Cattleya dowiana new growth turning black?

[ramonypony]

I noticed that the back side of the new growth on my C. dowiana var. aurea is turning black and now it's started to spread to the other side. I just got the plant this year and I haven't repotted it yet.

Why would it do this? Do I need to cut this growth off low to keep it from spreading? Should I leave it alone? Do I need to treat it with something?

[katrina]

Heat and humidity and lots of moisture can cause this. It creates the perfect environment for the spores to go wild. I've had a few plants get hit this year.

You want to cut the entire growths off and make sure you're getting far behind the black tissue then treat the cut w/cinnamon. Even cutting well behind the black is no guarantee if the plant has true "black rot". Hard to tell via a pic. I have cut and cut this year (lots of rain early and then the heat and humidity hit later this summer) and I've still lost a few. As a matter of fact, I haven't been able to save any so I'm now at a point where I'm just pitching if it shows up because true black rot is very contagious and can spread pretty fast.

Given it's your first showing signs...I would cut, treat w/cinnamon, spray a fungicide, and isolate while you watch it. And you'll want to watch for a few weeks because it can pop up again later. The problem with true black rot is that it starts in the roots but presents in the leaves so by the time we see it, it's usually in the plant and very hard to eliminate.

Here's an article on it. http://www.phelpsfarm.com/OrchidPestsandDiseases.pdf Scroll down to the subject line of Symptoms of Black Rot Pythium & Phytophthora spp.

If you have some other kind of fungal/bacterial thing then it's possible you can get behind it and stop it. Only time will tell but you want to act fast. And, again, isolate this plant or risk it spreading to others.

[Leafmite]

I agree with the chopping and use of a fungicide.
A way to help prevent fungus problems is to give the plants a little extra calcium. For some reason, this makes them more resistant to bacterial and fungus issues. When I was a child, some old-time gardeners told me that they had learned to spray the leaves of plants with milk to prevent fungus infections. I do add powdered milk to the watering can in the summer and eggshells to the orchid medium and it seems to work. We had quite a bit of rain and humidity early this summer and my plants (including the orchids) didn't seem to have any issues.
Good luck!

[brsucculents]

This is an excellent question.
It looks like black rot to me.
For the immediate action, I think Katrina gave good advice. Cut the stem back till you don't see black or brown. Sterilize the blade between cuts and use cinnamon. I would try to cut it off above the rhizome so the eyes can initiate new growth. I think the black stuff at the rhizome is just the sheath. It can be pulled off.
The root cause /or prevention is the real question. I had a real problem last year. I treated eveything with a very expensive systemic fungicide for black rot. There is a lot of information out there that this is related to low Calcium. I use rain water to water my Orchids which contains no Calcium. I now alternate with my regular fertirlizer with micro nutrients and Ammonium Nitrate/Epsom Salt/Cal-Mag. This seems to have really helped the problem. But I recently noticed some brown shoots.
What's the cause of the recent problems? Has the systemic fungicide worn off? Has all the rain eliminated the Calcium in the media (I grow outside during the Summer)? I suspect the plant isn't getting something it needed and aborted.
I would greatly appreciate the input of other more experienced growers.

[Leafmite]

We had quite a bit of rain in the earlier part of the summer, too, and so I added fertilizer, Ironite and powdered milk to the watering can and watered in between rains (my orchids are all in basket pots, Vanda baskets or mounted with either LECA or red lava rock as a medium so, no problem with getting more water). When you get plenty of rain, the medium is flushed. That is actually a good thing as it gets rid of all the excess but it does mean that you need to replace what is needed by the plant.

[katrina]

FWIW - I have been using a Ca/Mg supp regularly for a couple of years now so I know my issue wasn't a lack of calcium but rather ideal environmental conditions for the pathogen. When the orchids are outside and at the mercy of Mother Nature...there is only so much one can do. It happens some years, unfortunately.

Side note - I also lost my cucumbers, watermelons and all my summer type squash this year. The basically just rotted away from all the soaking rains. There were weeks of standing water in many places around the yard. I would consider it one of the worst early summer growing seasons I've had in years and I'm just thankful I didn't lose more orchids than I did. All in all...I think it was less than 10. Could've been much worse.

[Leafmite]

Cattleya dowiana, I just remembered, doesn't like too much fertilizer. It also likes to dry out very quickly when the cooler weather sets in. For specific care for it:
Chadwick and Sons Cattleya dowiana

Cattleya dowiana | Chadwick and Son Orchids


Katrina, I am sorry to hear that you have lost a few. Ohio weather is just so unpredictable. I know a few people in our OS have been having problems, too, with their orchids rotting away and some others just gave up and brought them all inside. I think that I must be lucky, then, or the fates are showing mercy after my attempt at growing under lights.

[isurus79]

Originally Posted by ramonypony

Why would it do this? Do I need to cut this growth off low to keep it from spreading? Should I leave it alone? Do I need to treat it with something?

Time to do some cutting! I think Katrina nailed it. Using Physan regularly for a few months might help as well. This species is very sensitive to excess moisture and needs to dry off quickly otherwise it is susceptible to rot. Things would have be very wet for this to happen during the growth season. Rot of new growth in Cattleyas can also be linked to calcium deficiency. Check this site out:

Orchid Environmental Damage

What part of Texas you in?

Originally Posted by brsucculents

I now alternate with my regular fertirlizer with micro nutrients and Ammonium Nitrate/Epsom Salt/Cal-Mag. This seems to have really helped the problem. But I recently noticed some brown shoots.
What's the cause of the recent problems? Has the systemic fungicide worn off? Has all the rain eliminated the Calcium in the media (I grow outside during the Summer)? I suspect the plant isn't getting something it needed and aborted.
I would greatly appreciate the input of other more experienced growers.

Less is more! We just had back to back lectures at the local orchid society from Alan Koch and Rick Lockwood about nutrition in orchids. Basically, we feed WAY too much. MSU fertilizing dosages are much too high for most orchids. Try cutting your fertilizing regime way back. Specifically, over fertilizing with potassium can lead to calcium deficiency as it interferes with Ca uptake. Over fertilizing leads to smaller plants with short lives. I'm cutting way back for the rest of the growing season (which lasts until about mid to late October here in central Texas) and into next year.

Originally Posted by Leafmite

Cattleya dowiana, I just remembered, doesn't like too much fertilizer. It also likes to dry out very quickly when the cooler weather sets in. For specific care for it:
Chadwick and Sons Cattleya dowiana

Cattleya dowiana | Chadwick and Son Orchids

You beat me to it!

[ramonypony]

Thanks for all the help y'all! I'm going to repot and perform surgery on this growth all at once. I will start giving the plant calcium to be safe.

I have some Physan 20 but have never used it. What would be the recommended treatment? Just dilute it and spray the whole plant? Should I spray the roots?

Steve, I'm in Tyler. And it has been pretty dry here this year (comparatively.) Only had about two substantial rains since May. But I guess the air is still more humid than this dowiana likes it, none of my other orchids have had anything like this.

[ramonypony]

I had to cut down a lot further than I thought I would have to to reach green tissue, down to the base. In the pic you can see the first cut I made which was quite nasty. Hopefully it was enough to stop it.
I repotted it into a wooden basket with lava rock and separated it from the others.