Olive Fruit Fly

What is the Olive Fruit Fly?

The Olive Fruit Fly is the main pest posing a risk for olives and has infiltrated the olive industry in North America since it was first detected in 1998. It’s important for olive growers, commercial growers and hobbyists alike, to understand how to identify and deal with the problem. Letting an infestation go without management will not only ruin your crop but will attract more to the area and will only worsen as the years go by. So let’s band together, fellow California olive enthusiasts, and maintain this optimal terroir for olive growing!

The cycle of infestation:

The early-emerging fruit flies infest old, unharvested fruit in the spring, and the later-emerging fruit flies can infest new fruit closer to the summer. Fruit flies can also develop in unharvested fruit during the winter/spring, emerge and lay eggs in new fruit by the summer. They migrate to the soil during the fall and winter, so it’s important to get rid of old fruit to reduce infestation possibilities. Scroll down to read about harvesting old fruit and properly disposing of infested fruit.

What does an Olive Fruit Fly look like?

Adult fruit flies are about 0.2 inches long with clear wings, dark veins, and a small dark spot at the wing tip. The head, thorax, and abdomen are brown with dark markings and the thorax has several white or yellow patches on each side. Larvae are yellowish white maggots with a pointed head.

Adult Olive Fruit Fly, Source: UC Davis Olive Center

Adult Olive Fruit Fly, Source: UC Davis Olive Center

What does infested fruit look like?

There will be “stings” on the surface, which look like little brown spots or even tiny dimples. This will indicate destruction of the pulp, leaving the fruit useless for table olives and poses a possibility of damaged olive oil, depending on the breadth of infestation.

Olives with brown spots and

Olives with brown spots and "stings," Source: UC Davis Olive Center

Infested Olive, Source: UC Davis Olive Center

Infested Olive, Source: UC Davis Olive Center

How much damage is too much damage?

If you’re producing olive oil, the damage in your harvest cannot exceed 10% and there is zero tolerance for table olives.

How can I manage my infestation problem?

It’s recommended to harvest all fruit each year and properly dispose of the damaged fruit. There are a few types of traps, which will not only help manage the fly population, but will also help monitor the size of the population. If you notice the populations are increasing in early summer, it’s prudent to apply bait sprays. And don’t get too discouraged by the word “spray,” these sprays comply with growing organically. Keep in mind that our farmers usually don’t need to go so far as to apply bait sprays, the traps and keeping a clean grove should do the trick.

  • Properly disposing of infested fruit: at The Olive Press, we always suggest bagging your fruit and sealing it tight to create a closed quarantine for about two weeks. This will kill the flies and keep them securely inside the bag and away from your quality fruit. You can then dispose of them or bury them at least 4 inches into the ground.
  • Traps
    • Place traps in fruiting trees before March 1 in the second tree row or further to reduce dust accumulation
    • McPhail traps – plastic/glass containers with a reservoir for liquid baits, flies enter through the bottom and drown in the solution – place two traps for each 5 to 10 acre block – strain flies through a sieve to count and get an idea of your infestation level.
    • Olipe trap: 1.5 to 2 liter plastic bottles with holes drilled at the top and baited with 3-4 torula yeast tablets per liter of water. The flies crawl in the top and drown. Strain flies through a sieve to count and get an idea of your infestation level.
    • Yellow sticky traps are baited with a sex pheromone.
    • Magnet OL traps attract flies with a food lure in every trap and a sex pheromone in every fourth trap and contain insecticide to kill the flies. Click here to purchase from our trusted source.
  • Spray
    • GF-120 NF Naturalyte Fruit Fly Bait, an organically acceptable product containing the biologically produced insecticide spinosad, recently has received registration for use on olives in California. 
    • Barrier Film Sprays: These sprays have an active ingredient called kaolin clay, which is a barrier film surrounding the olive and prevents any egg laying or damage.
    • Keep it clean! Dispose of fruit again during harvest season, keep a close eye on fallen fruit and clean it up right away to prevent the flies from infesting your soil.

Now let’s grow some olives!

Source: UC Davis Olive Center

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