The olive fruit fly is a serious new pest that threatens olive growers and olive oil producers throughout California. Olive fruit flies develop inside olive fruit, making the olives unsuitable for canning or for olive oil production. The olive fruit fly was first detected in California in 1998. It is now found throughout most of the state. In Napa County, it was first found in 2001 and now exists throughout the county. Flies can travel several miles in search of olives in which to lay their eggs. The largest populations occur in the fall when there are olives on most trees.

• Plant Fruitless Olive Trees. In many landscape settings, olive trees are desired for their beauty, but not for fruit production. Fruitless varieties are available from most retail nurseries upon request. Since olive fruit flies only reproduce in the fruit, fruitless varieties will not support their development.
• Eliminate Fruit From Existing Trees. If you do not want olive fruit, spray your trees during bloom (May/June) to reduce fruit set. High-pressure water alone can be effective. Products containing ethephon, a plant growth regulator used to eliminate undesirable fruit, are available at most garden centers. They must be sprayed onto trees during bloom.  Also used: NAPHTHALENEACETIC ACID (Fruit Stop)
  4 fl oz/10 gal water with 0.5-1 fl oz of nonionic wetting agent to each 10 gal of spray mix.
• Harvest Early. By harvesting your olives early (November), you can reduce the number of fruit flies produced on your tree.
• Remove All Olives From The Tree And The Ground. Any olives left on the tree after harvest can support olive fruit fly reproduction during the winter. Olives left on the ground may contain larvae that can complete their development in the ground. Dispose of unwanted olives in sealed plastic bags.
• Spray with GF-120 Naturalyte. This is an organic insecticide containing spinosad. It is available from Dow AgroSciences and no longer has any restrictions associated with it. The combination bait and insecticide is sprayed  at a rate of 1 part  to between 1.5 and 4 parts water and applied at a rate of one ounce per tree. The bait is sprayed only on a portion of the tree.

  Some label highlights:

  Federally Restricted: No State Restricted: No Toxic to Bees: No Toxic to Fish: No Notice of Intent required: No Closed Mixing System: No Toxic to Birds: No

  Avoid Drift: Yes Avoid Water Contamination: Yes REI: 4 Hours Posting Required: No Organophosphate: No Carbamate: No Feed/Graze Treated Area/Crop: No

  Click For complete Label
   

• Spray with Kaolin clay (Surround WP). This deters the fly but creates ghostly white trees which may not be ornamental

• UC Master Gardeners of Napa County: 707.253.4221
• Weekly updated olive fly catch data
• Napa County Agricultural Commissioner: 707.253.4357
• Napa County Farm Bureau ( For commercial growers): 707:224.5403
• California Olive Oil Council: www.cooc.com
• The Olive Oil Source http://www.oliveoilsource.com/olive_fly.htm
• UC Davis http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74112.html
  reprinted from the University of California Agriculture and Natural Resources Cooperative extension - Napa County
• 1710 Soscol Avenue #4, Napa, CA 94559    Tel.707-253-4221  Fax 707-253-4434

Several thousand certified organic acres in Spain around Córdoba and in sensitive areas near homes and some of the natural parks have been using the OLIPE (Olivarera los Pedroches) trap for about 4 years to control Olive Fruit Fly populations and maintain damage to oil olives below 10%.  Without some form of control these areas would have 100% infested fruit, because of the very high endemic populations of Olive Fruit Fly.  They usually put up 8-10 traps per acre (20 per Hectare) in late June or early July and leave them for the entire season until harvest.  Fruit is checked on a weekly basis and evaluated for fruit damage and live larvae or pupae, because high summer temperatures (above 100^oF) can kill the larvae and pupae inside the fruit.  If live forms are found in more than 3% of the fruit the numbers of traps are doubled per acre.  A liquid formulation of microencapsulated spiroketal pheromone (2%) can also be added to the bottles to further attract the male flies and reduce the population.

In coastal California, it is unlikely that the insect larvae will be killed inside the fruit due to temperature, so stings might be used to identify damage.  Stings are easier to identify and quicker to count, but for now stung fruit should be checked to see if there is a live form of the insect present.  Young larvae are very difficult to see, but as they get older and larger the feeding track is bigger and usually turns brown.  The threshold level of 3% adapted from Spain is a starting point until more research is done here to verify those levels and what they mean at harvest.

The OLIPE trap is nothing more than a 1 to 2 liter plastic bottle with 5mm (13/64) sized holes melted into the shoulder.  It is filled about 2/3 full with a 3-5% solution of ammonium carbonate, ammonium bicarbonate or di- ammonium phosphate.  Ammonium carbonate is allowed for use in certified organic orchards according to US standards.  The flies are attracted to the ammonia bait, crawl inside the bottle, and die.  Thirty to fifty grams per liter gives a 3-5% solution.  There are 28 grams in an ounce. The holes can easily be made by taking a 13/64” size drill bit, hold it with a vise grips, heat it on a gas burner, and melt 4-5 holes into the bottle neck area (shoulder).  Hang the trap in the shade of the south side of the tree. 

Research is being conducted in California on the effectiveness of this trap and other control methods.  It is new and there is no data in California yet to indicate how well it really works.  It is low cost, low tech, very effective in Spain, and very few alternatives exist for the organic grower.  Bottle color, size, and placement; bait concentration; use of the pheromone attractant; number of traps per acre; and damage thresholds all have to be worked out yet.  Bottles with caps can be purchased from the local recycling center; the ammonium baits are available from Univar in bulk (800-659-5908), www.sigma-aldrich.com, other chemical suppliers, and from local pest control suppliers in smaller quantities. The source of liquid microencapsulated pheromone in the USA is ISCA Tech (909) 686-5008.  The OLIPE trap has not been formally approved as an organic treatment for olive fruit fly control in California or the USA, but some certifiers are allowing its use as a pheromone trap when the pheromone is included, and ammonium carbonate is on the approved list.

For more information contact:                     

Paul Vossen
University of California
Cooperative Extension
Santa Rosa, CA  95403
(707) 565-2621

pmvossen@ucdavis.edu