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Cattleya leaves turning black

Posted by mulchlady 6 NJ (My Page) on
Wed, Nov 11, 09 at 14:24

I recently purchased several Cattleyas. As a standard practice, I dunk all new orchids in a solution of Physan 20 and water in the hope that I'm killing anything that may come in with the plants.

After several days, I noticed that leaves on several, but not all, the plants were turning a reddish-purple so I took them out of full sun and gave them some shade. Now, I see that some of the smaller leaves are turning black and some of the pseudobulb sheaths have black splothes. Could this be due to too much sun, using Physan 20, or caused by something elese like a disease or fungas?

Follow-Up Postings:

RE: Cattleya leaves turning black

Physan 20 is for fungus problems. It won't kill any insects or cure any diseases. You need an insecticide for insects.

The reddish-purple is from a lot of light and is not necessarily bad. My Iwanagara literally turned purple while it was outside and then slowly reverted back to green when brought inside. You might not want to give the catts too much shade, they need all the light they can get, especially here in light-starved zone 6, NJ. Mine are right up against the glass in my south window.

Don't know what the black leaves or the black splotches are on the sheaths. Could you possibly post a picture?

RE: Cattleya leaves turning black

I will try to post a picture. Hopefully the leaves are changing color from high light. They're in greenhouse direct sun and may just need to get used to their new home. But the black leaves have me a little worried.
I pulled two small black leaves off today. They appear to have rotted.

RE: Cattleya leaves turning black

Physan is an algecide not a fungicide.

If you are not convinced look at the label of ingedients and go to a swimming pool store and compare it to the algaecides sold for pools. HTH and several other companies use the exact formula for killing algae in pools. The pool algaecide is much cheaper by the way.

I have never found it effective against fungus and is a danger to damaging roots if used too strong.

Black rot on leaves and pseudobulbs is phythiopn fungus and very bad. Cutting it out is the best procedure. The only chemicals I have found effective are Subdue, allette, heritage and a few others all of which cost $300-500 a pound

Scissors are the best treatment.

RE: Cattleya leaves turning black

See my post below: "blasted leaf sheath on cattleya". One of my catts had a very healthy leaf sheath developing and it suddenly turned black and dry. The leaf it was contained within had turned dark purplish. That's the first time I've run into this problem. Perhaps stupidly, I cut out the black sheath and have given the catt more sun. There wasn't any flower bud forming, so I think there wasn't any point in keeping the black sheath. I also repotted it into one of those clear plastic orchid pots with the cone air vent. Can't describe it but I'm sure some of you know what I mean. Hope it remains alive. It's a "chia Lin New City". Good luck with yours.

RE: Cattleya leaves turning black

The "leaf sheaths" on a developing Cattleya pseudobulb are actually called Sarongs and it is a much more serious problem if they go black than if the flowering sheath goes black. Though that is a problem too. i would rather see it get dry and papery if it on one of those Cattleyas that form the sheath and wait months and months before the flowers develop.

Not too sure about the flowering pattern of Blc. Chia Lin 'New City' but from looking at the parents perhaps it is one of those that flower in Autumn rather than waiting till winter and spring.

RE: Cattleya leaves turning black

It could be black rot or something else which causes the leaves to dry up and turn black without involving the bulbs. I've had both. Black rot spreads fast and you could loose the whole plant in a week if you don't do something fast. Use a sharp knife or straight edge to cut away the bad bulbs until you hit good tissue. Use new straight edges each time you cut to not infect the good tissue. Let the plant dry well and only water sparingly until you see the plant start to recover.

vtandrea, what you saw is fairly common. It is not what mulchlady has. Sheaths can stall or fail to form and dry up. There are many reasons but none of them fatal.


RE: Cattleya leaves turning black

Per the label on Physan - disinfectant, sanitizer, deodorizer, fungicide, algaecide, virucide

This product won't damage roots if used at the recommended dosage. The label also lists the needs specific to orchids.

Black rot is the fungus phytophtora or pythium. Here is a link to keep on hand to hopefully let you diagnose any problems that arise.


Here is a link that might be useful: Pests & Disease

RE: Cattleya leaves turning black

Jerry wrote, "Physan is an algecide not a fungicide. "

Please reference the link that I provided below. The link includes the following claim: PHYSAN 20 is a broad range disinfectant, fungicide, virucide, and algaecide which effectively controls a wide variety of pathogens on hard surfaces and plants.

The product contains quaternary ammonium compounds. These have been in use for decades. Physan 20 is not a STERILANT nor does Physan make that claim. This product isn't magical.

It is essential to read the Physan product directions. Then, follow the instructions....

Jerry wrote, "Scissors are the best treatment." PLEASE, people -- do not follow his advice! Remove infected plant tissues with inexpensive, disposable blades available at any hardware store (oh!). Dispose of a used (contaminated) blade immediately after completing procedures on a single plant.



Here is a link that might be useful: Physan

RE: Cattleya leaves turning black

As someone who has - ah - professionally roasted more orchids than I care to remember, I think you gave them too much full sun, too quickly. Even your sissified NJ sun in November is pretty severe for a greenhouse-grown orchid plant.
You live and learn, though. The plants generally survive, they just look unsightly ("street") for awhile until you get enough new foliage to camoflage the toasted parts.
Most cattleyas can take a lot of sun without damage, but you have to work them into it slowly, over time.
The flowers will still be lovely!
Regards - Nancy

RE: Cattleya leaves turning black

6" tall plant is now 8" from a screened southern window in phx az. Exposed to too much sun-leaves turned black-no more H2O/fert until...?
Will plant survive? Any first aid?
Knowledgeable folks pls respond asap.
Thks in advance.
Bob C.

RE: Cattleya leaves turning black

I had this happen to me once when I put lights too close to a pair of new Catts. I knew it was the lights, because the redness formed in a pattern that radiated out from where the blubs were nearest. It was darkest there. The most severely purply-red areas were the ones that turned black and mushy within a day or two. I cut that away from the leaves, and dusted with cinnamon, which is a natural fungicide. It prohibits fungal growth, but I'm not sure whether it will kill fungus that's already there, since I've never tried it.

Anyway, your plants should be fine, and I think your intuition about it being the light is probably spot-on. Maybe provide a little shade and gradually take it away so that they can adjust without getting burnt. Good luck!

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