In This Issue

Why Thin Your Olive Crop?

Larger fruit. Overloaded trees bear small, unprofitable fruit. If you thin the crop (remove excess olives) during the fruit's early growing period, the remaining fruit will grow larger. The larger fruit command a higher price that more than offsets any reduction in total yield. By thinning the crop, you will bring otherwise substandard-sized olives up to canning sizes.

Higher-quality fruit. Olives harvested from spray-thinned trees have a greater flesh-to-pit ratio and a higher oil content than do fruit from untreated trees.

More consistent yearly crops. After a modest crop, shoot growth and prospects for a satisfactory crop the following year are good. In contrast, a heavy crop of olives is followed almost invariably by a light crop.

Early maturity. A moderate crop matures earlier than a heavy crop. An early crop is more likely to get a good reception from the handler, has less competition for harvest labor, is less likely to fall victim to cold weather in the early fall, and ensures a good bloom for the next year.

Lower harvest costs. Olive picking costs are figured on a per-ton basis, so the per-acre harvest costs for a moderate crop are less than for a large crop.

Spray Thinning With NAA

The plant growth regulator naphthaleneacetic acid (NAA) absorbs into the leaves and fruit of the olive tree and is then translocated to the fruit stems. An abscission layer forms during the first two weeks after NAA application, causing some fruit to drop.

NAA Formulation for Olive Thinning

NAA is manufactured in the form of an ammonium salt for commercial use on olive orchards, with 200 grams of active ingredient per gallon. This formulation is marketed as Liqui-Stik Concentrate (EPA reg #34704-382) by Platte Chemical Company. NOTE: This material does not contain wetting agents.

When to Apply NAA

Timing is critical. You can use either of two methods to determine the proper time for NAA application.

Full bloom date method. To use the full bloom date method, you must establish the date of full bloom for your orchard. For our purposes, full bloom is the point at which 80 percent of the olive flowers are open (10 percent of the flowers are not yet open and 10 percent of the flowers are dropping petals), petals are white (not brown), and pollen is shedding. To see whether pollen is shedding, you can run your hand down the full length of a blooming shoot. Yellow pollen in your hand indicates shedding. Record the date of full bloom, and apply NAA 12 to 18 days after that date.

Fruit size method. If you base your spray timing on fruit size, spray the trees when young fruit are 1/8 to 3/16 inch in diameter. Figured this way, the time of application varies from 12 to 18 days after full bloom, depending on weather. Most growers and advisors favor using a combination of the full bloom date and fruit size methods to determine the proper time for application.

NOTE: Once again, timing is critical. EPA registration for NAA covers the period from full bloom to 2-1/2 weeks after bloom. NAA applications after that point are both illegal and useless. Too early an application will overthin the orchard. Too late an application will yield unsatisfactory results. An application during bloom will destroy the crop.

What Concentration to Use

The concentration of NAA you use will depend on how you determine spray timing and whether or not you use a spray oil.

Full bloom date method. If you time your spray according to the full bloom date, apply NAA as a dilute spray (300 to 500 gallons per acre [gpa] [approximately 2800 to 4700 liters/hectare]) 12 to 18 days after full bloom. If applied at 10 days, use a concentration of 100 parts per million (ppm). Thereafter, increase the concentration by 10 ppm for each day that treatment is delayed. For example, if you spray 15 days after full bloom, use a concentration of 150 ppm.

CAUTION: Abnormally cool weather will delay fruit growth. In such a circumstance, use the fruit size method for spray timing.

Fruit size method. If you use the fruit size method and spray without a spray oil, apply a concentration of 150 ppm NAA with a wetting agent or spreader-sticker, used according to the chemical manufacturer's recommendation. The commercially available NAA formulation Liqui-Stik Concentrate does not contain a wetting agent.

If you do use a spray oil, mix 100 ppm NAA with a light or light medium summer oil emulsion at a rate of 1-1/2 gallons of oil per 100 gallons of spray mix. Do not use a wetting agent if you use oil.

The data in Table 1 show how to mix NAA Liqui-Stik Concentrate to produce specific concentrations.

CAUTION: Do not use oil with NAA when daytime temperatures are 90° F (32.2°C) or higher or when soil moisture is low. Failure to observe these precautions may result in leaf and shoot burn, defoliation, fruit injury, and excessive thinning.

Varietal Responses Vary

Manzanillo, Mission, and Ascolano varieties respond well to spray thinning. Sevillano olives do not respond well to this treatment.

