I showed the image to my ex wife who is a horticultural consultant and she said the problem is caused by mites, so you're hunch is correct. Insecticidal soap should eventually work but you might try some of the insecticidal oils on the market. What on earth are you going to do with that many Curryleaf trees? One is usually plenty. Here in Florida they produce abundant root suckers that have to be controlled. When in flower it's a superior butterfly attractor, especially for hairstreaks.

Thanks for the reply, and sorry for the delayed response. From what we could find on growing them from seed, the germination rate was not good. So we bought a few extra seeds! They may grow well in Florida, but not in Maryland. Other than looking a bit sick, they are still growing. I want to start fertilizing with fish fertilizer, but the hydrolyzed type I've found so far is 2-4-1, and I hope to find something with a bit more Nitrogen. We have been using the type that is not hydrolyzed in the garden, but it would be a bit much for our laundry room which is the current nursery. Thanks again for your reply.