Hi there

4 hectares hmmm.... if I had 4 hectares, I would consider dragging the land clean with a tractor. This is what my neighbour does and he has about that much.

I have two main reasons why I prefer not to use weedkiller:

Numero uno: Being a permaculture sort of chàp, I prefer to let the land do the work rather than me! I do not mind the weeds, and I merely run round my finca with a strimmer and a lawnmover (seriously) once in a while, and certainly just before olive harvest.
I still manage to harvest plenty of olives, and it costs me very little.
In the meantime, when we get the heavy (but infrquent) rains, because of the 'stubble', the rain soaks directly into the ground rather than running off. Furthermore, the quasi-mulch that is created by said strimming actually benefits the soil.
I am sure that this lowers my potential olive harvest, but it costs almost nothing in comparison to another neighbour who generally gets his sprayer out at least five times a year.

My second reason: I believe that stuff like glyphosate is not good to have on your land.
A recent WHO report has recent stated that "Glyphosate Herbicides Probably Cause Cancer" and furthermore, it appears that it does break down as advertised as traces are found in groundwater, food, and even the atmosphere.

There is a good link here - http://gmo-awareness.com/resources/glyphosate/ - which outlines some pretty horrible effects.

Me, I just prefer not to have the stuff any where near my olives.

In answer to Smidge - leaf curl - I do not get much of it. I prune the trees lightly and allow air to get in. I have had almost no 'repilo' over the last few years, and I put this down to the fact that I allow the trees to get stronger and fight off these ailments themselves.

My 'spraying' neighbour actually commented on the lack of repilo on my trees this year and could not believe that I did not spray.

Not saying I am great ;) but applying a spray to counteract something like this does not make sense to me. I understand your point about income 'tho, and it is difficult to strike a balance.

BTW - we have goats, and they are completely useless as weed-eaters, they just munch on a bit of this, and a bit of that.