Check out infected Dendrobium Amabile? :0:;~~`(
 

I am providing pictures of the entire plant.

Some concentric circular brown spots and white-ish patchy areas on leaves of older canes.

Most new growth appears normal.

The close-up photos are of both normal areas and areas that appear to have damage.

Can someone ID what could be the cause? Thanks!

First, Welcome!

The more bleached/brownish areas look to me a lot like sunburn. The black spots could be fungal... how important they are depends on whether they show signs of spreading. One trick for tracking that would be to use a Sharpie to draw a circle around them, so you can more easily see changes. Can you tell us a bit more about your growing conditions? Temperature, light, etc.

Hello and thanks for the warm welcome and great sharpie tip!!!!

I live in Miami, Florida.

January is our coldest month and we have had plenty of days when the temp. dipped below 65F during the day, colder in the early morning, and below 55F at night.

Most nights I brought the plant inside.

During the day it was getting full sun.

It has been pretty dry and I water it occasionally.

I purchased the plant on January 16th, and It appeared to have some damaged leaves, but I disregarded it at the time.

Just recently, I became more concerned because it appeared to be getting worse instead of staying the same.

I removed it from the densely packed sphagnum medium, so I could see the roots, and they appear to be ok. Some rot but nothing too crazy.

---------- Post added at 03:38 PM ---------- Previous post was at 03:35 PM ----------

Hello and thanks for the warm welcome and great sharpie tip!!!!

I live in Miami, Florida.

January is our coldest month and we have had plenty of days when the temp. dipped below 65F during the day, colder in the early morning, and below 55F at night.

Most nights I brought the plant inside.

During the day it was getting full sun.

It has been pretty dry and I water it occasionally.

I purchased the plant on January 16th, and It appeared to have some damaged leaves, but I disregarded it at the time.

Just recently, I became more concerned because it appeared to be getting worse instead of staying the same.

I removed it from the densely packed sphagnum medium, so I could see the roots, and they appear to be ok. Some rot but nothing too crazy.

By my standards, the cold isn't all THAT cold... but this plant was acclimated to south Florida not southern California. Especially if the leaves were wet, it did get enough chill for bacterial issues (like botrytis), which however are probably not harmful. The old damage could be the same - either cold, or a blast of direct sun. I think at this point, just keep an eye on it. Be sure to water early in the day, so that it can dry off before the overnight chill.

Awesome, thanks!

I will keep my eye on it for sure.

Wonder whether I should spritz it w/ an anti-fungal anyway?

I'll let someone who lives in your area weigh in on that one... what anti-fungal were you planning to use?

could try liquid copper or thiomyl.

I don't have too many options at the moment.

Some Dendrobiums have issues with copper-based fungicides, don't know which ones do and which don't... some members of the board have direct experience that might shed some light. I don't think thiomyl has issues, but again I don't have direct experience.

Thanks! Maybe I will just keep a close eye on it and see if I can get away with not treating it?

That is the approach that I would use. I do very little in the way of treatments on my orchids... so many problems resolve themselves if the culture is adjusted to mitigate the issue... leaf damage doesn't go away, but as long as it isn't progressing, the "uglies" are easy to ignore once you have flowers. :)

Welcome to the Orchid Board!

It does look like sunburn. If you've had a dry winter, and humidity isn't high, it's unlikely to be fungal. I wouldn't use a fungicide unless I knew the identity of the fungus and I knew the fungus were susceptible to the fungicide I chose. Not all fungicides kill all fungi.

Thank you, I moved it to have a bit more shade!