Friday, 28 November 2014

Flies and more flies - 2014 harvest

We've been really quiet on the blog but we've been really busy at work.

So - 2014 turned out to be a disastrous year for oil production in the whole of Europe and in our small part of Italy it was terrible. Around 70% of the crop was lost due to a major fly infestation.

The olive fly (Bactrocera Oleae) is a nasty little beast who is only killed by a nice cold winter or a hot dry summer. In 2013/2014 we had neither and so the population took off.

We didn't even harvest in 2014 as the few olives we had were infested. The problem is that the female fly mates and then deposits her eggs in the fleshy olive. Each egg hatches into a tiny larva (maggot) that feeds throughout the olive and develops into a pupa (pupates) in a hollow area just beneath the outer skin. The adult fly emerges from the pupa and the cycle starts again. The olive fruit fly has around three generations per year in a typical summer.

Depositing the egg makes a tiny hole in the olive which allows oxygen inside the fruit. The maggot alos them eats the flesh of the olive as it grows. Both of these things cause the olive to go black (almost like ripening but in fact the olive is damaged) and fall off the tree much earlier than usual so a strong wind or heavy rain will remove most of the dmaaged crop. The oxidisation of the flesh of the olive changes its attributes and makes it less rich in nutrients. The oil’s free fatty acid level (“acidity”) increases considerably. At levels of over 10% damage to the harvested olives it is not advisable to go to the mill.

To make matters worse, the adult fly can survive winter and the pupa can survice in fallen fruit or the top layer of the soil or even in unharvested fruit still hanging on the trees.

So what we hope for is summer temperatures over 38°C and a cold winter (around zero or lower) as they become active at around 15°C.

So, what can we do about it? Well for us it's quite difficult. There are several reasons for this:

1. We're organic so as a treatment we only have the use of Kaolin available to us. This acts as a physical barrier on the fruit, hopefully stopping the egg being deposited. The problem is it is water soluble and needs to be regularly re-applied.
2. Our actual terraces and not all rock free as we are slowly (it's a BIG job) rebuilding the dry-stone walls. This makes tilling the soil at the base of the trees (to bury any surviving flies or larvae) is not practical yet.
3. Our trees are super high. They average about 4m in height and many are as tall a 6m. This causes a problem for spraying with Kaolin as it means we can't be sure everything is covered (if we can even find hand-held machinery that powerful) and also means a lot of waste.

We have to keep our fingers crossed for a nice cold winter in 2014/2015!