What is ailing my brugmansias?
I have seven brugmansias. Six of them have leaves that turn ugly and fall off. The underneath side of the leaves look like they are covered in tiny, tiny specs. Can't tell if it's a bug or not. Hopefully, you can see it on the leaf in the right hand side of the picture. Plants still produce some flowers, but overall they look pretty sick.
It sounds like you are having an insect problem. Small black spots often mean spider mites. If the insect is still their, put a white piece of paper under the leaf and shake. If it is mites, you will see the spots move on the white paper. Control is using 1 tbspn liquid soap in a quart of water ora product called Safer Insecticial soap.
The color of the cells also show symptoms of insects sucking the juices out of the leaves - ie - spider mites.
i would suggest taking the leaves to the Extension offie in Goldbeach, by the fairground and have them take a look under the microscope so we know for sure the problem.