California olive farmers battle blight with ancient solution from China

We all love olive trees.

Men’s oldest symbol of peace and for providing light in his transition from cave to castle.

First cultivated around 6,000 B.C.E. as an edible food, it’s use as a fuel begin around 3000 BC and spread across the Mediterranean with early Greek and Phoenician traders. The Jewish festival of Hannukah is all about the limited olive oil burning for eight days after the cleansing of the Temple.

The olive tree has proliferated throughout America even in cold climates because of its beauty when properly trimmed or for the harvest of olives and olive oil production.

However, we’ve also received a gift from the North Africa: The Mediterranean olive fruit fly has proliferated and ravaged olive harvests for the last 10 years and only grown worse in California

The pest first appeared in California in 1998 and quickly spread to all olive-growing regions in the state. The female olive fruit fly lays her eggs in developing fruit and the hatched larvae destroy the pulp that rots the fruit. Olive oil production can tolerate some infestation, not over 10%, and preferable less.

As a small olive farmer, there have been times in the last few years where the North Bay had virtually no olive oil because of the infestation.

Most of us producers have been using organic bait such as Spinosad GF-120 spray that draws the males to one spot on the tree where they die. But the ratio of concentrated bait liquid to added water is getting smaller, going from 4 parts water to one part GF-120, now 1.5 parts water to one part GF-120.

What else can we use?

An unusual solution comes from southeast China, where in the seventh century the Chinese used kaolin to make porcelain. This almost white mineral powder is mined in the Eastern U.S. and when mixed with water and dish detergent can be used to spray other fruit trees for their protection.

A fine spray is applied all over the trees when the fruit pits start to harden anytime from June through August. The kaolin clay spray turns everything a light sage green. The view over an orchard is quite serene and peaceful.

Samantha Dorsey is president of Petaluma’s McEvoy Ranch, the largest olive oil producer west of Sacramento and considered to be the world’s best estate producer of extra-virgin olive oil. She considers the kaolin clay spray to be the new weapon in your arsenal against bugs.

“I think the clay is very effective,” Dorsey said. “It usually takes two sprays to achieve good coverage and then we will reapply in October.”