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V \ UNIVERSITY

C A L I F O RfcN I A

LIVE

PRODUCTION
IN CALIFORNIA

H. T. HARTMANN

CALIFORNIA AGRICULTURAL
Experiment Station
Extension Service

MAI^AL 7

LIVE

PRODUCTION
IN CALIFORNIA

H. T. HARTMANN

UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE
Agricultural Experiment Station and Extension Service

THIS MANUAL is one of a series published by the University of California College of Agri-
culture and sold for a charge which is based on returning only a portion of the production
cost. By this means it is possible to make available publications which, due to relatively high
cost of production, or limited audience, would otherwise be beyond the scope of the College
publishing program.

CONTENTS

SECTION 1 1

The Economic Background ... a short history of olive produc-
tion . . . importance of the crop . . . the major varieties.

SECTION 2 12

Getting Started . . . choosing a site . . . preparing the land . . .
planting and caring for young trees.

SECTION 3 15

Propagation, Training, and Pruning . . . information about olive
trees that the grower can profitably use.

SECTION 4 33

Setting a Satisfactory Crop . . . the effects of controllable and non-
controllable influences on fruit set.

SECTION 5 39

Production of the Crop . . . the cultural practices that will con-
tribute to satisfactory yield through the years.

SECTION 6 50

Pests and Diseases . . . how to identify them . . . some recom-
mended controls.

Distribution of olive acreage in California. Each dot represents 100 acres. Data from
California Crop and Livestock Reporting Service. Tulare County leads with 9,019 acres,
followed by Butte County with 5,041 acres, and Tehama County with 3,392 acres.

THE AUTHOR:

H. T. Hartmann is Assistant Professor of Pomology and Assistant Pomologist in the Experiment
Station, Davis.

OLIVE PRODUCTION

in California

H. T. HARTMANN

l.The Economic Background ... a short

history of olive production . • impor-
tance of the crop . • the major varieties.

lives are among the important tree
fruits produced commercially in Califor-
nia. Crop values of olives for a five-year
period ending in 1950 held ninth place in
the list of California tree fruits — above
plums and cherries, but below almonds
and apricots. The olive crops showed an
average annual valuation of $9,763,000.
In bearing acreage, olives ranked tenth
in 1950, above apples, plums, and avoca-
dos, and just below figs and pears.

Commercial olive orchards in Califor-
nia are located mostly in the Sacramento
and San Joaquin valleys. With their rela-
tively cold winters and warm summers
free of fog, they are more suitable for
olive production than the coastal re-
gions or southern California. Yields are
heavier and more regular, and insect
control is less difficult than along the
coast. Although many olive plantings
were made along the coast in the past,
there are few new plantings in this area.
However, the olive will grow in all Cali-
fornia counties except where winter tem-
peratures are low enough to kill the trees.

How did olive production
start in California?

Commercial olive production is gen-
erally found in two belts around the
world, one between 30° and 45° N. lati-
tude, the other between 30° and 45° S.

latitude. At higher latitudes the olive can-
not be cultivated because of low winter
temperatures. Olive trees will not survive
temperatures below 10°F. (-12.2°C),
most varieties being injured at 15° F.
(-9.4°C). Olives will grow vegetatively
nearer the equator than 30° N. or S. lati-
tude, but with few exceptions are un-
fruitful. This is due probably to insuf-
ficient winter chilling for proper flower
formation.

There is evidence that olives were first
grown on the island of Crete in the Medi-
terranean Sea about 3500 B.C., although
some historians state that they originally
spread from a range in Syria westward
along the southern coast of Turkey to-
ward Greece. They were not planted in
California, however, until 1769, when
olive seeds were brought to Mission San
Diego from Mexico by Father Junipero
Serra and Don Jose de Galvez.

The variety resulting from this early
planting was named the Mission and is,
perhaps, a seedling of the Spanish vari-
ety, Cornicabra, which it resembles. The
Mission today comprises about half of the
bearing acreage of olives in California.
Other commercial varieties currently
grown here were introduced about 1875
from Spain and Italy, where they existed
as standard pickling varieties.

Numerous varieties were introduced

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between 1850 and 1900 from the Medi-
terranean countries, and much effort was
given to testing them, chiefly for oil pro-
duction. By 1875 the industry showed
promise of becoming important in Cali-
fornia agriculture, with about 11,500
trees in bearing. In 1910 trees of bearing
age numbered 958,000, but the emphasis
was shifting from oil to table varieties,
with many orchards grafted to the more
profitable pickling types. A peak in bear-
ing acreage was reached in 1928, but by
1950 it had declined from 29,000 to
26,826 acres. During the past 4 or 5 years,
however, many new olive plantings have
been made in California. The nonbearing
acreage in 1950 was 4,193 as compared
with 620 in 1940.

The present industry
in California

California produces more than 99 per
cent of the olives grown in the United
States. Arizona is the only other state
having a commercial acreage, with a pro-
duction of 100 to 600 tons per year. Olive
production in the United States averages
about 47,000 tons per year, or almost 1
per cent of the total world production.

The California output of olive oil sup-
plied only 14 per cent of the total needs of
the United States during the years 1945-
50, the remainder being imported, mostly
from Spain, Italy, Tunisia, and France.

Imports of olive oil into the United
States are increasing, 10,419,000 gallons
having been imported in 1950 — the larg-
est amount entering this country in 20
years.

Spanish-green olive production in Cali-
fornia accounted for only about 12 per
cent of this product consumed in the
United States during the years 1945-50,
the remainder being imported, mostly
from Spain. This type of olive was not
processed commercially in California
until 1935, and the output has not in-
creased since 1940 chiefly because of com-
petition from the imported product.

It is apparent from the data on page

4 that the olive industry of California
is based on the production of canned ripe
olives (black-ripe and green-ripe), with
the output increasing from 2,300 tons in
1919 to 20,400 tons in 1949.

The production, utilization, and aver-
age returns to California olive growers
for the postwar years 1945-50 are given
on page 6. It may be seen from this
table that production of olives for can-
ning is usually the most profitable outlet
for the grower. During the war years,
however, when foreign shipments of olive
oil were cut off, the sale of olives for oil
manufacture was as profitable as for can-
ning. A limited market exists for the ship-
ment to eastern cities of fresh, uncured
olives that are bought by persons of
Mediterranean descent for processing at
home.

The yield per acre for olives varies
considerably throughout the state, de-
pending upon the district, age of trees,
variety, and cultural care. For the 10-
year period ending in 1950 the average
bearing acreage of all varieties of olives

Acreage, yields, and returns to growers for
California olives from 1922 to 1950. Sharp
drop in acreage in 1933 was due to freeze from
which trees made a rapid recovery. Data in the
graph from Calif. Crop and Livestock Reporting
Service.

[3]

in the state was 24,946, and the average
marketable crop was 46,727 tons, giving
an average yield per acre for the state of
1.87 tons. Heaviest yields are obtained
with all varieties in the Tulare County
district, with the Manzanillo tending to
outyield other commercial varieties in all
districts.

Olive trees generally start bearing in
California during the fourth or fifth year
and gradually reach full production by
the twelfth to twentieth year. It has been
the experience of many California olive
growers that older trees, 40 to 50 years
old, start declining in productivity, espe-

cially if planted too close together. Close-
ness of planting, which affects the ulti-
mate size of the tree, is an important fac-
tor treated under the section on Establish-
ing Your Orchard.

Marketing your olives

Processor-canners, of whom there are
about 30 in California, handle the mar-
keting of olives. Their output is chiefly
the canned ripe olive, although most also
pack Spanish-green, chopped olives, and
other types; some also manufacture olive
oil. A few grower-owned cooperatives
market a considerable quantity of the

Comparisons between California production and imports of olive
oil, Spanish-green olives, and canned ripe olives.

1930-1940

1940-1945

1945-1950

Olive Oil
Average annual California

production

Average annual U.S. imports
Per cent of U.S. consumption
of olive oil supplied by
California (1945-1950) . . .

428,000 gal.
7,328,000 gal.

1,200,000 gal.
779,000 gal.

680,000 gal.
4,221,000 gal.

13.9

Spanish green olives

Average annual California
production

Average annual U.S.
imports

Per cent of U.S. consump-
tion of Spanish-green
olives supplied by Cali-
fornia (1945-1950)

588,000 gal.

(1935-1939)

6,188,000 gal.

1,738,000 gal.
7,687,000 gal.

1,251,000 gal.
9,437,000 gal.

11.7

Canned ripe olives (Black ripe,
green ripe)
Average annual California
production

Average annual U.S. imports
Per cent of U.S. consump-
tion of canned ripe olives
supplied by California ....

3,349,000 gal.*

(9,210 tons)

none

5,330,900 gal.*

(14,660 tons)

none

6,878,545 gal.*

(18,916 tons)

none

100

* A gallon is approximately equal to 5.5 pounds of olives.

Data from: California Olive Association; Calif. Agr. Exp. Sta. Bui. 678. Production of Spanish-type green
olives; Calif. Agr. Exp. Sta. Cir. 370. California olives, Situation and Outlook, 1947.

[4]

olives produced. About 80 olive-oil plants
operate in California, although some do
not run every year. Processing olives and
olive oil requires considerable capital as
well as technical knowledge.

The California Olive Association, with
headquarters in San Francisco, was or-
ganized in 1920 to promote the interests
of the ripe olive industry, largely through
collecting and pooling information. It is
a trade association of ripe-olive canners

but does no marketing of olive products.
Under the California Marketing Act of
1937 an order was issued entitled, "Mar-
keting Order for California Canned
Olives and California Green Olives."
This was made effective in February,
1948. Its principal objectives are: (1) to
carry out advertising and sales promotion
activities for California canned olives;
(2) to establish certain minimum-quality
requirements for canned olives and Cali-

Bearing and nonbearing acreage of olives
most important districts as of

in California in the
1950.

County

Bearing
acreage

Non-bearing
acreage

Total

Sacramento valley
Butte

4,473
704

1,813
760

2,839
377
727

568

129

553

5,041

Glenn

833

Sacramento

1,824

Shasta

770

Tehama

3,392

Yolo

416

Yuba

727

Total

11,693

1,265
380
344
494
353

7,075

9,911

1,066

1,133

471

1,062

1,310

192

150

1,944

13,003

San Joaquin valley
Fresno

1,457

Kern

461

Kings

344

Madera

San Joaquin

644
438

Tulare

9,019

Total

2,452

136

12,363

Southern California
Los Angeles

1,107

Riverside

San Bernardino

1,212
607

San Diego

1,070

Total

All others

3,732
1,490

264
167

3,996
1,657

State total

26,826

4,193

31,019

Data from California Crop and Livestock Reporting Service.

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fornia green olives; and (3) to establish
certain minimum-size requirements for
canned, whole, or pitted olives.

An Olive Advisory Board of seven olive
producers and seven processors was
established to make recommendations
and assist the Director of Agriculture,
California State Department of Agricul-
ture, in the administration of the Market-
ing Order.

To carry out the objectives of the Order
a compulsory fee not to exceed $12.00 per
ton is assessed on all olives received by
processors for canning or preservation.
One-half this assessment is paid by the
processor and one-half by the producer.
It is generally believed that the nation-
wide advertising campaign carried out
under this marketing order has stimu-
lated the demand and sale for California
ripe olives.

A second olive Marketing Order en-
titled, "Marketing Order for Canned
Olive Stabilization," was placed in effect
in March, 1952. The principal objectives
of this Marketing Order are: (1) to pro-
vide reasonable correlation between the
supply of canned olives and the consumer
demand, and (2) to establish more stable
marketing conditions in the canned olive
industry. Under this Marketing Order an
Olive Stabilization Advisory Board was
established consisting of nine members,
each a processor of canned olives.

This marketing order affects the olive
grower indirectly, inasmuch as the me-
chanics of the order apply only to proces-
sors. Should this Marketing Order suc-
cessfully attain its stated objectives, how-
ever, olive growers will benefit through
the increased stability brought to the in-
dustry.

Five varieties are commercially
important

The Mission variety is grown on about
52 per cent of the bearing acreage in Cali-
fornia (13,846 acres in 1950). Next in
order are the Manzanillo, Sevillano, Asco-
lano, and Barouni. In nonbearing acres

[6]

Fruits and pits of the most commonly grown olive varieties in California. Top to bottom: Redding
Picholine; Nevadillo; Mission; Manzanillo; Barouni; Ascolano; Sevillano. The sample fru/ts, half-
fruits, and pits shown are about nine-tenths actual size.

in 1950 Manzanillo led with 2,229 acres
(or about 53 per cent of the total) fol-
lowed by Sevillano, Mission, Ascolano,
and Barouni.

The value per ton of olives increases
considerably as the size of the fruit in-
creases. Therefore varieties producing
large fruits, such as the Sevillano and
Ascolano, should be considered in making
any new plantings. If these large-fruited
varieties were available to processors in
considerably greater quantities, however,
price differentials between size grades
might not be so large.

In the Tehama County district, Se-
villano and, to a lesser extent, Manzanillo
are preferred for new plantings and for
top-working other varieties. In Butte
County, Mission is chiefly grown, the
packers in that area favoring this variety.
There are small acreages of all the other
varieties, with Manzanillo increasing. In
Tulare County, Manzanillo is considered
the most suitable, with Sevillano and As-
colano recommended for more limited
plantings. Mission is not advised for new
orchards in the Tulare district.

All the olive varieties grown commer-
cially in California are table olives for
pickling. No orchards are planted for the
express purpose of producing olive oil,
as experience has shown that California
is unable to produce it as cheaply as the
Mediterranean countries. Olive oil pro-
duction in California is largely a salvage
operation, usually for small, cull, or
frozen fruits.

Each of the five commercial varieties
will be treated briefly below. You may
find a fuller discussion of varieties in
California Agr. Exp. Station Bulletin 720,
Olive Varieties in California.*

Mission. The fruit of this variety is
easy to process and its high oil content
provides an alternative market for the
grower in years when olive-oil prices are
satisfactory. Furthermore, this variety is
most resistant to cold of any commer-

* Out of print, but may be obtained in many
libraries.

cial variety grown in California, some old
trees surviving temperatures as low as 8°
F. in the 1932 freeze. Its disadvantages,
however, tend to outweigh its advantages.
The fruit is relatively small, with the low-
est flesh-pit ratio of any commercial vari-
ety. Since the demand is for the larger
fruits, this must be met with other vari-
eties. Missions of "Mammoth" or larger
size are rare. The fruit matures for
pickling rather late in the season, during
late October or November, when there is
danger of freezing injury. If this occurs,
the fruit shrivels and is no longer suit-
able for pickling but is useful only for
oil extraction.