How Much Spray to Apply

To be effective, the spray must cover the undersides of leaves on fruiting branches, but a heavy drenching application such as is used for scale control is usually unnecessary and wasteful. NOTE: No less than 108 ounces of NAA from Liqui-Stik Concentrate (NAA ammonium salt, 200 grams active ingredient [a.i.] per gallon) should be applied per acre (1239 grams a.i. per hectare). See Table 2 for the number of gallons per acre required to apply 108 ounces a.i. per acre at various concentrations.

Equipment and How to Use It

Air blast sprayers. When most trees bear a heavy crop, an air blast sprayer will do the best job of covering the whole tree. For good spray distribution, drive a properly adjusted air blast sprayer at 1.5 to 2 miles per hour.

High-pressure hand gun sprayers. Use high-pressure hand guns with number 8 discs at 200 to 400 pounds per square inch (psi) pressure if some trees in the orchard are overloaded and others are not. If only certain limbs in each tree require thinning, spot spraying may be effective. NOTE: Always leave some unsprayed check areas to help gauge the effectiveness of spray thinning.

Potential for Damage

If used as directed and at moderate temperatures, NAA will not damage fruit or retard fruit growth. Sometimes it does kill or curl young, tender tip growth on some new shoots, but this has no lasting effect.

Points to Remember

The effects of NAA depend upon dose, temperature at time of application, and tree condition.

Dose. The greater the applied concentration of NAA, the greater its thinning activity. You can further increase NAA activity by adding oils to the application mix.

Temperature. As temperatures rise, NAA activity increases. High temperatures (i.e., in excess of 100°F [37.8°C]) within two weeks after application can cause additional thinning.

Tree condition. Never spray water-stressed trees with NAA: it will cause excessive thinning. Trees to be sprayed with NAA must be well watered both as bloom develops and after spraying to mitigate any negative effects related to high temperatures.

In response to last fall's finds of Olive Fruit Fly (OLFF) in the Los Angeles Basin, the olive producing counties in the San Joaquin Valley Agricultural Commissioner/Sealer's Offices will be initiating a trapping program. Here in Tulare County, where we have half of the state's 35,000 acres, we will be placing and monitoring approximately 1,000 traps. While the majority of these traps will be placed in commercial orchards to confirm that we do not have OLFF in our production areas, we will also be placing over 150 urban traps. It's these urban areas that represent the greatest risk for the spread of OLFF. It's long been recognized that these types of pests don't spread long distances on their own, but rely on people moving infested products from one area to another.

Description: The adult olive fruit fly is about 5 mm long. The head is yellowish to light brown and the thorax is dark brown with three darker parallel lines. The abdomen is pale brown with three pairs of black bands. The clear wings have a dark spot at the apex. The yellowish-white maggots (larvae) attain a length of 5 to 6 mm and occur one per fruit.

History and Economic Importance: The olive fruit fly, the most serious pest of olives, is found in many olive-producing areas in the world. The larvae cause premature fruit drop and yield reduction. An infestation seriously affects oil volume, alters its color and increases acidity. The larger, earlier maturing olive varieties, such as those grown in California, are preferred for egg laying.

Impact on California: California, with 35,000 acres of olives, is the nation's sole producer of commercial olives. Olive production was valued at more than $100 million in 1996 and $66.8 million in 1997 (crop has alternate heavy/light crop years). The leading olive producing counties are: Tulare, Tehama, Glenn, Madera and Butte.

Distribution: The Olive Fruit Fly is widespread throughout the growing regions of the Mediterranean in Europe and Africa, including Greece, France, Portugal, Spain, Israel, Turkey, Lebanon and Syria. The fly also is found in Sudan, South Africa, Libya, Kenya, India and Pakistan.

Life Cycle: The olive fruit fly typically has two to five generations a year. In early August, the female pierces the skin of the olive and deposits a single egg in the pulp. Olive juice of the pierced olive repels other females for about five days. A female may lay from 50 to 400 eggs in her lifetime. The larva feeds throughout the olive and pupates in a hollow area just beneath the epidermis or outer skin. Development from egg to adult takes 30 to 40 days. Other generations during the year follow this same pattern but the last generation larvae abandon the fruit to pupate outside the olive. The fruit fly spends the winter either as a pupae in the soil (the pupae stage may last five to six months) or as an adult in or outside the olive grove.

Hosts and Damage: Wild and domestic olives are the only host plants. Crop losses are due primarily to larvae feeding and premature fruit drop. Oil content and quality are seriously reduced. The larvae tunnel throughout the fruit leaving grayish white areas under the skin.