I don't know much about houseplants, so I'd appreciate suggestions here. I realize this may be a common question, so forgive me.
I always put my house plants out for the summer. They always love it. It's now time to bring them in, of course.
Unfortunately, several of them spent the summer under the shade of a japanese apricot which developed a black rust which thickly coated not only it's own leaves in a black coal powder, but the houseplants underneath it now also have the same black coating. How do I clean them up? If the disease is really from the apricot, are my houseplants just cosmetically affected, so I just hose off the leaves? Or did the disease actually infect my houseplants and they need more active intervention?
Any help is appreciated.
Here are a couple examples, though not the greatest pictures.
What you have is sooty mold growing on honeydew from scale in the infested tree your plants were under. The mold is seriously affecting your plants' ability to carry on photosynthesis, and the problem will be compounded when you bring the plants indoors. I'd use a solution of insecticidal soap or Murphy's oil soap to clean the leaves and then rinse well. Inspect the plants carefully for their own scale infestations as well, and treat as needed.