This variety tends toward alternate-
bearing, in which a large crop of small
fruit is produced during the "on" year
and a small crop of relatively large fruit
in the "off" year. Some Mission orchards,
however, especially in the Butte County
section, bear quite regularly and have
been profitable. Mission trees tend to
grow tall and unless kept pruned become
difficult to harvest. While resistant to
attacks of olive knot, Mission is quite
susceptible to infections of peacock spot.
It is believed that there are several dis-
tinct strains of Mission.

Manzanillo. According to data of the
California Livestock and Crop Reporting
Service, this is consistently the highest-
yielding of the four leading commercial
varieties, averaging about 75 per cent
higher than Mission. The trees are rela-
tively low and spreading and easy to har-
vest. Fruits of this variety process easily,
are generally larger than those of the
Mission, and have a much higher flesh-
pit ratio. The oil content is sufficiently
high to justify use of the crop for oil ex-
traction, if this becomes necessary. Bear-
ing is fairly regular, not fluctuating in
yield as much as some of the other vari-
eties. The fruit matures early enough so
that it is rarely injured by early frosts,
but trees of this variety are considered to
be quite susceptible to low-temperature
injury. Manzanillo is not likely to be-

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come severely infected with the peacock
spot disease, but it is much more suscepti-
ble to olive knot than Mission, and young
trees or new grafts have become heavily
infected with this disease, especially in the
Butte County area.

Sevillano. The chief advantage of the
Sevillano is its large-sized fruit, for which
a considerable premium is paid. It also
ranks next to Manzanillo in yields per
acre, and the flesh-pit ratio is above both
Mission and Barouni. The oil content is
not high enough to justify oil extraction
in most years. Fruit is usually harvested
before danger of early frosts. Because the
trees are not upright-growing like the
Mission, the fruits are easy to pick. Most
packers consider the fruits of this vari-
ety more difficult to process and the qual-
ity somewhat lower than either Mission or
Manzanillo, although with proper treat-
ment a very satisfactory product can be
obtained. Trees are quite susceptible to
olive knot but resistant to peacock spot.

This variety is susceptible to three physio-
logical diseases called "shotberries,"
"split-pits," and "soft-nose." They are
discussed on page 55 et seq.

Ascolano. Since these fruits are quite
tender at maturity, extra care must be
taken to avoid bruising during harvest
and processing. This is probably why
Ascolano is not more widely planted. In
addition, yields are usually rather low
compared to other varieties. The fruit is
almost as large as Sevillano and has a
high flesh-pit ratio (8.2:1), which, with
its good quality, makes this a fine table
olive. Although canned ripe olives of this
variety are generally considered excel-
lent, they are not suited to Spanish-green
pickling because of "salt shrivel" during
fermentation. Although its oil content is
almost as high as Manzanillo, the fruit is
not often used for oil extraction. Its fruits
mature earlier than any other commercial
variety, usually in late September, so that
frost damage is not a problem. Trees are

4.0

MANZANILLO

'^'''•—A SCO LA NO \

1940

Fluctuation of yields of olives by variety, 1940 to 1946. Yields between varieties cannot be com-
pared, as different varieties are grown largely in different parts of the state.

[10]

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relatively easy to harvest and are fairly
resistant to peacock spot and olive knot.
Barouni. The fruits of this variety are
considered somewhat difficult to process,
and the resulting product not as high in
quality as some of the other varieties.
Fruit is of good size, almost as large as
Ascolano, but the flesh-pit ratio is rela-
tively low (6.8:1). A considerable por-
tion of the crop (500 to 700 tons) is ship-
ped fresh each year to eastern cities for
home processing. In the north part of the
state, Barouni consistently bears very
good crops, but in southern California it
is reported to be a shy bearer. This vari-
ety, the last to be planted in commercial
acreages in the state, was introduced in
1905 from Tunisia by the U.S.D.A. Divi-
sion of Plant Exploration and Introduc-
tion. It was widely planted throughout the
state in 1920 to 1925, particularly in Butte
County. Very few new plantings are now
being made. Fruits mature for pickling
about the same time as Manzanillo, dur-
ing October or early November. The trees
are somewhat spreading and are easy to
harvest. Barouni is more susceptible to
olive knot than Mission, and in the 1932
freeze showed greater tree injury.

Other varieties. A number of vari-
eties — mostly remnants of variety intro-
ductions from the early days of the in-
dustry — are found in scattered locations
throughout California. Strictly oil olives,
such as the Nevadillo, Redding Picholine,
Rubra, Pendulina, and Chemlali, are gen-
erally top-worked to large-fruited vari-
eties. Pickling varieties include Amellau,
Cucco, Lucques, Macrocarpa, Obliza,
Polymorpha, Rouget, St. Agostino, and
Santa Catarina. Some of these are still
being tested for possible commercial
value.

New introductions. Since 1900 the
U.S.D.A. Division of Plant Introduction
and Exploration has imported some 50
olive varieties from all parts of the world.
In addition, since 1946 the Department of
Pomology of the University of California
has imported about 50 varieties, princi-
pally from the Mediterranean region.
They are all growing and being tested at
the University's Wolfskill Experimental
Orchards at Winters, California.

An olive-breeding program by the Uni-
versity of California for the possible
development of improved varieties is now
in progress.

2. Getting Started . • . choosing a site . .

preparing the land . • . planting and
caring for young trees.

Choose the right location
for your orchard

Climate. It is probable that the climate
throughout the San Joaquin and Sacra-
mento valleys of California is suitable for
satisfactory yields of olives, with the pos-
sible exception of the delta area, where
some partial coastal-weather influence is
present. In the lower foothills of the
Sierra Nevadas, such as the Butte County
olive district, satisfactory yields can also
be expected.

While there have been profitable olive
orchards south of the Tehachapi Moun-

tains in southern California, it is some-
what difficult to obtain there the yields
possible in the Sacramento-San Joaquin
valleys. New commercial plantings are
not recommended for the southern area,
nor for the coastal regions, where low
yields and difficult control of black scale
have been experienced. Avoid areas
where early frosts are probable, as the
harvesting of most varieties continues
through October and November. Frozen
fruits, as explained in Section 5 of this
manual, shrivel and cannot be used for
pickling.

[12

Water supply. Few, if any, commer-
cial olive orchards are grown in Califor-
nia without provision for irrigation, al-
though olive trees will live and bear some
fruit with only the normal rainfall. The
benefits of irrigation are found in larger
trees with heavier crops, and larger and
non-shrivelled fruits.

Soil. Olives grow satisfactorily on a
wide variety of soil types, from the deep,
fertile soils of the central valley to the
rocky, shallow soils of the foothills. It is
important, however, that olives be
planted only on well-drained soils free
from alkali.

Transportation and marketing
facilities. The olive grower's immediate
market is one of the processors. They are
located chiefly in the main olive-produc-
ing areas around Corning, Oroville, and
Lindsay — in Tehama, Butte, and Tulare
counties, respectively — although some
are found in other parts of the state. Un-
processed olives can be hauled by motor
truck for considerable distances, and
orchards do not necessarily have to be
located close to the processing centers.

To establish your orchard

You must usually grade or level the
land before installing an irrigation
system.

Grading and leveling. This is highly
important as a preliminary step to install-
ing some types of irrigation systems, to
facilitate the proper distribution of water.
If subsoiling appears desirable with hard-
pan soils, it should be done before the
trees are planted. If sprinkler irrigation
is to be used, little, if any, leveling may
be necessary.

Installing the irrigation system.
Plan and install this before planting your
orchard. The most common systems are
the square basin, the check, the contour
check, and the furrow. However, the
sprinkler system of irrigation coming into
widespread use in olive orchards is prov-
ing very satisfactory. Because it elimi-
nated the need for land leveling it is espe-

cially valuable in the rolling foothill sec-
tions where leveling is impossible and the
usual furrow system leads to erosion.
Sprinkling also generally results in bet-
ter soil-moisture distribution and soil
utilization by the roots, especially where
the depth of the soil is limited, or in sandy
soils where water penetration is very
rapid. The first year or two after planting,
it is practical to haul water to small basins
around the young trees by tank wagons
rather than to use the irrigation system.
You can find a full discussion of this sub-
ject in California Agr. Ext. Cir. 362,
Farm Irrigation Structures * and Califor-
nia Agr. Ext. Cir. 388, Sprinkling for Irri-
gation.

Laying out the orchard. Most olive
orchards in California are planted by
the square system. A satisfactory plant-
ing distance would be 35 x 35 or — in
Tulare County especially — 40 x 40 feet.
Some California olive orchards have been
planted with a 20 x 20 foot spacing, which
has proved far too close. With close plant-
ing, yields start declining soon after the
trees come into full bearing because of
shading out the bearing areas on the sides
of the trees and also because of root com-
petition.

Planting the trees. Nursery stock
may be obtained growing in gallon cans
or bare-rooted. In the latter case the
leaves should be removed and the tree cut
back to one trunk without branches. The
roots should be kept covered and moist at
all times. Set out young trees during
December, January, or February, but
only during times when the soil is not too
wet to work. In heavy adobe soils it may
be best to delay planting until February.
Trees can be kept heeled-in in trenches
until the soil is dry enough to handle
properly. In planting, the holes need be
only large enough to accommodate the
roots in their natural position. Extra-
long roots can be pruned back, and
broken and torn ones cut off. Set the trees

* This publication is currently out of print,
but may be consulted in many libraries.

[13]

Trees above were set 22 x 22 feet apart. Yields are low, as all the lower fruiting wood has died
out because of lack of light. Harvesting and pest control are difficult.

TREE SPACING IS IMPORTANT

Planted 40 x 40, trees below are well-shaped and heavy-bearing. Fruit-bearing surfaces reach
almost to the ground and are easily harvested and kept free from pests.

[14

at the same depth to which they grew in
the nursery. It is important to firm the
soil around the roots as the hole is filled
in and to soak the soil thoroughly around
the newly planted tree. If spring rains
do not occur, further frequent irrigations
will be necessary.

It is advisable to whitewash the trees
after planting to prevent sunburning of
the trunk. A satisfactory whitewash may
be made as follows : quicklime, 5 lb. ; salt,
% lb.; sulfur, % lb. Add the salt and sul-
fur while the lime is slaking. Age the
whitewash several days before using and
dilute to a thick consistency so that it can
be easily applied with a brush. Although
more expensive, a white cold-water paint
is a satisfactory substitute for whitewash
and will last two to four times as long as
the cheaper product.

Care of the young trees. Keep them
growing vigorously with proper weed
control and ample irrigation in order to
bring them into bearing as soon as possi-
ble. Ordinarily nitrogen fertilizers are not
necessary until after the trees come into
bearing unless the soil is particularly
deficient in nitrogen.

Intercrops can be profitably used the
first few years after planting, provided
they do not interfere with the growth of
the trees. Certain deciduous fruits, such
as plums, peaches, and pomegranates
have been used successfully as intercrops
with olives, 4 or 5 crops being harvested
before they were pulled out. Cotton,
tomatoes, and most vegetables should be
avoided. They tend to spread the fungus
disease, Verticillium, which is becoming
a serious problem with California olives.

3. Propagation, Training, and Pruning . • .

information about olive trees that the
grower can profitably use.

Botany of the olive

The olive is a broad-leaved evergreen
tree capable of living more than a thou-
sand years. The wood is very resistant to
decay, and if the top dies a new trunk will
arise from the roots. Trees are quite shal-
low-rooted even on deep soils. The thick,
leathery leaves will adhere to the tree for
2 to 3 years, dropping mostly in spring.

Cultivated varieties of the olive of com-
merce belong to the species, Olea euro-
paea L. of the genus Olea. About 30 spe-
cies of this genus are found in the tropical
and subtropical areas of the world, but
other than Olea europaea L. none of them
produces edible fruit. The genus Olea is
a member of the family, Oleaceae, which
also contains the following well-known
genera: Fraxinus (ash) , Syringa (lilac),
Ligustrum (privet), Forsythia (Golden
Bell), Jasminium (the jasmines), and
Forestiera (Forestiera neomexicana — the
California "wild olive") . The varieties of

Olea europaea L. can be grafted success-
fully on most of the above genera.

Flowers of Olea europaea L. are borne
on a paniculate inflorescence arising in
the axil of each of the oppositely arranged
leaves. They are usually produced on
branches formed the previous season,
but may arise from dormant buds one
or two years old. The flowers are small
and yellowish-white, with a short, 4-
toothed calyx, and a short-tubed corolla
with four lobes. There are two stamens
and a 2-loculed ovary, bearing a short
style and capitate stigma.

The flowers are of two types: (1) per-
fect, containing both stamens and pistil;
and (2) staminate, containing only sta-
mens, the pistils being abortive and non-
functioning. The relative proportion of
perfect and staminate flowers varies with
varieties. No purely pistillate flowers
occur. In the perfect flower the pistil is
large, almost filling the entire space with-

[15]

A*'- S;i'-ir:>

•\«f2P8fes l ><>

Top— Enlarged views of olive flowers at full bloom: A, staminate (male) flower; B, perfect (male
and female) flower; P, pistil. Center— Photomicrographs of olive pistils (female part that develops
into fruit) shortly before bloom; C, aborted pistil in staminate flower; D, developed pistil in perfect
flower. Bottom— Inflorescences (flower clusters) shortly before and during bloom. (A and B after
Brooks.)

[16]

in the floral tube. Its color is a light green
in the bud, becoming a deep green at
full bloom. In the staminate flower, the
pistil is rudimentary, barely raised above
the floor of the floral tube, while the style
is small and either brown, greenish-white,
or white. The stigma is not large and plu-
mose as it is with functioning pistils.
Occasionally, pistils reach an almost nor-
mal size before aborting. The reason for
the abortion of the pistil in staminate
flowers is not known, but it is possibly
some nutritive or hormone relationship.

The normal pistil in the olive flower
has two carpels originally, each contain-
ing two mature normal ovules capable of
fertilization and development. However,
in the subsequent fruit only one carpel is
found, usually having only one seed.

The olive fruit is considered a drupe
(like the peach, apricot, and plum). It
consists entirely of carpel tissue, the wall
of the ovary having both fleshy and dry
portions, the skin being the exocarp, the
flesh the mesocarp, and the stone or pit,
the endocarp. The seed is within the endo-
carp.

