a shape as it could be which affects the size above all else.

---------- Post added at 07:52 PM ---------- Previous post was at 07:51 PM ----------

For calcium I smash up egg sheels into real fine powder and sprinkle that on the media. I jsed it like that on bonsai for years. And my tropical and fuscias.