Sudden Large Black Spots on Mature Catts

[realoldbeachbum]

Catt Black Spots 09242021 — Postimages

Four days ago, a very large dark brown/black spot appeared one of my large Catts. The spot was about the size of a quarter, in the middle of the newest growth, and did not reach down to the pbulb or tip of the leaf. There was no sap oozing and no yellow leading edge. Also, it was NOT sunken.

I isolated the plant and tested it for CymMV & ORSV. It was negative for both.

Today, the same spots appeared on three more Catts that had been sitting near it, and the leaf on the original sick plant dropped in half and is now fully black.

Environment: Outside most days for the past 6 weeks in temps between 80 & 95 F. No full sun. Drenched with well water every other day if no rain. At the beginning of Sep (24 days ago) I gave them their first monthly dose of KelpMax/QuantamTotal per Rays recipe.

Based on pics from St. Augustine Orchid Society and other websites, I cannot determine for sure what this is; possibly Black Rot? (It rained for three days straight due to hurricane in the Gulf and was humid and warm.)

I cut the affected leaves, sprayed with Phyton27, then sealed the cuts with cinnamon.

Should I just put these in the trash to avoid further spread or is there hope for recovery?

Thanks so much, ROBB

[WaterWitchin]

Sure looks like black rot to me, along with the comment about wet, warm humid. There's hope for recovery, and you've already done what I'd suggest... cut off black, seal cuts, spray with a fungicide.

Black rot spreads by splashing water from infected plant onto other plants. Were they mine, I'd get them away from other plants, get some really good air circulation going on them, and keep the leaves dry for awhile, only watering roots. And keep a really close eye on them for new spots. Plus keep an eye on any others that were in close range to them. Black rot spreads pretty quickly, and the spots appear pretty fast.

[My Green Pets]

i agree; isolate it, and you may also want to spread out your other plants if possible with as much space as you can between it. i have not had the pleasure of personally dealing with black rot yet, but everything i have seen about it describes it as fast, deadly, and unbelievably contagious. i would consider it a full collection-wide emergency. please keep us updated and good luck!!

[Leafmite]

If you can quickly find a systemic fungicide (Daconil, etc.) and treat all your Cattleyas, that would be best as this tends to go through the entire plant quite quickly. If not, any good fungicide with copper will do. Avoid getting it on any Dendrobiums. Good luck!

This is what I have heard recommended in my orchid society: Thiomyl Systemic Fungicide 6oz
– Carter and Holmes Orchids

---------- Post added at 02:50 AM ---------- Previous post was at 02:42 AM ----------

I had this many years ago and lost most of my treasured Cattleyas. Now, when the Cattleyas are actively growing, I make certain they get plenty of Calcium.

[Ray]

Phyton 27 is a systemic, copper-based bactericide and fungicide. I like Thiomyl, too, but if it’s a bacterial infection, it won’t touch it.

[Leafmite]

That is good to know. Thanks, Ray. I have never used a systemic fungicide/bactericide (though it would probably have saved my Cattleyas all those years ago). The only fungicide I have ever used was Captan for the fruit trees. I still get paranoid when I hear something like this...will probably give all my plants a dose of Cali-mag when I water tomorrow.

[realoldbeachbum]

Thanks everyone for the advice. I have hope now and will NOT trash them just yet.

When I entered the grow room this morning, there was Pot. Jessie Lee "Hawaii" with a big black spot!!! She has now been isolated, leaf removed, Phyton27 treatment, and cinnamon.

One other bit of information that I did not mention in the original email is: When I removed the affected growths, the cut was clean and bright green. No red circles or brown/black areas or oozing. Hopefully I cut far enough into good growth to avoid speading. We will see!

Thanks again, kind OB experts, you have probably saved my collection! ROBB