The mature seed is made up of a thin
seed coat, enclosing the starch-filled endo-
sperm, which surrounds the tapering,
flat, leaflike cotyledons and short radicle
(root) and plumule (stem).

The first evidence of flower formation
in olive buds is found about 8 weeks be-
fore bloom, with a subsequent rapid de-
velopment of floral parts. Full bloom in
California occurs from about May 1 to
June 1, depending upon the variety, sea-
son, and location. The blooming period
is generally one to two weeks earlier in the
southern than in the northern sections.

Propagation

The olive, like other fruit species, fails
to produce the true variety from seed,
hence must be propagated by budding or
grafting the desired variety onto seed-
lings, or by some other vegetative method
such as cuttings or suckers. A full dis-
cussion of propagation will be found in

California Agr. Exp. Sta. Cir. 96, Propa-
gation of Fruit Plants.

Nursery stock. Of the methods for
starting olive trees used in olive-produc-
ing countries, the first three in the list
below are the most important.

1) Grafting or budding seedlings in the
nursery or volunteer trees in orchards
or forests.

2 ) Removing suckers from the base of old
trees and starting them in the nursery
or orchard.

3) Making cuttings of wood several years
old, 1 to 3 inches in diameter.

4) Making cuttings of year-old growth
with leaves attached.

5) Removing and planting knobby-type
growth (ovuli) from trunk and roots of
old trees.

6) Layering suckers from old trees by
mounding soil around the base of trees.

7) Planting truncheons (large pieces of
wood horizontally just under the soil) .

8) Layering the shoots arising from trun-
cheons.

9) Bench-grafting (whip-grafting of
scions onto whole or piece roots).

All the above methods have been used
to some extent in California, but the most
satisfactory are : propagation by cuttings,
both hardwood and softwood, use of de-
tached suckers from old trees, and graft-
ing or budding onto seedlings.

Propagation by hardwood cut-
tings. If properly done this is probably
the best method, as it requires no special
equipment. It has the disadvantage of
using relatively large branches ; therefore
if you want a considerable quantity of
cuttings it involves removal of much fruit-
ing wood from trees. If you can find an
orchard that is being pruned heavily, you
can use pruning wood gathering imme-
diately after cutting.

Take care in all types of propagation
not to use wood infected with Olive Knot,
or the new trees will have this disease.
Do not try to start Sevillano trees from
cuttings, as they root with difficulty. The
use of hormones is beneficial. The figure

[17]

Mission olive nursery stock after 2 years in nursery propagated in 3 ways: left— suckers with piece
of old root attached; center— hardwood cuttings; right— softwood cuttings.

on page 20 shows trees propagated by

this method after one year in the nursery.

Directions, Prepare cuttings in late

January or early February from wood 3

One-year-old cuttings: left, no treatment;
right, soaked 24 hours in indoleacetic acid and
callused in moist sawdust 30 days at 65° F.

to 4 years old, and from 1 to 3 inches in
diameter. Cut into 1-foot lengths and re-
move all leaves.

Soak the basal few inches of the cut-
tings for 24 hours in a fresh solution of
indoleacetic acid or indolebutyric acid at
a strength of about 13 p. p.m. (% gram
in 1 gallon water).* Dissolve the chemi-
cal in a small amount of alcohol before
adding to the water.

Bury the cuttings in moist (not wet)
sawdust for about 30 days for callusing,
preferably in a building where the tem-
perature will be from 60° to 70°F. The
callusing treatment is essential for this
method. Hormone treatments without cal-
lusing are of no value.

After callusing, it has been recom-
mended that the cuttings be soaked in a
Vitamin B x solution for another 24 hours
before planting. Results of tests conducted
by the California Agricultural Experi-
ment Station showed no benefit from this.

Plant cuttings in a well-prepared nurs-
ery soil, with about % of the cutting
above ground. Frequent irrigations dur-
ing the summer are essential.

* Most druggists will weigh these small
amounts.

[18]

Indoleacetic acid and indolebutyric
acid, referred to on this page and else-
where, are available from the Eastman
Kodak Co., Organic Chemicals Division,
Rochester 4, N.Y.; or from Thompson
Horticultural Chemicals Co., 3600 Monon
St., Los Angeles 27, Calif.

Propagation by softwood cut-
tings. With this method many cuttings
can be prepared without the removal of
an excessive amount of fruiting wood
from trees. It has the disadvantage of
requiring glass-covered beds or green-
house facilities and, preferably, provision
for maintaining bottom heat. While the
cuttings of most varieties will root even-
tually without any hormone treatment,
the response is so marked that it is well
worth while to use it. This type of cut-
ting, even after having rooted, must be
handled under almost greenhouse condi-

tions, or the losses will be heavy. How-
ever, if cuttings are properly hardened off
they can be lined out in the nursery row.
Some nurserymen prefer to transplant
rooted cuttings into gallon cans and grow
them in the cans until they are large
enough to plant in the orchard. Rooted
softwood cuttings are shown on page 20.

Directions. Take cutting wood in Sep-
tember from wood of the previous sum-
mer's growth, using fairly vigorous water-
sprout type of wood. If greenhouse facili-
ties are not available, the cuttings should
be started soon enough so that they will
be rooted before cold weather.

Prepare the cuttings as indicated
above, avoiding the use of the succu-
lent terminal portions of the shoots. They
should be about 4 or 5 inches long, with
the basal cut just below a node. Retain
two leaves at the top of the cutting. Keep
cutting-wood and cuttings damp at all
times.

Dip the basal ends of the cuttings for

The use of hormones, callusing treatment, and Vitamin B* in the

propagation of olives by hardwood cuttings. Cuttings started in

nursery on April 6, 1951. Mission variety, Davis, California.

Treatment

Per cent

of cuttings

rooted

Av. no. of

roots
per cutting

Av. shoot

length
per cutting

Check (no treatment)

cm.
4

Callused in moist sawdust for 30 days

Callused in moist sawdust for 30 days. Soaked in hor-
mone for 24 hours before callusing and Vitamin B ,
for 24 hours after callusing.
1 Indoleacetic acid (13 p.p.m.f)

Indolebutyric acid (13 p.p.m.)

Water check

50
95
35

8
22

124

Callused in moist sawdust for 30 days. Soaked in hor-
mone for 24 hours before callusing but not in Vitamin

Indoleacetic acid (13 p.p.m.)

Water check

65
50

131
32

* Several Vitamin Bi preparations are available' for use on plants. The one used in this test was "Vita-
Flor," containing 0.1 per cent thiamin chloride, used at 8 drops per gallon.
t Parts per million.

[19]

Softwood cuttings after 7 weeks in the rooting medium: left to right, dipped for 1 second in
indolebutyric acid at 4,000 p. p.m.; leaves retained but not treated; leaves removed but treated
with IBA; leaves removed and not treated.

1 second in a 50 per cent alcohol solu-
tion of indolebutyric acid (see above)
at about 4,000 p.p.m. (Add an equal
amount of water to 95 per cent alcohol to
obtain approximately a 50 per cent alco-
hol solution. Dissolve % gram of indole-
butyric acid in % pint of the 50 per cent
alcohol solution. This will be enough to
treat several thousand cuttings. Rubbing
alcohol may be used.)

Place the cuttings in beds of clean sand,
or sand and peat moss, or sand and coarse
(insulation grade) vermiculite, or coarse
vermiculite alone. Keep the cuttings cov-
ered with glass at all times and water them
frequently, but not excessively, to main-
tain a high humidity. Protect them from
the full sun. Some provision for bottom
heat under the cuttings, such as electric
soil cables or a one- or two-foot layer of
fresh manure, is desirable but not
essential.

The cuttings will usually root in 10
to 15 weeks, when you can remove them
and transfer them to pots or gallon cans.
Keep them under conditions of high hu-
midity for a time after this to prevent

losses. After being well-established in
the soil, they can be moved to the nurs-
ery or, if in gallon cans, left until large
enough to set out in the orchard.

Propagation by the use of de-
tached suckers. This very simple
method of starting new trees is highly
successful, requiring no special equip-
ment. The suckers are'sometimes planted
directly in the orchard, but it is prefer-
able to grow them a year in the nursery.
All that is necessary is a source of large
trees which produce an abundance of
suckers from the base. One disadvantage
of this method is that the suckers may be
of an unknown or an unwanted variety,
in which case they must later be budded
or grafted to the variety desired.

Directions. In February remove the
suckers from the old tree, using an ax
or sharpened heavy shovel to take a piece
of the old root with the sucker. Cut back
to about 18 inches and remove all leaves.
Plant immediately in the nursery with the
root piece about 6 inches deep. Irrigate
when necessary through the summer.
After one year in the nursery, trees are

[20]

usually large enough to set out in the
orchard.

Propagation by grafting or bud-
ding seedlings. There are some claims
that olive trees on seedling roots are
longer-lived and less likely to blow over
in heavy winds than trees started from
cuttings. However, no experimental evi-
dence exists to support this belief. In
California very fine orchards have been
propagated by both methods. Starting
trees from seedlings is generally slower
than using cuttings, but where a very
large number of trees is needed and time
is not important this is probably the best
method. It is almost necessary to use it
for propagating the Sevillano variety,
which is difficult to root from cuttings,
even with the use of root-promoting hor-
mones.

Directions, Germination of seeds. It
is advisable to secure seeds in November
from black fruits of the Redding Picho-
line or some other variety such as the
Chemlali, in which a high percentage of
the seeds germinate. The seeds are planted
in rows in a nursery and grown until they
are large enough to bud or graft, which
usually requires two years.

To facilitate germination, gently crack
the pits or clip off the tip end. Germina-
tion can also be hastened by soaking the
pits in concentrated sulfuric acid, which
causes partial disintegration of the pit
and allows the seedling to emerge more
readily. Pits of the Redding Picholine
variety were soaked in acid for 26 hours,
then washed thoroughly in running water
for 2 hours and planted. The seedlings
germinated in about 6 weeks, whereas un-
treated seed required 5 to 6 months to
germinate. The acid-soaking period may
be different for different varieties.

Some nurserymen have as sources of
seedlings large Redding Picholine, Mis-

EXTREME CAUTION should be taken
when using concentrated sulfuric acid to
avoid contact with the skin or eyes.

sion, or Manzanillo trees, under which
volunteer seedlings can be pulled up each
year after rainy periods during the win-
ter, thus saving the trouble of germinat-
ing seeds. Such seedlings are usually
grown another year in the nursery before
grafting or budding.

Grafting or budding the seedlings. The
seedlings may be grafted in the nursery,
using preferably the side graft shown
on page 22, in late February or early
March. Cut back the tops above the graft
about a month after grafting. Some nur-
sery trees are started in California by
whip-grafting scions onto seedlings or to
short pieces of olive roots dug up from
mature trees. After a callusing period in
moist sawdust, they are planted in nur-
sery rows in March.

The seedlings may be budded (see
lower picture, page 22) in late February
or early March, using the "T" or shield-
bud method. It is essential to cut back
the seedling to the bud 2 to 3 weeks after
budding. If the soil is somewhat dry, an
irrigation shortly before budding is help-
ful in getting the buds to "take."

The grafted or budded seedlings are
usually grown in the nursery row for one
or two years before the trees are large
enough to set out in the orchard.

Top-grafting. In many cases it is
desired to change the variety of a tree
or orchard. This can easily be done by
grafting.

Directions. Do the work in spring —
any time from early March to late April.
Select 3 to 5 well-spaced scaffold
branches, cutting them off as low as pos-
sible but leaving a smooth place to graft.
Cutting the branches low will eliminate
considerable water-sprout growth and
will start the tree at a desirably low
height. With large branches it is neces-
sary to use enough scions (spaced 3 or 4
inches apart around the trunk) to obtain
satisfactory healing of the stub. One
branch, preferably on the south or south-
west, should be retained as a "nurse" or
"safety" branch to be removed the follow-

[21]

Left— "Side graft": (A) method of making cuts in stock and scion; (B) graft union tied with plastic
tape; (C) graft after 1 year's growth; (D) section cut through graft union. Right— "Whip grafting":
scion is about 4 inches long with 4 to 6 buds. Union is tied with string and waxed, or it may be
wrapped with tape.

SOME POINTERS ON GRAFTING

Satisfactory method of making bark graft for top-working olives: (A) side of scion that rests
against the wood of the stock; (B) side view of scion; (C) opposite side from A. Right— Scions in
place, held firmly by 2 flat-headed wire nails driven through scion (% inch, 20-gauge nails will
serve). After grafting, all cut surfaces are thoroughly covered with grafting wax.

B C

[22]

/^i

"Twig-bud" method of budding olives, using the T, or shield bud technique: A— bud stick with
desirable "twig-bud"; B— "twig-bud" removed; C— stock cut and prepared for insertion of bud
piece; D— bud in place and tied with budding rubber. Ordinary dormant buds may be used satis-
factorily rather than "twig-buds."

ing year. The other branches can be re-
moved at the trunk, either at the time of
grafting or a year later.

Graft the stubs not more than 3 or 4
hours after the limbs are cut back, using
the bark-graft method with 2 to 4 scions
in each stub unless the branches are quite
large, in which case more scions would
be necessary. Use scion wood of the de-
sired variety taken at the time of graft-
ing from trees with good fruit and bear-
ing characteristics. It should be % to %
inch in diameter, obtained from wood one
or two years old. Remove the leaves im-
mediately and keep the scion sticks con-
stantly moist and cool in damp burlap.
Scions ready for insertion should be 5 or
6 inches long, with 2 nodes (4 buds)

Mature tree top-worked to another variety
by bark-graft method; branches white-washed
to prevent sunburn. "Nurse branch" will be re-
moved when grafts can sustain tree.

above the stub, as shown above. Some-
times a longer, slanting cut can be made
on the scion, and it can be inserted
between the bark and the wood of the stub
without slitting the bark.

Above— Mature olive trees shortly after being
transplanted to a new location. Below— Tree cut
back and ready to be replanted. Photographs
courtesy B. E. Glick & Sons, Corning.

In a test conducted in 1946 by the Cali-
fornia Agricultural Experiment Station,
a comparison was made between the bark-
graft and the cleft-graft methods for top-
working olives. Of 152 scions inserted
by the bark-graft method, 55 per cent
grew vigorously, 30 per cent were weak,
and 15 per cent failed to grow. With the
cleft-graft method, using 70 scions, 26
per cent were vigorous, 41 per cent were
weak, and 33 per cent died.

