Mystery Diseases

As summer is slowly arriving, our orchids are putting on their new growth as the temps are rising and occasionally the sun peaks through the grayness. Along with this welcomed event come new diseases and pests.

Every year for the last four years, my Pholidota chinensis would be starting to put on the new growth and shortly before that, the existing leaves would turn a strange orange brown at the leaf tips and get some odd spots in the middle of the leafs.

Discoloration on Pholidota chinensis

While it may be tempting to default to posting on Facebook for an opinion, you can guarantee that you will get the response of “it’s a fungus”, or “it’s a virus” or sometimes “it’s bacterial”. A picture may be worth a thousand words, but if you want a diagnosis and really want to treat the problem, that’s not enough.
Even though you may feel it is a fungus, you should rule out all the other possibilities to confirm that. The only way to know if it is a virus is to test it. I can present many pictures that look like viruses while those that did not, did have a virus. And the following case I will show demonstrates that insects can be the source of disease, even though not readily visible.
Back to the failing Pholidota. In the past, I had sprayed various fungicides in attempt to getting ahead of the damage. Each year the new growth would develop normally and I thought I had solved the problem. But in the first appearance of the new growth buds, it was the same old thing.
Because I had finally broken down and purchased a stereoscope, I decided that I should really investigate further. The tip of the leaf was unremarkable, and I had noticed that the rings on the leaves had visible darker dot in the middle. On the top side it was just a dark spot, but on the underside, there was a visible puncture of the surface.

And after looking at a few of these holes, I saw a white carcass next to one.

Carcass Next to Wound

I then scanned the surface for anything else and suddenly I saw something moving. A mite! A tiny mite – Arghh!

Live Mite on Leaf

Soft leaved orchids are more susceptible than thick leaves, but all could have infestations. Unlike typical spider mites, these developed no webs such as you typically see. I had similar issues with some Stanhopea that grew well and then suddenly all of them developed a weird light grey look under the leaves with very tiny white spots. As with this plant, I found what was called two spot mites. No webbing with those also.

Although you can treat a small amount of mites with soap and isopropyl alcohol, I personally have higher long term success with seasonal application of miticide. Don’t assume the insecticide you use will work on mites. Read the target insects on the product list.

Hopefully you will have a bug free and fungus free summer, but if not, be diligent on investigating the issue. And plants can have more than one at a time, so look at all the possibilities.
Happy Growing and have a blossom filled summer.