• Marije Passos

Olive Fly Nightmares

Updated: Apr 15, 2019


It's an olive fly year and that is difficult. We figured out we were just a bit too late with the protection of the trees. This because spring had too much showers and wind so we could not get the trees protected and once the weather turned better we were just slightly too late with the barrier control. (we only go biological, so no pesticides)

Fortunately they have only attacked Gordal and Manzanilla which means the other crops are ok. We therefore decided to sell of these olives since it was never going to be the quality we longed for.

For you non-farmers out there some info on the fly and why we hate them so much.

First, the most basic concepts: the female olive fly mates and lays eggs into the olive fruits. Each egg hatches into a tiny maggot that eats himself through the olive and develops into a pupa beneath the outer skin. The adult fly emerges from the pupa leaving a hole in the olive. And the cycle starts again. The olive fruit fly has as many as six, generations per year depending on local conditions. During the summer the fly can complete a generation is as little as 35 days. Eggs hatch in 2/3 days, larvea in 20 days and pupae in 10 days. The adult lives up to 6 months all depending on the right temperatures and foods. A female can lay up to 400!! eggs in her life. The olives are the only breeding host plants and larger olives are the preferred choice.

So what happened then if a olive fly lays an egg?


The first sign you've been attacked is a small sting on the fruit. Sometimes there is discoloration as well. While growing up the larvea eats his way through the inside of the olive, where all the good parts are. Eventually the fly creates hole and gets out of the olive leaving a tunnel which destroys the pulp because bacteria and fungi will make the fruit start rotting. In terms of quality this translates in an increase of acidity (free fatty acid level) and this means you will most likely not have Extra Virgin or Virgin oil. If the damage is extensive enough, it may cause premature fruit drop. And of course if you want table olives, you can forget it if they are attacked. If partly attacked, manual sorting of the table olives can be done but very time consuming.


Barrier Control Kaolin clay is a particle film. The product is mixed with water and applied with a high-pressure sprayer. The solution dries to a white powder that repels the olive flies. The exact mechanism by which this happens is not known. The mode of action is thought to be tactile or visual in nature. Kaolin clay has no nutrient value for the plant. But it is not toxic for animals and insects.

Plastic bottle traps

We also use Plastic bottles with an "bait" that attracts the males so they cannot fertilise the females. And we have also biological traps that catches both. We use old bottles from the Taberna and the Coimbra neighbours so we totally upcycle and take care of the environment a little as well!

If you want to know more, read more about the fly on the Olive Oil Source.