Den spectabile spots on young leaves

[legion80]

Hi all! I've noticed that one of the canes of my Den spectabile has its leaves with brown-turning-to-black lesions, and I think they are growing. Is it bacterial/fungal, and should I just cut off the cane or leaves, or is it not a big deal?

I've not seen this in any of the other half dozen or so canes that have grown since my purchase. But I do see some black spots on older more mature leaves (which I've circled in red).

[CourtneyT]

Two days ago, I just posted a thread about spreading black dots on my Dec. Spectabile too! Mines has more dots. Some people said that it's quite normal. I just moved it to brighter spot and hope that the spreading will stop.

[legion80]

Originally Posted by CourtneyT

Two days ago, I just posted a thread about spreading black dots on my Dec. Spectabile too! Mines has more dots. Some people said that it's quite normal. I just moved it to brighter spot and hope that the spreading will stop.

Thanks CourtneyT. My plant is facing east, and it gets a lot of the warm San Francisco sun.

Yesterday I tried applying some hydrogen peroxide on the leaves. If the condition worsens I think I'll have to cut off all of the affected leaves. As I understand it hydrogen peroxide is good for addressing bacterial causes, but if it's viral it does nothing. I hope I don't spread the disease around!

[estación seca]

You have two different problems. I don't think your plant has an infection.

The large brown spots on the top leaves are sunburn. Spring is progressing; the sun is moving north, and strengthening. The spots will dry up and turn light brown. They are not a problem to the plant, but the plant can continue to sunburn as spring progresses. Think about how to improve air circulation, or filter the sun a little.

Almost all spots on leaves are caused by cultivation problems. Almost all fungal and bacterial infections are caused by cultivation problems. The fungus and bacteria are everywhere in the environment. Healthy plants are not very susceptible to infection, but struggling plants are susceptible.

Most infectious problems are caused by too-high relative humidity, too-high or too-low temperatures, or inadequate air circulation. People in most of the US are not going to have a too-high humidity problem inside their homes, ever. (Florida, gulf coast and Hawaii, maybe yes.) This does happen inside terrariums. Most people don't like high temperatures in their homes. So that leaves too-low humidity, too-low temperatures and inadequate air circulation as the cause of most leaf spots.

The black spots happen to lots of thin-leaved orchids growing on windowsills. Recall we are growing them in houses, in much less than ideal conditions. Spots are areas of leaf damage. They are not necessarily infection. They can be areas of dying tissue from injury, temperature or humidity problems. A bug might have bit the leaf, and some of the leaf around the bite dies.

Don't cut off leaves with spots unless infection is spreading. Black spots like this rarely spread; more may occur, but as long as the rest of the leaf appears healthy, leave it alone. It is providing food to make more growth and more flowers.

You are not going to have a perfect-looking jungle plant, with spotless leaves, on a windowsill. For this plant, focus on trying to keep it humid and warm through the winter.

Hydrogen peroxide only kills fungus and bacteria it touches. It kills a lot of things it touches, like orchid roots, and very young growth. When infection causes spots on leaves, the germs are inside the leaf, out of reach of the hydrogen peroxide. Hydrogen peroxide is not a useful treatment for spots on orchid leaves. I know a lot of people on YouTube throw hydrogen peroxide around as though it were holy water, but this is irrational. The only circumstance in which I would use it would be for crown rot. In this case I would put just a few drops in the crown of the affected plant.

If there truly is a fungus infection causing trouble, a fungicide would need to be used. The problem is, not all fungus are susceptible to all fungicides. One should not use a fungicide without knowing exactly what the fungus is, and whether it is susceptible to the fungicide. Using a fungicide to which the fungus in not susceptible not only will not help the situation; it may kill beneficial fungi that would otherwise keep harmful fungi in check.

[Roberta]

Actually, orchids in nature don't have perfect leaves either. (I have seen plenty, and they have spots, bites, etc) Nursery owners pamper the plants, use stuff that us mere mortals can't even get, and probably wouldn't want to, to "make pretty" so that plants are easier to sell. It is important to provide the basics for the plant to thrive - light, water, temperature, air movement. And not stress over ever little flaw - all living things have them, including us.

[legion80]

Thank you, estación seca and Roberta!

I live in San Francisco and the plant in by a window that faces east. It can get pretty warm during the summer where I live, and I thought the morning sun wouldn't be too warm (and the sunlight disappears at noon). But you can tell from the canes that they do get red, so I guess it's getting warmer than I thought.

I appreciate the tip about avoiding cutting the leaves. I don't care too much about a perfect looking plant; just a healthy one. The lesions are growing, albeit slowly, but they don't seem to be turning into mush or smell; instead they're just drying out and it doesn't seem like it's spreading to other leaves.

The black spots happen to lots of thin-leaved orchids growing on windowsills.

I guess the spectabile isn't as thick as a phal leaf, but it's certainly not as thin as those in a catasetum or many other dens. They do get pretty tough and leathery once the cane hardens; for some reason this younger cane is taking its sweet time to mature (or this is the newest cane to grow and I just don't remember) and became vulnerable to what ended up being intense sunlight.

[estación seca]

Did you go to POE last weekend in the Hall of Flowers? I saw a lot of big Dens for sale there.

[Roberta]

Originally Posted by legion80

I live in San Francisco and the plant in by a window that faces east. It can get pretty warm during the summer where I live, and I thought the morning sun wouldn't be too warm (and the sunlight disappears at noon). But you can tell from the canes that they do get red, so I guess it's getting warmer than I thought.

Even a short burst of direct sun through a window can get hot enough to burn leaves... and if you don't catch it in the act, the sun shifts before you notice and don't realize the blast that it got. You might try moving it back from the window a little, or add a sheer curtain to "take the edge off" the heat. Also, you can feel the leaves - if hot to the touch, move the plant. The "daily average" amount of light may be be perfect, but the peak may be too intense and you do have to be concerned about the extremes.

[legion80]

Originally Posted by estación seca

Did you go to POE last weekend in the Hall of Flowers? I saw a lot of big Dens for sale there.

I did! I go every year, and always walk out with new plants when I promise myself to stop doing that.

I didn't go for the big Dens, but this year I got several smaller Dens (crocatum, usitae, officinale), and trying an experiment of potting them together. I know there's the likelihood of competing plants, etc, but I wanted to try anyway. I'm running out of room.

Also, I splurged on coel. multiflora.

---------- Post added at 12:51 PM ---------- Previous post was at 12:49 PM ----------

Originally Posted by Roberta

You might try moving it back from the window a little, or add a sheer curtain to "take the edge off" the heat.

Indeed. My living room has a bay-window-like structure, so I shifted the plant to a corner nook between two windows. We'll see how that fares for the new canes.

[estación seca]

Dendrobium is an enormous genus, with different species from a huge geographic and climate range. If you're going to pot plants together, they need to be from similar climate types and sun exposure.

Dendrobium officinale requires very different conditions from crocatum and usitae, and it is not likely to enjoy growing with them at all. I would suggest removing the officinale and potting it up by itself. Den. officinale needs a cool and moist summer, with temperatures like SF outdoors, and a very cool winter, like SF outdoors, but mostly dry. The other two need to be warm to hot and moist all year.

A good place to read about orchid species is the Internet Orchid Species Photo Encyclopedia.