Immediately after grafting it is very
important that all the exposed cut sur-
faces be thoroughly covered with grafting
wax, either hot wax or one of the commer-
cial asphalt-emulsion grafting prepara-
tions. The latter type will wash off if rains
occur before it dries. The wax often
cracks; when this happens the graft
unions should be rewaxed once about a
week after grafting.

After waxing, whitewash the scions,
branches, and trunk of each tree. This
facilitates healing of the graft union by
reducing the temperature and prevents
death of the exposed wood due to sun-
burning.

If the grafts become very vigorous and
top-heavy by midsummer, especially in
areas where strong winds may occur, tie
them to stakes or prune them back to pre-
vent their breaking off. A vigorous sucker
and water sprout growth is usually ex-
perienced following top-working. These
should be removed around the scions but
can be left on the trunk for a time during
the summer to nourish the tree and to pro-
tect the bark from the sun. Head them
back, however, to prevent excessive
growth. Withhold nitrogenous fertilizers
from newly grafted trees for 2 or 3 years,
but continue irrigation, although the
water requirements are, in many cases,
considerably less because of the reduction
in leaf area.

During the next year or two after graft-
ing, remove the nurse branch and prune
the grafts lightly and judiciously to select
the branches that are to be retained per-
manently, while cutting back the other

[24]

grafts gradually until the stub heals over.
At this time the excess grafts should
be completely removed. The grafted
branches will usually be in bearing the
third season after grafting.

Moving large trees

If the trees have been planted too close
together (e.g. 20 x 20), orchards are
benefited by the removal of some of them.
In such cases, the trees can be pulled out,
moved to a new location, and replanted,
and will be in bearing again by 3 or 4
years. For such an operation to be a suc-
cess all the primary scaffold branches
should be cut back to the trunk and the
digging and moving done during the cool,
wet winter months. After replanting, the
trees should be thoroughly watered and
frequent irrigations continued through
the summer.

Training and pruning
olive trees

The purposes of pruning olives are
the same as those outlined by W. P. Tufts
in California Ext. Cir. 112, Pruning De-
ciduous Fruit Trees: (1) to produce a

vigorous, mechanically strong, healthy
tree, free from sunburn, and capable of
producing heavy crops over a long period
of years; (2) to secure a tree well-shaped
for convenience and economy in orchard
management; (3) to distribute the fruit-
ing area well over the tree; (4) to insure
a succession of profitable crops; and (5)
to secure desired size and quality of fruit.

Young trees. Olive nursery stock in
gallon cans or balled and burlaped can
be planted with no pruning other than
removal of suckers or badly placed
branches. Bare-rooted trees should be cut
back to 24-30 inches from the ground.
After the first growing season, 3 to 5
laterals, well distributed around the tree
and spaced as widely apart along the
trunk as possible, should be selected and
the remaining branches, especially suck-
ers from the base, removed. By giving the
young orchard several summer prunings
much can be done at little expense in cre-
ating a desirable framework and elimi-
nating unwanted branches before they
develop.

The first pruning should be in May or
early June with another in August. It is

i %.<:.

Left tree— trained to 3 scaffold branches by two summer prunings for two years and one the
third. Total pruning time 5 minutes; little or no further pruning needed until tree comes into
full bearing. Right— no pruning. Both trees started bearing in their fourth year.

[25]

The natural fruit-bearing area of olives is a
hemispherical shell. If this is kept in a healthy
growing condition production is better than if
tree is opened at top to try to promote fruit pro-
duction inside the tree.

important that the branches be removed
while they are small. Delaying the time
of pruning until the unwanted branches
attain a considerable size will result in
the removal of so much wood that the
growth of the tree will be retarded.

During the second, third, and fourth
growing seasons the pruning should con-
sist of removal of suckers from the base
of the tree, any broken branches, or those
crossing over in unwanted positions. Fre-
quently in olives there will be a number
of vigorous water sprouts rising verti-
cally up through the other branches. It
is advisable to remove these while they
are still small. Keep the pruning at a mini-
mum, but at the same time try to develop
a satisfactory system of scaffold branches.
Excessive cutting will delay the age at
which young olive trees come into bear-
ing. However, it is not wise to eliminate
pruning altogether, as this will necessitate
a heavy pruning and the removal of large
branches after the tree comes into bear-
ing, with no provision for selecting a
strong framework of branches.

Bearing trees. In the olive the fruits
are usually borne laterally along shoots
of the previous season's growth. The bear-
ing area is a more or less hemispherical
shell 2 to 3 feet in depth surrounding the
tree. Very few fruits are borne inside this

shell. To get maximum crops the pruning
should be designed to keep a continuing
supply of new fruiting wood and to keep
this entire bearing region in a vigorous
condition with a maximum leaf area.

This is impossible if the trees are
planted too close together, in which case
excessive shading will reduce the bearing
surface to the top, the south half, and
perhaps the upper sides of the east and
west halves of the tree. This of course
results in a reduction in yields. Cutting
out the top in order to let light into the
north half of the tree will not solve the
problem, as this merely eliminates fruit-
ing wood from one portion in an attempt
to produce it in another. Closely planted
orchards should have some trees removed.

Moderate annual pruning is necessary
in mature, bearing olive trees for the
following reasons: (1) The stimulation
of pruning is necessary to maintain the
growth of new fruiting shoots of moder-
ate vigor. (2) There is a continuing pro-
duction of dead or dying unfruitful twigs
caused by shading out in the fruit-bearing
"shell." These should be thinned out to
admit more light, facilitate harvesting
and spraying, and reduce the chance for
infestation by insects and diseases. (3)
After the tree occupies all the space that
can be allotted to it, with allowance for
good light conditions on all sides, a mod-
erate pruning is necessary to hold it to
the desired size.

Continuing unchecked growth, espe-
cially where trees are planted fairly close
together, will gradually result in the shad-
ing out and death of fruiting wood on the
sides, confining the bearing suface to the
tops. This condition is accompanied by
a marked reduction in yields. With ex-
tremely close planting, such as 20 x 20
feet, little can be done by pruning to
obtain satisfactory yields. Some program
of partial tree removal should be consid-
ered.

Sometimes a more severe type of prun-
ing is justified. Occasionally the trees
show numerous large scaffold branches

[26]

with, at the top of each one, a small tuft
of fruiting wood. A gradual removal, over
a period of several years, of a number of
these large branches will finally result in
a better distribution of fruiting wood.
Older trees, especially of the Mission vari-
ety, sometimes grow to such great heights
that it is impossible to harvest the fruit
in the tops. In such cases a severe heading
back of the upright branches is justified,
followed by an annual cutting back of the
branches tending to grow out of reach.

Neglected orchards, having had little
or no pruning for many years, sometimes
require severe cutting to remove dead
wood and broken or crossing branches.
When heavy cutting is practiced, nitrogen
fertilizers should be withheld for a year
or two to avoid excessive sucker and
water-sprout growth. If much bark area
is opened to direct sunlight in pruning,
whitewash should be applied to avoid
sunburning and death of the tissues.

Once a well-spaced system of scaffold
branches has been established and all un-
necessary branches eliminated, avoid any
type of excessive or severe pruning. This
results only in the removal of fruiting
wood with a consequent reduction in
yields. Encourage instead a maximum
fruit-bearing "shell," reaching almost to
the ground around the entire tree. All
experimental evidence in California has
consistently shown that, under irrigated
conditions, continued severe pruning of
olive trees reduces yields markedly with-
out a sufficient increase in fruit size to
offset the reduced yields. Many of the
Mediterranean olive orchards grown un-
der nonirrigated conditions are severely
pruned, however, in order to reduce the
leaf surface so as to reduce water loss and
the development of shrivelled fruits.

When "Olive Knot" is present in an
orchard, the pruning should be done in
the summer if possible to guard against
spreading the disease. If the pruning must
be done in the winter, the tools should
be sterilized frequently. A satisfactory
solution for sterilizing pruning tools con-

Tree above too severely pruned— most lower
fruiting branches removed; tuft of fruiting wood
at end of each scaffold branch is hard to har-
vest. Tree below had moderate annual pruning
for 5 years; vigorous, well-developed bearing
surface has low branches easy to harvest. Such
pruning results in heaviest yields.

sists of 1 ounce of corrosive sublimate
(mercuric chloride) , 3% gallons distilled
water, and y% gallon glycerine. This so-
lution is very poisonous.

In years of excessive fruit set summer
pruning may be done about July 1 to thin
the crop. Most growers, however, prune
during late winter or early spring when
labor is more plentiful and working con-
ditions are favorable.

The brush from pruning should be
shredded or hauled out of the orchard.

[27]

Brush burning in the orchard injures the
trees and should be avoided whenever
possible.

Fruit growth

The growth of the olive fruit exhibits
a cyclic pattern, the first stage being one
of very rapid growth followed by a
second stage in August and September
when increase in size is slower. The
third stage, occurring in October, is again
one of rapid growth and comes just be-
fore the normal harvest period. There
seems to be a further gradual increase in
size if the fruit is allowed to remain on
the tree, due perhaps to the increased
accumulation of oil. This latter stage may
not be evident if the fruits are shrivelled
by winter freezes. Inasmuch as the value
of olive fruits increases markedly with
size, it would be very much to the
grower's benefit to delay the harvest of
canning olives as long as possible to take
advantage of the rapid increase in fruit

MISSION OLIVE

DAVIS 1947

FRUIT STARTING
~T0 COLOR

<— FRESH WEIGHT

• s

•

U — MOISTURE

'•/

. DRY MATTER

OTHER THAN OIL

•/■

l//

• ^^^

•^OIL

. r

JUNE JULY AUG SEPT. OCT. NOV DEC. JAN.

Graph showing growth curve of olive fruits.

Fruit growth #

I Vegetative growth

100

BRANCH GROWTH
BAR0UNI VARIETY*^

ACCUMULATED
HOURS OVER 70"

BRANCH GROWTH
MISSION VARIETY ""^

1000 <
o

500

>
-I

2
Z>

I-:

</>

<-»

1949

1950

Olives show no distinct "flushes" of growth such as are found in citrus; active vegetative growth
seems rather to be correlated with occurrence of temperatures over 70° F.

[28]

Potassium-deficient leaves (left) show dead areas at tip and along lateral margins. Boron-deficient
leaves (right) have dead areas only at tip together with a yellow transition zone. See pages 41-42.

[29]

Olive parlatoria scale. Purple spots appear on green and red fruits at harvest. See page 50.

[30]

Oleander scale. Green spots remaining on the dark, ripening fruit are caused by this insect.

See page 52.

[31]

Peacock spot. Black spots first appear on the green leaves causing them to turn yellow and drop.

See page 56.

[32]

size occurring in October. It is inadvis-
able, of course, to delay harvest to the
point where the processing qualities of the
fruit would be affected, or where damage
from early frosts is likely.

The increase in fruit size coming in
October is accounted for largely by an
increase in the moisture content of the
fruit. Obviously if the tree is suffering
from a lack of readily available soil mois-
ture during this period the expected in-
crease in fruit size might not occur. On
the contrary, it is well known that under
conditions of high transpiration and low
soil moisture the leaves will withdraw
water from the fruits, causing them to
shrivel. It would seem very important for
the grower to keep his trees amply, but
not excessively, supplied with water dur-
ing the period just preceding harvest of
the fruit.

About August 1 the accumulation of
oil in the fruit begins with a gradual in-

crease through the fall and winter months,
reaching its maximum perhaps in late
December or January.

Vegetative growth

The graph on page 28 shows measure-
ments made of the shoot growth of the
Barouni and Mission varieties during the
period from March 15, 1949, to Decem-
ber 15, 1950. Vegetative growth com-
mences about the first of April and con-
tinues until about the middle of October.
The growth rate is fairly uniform, with
no abrupt flushes of growth as found in
citrus fruits. Also shown in the graph is
a curve for the accumulated hours over
70 °F., which seems to coincide fairly
well with the growth curves. This would
indicate that vegetative growth in the
olive starts when an appreciable number
of hours over 70°F. are experienced daily
and ceases when there is a lack of hours
above this temperature.

4. Setting a Satisfactory Crop . . • the

effects of controllable and noncon-
trollable influences on fruit set.

Olive trees throughout the world some-
times fail to set a satisfactory crop even
though they are well cared for and make
excellent vegetative growth. Part of the
problem is simply that of alternate-bear-
ing, the trees so exhausting their nutrient
reserves with one heavy crop that they
are unable to produce in the year fol-
lowing.

However, it is quite common for some
orchards to continue for several years
setting little or no fruit each year. The
causes for such nonbearing are not clear.
Evidence indicates that over a period of
years the importance of cultural methods
as they influence the yields is probably
secondary to influences of climate.
Weather conditions, varying with seasons
and years, are probably the most funda-
mental forces.

In California the period from about
February 1 to July 1 is an important one

in the setting of an olive crop. From
March 1 to 15 the first microscopic evi-
dence of flower formation in the buds
can be seen. Following this is a very rapid
development of the floral parts, with the
extension of the flower clusters — full
bloom occurring about 8 weeks after ini-
tiation of the floral parts. Coinciding with
this is the beginning of vegetative growth,
taking place about April 1 in California.
It is obvious, therefore, that a heavy drain
on the food reserves in the tree is occur-
ring during this period. It would be to
the grower's advantage in obtaining a
good fruit set to have his trees in top con-
dition during this time.

One of the causes for an unsatisfactory
fruit set in some orchards in certain years
is the lack of a sufficient number of per-
fect flowers. Orchards have been observed
where practically the entire bloom was
composed of staminate flowers. These are

[33]

believed to be the result of an abortion of
the pistil, occurring during the early de-
velopment of the floral parts. It may be
that a deficiency of water, mineral nu-
trients, carbohydrates, or even some
natural flower-forming hormone during
the period of floral development (March
and April) could lead to an abortion of
the pistil. Other factors that influence
fruitfulness in the olive will be discussed
below.

Temperature

The olive tree is unfruitful unless it is
exposed to a certain amount of cold dur-
ing the winter period. In experiments at
Davis, half of a group of young bearing

trees growing in large containers were
kept in a warm greenhouse throughout
the winter, while the other half remained
out-of-doors. None of the greenhouse
trees bloomed or fruited, whereas the out-
door trees bloomed and fruited normally.
As shown in the table below, high winter
temperatures seem to be associated with
low-yielding or unfruitful trees. The win-
ter-chilling requirement is probably dif-
ferent for different varieties.

