If you look at the underside of the leaves you will find that the crawlers are already on the move.
You need to spray NOW.
If you do not have a proper spray unit, get a contractor in. You need to have a high pressure sprayer which can deliver in excess of 1000 litres per hectare. The oil should be of the order of 1 to 2 %.
We have the same problem and have had a contractor in to spray Supracide, a terrible chemicle (Category 7 poison) It kills everything - good bugs and bad bugs. I don't want to use it again and it is not approved for olives. However I have like the rest of you a large investment in these trees and the sooty mold is killing the trees, drastically reducing crop and affecting badly next years crop.
Take some advice from experts imn the field. However for bad infestations oil is not going to be the solution.

Cheers
Andrew Brown

__________________
Andrew & Val Brown
Adelaide Hills
South Australia

Good afternoon,
Insegar has been registered for use with olives. It is less ubiqutous in its effects than Supracide. The details can be found on the Australian Olive Association web site, cPanel
Good luck,
Dan