What you have on the tree is an insect called Hard Scale. It will eventually kill a small tree. These insects are like barnacles. They are hard and they are permanently attached. When you kill them they will not fall off very soon but eventually will. You kill them by suffocation with an oil, Neem Oil is the one I use. On hard scale spray once a week for 4 weeks. This will assure that you have covered them all. But don't get mad because they are still visible, at least for a couple of months. The following link shows some pictures of different hard scale insects.I'm spending a week in my parent's flat in Estepona (Spain), and they have this little olive tree that they haven't been taking particularly good care of. They nearly drowned it with too much water and now it's also covered in these weird things. I have zero gardening skills so if anyone can tell me what they are and how to get rid of them I would greatly appreciate it!