Olives in California usually bloom
from about May 1 to June 1, depending
upon the season, variety, and location.
Damage to the crop from spring frosts is
rare during bloom, as the average dates
for the last killing frost are: Oroville,

Relationship between the amount of winter cold and
fruitfulness in olives.

Locality

Mean

January

temperature

Minimum

recorded

temperature

deg. F.

45.3

45.0

45.4

44.2

47.6

49.6

45.0

50.6

53.3

53.5

55.0

52.0

53.0

57.6

59.8

66.8

63.0

60.2*

71.1

Satisfactory yields

Orland, California

Oroville, California

Lindsay, California

Marseilles, France

Athens, Greece

Seville, Spain

Rome, Italy

Tunis, Tunisia

Unsatisfactory yields

Santa Barbara, California

San Fernando, California

San Diego, California

Riverside, California

Famagusta, Cyprus

Bogota, Colombia

Trees unfruitful

Weslaco, Texas

Homestead, Florida

Guatemala City, Guatemala .
Nairobi, Kenya, Central Africa
Honolulu, T.H

Mean July temperature, corresponding to January temperature in localities north of the equator.

[34]

March 17; Corning, March 8; Orland,
March 4; and Lindsay, March 19. There
have been years, however, when the un-
opened buds were damaged by late cold
spells coming in April.

The occasional occurrence of hot, dry
winds during the blooming period is
associated with poor sets of fruit. Such
winds occurring during June, when there
is a period of natural drop of the young
fruit, may increase the amount of fruit
dropping. Fruits that are still on the tree
by July 1 will as a rule continue on to ma-
turity. This is in contrast to the situation
in some Mediterranean countries, where
there may be several periods of fruit drop
throughout the summer.

Irrigation

The fact that practically the entire olive
acreage in California is grown under sum-
mer irrigation is argument for the bene-
fits of this practice in securing satisfac-
tory crops. Irrigation results in increased
yields because of its effect in causing the
production of new fruiting wood, increas-
ing fruit set as well as fruit size, and pre*
venting shrivelled fruits.

If the normal spring rainfall has been
lacking or light, so that the trees may be
suffering from a lack of moisture during
the critical spring period, one or two pre-
bloom irrigations would certainly seem
advisable. This is borne out by an irri-
gation experiment conducted in the

spring of 1951 in a Sevillano orchard at
Corning in cooperation with the Agricul-
tural Extension Service.

March and April, critical months in the
floral development of the olive, were ex-
tremely dry — only 0.2 inch of rain fall-
ing from about the first of March until
April 28. The normal amount of rainfall
expected during this period at Corning is
about five inches. Three adjacent experi-
mental plots were established: No. 1 had
one irrigation on April 1; No. 2 had
one on April 14; No. 3, the unirrigated
plot, had no irrigation until after bloom.

All three plots experienced about 1.9
inches of rain from April 28 to May 7.
The unirrigated plot, therefore, was with-
out water during most of the time the
flower buds were forming, from March 1
to April 28. The effect of the three differ-
ent irrigation treatments on the crop was
determined by making counts of the num-
ber of fruits per 100 inflorescences and by
obtaining yield records per tree at har-
vest. These results are given in the table
below. In years of normal or excessive
spring rainfall a pre-bloom irrigation
would, of course, be unnecessary.

Rainfall during bloom does not
decrease fruit set. Occasionally
showers will fall during the olive-bloom-
ing period, and the question arises as to
how this may affect the set of fruit. Ex-
periments were conducted at Davis in
1950 in which one tree was kept wet 8

The effect of pre-bloom irrigation on fruit set and yields of olives

in a year of low spring rainfall (0.2 inch from March 1 to

April 28 — normal rainfall, 5 inches), Sevillano variety,

Corning, thirty trees per plot.

Plotl
Plot 2
Plot 3

Date of first irrigation

April 1

April 14. . . .
After bloom

Soil moisture
on April 20

(per cent)

11.4
8.7

Fruits per 100
inflorescences

2.7
2.3

1.4

Yields per tree

lb.
101
113

[35]

hours a day during the blooming period
by a sprinkler placed in the top of the tree,
while an adjacent tree received the same
amount of water on the ground under the
tree. Fruit-set counts made on both trees
showed the sprinkled tree to have a
slightly heavier set than the nonsprinkled.
The sprinkling seemed to have no adverse
effects under the conditions of this test.

Mineral nutrients

Nitrogen. Apply nitrogen fertilizers
early enough so that they will be absorbed
by the tree by March 1. Applications of
commercial fertilizers should be made in
late December or January, and manures
should be applied the previous fall. It is
well known that continued application
of nitrogen fertilizers will cause increased
yields of olives in California. This is due,
in part, to the increased production of
fruiting wood. Also there is evidence,
especially in the shallow soils of Butte
County, that nitrogen applied several
months prior to bloom will result in in-
creased fruit set. Some growers in that
area are cautious about applying too
much nitrogen for fear of causing an ex-
cessive fruit set and developing an alter-
nate-bearing condition. Olive trees in
deeper and more fertile soils are not so
responsive to changes in the nitrogen
fertilization practices.

Boron. One of the symptoms of boron
deficiency in Butte County was unfruitful
olive trees. Some trees appeared to blos-
som and set fruit normally; then most of
the immature fruit dropped during July
and August. Such trees would be expected
to have a boron content of 14 to 15 p.p.m.
in the leaves. However, severely affected
trees, which would have a boron leaf con-
tent of 7 to 13 p.p.m., produced few, if
any, blooms.

Potassium. As shown in the table on
page 42, potassium deficiency in olives
causes marked reduction in yields. This
is due to the lack of new vegetative
growth, failure to produce a satisfactory
bloom, and a reduction in fruit size.

Other than the mineral nutrients men-
tioned above, there is no evidence that a
mineral deficiency in California soils
exists sufficient to result in a reduction
in the fruit set and yield of olives.

Carbohydrates

Little can be done by the grower to
increase the carbohydrate level in the tree
other than maintaining a heavy, vigorous
leaf area. This can be accomplished by
irrigation, nitrogen fertilization, wide
spacing of the trees, minimum pruning,
and control of such diseases as Peacock
Spot, which tends to partially defoliate
the tree.

Artifically increasing the carbohydrate
level in the tops of trees during the flower-
forming period of March and April has
been done experimentally by girdling the
branches in mid-February. In some cases
this has resulted in definite increases in
the percentage of perfect flowers, fruit
set, and yields. In girdling, a strip of
bark about *4 inch wide is removed from
most of the primary scaffold branches on
the tree. A grape-girdling knife does this
very rapidly. The girdled area is covered
immediately with grafting compound.

This practice has been most effective
when performed on young, vigorous
trees. It has, however, several disadvan-
tages and is advisable only as a last resort
in getting the trees to set a crop. In or-
chards infected with olive knot, it is quite
likely that the bacteria will become estab-
lished in the girdling cuts. The olive knot
can usually be kept out, however, if the
cuts are immediately covered with hot
grafting wax, then with a Bordeaux-mix-
ture paste, and finally with an asphalt-
emulsion grafting compound. Bordeaux
paste applied directly to the girdling cut
causes considerable injury to the tissues
and is not advised.

Alternate bearing

This occurs in olives as it does in
apples, pears, and many other fruit spe-
cies. The physiological basis for this con-

[36]

dition is the fact that flowering and fruit-
ing is an exhaustive process, a heavy crop
removing a considerable amount of the
various carbohydrate materials, organic
nitrogenous substances, and other essen-
tial nutrients from the tree. Thus ade-
quate stored-food reserves are not avail-
able for the production of a crop the fol-
lowing year.

Alternate bearing may develop follow-
ing an unusually heavy crop. The most
satisfactory method for preventing it is
the prevention of excessively large crops.
In the olive, with its erratic bearing be-
havior, it is difficult to predict the occur-
rence of an excessive fruit set. Usually it
cannot be determined until about the mid-
dle to the last of June. Therefore the only
practical way to prevent excessively heavy
crops is to remove by thinning some of
the young fruits after they have set.

Experiments conducted with olives in
Butte County by the Agricultural Exten-
sion Service and later experiments con-
ducted by the Agricultural Experiment
Station in Davis indicate that the alter-
nate-bearing tendency can be overcome
by fruit-thinning. This must be done early
in the season, however, preferably in late
June or early July. In controlling alter-
nate bearing, thinning would, of course,
be done only in years of heavy crop set;
and once a regular bearing pattern was
established, the thinning could be dis-
continued, perhaps for several years.

There is no clear-cut evidence that al-
ternate bearing can be controlled by any
pruning method. However, it is possible
that, where it is a continuing problem,
if the pruning given the trees can be de-
layed until late June of the "on" year,
it may be used as a substitute for fruit
thinning. Pruning may not be as effective
as thinning in overcoming alternate bear-
ing, however, since leaves as well as fruit
are removed. This type of pruning should
be "detailed" rather than the removal of
large branches.

With olives as with other fruit crops,
no fertilizer practice, either as regards

time or amount of application, can be re-
lied upon to eliminate alternate bearing.
Nitrogen fertilization may raise the vol-
ume of production without greatly chang-
ing the pattern of fluctuating yields
through the years, the trend being about
parallel with unfertilized orchards. How-
ever, excessive applications of nitrogen
in the winter or early spring may result in
a heavy fruit set and lead to alternate
bearing. This is especially true in the
Butte County districts.

Thinning

Other than the possible alleviation of
alternate bearing, the benefits of fruit
thinning are as follows: (1) increased
fruit size, (2) earlier fruit maturity with
less chance for frost-damage and shrivel-
ling at harvest, (3) higher oil content,
(4) greater flesh-pit ratio, (5) reduction
in harvesting cost, (6) less limb break-
age, (7) production of more fruiting
wood for the next season's crop, and (8)
increased yields over a period of years.

The disadvantages of thinning are the
difficulty and cost of obtaining thinning
labor and the reduction in total yield the
year the thinning is done. The increased
fruit size will not offset the reduced num-
ber of fruits ; therefore the premium paid
for larger fruits must be enough to over-
come reduced yields.

In general, thinning will not pay unless
trees are definitely overloaded. When
they do have an excessive fruit set, how-
ever, especially the Mission olive, thin-
ning may be very profitable because it
increases to canning size fruit that other-
wise may have to be sold for oil extrac-
tion. In years when high prices are paid
for oil olives, thinning would be of less
value, as there is a smaller price differ-
ential between the various fruit sizes.
Thinning relatively young trees is fairly
inexpensive, taking from % to 1% mam
hours per tree. For the older, large trees
the task is formidable, almost discourag-
ing the grower from spending money for
thinning. It is possible, however, that

[37]

satisfactory post-bloom chemical spray
thinning may develop to the point where
hand labor would be unnecessary.

Hand thinning. Do not thin trees un-
less they are definitely overloaded. Ex-
perienced growers know the maximum
fruit set their trees can handle and still
maintain a satisfactory fruit size at ma-
turity. This is approximately 3 to 5 fruits
per foot of twig, depending on such fac-
tors as age and vigor of trees.

Do the thinning as early as possible
for maximum benefits. From mid-June to
July 10 is the preferable time. The bene-
fits of reduction in alternate-bearing are
obtained only with very early thinning.
Later thinning, in late July or August,
will cause increased fruit size for the
remaining fruits — but the total reduc-
tion in yield is proportionately increased.

For protecting the hands, wear heavy
rubber gloves or tape the fingers.

Use both hands, stripping fruit from
several twigs at once.

Thin only those twigs where at least
5 or 6 olives can be removed at one pull.
Try to leave, on an average, 3 to 5 olives
per foot of twig. Unless enough fruits are
removed the benefits of thinning will not
be obtained.

To check on results, at least at first,
leave overloaded, unthinned trees near
the thinned ones.

Pollination

The need for cross-pollination in olives
has long been a debated question, both in
the Mediterranean countries and in Cali-
fornia. Experimental work in Italy
showed that most varieties examined
were self-sterile, a few were self-fertile,
and some were partially self-fertile. The
planting of pollinizer varieties was rec-
ommended. On the other hand, workers
in Portugal found that hundreds of acres
of isolated olive orchards of one variety
are planted alone where, in some years,
fruit production is excessive.

In California many large orchards of
a single variety have borne satisfactory

crops, although some of the highest and
most consistent yields are in orchards
where two varieties are interplanted.

Experimental work now in progress at
the California Agricultural Experiment
Station has shown that, in some years at
least, cross-pollination is decidedly bene-
ficial in increasing fruit set.

Growers contemplating the planting of
new orchards of two or more varieties
may find it profitable to interplant them,
especially if orchards of other varieties
are not nearby. It would probably facili-
tate harvesting operations to plant the
varieties in groups of four rows each.

Delayed harvest

Excessively loaded olive trees usually
fail to produce fruit of sufficient size by
October to justify harvesting them for
canning olives. Consequently the fruits
are allowed to remain on the trees until
January or February and are harvested
then for oil extraction. Such late-har-
vested trees produce little, if any, fruit
the following year. Trees with a light to
moderate crop, however, usually produce
fruits of size sufficient to be harvested
in October for canning olives. These
early-harvested trees have usually been
observed to return a satisfactory crop
the following year. It was concluded from
this that late-harvesting was detrimental
to the subsequent crop. However, recent
experiments in two Mission orchards in
Butte County have failed to bear out this
opinion. Adjacent groups of trees in the
same orchard have been harvested early
(October), medium (December), and
late (February). Yields the following
year were practically the same in each of
the three plots. The same results were
obtained each year for four years.

It may be that the lack of a subsequent
crop with heavily loaded, late-harvested
trees is due simply to alternate-bearing.
The trees probably exhausted their stored
foods maturing the heavy crop and would
not have set a crop the following year
even if they had been harvested early.

[38]

5. Production of the Crop • • • the cuf-

turai practices that will contribute

to satisfactory yield through the years.

Fertilizers

Nitrogen fertilizers in California
olive orchards have been so beneficial in
causing increased yields that most grow-
ers annually apply nitrogen to their trees
at the rate of about % to 2 lb. of actual
nitrogen per tree.

This can be applied as animal manures
or as one of the chemical fertilizers listed
in the table on page 40. The choice of fer-
tilizers should be determined on the basis
of which will supply a pound of nitrogen
at the lowest cost. Manures should be ap-
plied in the fall as they are rather slowly
available to the trees, but commercial
fertilizers are best applied in late Decem-
ber or January. As fruit bud differentia-
tion, floral development, and fruit setting
occurs in the olive during the period from
March 1 to June 15, apply the fertilizers
far enough in advance so that they may
be absorbed and available to the trees
during this time.

