Dendrobium with black spots on the leaves

Question

There are these black spots on almost every leaf of our Dendrobium (?). It has flowered once but has kind of gone into a resting phase ever since, I guess that is normal (please correct me if it's not).

It is kept indoors, just by the side of a South facing window, so gets indirect sunlight the entire day. We water it once every 4 or so days and is fed water soluble NPK 20:20:20 every couple weeks.

The climate here is tropical so it is warm/hot and humid except for the few winter months of the year.

What are these spots and what should we do to prevent them?

Is it advisable to put it in a place where it gets direct sunlight for a few hours of the day?

Answer 1

It looks like your orchid may have pyllosticta leaf-spot fungus. It is commonly seen on dendrobiums in warm climates, like yours. If you have other orchids, you should remove the infected one away, as it is easily spread.

Since I don't have direct experience with orchids, I don't want to recommend a specific cure, but there are a number of fungicides you can research.

Here are some tips to prevent it if you have other orchids around:

• Do not over-water
• Water the plants in the morning
• Avoid getting water on the leaves
• Ensure good air circulation (use a fan if needed)
• Remove dead or rotted leaves

The American Orchid Society has some great info on this fungus, as well as other Orchid care recommendations.