I'm ashamed to admit that through a combination of ignorance and complacency I have not previously taken any action to control olive fly in my olive grove. I tend to be guided by my neighbours who, as fly infestation has not been a major problem in this area recently, don't put out fly traps.
Last year was a big crop from my trees so the loss of the comparatively few olives I had this year is not such a big problem for me, but obviously this has made me think seriously about what I need to do to protect next years crop. I sought advice at my local Agrotica who advised against fly traps, their view was that unless all the other olive growers in the area are putting up fly traps, hanging traps in one grove would simply attract all the flies from the surrounding area - so completely counter productive. They recommended spraying but since to be effective this requires specialist equipment, not the back pack I'm used to using it, would mean bringing in a local contractor - hardly worth it for the 50 trees in my olive grove.
Ignoring their advice and on the basis that following this years heavy infestation my neighbours will put up traps I have decided to use traps in my olive grove in an attempt to control fly numbers.
If your neighbours are anything like mine I'm sure you are getting plenty of advice (often conflicting) about olive tree management, searching the internet a few years ago for more considered advice I came across this site:-http://www.mediterraneangardensociety.org/olives.html
Although the author Brian Chatterton farms in Italy I have found his advice on all matters olive growing invaluable, if you click on the link you will find his description of a home made olive fly trap which he calls the Ureaka trap. This is the method of control I have decided to use in the future and although it is now too late to save this years harvest I have already made and hung Ureaka traps in my olive grove. If you want to try this method it's worth knowing the Urea based fertiliser he mentions is also labelled 21-0-0 in Crete. I had no problem obtaining the stuff but only in a 15kilo sack so I now have supplies to last the rest of my life. The yellow bottles look very pretty hanging from the trees, I will let you know next year if they are effective!
You will also see that Chatterton has some thoughts on the benefits or otherwise of cultivating the ground around the trees, personally I strim a couple of times a year rather than rotovate but this is for cosmetic reasons rather than any perceived benefit, its also less hassle than getting the rotovator down to my olive grove!
Incidentally, the olive fly infestation in this area is so bad that the local Dimos is funding a contractor to tour the villages spraying olive groves at no cost to the owners, he is apparently due to cover our village on Tuesday and I have been advised to leave my olive grove open.
On a slightly different subject, I don't know how you harvest your trees but in January this year I decided to harvest entirely by hand, not for any other reason than I wanted to enjoy the experience without a generator buzzing away in the background and I wanted a more 'traditional' harvesting experience. Of course it took longer but with only 50 trees that's not major consideration. However, I would not harvest in this way again, thrashing the trees with those four-pronged beaters causes far more damage to the trees than the mechanical method and I notice that now the olive knot disease has spread more quickly on the new growth, I'm pretty certain through spores getting into the wounded branches. Could be just a coincidence of course but its back to the generator for me in future.
Good luck with this years harvest.