Concentrated organic nitrogen (urea)
fertilizers have been applied experimen-
tally to olives at the rate of 12 lb. per 100
gallons as foliage sprays, during the
period of floral development (March 1 to
April 15) . Leaf analysis showed that the
olive absorbs nitrogen in this form
through the leaves. In some experiments
fruit set has been increased over the non-
fertilized trees, although in general the
benefits have not been sufficient to justify
the increased cost of this method of ap-
plication.

Nitrogen fertilizers have been applied
to olive trees experimentally as high as
30 lb. of ammonium nitrate per tree (10
lb. of actual nitrogen) without causing
any leaf injury or other injurious effects.
However, it is uneconomical to practice
continued heavy applications of nitrogen
fertilizers to olives. Under such condi-
tions, the amount of nitrogen in the tree,
as determined by leaf analysis, never ex-

[

ceeds about 2 per cent of the dry weight
of the leaves, indicating that there is a
maximum limit the tree will absorb. Addi-
tional nitrogen will be leached out of the
soil. At the other extreme, trees greatly
deficient in nitrogen never drop below a
nitrogen level of about 0.9 per cent of the
dry weight of the leaves. Average or-
chards in good condition show a nitrogen
level in the leaves of about 1.4 to 1.8 per
cent.

If leaves are dark green and the new
shoot growth is 4 to 12 inches a year, the
trees are probably adequately supplied
with nitrogen. If leaves are a medium to
light green and are not making a shoot
growth of at least 4 inches per year, it is
likely that the trees are deficient in nitro-
gen and would respond to fertilizer appli-
cations. Chemical soil analyses are not
considered to be a reliable means of judg-
ing the fertilizer requirements of trees
because they do not allow for the tree's
ability to absorb the elements — nor is it
possible to get a soil sample representa-
tive of the entire orchard. Leaf analysis
is a much better method, although fer-
tilizer requirements probably can best be
judged by the trees' response to test appli-
cations.

There is some evidence, especially in
Butte County, that increased fruit set can
be caused by heavy applications of nitro-
gen, which have resulted in excessive
crops and have caused an alternate-bear-
ing condition to develop. This will not
always hold true, however, especially if
the trees are planted in deep, fertile soils
and are already adequately supplied with
nitrogen. It has also been reported that
applied nitrogen will delay fruit maturity
as it does in other fruit crops. This may
not necessarily be true unless trees are
heavily loaded, in which case fruit matu-
rity is generally delayed, regardless of
cause.

39]

It is believed by some that applications
of nitrogen following bloom will cause
increased fruit size. In general, the ex-
perimental work with nitrogen fertiliza-
tion of olives, as well as other fruit crops,
has not substantiated this belief. It is also
the observation of some growers that
"soft-nose" (see page 55) may be asso-
ciated with heavy nitrogen fertilization
practices, especially when nitrogen is ap-
plied as manure.

Two 4-year nitrogen fertilization ex-
periments were conducted with Manza-
nillo olives by the Agricultural Extension
Service in Tulare County from 1937 to
1940. One was in an orchard in poor con-

dition with trees planted 24 x 24 feet, the
other in an orchard in fair condition with
trees 30 x 30 feet apart. In addition to the
check treatment, nitrogen was added to
plots in each orchard at the rate of 1 lb.,
and 2 lbs., of actual nitrogen per tree per
year. The average yield per tree for the
4-year period was as shown at the top of
page 41.

The main responses to fertilization in
both these tests were (1) increased tree
growth, providing a large increase in
bearing surface; and (2) the setting of
larger numbers of fruits. Fruit size was
not increased; in fact with some of the
very heavy sets size decreased proportion-

Comparison of some of the common forms of nitrogen-containing

fertilizers.

Per cent
nitrogen

(N)

Per cent
phosphate

(P 2 6 )

Per cent
potash

(K 2 Q)

Approximate
number of
pounds required
to supply
one pound
of nitrogen

Inorganic concentrated fertilizers

Ammonium sulfate

Calcium nitrate

Sodium nitrate

Ammonium nitrate

Ammonium phosphate (16-20) .
Anhydrous ammonia

Organic concentrated fertilizers

Nu Green (urea)

Fish meal*

Tankage*

Dried blood*

Cottonseed meal*

Bulky organic fertilizers
Dairy manure (wet)*. .
Dairy manure (dry) * . .
Lot fed steer manure* .
Poultry manure (wet) *
Poultry manure (dry) * .
Rabbit manure*

Sheep manure*
Olive pomace*.

20.5
16.0
16.0
33.0
16.0
81.0 +

44.0
10.0

8.0
12.0

7.0

0.5
1.0
2.0
1.6
2.5
2.0
1.6
1.0

20.0

6.0
10.0

3.0

0.3
0.5
0.6
1.3
2.3
1.3
1.0
0.3

2.4

12.0

8.0

2.0

0.7
1.8
1.9
0.9
1.2
1.2
3.0
0.7

5.0
6.3
6.3
3.0
6.3
1.2

2.3
10.0
12.0

8.0
14.3

200
100
50
63
40
50
63
100

* These organic materials vary widely in analysis between lots. The figures given are averages and useful
only for estimates.

[40]

Orchard I (24x24)
(poor condition)
Orchard II (30x30)
(fair condition)

No fertilizer
181b.
161

1 lb. N. per
tree per year

141 lb.
323

2 lb. N. per
tree per year

186 lb.
367

ately. No particular difference in time of
fruit maturity was reported.

In orchards already under a high level
of nitrogen fertilization, the marked re-
sponces obtained above with nitrogen-
deficient trees would not be experienced
by further increases in nitrogen appli-
cations.

In similar tests conducted by the Agri-
cultural Extension Service in Tehama
County with Sevillano olives the follow-
ing conclusions were drawn:

( 1 ) Yield and income tended to increase
with each year of application of nitrogen.
The fertilizers induced better bud devel-
opment and additional growth so that the
effect of annual applications was cumula-
tive.

(2) Sizes were reduced by nitrogen ferti-
lizers, when expressed on a percentage
basis, but the greater total yield resulted
in greater production of larger sizes as
well as of the smaller sizes.

(3) The percentages of culls in the ferti-
lized olives was higher than in the non-
fertilized and seemed to be associated

with a vigorous, rank type of growth. No
marked difference in pickling quality or
flavor was apparent in olives from trees
with or without nitrogen fertilization.

Potassium. The paragraphs on potas-
sium and boron deficiencies apply only
to Butte County; at present there is no
record of deficiency of these minerals in
any other olive-producing area.

In 1947, olive trees in the Wyandotte
area of Butte County showed leaf symp-
toms later identified as caused by potas-
sium deficiency. Analysis of these leaves
showed them to contain 0.11 per cent
potassium on a dry-weight basis. Previous
extensive work by Lilleland and Brown
of the California Agricultural Experiment
Station in orchards in different parts of
California had established the average
potassium level for olives to be from 0.8
to 1.0 per cent.

Heavy applications of potassium (25
to 50 lb. of potassium sulfate per tree)
to olive trees in the potassium-deficient
areas of Butte County have produced the
following responses:

Left: Mission olives from trees fertilized with one application of 50 lb. potassium sulfate per tree.
Right: Fruits from potassium-deficient trees.

[41]

(1) a change in leaf color from a light
bronze-green to dark green;

(2) elimination of the development of
dead areas in margins and tips of the
older leaves;

(3) increased shoot growth;

(4) increased fruit size; and

(5) increased yields.

These responses have been accom-
panied by an increase in the potassium
content of the leaves. With the exception
of the Palermo and Wyandotte areas of
Butte County, it is unlikely that olives in
the commercial olive-producing sections
of the state will respond at the present
time to potassium fertilizers.

Boron. For a number of years olive
trees in the Wyandotte area of Butte
County exhibited the following symp-
toms, diagnosed as being caused by

For differences in the leaf symptoms
of potassium- and boron-deficient trees
see page 29.

boron deficiency: (1) Short, branched
growth takes place in contrast to the long,
straight shoots of normal trees. (This
branching is apparently caused by the
death of the terminal bud, which forces
growth out from lateral buds. These new
terminal buds in turn die, and additional
branching occurs.) (2) In severe cases
the ends of the limbs die, and, in some
cases, the limbs may die back to the main
trunk. (3) The leaves are small with
brown, scorched tips, and with an inter-
mediate golden-yellow area between the
dead tips and the green basal area. There
are no dead areas along the lateral mar-
gins such as occur with potassium-defi-

Effect of potassium fertilizers on Mission olives in a potassium-
deficient soil (Graves orchard), Wyandotte,
Butte County, California.

Check
(No treatment)

10 lb. potassium sulfate

per tree

(Applied Jan. 1949)

« *

50 lb. potassium sulfate

per tree

(Applied Nov. 1947)

Yields per tree

1948

lb.

40
36

21
47

lb.

116

lb.
151

1949

1950

128
173

1951

157

Size grades (per cent)
Extra large

(1949) (1950) (1951)

3 2 1

17 17 4

80 81 97

(1949) (1950) (1951)

10 3

6 2 10

50 18 36

43 80 51

(1949) (1950) (1951)
113

Large

Medium

Standard

Sub-standard

11 3 2
17 20 6
49 38 22
22 37 67

Oil content of fruits
(Fresh weight basis)

23.8 per cent

24.9 per cent

Leaf analysis (Potassium
as per cent dry weight)
June, 1947

0.11
0.21
0.15

0.11

Nov., 1948

0.82

Aug., 1951

0.50

[42]

Boron deficiency is shown in defective olives (upper) known as "monkey-face" fruits; and in twig
dieback (lower), with death of terminal growing point and subsequent branching.

[43]

cient leaves. (4) The Ijark may become
thickened and corky, and in some cases
may develop a rough, blister-like appear-
ance. (5) Trees affected with this diffi-
culty have a high percentage of defective
fruits, locally termed "monkey-faced."
(6) Yields are reduced because of the
early dropping of fruits before harvest.

Experimental injections of copper,
manganese, boron, and zinc salts directly
into limbs of affected trees were made in
the spring of 1941. A definite response
was found only with the boron injections.
Later tests showed that this same favor-
able response could be obtained by apply-
ing borax to the soil under the trees at 1
pound per tree.

There is a correlation between the
severity of the symptoms and the boron
content of the leaves. Trees showing
severe deficiency symptoms have a boron
content of 7 to 13 p. p.m. ; mild symptoms,
14 to 15 p.p.m.; doubtful range, 16 to 18
p.p.m.; normal boron content, 19 p.p.m.,
and up.

Olives are semi-tolerant to excess boron
and are not likely to be injured by borax
applications continued for several years
at the recommended rate of % to 1 pound
per tree. With the exception of a few
isolated cases, definite response of olives
to boron applications has been found
to occur only in the Butte County olive
district. Leaf analyses from trees in well
maintained orchards in other commercial
areas have shown they are in the normal
range for boron, although it is possible
for future deficiencies to develop.

No evidence exists at this time that
olives in California will respond to any
fertilizer other than nitrogen and (in
Butte County only) potassium and boron.
Orchards will not respond even to ferti-
lizers containing these elements if the
trees already have an adequate supply.

Irrigation is essential
in California

The majority of the olive trees in the
world are grown without supplementary

irrigation, depending only upon natural
rainfall. Exceptions are Greece, with 7
per cent of the acreage under irrigation;
Spain, with 10 per cent; Egypt, with 40
per cent; Chile, with 90 per cent; and
California with almost 100 per cent. You
may want to consult one of the two follow-
ing University of California publications
for further information: California Agr.
Ext. Cir. 50 — Essentials of Irrigation and
Cultivation of Orchards; and Calif. Agr.
Exp. Sta. Bulletin 715, Irrigation Experi-
ments with Olives.

The olive appears to be well adapted
to withstanding drought. The leaves are
relatively small and leathery and have a
thick cuticle on the upper surface that
tends to restrict the loss of water. On the
under surface the leaves are protected by
a mass of peltate hairs. The stomata,
while numerous on the lower surface, are
sunken and have small openings. The
leaves are apparently uninjured by long
periods of hot weather and dry soil condi-
tions. It is, however, a misconception that
the olive does not use much water. It will
use as much as other species, and possibly
more if water is available. Oil varieties
of olives can be grown quite successfully
without irrigation; but table varieties,
at least under California conditions, re-
quire irrigation to prevent the fruit's
shrivelling and to obtain profitable yields.

Recent experimental work in Califor-
nia has shown that olives respond to a
lack of readily available soil moisture
just as other trees do. The growth rate of
the olive fruits is decreased by a lack of
readily available soil moisture. In addi-
tion to summer irrigation, olives should
have earlier spring and later fall irriga-
tions than are necessary with deciduous
fruits.

There is no "optimum" or best soil-
moisture content for plant growth. Exper-
iments with various fruit tree species
have shown that water may be used by
plants with equal ease throughout the
entire range of soil-moisture content

[44

between the field capacity and the per-
manent wilting percentage.

Field capacity is all the water a soil will hold
after it is drained. Permanent wilting percent-
age is the soil-moisture condition at which plants
cannot obtain water readily.

Water taken by trees from the soil is
almost entirely given off as water vapor
through the leaves by transpiration. Soil
moisture, sunlight, temperature, humid-
ity, and wind all affect the rate of trans-
piration. Large trees because of greater
leaf area use more water than small ones.
The presence or absence of fruit does not
materially affect the amount of water
used, since the main water loss is through
the leaves. Evergreen trees, such as the
olive, will use water throughout the year,
but much less in winter than in summer.

The total amount of water that com-
parable trees use will not be greater on a
clay than on a sandy soil, if both are
fertile and have readily available water
at all times. Usually on sandy soils, how-
ever, water must be applied more fre-
quently and in smaller amounts than on
clay soils. Likewise, on shallow, hardpan
soils, trees should be irrigated more fre-

quently with smaller applications of water
than on deep soils.

One of the best methods by which the
grower can decide when his trees need
water is by watching some of the broad-
leaved weeds, which may be left as indi-
cator plants in various parts of the
orchard. Generally, such weeds are deep-
rooted enough to indicate by their wilt-
ing a lack of readily available water in
the soil occupied by the roots of the trees.
Where only small streams of irrigation
water are available, the time necessary to
cover the orchard may be so long that the
trees irrigated last are decidedly affected
before they receive water. It is important,
therefore, to anticipate when the per-
manent wilting percentage will be reached
so that irrigation may be started soon
enough.

