I got a ruby red grapefruit tree about a year ago that I keep in a large clay pot. Recently I have started seeing a layer of gel like goo on the underside of the leaves and any fruit that starts falls off. I have no clue what this goo like substance is or what to do for it.
Certified GKH Gardening Expert
This is likely honeydew, which is the residue from pests.
Treat the plant with Neem Oil.