Friday, June 16, 2017

Growing Olives in Coastal Southern California...or You Versus the Olive Fly

How our trees will look in 2,000 years

Olive trees grow really well here.  Rainy winter, drought winter, they don't care, they will just grow and grow.  Their leaves are beautiful and silvery.  If you planted the kind with fruit you may have dreams of making your own olive oil (takes about 10 trees) or curing your own olives.

Curing olives is pretty straightforward.  The hard part is keeping the olives from being devastated by their arch enemy, the olive fly.  In coastal California, where the flies love the temperate climate and the population numbers are not reduced by high heat (95 degrees+), you will find defeating these flies to be pretty hard.

Your opponent, who has been on the planet for at least 2,000 years

The first year our trees produced fruit, we did nothing to them and lost the entire crop due to flies (others say 88% loss but we had it worse).  The flies have been around forever (infestations recorded before Christ) and come from east Africa.  They only arrived in southern California in the late '90s.  But they have been really successful.  The good news is that the flies don't hurt the tree.  That is the only good news.

Most of the information I have found has been geared toward commercial growers. I write this post to help other residential olive lovers in their quest to defeat the olive fly.  I have developed a deep personal hatred toward this creature.  This is a gross understatement.

Any neighbors or vacant lots that have uncontrolled fruiting olives are a major liability to your crop.

Your first indication of a problem - the stings

The lovely offspring

The main ways to control the flies and try for a better crop (damage #s are from Sonoma, which is much hotter):

1.  Mass trapping (thought to reduce damage to 30%)
-Sticky traps with pheremones (31-36% damage)
-Olipe traps (easy to make, 33-66% damage)
-McPhail traps (31-36% damage)
-Magnet OL (13.6% damage)

2.  Spraying (thought to reduce damage to 3.6%)
-Naturylate GF-120 (spinosad) is an organic chemical that is now legal in CA  (1:4 ratio with water)

3.  Coating (thought to reduce damage to 1.6%)
-Commercial growers use a fine clay spray to coat the whole tree

4. More ways
-Harvest early when olives are green
-Pick and get rid of any fallen fruit and get rid of it.  It can re-infest your tree.

What we have tried so far:

Our arsenal

1. Sticky traps with pheremone hung in the spring through summer

Effectiveness - caught a lot of olive flies but still noticed a few stings as of June

2. Olipe traps with torula yeast bait

One per tree, 3 yeast tablets in each trap

Effectiveness: Unknown, started in June

3.  Spinosad

Once a week we spray a small part of the tree with Naturalyte spinosad fruit fly spray

Effectiveness: Unknown, I really don't know if this is helping or not

It's a little too early to tell anything.  I will update this when I have more information. It seems that a realistic goal may be 30% damage.  Wish me luck.

Here are some helpful links:,%20Hannah.pdf