Scale.

yeah, it looks like some kind of scale insect.
You need to use an insecticide.
Bayer-Insect, Disease, & Mite control is a good one.

Good Luck!

If the tree is small you can wipe every stem and leaf down with baby wipes. The scale will come off. Trick told me by a professional citrus grower. If you go the insecticide route make sure it says it deals with scale. It is very hard to penetrate under that shell.

Personally, as long as you don't live up a mountain or on a freezing moor top, I'd put the tree outside in a sheltered spot. Wrap in fleece if it gets very cold but they can take occasional temps down to 0c, or even lower for a couple of days. Scale doesn't much like being outdoors battling the wind and rain. It prefers the cosy indoor environment. However, your olive will prefer the fresh air. They don't make good house plants.

Looks like brown soft scale.

Hi Floral, how are you? Olive trees actually make great house plants. They don't mind being on a cool windowsill and stay fresh and green. This is my experience, and I tried my olive first in this way after reading about it in a book by the well-known Dutch indoor gardening writer, Rob Herwig. He advocated keeping the plant in a bright place in a living room, saying that it was happy in temperatures of 5 degrees to 10 degrees celsius, but that it would take temperatures up to 20 degs. celsius. This I found to be quite sound advice. The plant should be kept just moist, not of course waterlogged, and can be kept indoors year round or grown outside during the summer. You do need to prune it unless you have lots of space, and if it flowers outside in summer, the olives will continue to grow inside. The olive looks very pretty on a living room window, too, because of the silvery-green appearance of the leaves.
That particular book of Rob Herwig's was called The Hamlyn Encyclopaedia of House Plants. by the way.

Hi, Marguerite - I stand corrected. But it sounds as if you need a cool and light spot for it. I've seen a lot of olives suffering and dying and ending up being thrown out because people just stuck them in the living room and hoped for the best.

Marguerite

I am glad you posted about the olives (and the book); I have few & not that much info about growing them. Tallest one is about 4feet and has many branches (very 'unruly' - see photo)..

I keep them indoors during winter, and they are doing well. They are in relatively cool room, about 10C (50F). I do have supplemental lighting, I think that helps too. And luckily, no bugs - I have them just over 2yrs. now.

Gregg

I hope you can clean your tree of scale. There is a lot, but it could be done.
Do as floral_uk suggested, and check on it periodically. You probably will need to follow up. But it can be done - I had plant with similar scale infection, and was able to clean it up. It has been healthy ever since (abt. 6yrs now) and is growing well. Just persist - using baby wipes is a great suggestion since the stuff is pretty gross to begin with...and liberally spray small/harder to wipe branches & leaves with suggested insecticide. You can also use a mixture of water+rubbing alcohol if you don't have insecticide. It works well, I used it.
Good luck with it, looks like it is a quite mature plant.

Rina