The benefits derived from good irriga-
tion practices are cumulative and take
several years to appear. Increased crops
result chiefly from increased size of trees,
which in turn depends on trees being
kept healthy and vigorous. One of the
chief factors in keeping trees vigorous
is an irrigation plan providing readily
available soil moisture at all times. The

Trees on left are in a low, poorly drained spot, tree to right in a better drained area.

[45]

results of poor irrigation or failure to
irrigate, on the other hand, are quick to
appear and generally take the form of
smaller yields, smaller fruit, poorer fruit
quality, and stunted trees.

It is important that the grower of can-
ning olives supply his trees with enough
water to prevent fruit-shrivelling. On
shallow soils during the hot days of
August and September, especially if dry
winds are blowing, it may be impossible
to keep sufficient water on the entire
orchard to prevent at least some trees
from showing shrivelled fruit. Although
such fruits will regain their turgor after
irrigation, they often shrivel again dur-
ing processing and become a poor-quality
product.

Poor drainage

Olives cannot be grown profitably in
areas where either the surface or subsoil
drainage is poor. Trees in these locations
show stunted growth, numerous dead
twigs, small, yellowish-green leaves, poor
yields, and prematurely ripe fruit — with
eventual death of the trees. Unless such
portions of the orchard can be adequately
drained, it is advisable to discontinue
growing olives there; and if you are
planting a new orchard you will, of
course, want advance information about
the drainage characteristics of the site
you are considering.

Soil management

Covercrops are used chiefly for three
purposes: To maintain good soil struc-
ture and to increase water penetration.
In many soils there is better water pene-
tration after a few years of covercrops,
resulting in a more economical use of
water and a better supply to the roots.
The use of covercrops is not a substitute
for careful soil handling. Cultivation
when the soil is too wet will puddle many
soils so badly that years of good care may
be required to repair the damage. The
use of covercrops under the conditions
of California's interior valleys apparently

does not increase the moisture-holding
capacity of the soil, however, as it may
under cool, humid climatic conditions.
In experiments at Davis, 25 years of
annual covercrops have failed to change
measurably the moisture-holding capacity
of the soil.

To prevent erosion. Covercrops may
be of great value on slopes subject to
erosion. Not only do they increase the
rate of penetration of water and thus
reduce the runoff, but their roots tend to
hold the soil in place and reduce the
amount of washing by the part that does
flow away.

To increase soil nitrogen with legumi-
nous covercrops. Such covercrops with
proper inoculation of nitrogen-fixing bac-
teria have given increases of total nitro-
gen in the soil in cool, humid regions.
Experiments carried out in the hot, inte-
rior valley surrounding Davis, however,
failed to show any measurable nitrogen
increase with either summer or winter
legumes. In the climatic conditions under
which olives are grown, this benefit would
be unimportant and commercial fertili-
zers should be relied upon to maintain
the desired nitrogen level in the soil.

Some of the annual covercrops used
are: (1) the winter legumes — yellow
clover (Melilotus indica) , the vetches,
and bur clover; (2) the summer leg-
umes — cowpeas, soybeans; (3) the win-
ter non-legumes — the mustards, rye, oats,
barley, and volunteer weeds; (4) the
summer non-legumes — orchard grass,
sudan grass, and weeds.

Some of the benefits of covercrops such
as improved water penetration can be
obtained by bringing into the orchard
organic material — sawdust, straw, or
manures — and working it into the soil.
Strawy material, which is high in carbo-
hydrates and low in nitrogen, will cause
a depressed nitrate level in the soil for
months after being used. (This is due to
the utilization of the nitrogen by bacteria
in the decomposition of organic mate-
rial.) The applications of such material

[46]

should be accompanied, therefore, by
extra amounts of nitrogen fertilizers.

Remember that covercrops absorb
nitrogen while growing, and during that
period they may compete seriously with
the tree unless additional nitrogen is
supplied. The covercrops will use a con-
siderable portion of the soil moisture
and, if they are grown during the summer,
provision should be made for supplying
an additional amount of irrigation water.

Sod culture. Many California olive
growers are placing their orchards under
permanent sod culture, realizing that they
must provide extra water and nitrogen
for utilization by the sod. Permanent fur-
rows are established before planting the
sod, or irrigation may be by sprinkler
systems. The grass is kept low by mow-
ing, or in some cases livestock is allowed
to graze in the orchard. Stock will rarely
eat the olive leaves as long as a plentiful
supply of grass is available.

Under this system the expense of culti-
vation is eliminated, the entire root zone
is undisturbed by cultivation instruments,
the sod provides an excellent erosion

ItliC t.:i.

Olive orchard under sod culture with sprin-
kler irrigation; sod culture is not advisable
where water is limited.

check, and orchard operations are
feasible soon after irrigations. Sod cul-
ture would not be advisable unless ample
irrigation water is available and unless
nitrogen is supplied in addition to the
amount normally used for the trees alone.
For sod culture perennial rye grass has
proved satisfactory, and in some cases
volunteer native vegetation is sufficient.
Clean cultivation. Most California
olive orchards are grown under a system
of clean cultivation, whose chief purposes
are to:

(1) remove the competition of weeds for
available soil moisture;

(2) facilitate the distribution of irriga-
tion water; and

(3) incorporate covercrops and manure
with the soil.

Since olive trees are shallow-rooted,
even on deep soils, deep or excessive
cultivation may seriously injure the root
system. The practice of subsoiling
between tree rows is seldom justified.
Where olives are grown on very shallow
soils, it may be advisable to eliminate
cultivation entirely in order to allow
penetration of the entire soil mass by the
tree roots.

Oil sprays have for some years been
used to control weeds in citrus orchards
and, to a limited extent, in olive orchards.
Where this method has been used growers
report improved soil conditions, and no
harmful effects have been observed.
Because of the increasing cost of oil,
some olive growers have recently dropped
this practice in favor of weed control by
mowing.

Types of sprays that can be used are:
(1) the general-contact weed killers,
such as Diesel oil, fortified with phenol
compounds or sulfur. (For more infor-
mation see California Agr. Ext. Cir. 137,
General Contact Weed Killers.) (2) emul-
sions, made by combining water and oil;
and (3) water-soluble materials, such as
sodium trichloracetate, or the selective
weed killers such as 2,4-D and 2,4,5-T.
(See also California Agr. Ext. Cir. 133,

[47]

2,4-D as a Weed Killer — out of print, but
available for reference in most Farm
Advisor offices.) The selective weed
killers are widely used in grain fields for
controlling broad-leaved weeds.

The use of 2,4-D and related materials
is hazardous in olive orchards as the olive
is especially sensitive to injury, and it is
difficult to prevent drift from weeds onto
the trees.

Harvesting the crop

Harvesting the crop is the largest ex-
pense involved in growing olives, repre-
senting 50 to 70 per cent of the total pro-
duction labor cost, and 30 to 40 per cent
of the gross returns from the crop. This
expense is increased with very tall trees,

TO LOWER HARVESTING COSTS
Develop a system of pruning and tree
spacing that will encourage the natural
spreading tendencies of some varieties.
Annual removal of dead and interfering
branches facilitates picking and encour-
ages the production of higher-quality
fruit.

(2) Wherever possible adopt cultural
methods which permit the skirts of the
trees to reach the ground, using tillage
implements designed so that in moving
about the grove they will not injure the
lower branches.

(3) Teach pickers to use both hands
and pick toward the container. The hands
should move together rather than in-
dependently.

(4) The pickers should go to the highest
point for the fruit with each new set of
the ladder and pick coming down the
ladder.

(5) Many growers would obtain in-
creased picker efficiency if they could
arrange to manage the picking crew
themselves or at least have a good fore-
man handle the crew rather than leave
it to a picking contractor.

(These recommendations are based on
a harvesting study made in 1948 in Tu-
lare County by the Agricultural Extension
Service.)

an excessive amount of bushy, dead
growth in the trees, heavy grass in the
orchard, severe infestations of black
scale, or other factors that make picking
difficult

Canning olives. Olives are harvested
for pickles in California from mid-Sep-
tember to mid-November, depending
upon the variety (see the table on page
9). The optimum harvesting time is
determined by the color and texture of
the olives. It is advisable to delay harvest-
ing as long as possible to allow the fruit
to attain its maximum size.

Fruits are picked by hand and must be
handled carefully, especially the Ascolano
variety, to avoid bruising. Over-mature
or badly bruised olives will usually de-
velop spoilage during processing. It is
important that the olives be taken to the
processing plant as soon as possible after
picking. The maximum period between
picking and placing in the processing
solution should be from 12 to 14 hours.
For fruits that must be hauled long dis-
tances this presents an important prob-
lem. Olives kept too long in boxes after
harvesting start "sweating"; this gives
rise to deterioration during processing.

Low temperature injury to can-
ning fruit. The olive pickling harvest
season should be concluded before about
November 10 to avoid risk of freezing
injury to the fruits. If trees are heavily
overloaded the fruit may not be mature
enough for pickling by this time. Such
trees should have had the fruit thinned
in late June, so that proper size and
maturity could be obtained before danger
of frost.

The average date of the first killing
frost is December 3 at Corning, Novem-
ber 26 at Oroville, and November 14 at
Lindsay. Freezing temperatures as low as
25° to 28° F. (-3.9° to -2.2° C.) for an
hour may result in damage to fruits, con-
sisting of shrivelling, softening, or pitted
flesh. Injury is much more likely to occur
if moisture is present on the fruits than
if they are dry. When it is suspected that

[48]

SIZE AND COLOR GRADES OF
CANNING OLIVES

Fruits must reach a certain minimum
size at harvest, depending upon variety,
or they cannot be used for canning. This
is according to regulations of the Market-
ing Order for Olives. These are the mini-
mum sizes:

Mission and Manzanillo Standard
Obliza Medium

Ascolano, Barouni, and

St. Agostino Mammoth

Sevillano Giant

Generally accepted color standards
to determine harvesting time of the major
varieties are as follows:

Manzanillo — straw color, up to and
including a light red blush, covering not
more than half of any olive;

Mission straw color, up to and in-
cluding a complete coloring of light red;

Sevillano — straw color to a light red
coloring of not more than half of any
olive;

Ascolano — straw color to not more
than a faint blush of red on any olive;

Barouni — straw color.
In addition, any variety of olive is con-
sidered immature if it will not yield a
characteristic white juice under moderate
pressure between the thumb and finger.

the temperature has dropped to a danger-
ously low level during a still night, do not
touch the fruits until they warm up
gradually. It is possible for their tempera-
ture to drop considerably below the freez-
ing point without ice crystals forming
unless fruits are shaken or jarred, in
which case they freeze immediately.

The damage is variable between or-
chards and often does not appear until
after processing, when the olives become
mealy and soft. There seems to be no
difference between varieties in regard to
the freezing point of their fruits, although
small fruits will freeze more quickly than
large ones. Green fruits are more sus-
ceptible to freezing injury than red or

black. Olives that have been frozen are
permanently injured, become shrivelled,
and will not regain their normal turgor
even with added irrigation water or rain-
fall. Such fruits cannot be used for can-
ning and should be allowed to remain on
the tree and harvested for oil extraction
later in the winter.

During the latter part of the harvest-
ing period, another type of fruit shrivel-
ling often occurs, in which the cells of the
fruit are not injured and the canning
quality is not impaired. Such shrivelling
may develop when minimum night tem-
peratures of 32 to 35 degrees F. occur,
accompanied by strong, drying winds.
The loss of water from the leaves exceeds
the uptake of water by the roots, with the
consequent withdrawal of water from the
olives, shrivelling them. However, if such
conditions are followed by low transpira-
tion conditions, such as cloudy, rainy,
or foggy weather, with higher tempera-
tures, the fruit regains its normal turgor
and is apparently uninjured. This type
of shrivelling is more likely to occur with
heavy than with light crops, probably
because of the relative immaturity of the
fruit on heavily loaded trees. Such green
fruit would have a lower carbohydrate
content and would be unable to withstand
the removal of water by the leaves as well
as would more mature fruit with a higher
carbohydrate content.

Oil olives. If during October and
November you find that your fruits will
not be large enough for canning, you can
leave them on the tree until mid-December
or as late as mid-February. By this time
the fruit is completely black and has
attained its maximum oil content.
Although it will be shrivelled and perhaps
frozen because of the low winter tempera-
tures, this does not impair its value for
oil extraction. During the canning-harvest
season you can pick the trees over for the
larger fruits and let the small ones remain
for use later in oil extraction, especially
with Mission and Manzanillo. In Califor-
nia the returns from oil olives are lower in

[49]

most years than can be obtained for can-
ning fruit.

Oil olives may be harvested by hand-
picking or by spreading canvas sheets
under the tree and beating the limbs with
poles to cause the fruit to drop. This
practice is not desirable from the stand-
point of the tree as it tends to break off
fruiting twigs and causes openings in the

bark which allow the entrance of olive-
knot bacteria. Beating poles may also
cause the spread of olive knot through
the orchard. Mechanical devices, such as
tree shakers, have been tried in California
to facilitate the harvesting of oil olives,
but none has been entirely successful. In
some countries small rakes are used to
strip the fruit from the branches.

6. Pests and Diseases . • • how to identify

them ... some recommended controls.

This section on Insect Pests was prepared by E. M. Stafford, Associate Entomologist in the
Experiment Station, except for the paragraph on Nematodes, which was prepared by Dr. M. W.
Allen, Assistant Professor of Entomology.

Insect pests

The three principal pests which olive
growers may have to control are olive
scale, oleander or ivy scale, and black
scale. In some parts of California, grow-
ers use the term "olive scale" to designate
oleander or black scale. The term "olive
scale" can properly be applied only to the
olive parlatoria scale, generally distrib-
uted only in the San Joaquin Valley from
Kern County north through Stanislaus.
Oleander and black scales are commonly
found in all olive-growing regions of
California.

Olive scale {Parlatoria oleae [Col-
vee]). Often a grower finds olive scale
for the first time during harvest. Then the
sharply outlined dark purple spots caused
by the scale appear in marked contrast
with the yellow-green background of the
ripening fruit. (See color photo, page
30.)

What to look for. The adult female
scale has a small gray covering some-
what less than % 6 inch long. The cover
is circular or oval with a small black
spot near the edge.

The male scale has a narrow elongate
cover, with a smaller black spot at one
end. Beneath the coverings the bodies of
male and female scales are reddish purple.
Both male and female may live on any
part of the tree above ground. On leaves
they may cause a slight chlorosis, and on

small twigs the wood is often a little de-
formed and darkened.

