Spots on base of Den Smilliae Leaves

[KatieM]

Hey everyone. I've got a nice big Den Smilliae with some white and black spots on the underside of the leaves, only at the base. It doesn't appear to be mealybugs. The white is almost hard. Possibly scale? Scale is the one pest I've not experienced so any advice would be much appreciated. I have also noticed some black almost mildew looking stuff on some of the older canes. Not on the newer growths.

Care:

Zone 9a
Outdoors southwest facing screened lanai, moderate light.
Water before completely dry but do not keep it overly damp
Plenty of Florida humidity

I've hit it with physan, wiped off the white specs with rubbing alcohol 70 and a qtip but back they came.

Thoughts and advice are much appreciated!

[estación seca]

That's almost certainly a bug, probably scale. The black is probably mold growing on their sugary secretions. They are in your environment so you need to remain vigilant. A local orchid society should have better suggestions, and members will probably recognize it.

[KatieM]

Thanks, Est! From what I've read on St Aug it sure sounds like scale. Hadn't thought about the mold from excretion. First things first I need to get that scale under control. Would physan work on the mold do you suppose? I have Imidacloprid that I use for mealy bugs but I don't believe that works for the hard scales. I'll go to the neem oil with a little dish soap for now and look into what else works on them.

[estación seca]

The mold will wash off with water with or without a little soap. It won't harm the plant; it's growing on the surface of the leaves, not into them. Not all fungi damage plants. I wouldn't bother with Physan.

Soap and a brush remove visible scale. Since it's probably in the environment it will come back. Systemic insecticides may work for a while.

[Roberta]

If you are already using imidacloprid (which is systemic) for mealies, it works on scale too. But it's also possible that some of these bugs have built resistance - not necessarily from your use of it, but if it is used in the environment (like homeowner's association using it on lawns) that can be an effect. Take ES's advice... keep attacking it.

[KatieM]

Roberta, I I hadn't considered about it being used on lawns and the homeowners. But actually explains some of my mealy bug issues too. I bet. Super interesting. Do you have a different product you would recommend? I have your bonide 3 in 1 but that's about it. I've been pretty darn lucky with pests outside of mealies and the spider mites that love my ctsm.

[Roberta]

It would be very worthwhile for you to get involved with a local orchid society - others in your area are fighting the same battles. I don't know what might be available in your area, or what might have stopped working because of insect resistance due to overuse in the general environment. Local knowledge is extremely valuable!