When the infestation is heavy, the
scales settle on the fruit as soon as it is
formed in the spring. Often this results in
a badly deformed olive at harvest. In
early June the scales make their charac-
teristic dark purple spots on the small
fruit. These tend to fade out as the fruit

Olive fruits at harvest severely damaged by
olive (parlatoria) scale.

[50]

grows rapidly. A grower cannot survey
his orchard for the presence or absence
of olive scale by looking for purple-spot-
ted fruit in mid-season. By mid-August
the young, very small (and very difficult
to see) scales may be on the fruit without
causing any change in color.

What to do. Natural enemies have
given no effective control of olive scale
in California. It has been necessary to use
chemical control measures wherever sup-
pression of this insect was desired. Recent
introductions into California of new para-
sites and predators of the olive scale may,
in time, change this present situation of
total dependence on chemical control.

Best spray control is obtained from
treating eggs and young scale of the first
brood (late May to July 1) . Use 1 pound
of 25 per cent parathion wettable powder
plus 1% gallons of light-grade summer
oil emulsion per 100 gallons of water.
Because of the hazard to honeybees, pa-
rathion spray is not permitted until after
bloom. Thorough spray coverage is
necessary. General experience has shown
that better control has resulted from the
use of a greater number of gallons of
spray per tree. This has been true when
spraying with hand operated guns, oscil-
lating nozzle boom sprayers, or blower-
sprayers. If oil emulsion is not used, the
amount of parathion must be increased
to 2!/2 pounds of 25 per cent parathion
wettable powder per 100 gallons of water.

If spraying is not completed by July 1
the remainder of the application should
be delayed until the period — July 15 to
August 1. At this later time another brood
of eggs and young will be present. During
the first part of July the scales are adults
and are more difficult to kill.

Growers may not wish to disturb irri-
gation schedules or furrows to prepare
the orchard for a spray rig. Mechanical
difficulties such as closely set trees with
interlaced branches may make spraying
operations impractical. In such cases —
but only if the scale infestation is light —
two applications of 2 per cent parathion

WARNING— For safely handling pa-
rathion follow instructions printed on
the package. Orchards sprayed with pa-
rathion must be posted. The County Agri-
cultural Commissioner will supply infor-
mation on laws governing pest control
operations.

dust may be applied by ground rig, fixed-
wing airplane, or helicopter. Use 100
pounds of dust per acre per application
at an interval of from 10 to 15 days, and
dust during the period immediately after
bloom to June 15, or during the period
July 15 to August 1. Dusts applied during
the first period give somewhat better
control. In general, dusting with parath-
ion does not give as effective control
as full-coverage parathion sprays. This
is especially true of outside tree rows.

A much less effective spray than pa-
rathion, but much less hazardous to ap-
ply, is two gallons of medium summer oil
emulsion per 100 gallons of water.

To avoid possible injury to trees, do
not spray with either parathion-oil or
oil alone when the temperature is over
90 °F. Oil spray injury (especially when
an excessive dose of oil is used) appears
on the fruit as small dark spots or raised
corky tissues, where oil has penetrated
the pores of the fruit. Usually, the pores
of fruit sprayed with oil in July or August
are a little darker and more noticeable
than those of unsprayed fruit. This condi-
tion of the pores cannot be seen on dark
ripe olives. It is most easily seen on olives
pickled by the "green-ripe" process, but
it is not noticeable enough to affect the
quality of the canned olives.

Tent fumigation using HCN (hydrogen
cyanide) gas has generally been effective
but costly. Certain varieties — especially

DO NOT SPRAY OR DUST OLIVE FRUIT
WITH PARATHION AFTER AUGUST 1.
This is a regulation of the State Depart-
ment of Agriculture, Bureau of Chemistry.

[51]

the Mission olive — are susceptible to
HCN injury. Trees may be fumigated
from about mid-July through the autumn
and winter up to March 1.

Oleander scale (Aspidiotus hederae
[ Vallot] ) . In sharp contrast to symptoms
of the olive scale, that part of the olive
beneath and near an oleander scale is de-
layed in maturing. This results in green
spots on dark, ripe fruit. (See actual color
photo, page 31.)

What to look for. The whitish cover-
ing of the adult female oleander scale
may be slightly larger than Y^q inch in
diameter. It is circular, with a yellow or
light brown spot near the center. Male
scales are somewhat elongate. The female
scale body beneath the shell is yellow,
but that of the male is a brownish yellow.
These scales often appear in greatest num-
bers on the leaves of the lower inside part
of the tree. Oleander scales have the
ability to deform the fruit greatly. Very
heavy infestations may reduce the oil
content as much as 25 per cent.

What to do. Natural enemies of the
oleander scale may keep this insect at a
low level for many years. In some regions
and in certain years chemical control
becomes necessary.

Spray oleander scale with Yz to 1
pound of 25 per cent parathion wettable
powder plus 1% gallons of light-grade
summer oil emulsion per 100 gallons of
water. Sprays may be applied after bloom
through June and July up to August 1.
Thorough spray coverage is necessary.

The use of parathion without oil or oil
without parathion, tent fumigation, and
spraying at temperatures above 90° F.
are discussed under olive scale. This dis-
cussion also applies to control of oleander
scale.

Black scale (Saissetia oleae [Bern.]).
Trees infested with black scale often have
black sooty-appearing leaves which are
very sticky. Pickers do not like to harvest
the black, sticky fruit. Black scale may
greatly reduce the vigor and productivity
of olive trees.

What to look for. Black-scale adult
females are from % 2 to about % 6 inch
long. They are dark brown or black with
a very tough outer skin. The ridges on
their backs form a characteristic "H"
shape. Dead scales may remain attached
to the twigs for 2 or 3 years. The young,
found on the leaves, are yellow to orange
in color. These scales secrete a sticky
liquid, or honeydew, which supports the
growth of a black fungus. Often the feed-
ing of the scale so weakens the trees that
many leaves drop and the next season's
crop is reduced. Before reaching the adult
stage, most of the scales move to the twigs
to complete their growth.

What to do. Prolonged hot weather
may kill a large per cent of the very young
scale making chemical control unneces-
sary. In the northern part of the interior
valley of California the black scale is often
held in check by natural enemies. This is

Black scale on olives, in various stages of de-
velopment. Younger scales on leaves with "rub-
ber" and adult stages on twig. (Photograph by
E. M. Stafford.)

[52]

especially true where sprays for other
olive insects and diseases are not neces-
sary or are not regularly applied. In this
area chemical control of low infestations
of black scale may not be advisable. Con-
trol chemicals kill both the black scale
and its insect parasites and predators.
Once started, the grower may thereafter
have to depend on chemical control. On
the other hand, it has generally not been
necessary to spray olives more than two
consecutive years for control of black
scale anywhere in the interior valley.

Spray with light-medium grade sum-
mer oil at the rate of 1% to 2 gallons per
100 gallons of water. In the interior valley
this spray should be applied in late July
or early August to control the young scale
after all the eggs have hatched. In certain
regions in the valley — particularly the
northern part — hatching becomes ex-
tended through the summer and fall.
When this occurs oil sprays should be
applied from about August 10 to August
20. Do not spray when the temperature is
higher than 90° F.

A spray of 1% pounds of 50 per cent
DDT wettable powder plus 2 gallons of
kerosene per 100 gallons of water may be
used to kill young stages. As the scales
reach the large gray stages — or "rubber"
stage — preceding maturity, they become
very difficult to kill with either petroleum
oil or DDT. DDT sprays must not be used
on the fruit because of their penetration
into the oil of the olive. Thus DDT sprays
may be used in controlling black scale
only after the harvest of pickling varieties.
The earlier the olives mature and are
picked, the greater are the chances that
the grower may spray before the scales
reach the rubber stage.

The development of black scale varies
widely from year to year and from or-
chard to orchard, even within a county.
For best timing of either oil or DDT-
kerosene sprays, inspect each orchard to
see that (1) the eggs have nearly all
hatched and (2) the scales are not too
far developed for control. Do not time

sprays for black scale by calendar date
alone.

Tent fumigation using HCN gives very
effective control of black scale on olives.
Be very careful in fumigating olive vari-
eties susceptible to HCN injury.

Greedy scale (Aspidiotus camelliae
Sign.). This scale insect may easily be
mistaken for oleander or olive scale. The
shell covering is more conical in shape,
however, with a small black spot to one
side of the center. The body beneath the
shell is yellow. Use the same control meas-
ures as for olive scale.

Red scale (Aoinidiella aurandi
[Mask.]). This very important citrus
pest is often found on olives in southern
California. The female adult has a thin,
circular shell about % 6 inch in diameter.
The body color is reddish and shows
through the scale shell. Use the same con-
trol measures as for olive scale.

Thrips. Occasionally thrips and dam-
age attributed to thrips have been
reported on olives in California. In the
Mediterranean region a species of thrips
(not found in California) causes de-
formed leaves. Its feeding on the young
olives causes dimples, accompanied by
scarring typical of thrips. Damage by
thrips has never been serious enough in
this state to warrant a study of control
measures.

Grasshoppers. These insects cause
severe damage to olive fruit, but the
amount of fruit attacked does not usually
warrant control. Where necessary, spray
the ground cover with aldrin. Be very
careful that aldrin sprays are not applied
to the foliage or fruit on the trees. The
federal food and drug administration has
no tolerance for aldrin on olive fruit.

If strong-flying green grasshoppers are
in the trees, spray them with TEPP (tetra-
ethylpyrophosphate) .

Branch and twig borer (Polycaon
confertus Lee.) . This beetle bores a small,
round hole at the base of a bud or in the
fork of a small branch. As a result, the
twigs may break at these holes. The

[53]

beetles do not breed in live olive wood.
They normally breed in dead wood,
chiefly the madrone, oak, and old grape
canes. The elimination of such dead wood
is probably all that is necessary to prevent
severe attacks of this beetle.

Olive bark beetle {Leperisinus cali-
fornicus Swaine). Growers may notice
small dead twigs on olive trees near piles
of olive prunings. Often this is due to
the work of the olive bark beetle, which
bores holes in small twigs in much the
same manner as the branch and twig
borer. The olive-bark beetle is about %
inch long and black with a whitish pat-
tern on the back. It breeds on unhealthy
trees or olive prunings. In areas where
this insect is a pest, cut olive wood should
be burned, fumigated with HCN, or
sprayed with benzene hexachloride.

American plum borer {Euzophera
semifuneralis [Wlkr.]). The moths are
pale gray with reddish brown and black
markings. Full-grown larvae are about 1
inch in length. The larvae of the moth
attack soft, spongy tissue such as that of
tree wounds, grafts, and olive-knot tis-
sue. From such tissue the larvae may con-
tinue feeding into healthy tissue and thus

American plum borer common in Corning
area. Above— adult moth; below— larval stage
which causes the injury (photo by R. M. Hoff-
man).

Root-lesion nematode (Pratylenchus vulnus)
causes longitudinal cracking on olive roots at
right. At left are uninjured roots.

girdle fairly large limbs. No effective
easy control measure is known, since it
is difficult to keep rapidly growing tissue
protected by either insecticides, grafting
wax, or other coverings.

Nematodes. The root-lesion nem-
atode, Pratylenchus vulnus Allen and Jen-
sen, is known to attack the roots of olive
trees in several areas in California. In-
fested trees may be characterized by
symptoms of poor growth and dieback of
small branches. Young trees planted in
infested soil frequently fail to make satis-
factory growth and are dwarfed or
stunted. The larger roots of infested trees
have symptoms of longitudinal cracking
of the root cortex. The area underneath
these cracks is darkened and necrotic in
appearance. The necrotic lesions are typi-
cal of the attack of the root-lesion nema-
tode.

The nematodes are normally present in
the root tissue immediately adjacent to
the margins of the necrotic area. In addi-
tion to causing the formation of necrotic
lesions on the larger roots, the nematodes
attack and frequently kill small feeder
roots. This results in a considerable re-
duction in the number of feeder roots on
infested trees.

[54]

The citrus nematode, Tylenchulus
semipenetrans Cobb, has been found
attacking the roots of olive in a few local-
ities in California. In these instances the
olive trees have been adjacent to, or
planted on, land previously occupied by
citrus. Information is not available con-
cerning the effect of citrus nematode in-
festations on olives. However, infested
trees sometimes lack vigor, and their root
systems are characterized by considerable
disintegration of small feeder roots.

Poof -knot nematodes, Meloidogyne
spp., sometimes attack olive roots, caus-
ing the formation of galls or knots on the
roots. When roots are heavily infested
they cannot carry on their normal func-
tions. Infested trees may have reduced
vigor and show symptoms of decline.

There are no known methods of con-
trolling nematode infestations on the
roots of established trees. Preplanting
soil-fumigation treatment of infested soil
may be of some value, but has not been
tried with olives. The use of nematode-
free planting stock constitutes the best
available method for limiting the spread
of root-infesting nematodes.

Nonparasitic diseases

Shotberries. This trouble is most
prevalent with the Sevillano and Man-
zanillo varieties and takes the form of
undersized, round-shaped fruits. It occurs
more frequently in some years than
others. The fruits develop to varying sizes,
and while some of the larger ones have
been used in pickling they are generally
too small to be of much value. There is no
seed within the pits of such fruits, and it
is possible that this is a delayed form of
pistil abortion, the pistil having developed
sufficiently to give some stimulation to
fruit growth before aborting. Many of
these "shotberries" drop early in the sea-
son, but some adhere until maturity. No
method is known at present for causing
such fruits to develop to normal size.

Soft-nose. The Sevillano variety is
also susceptible to this trouble, which has

been shown to be nonparasitic. This de-
fect does not appear until late in the sea-
son, during or at the end of the harvesting
period. The fruit starts to color at the
apex end, and this is followed by a shriv-
elling and softening. This trouble, more
prevalent in years of heavy crops, varies
in intensity from one orchard to another.

It has been observed by many growers
that this condition may be correlated with
heavy nitrogen fertilization practices,
especially when nitrogen is applied as
manure. Attempts to produce this condi-
tion experimentally with very heavy ap-
plications of inorganic nitrogen fertilizers
were unsuccessful. Tests were established
in 1950, a light crop year, in cooperation
with the Agricultural Extension Service
with the Sevillano variety at Corning.
Heavy applications of poultry manure
(500 lbs. per tree) and amounts of ammo-
ium nitrate equivalent in nitrogen were
compared. Analysis of the manure showed
it to contain toxic amounts of both sodium
and chloride (% per cent sodium and 2
per cent chloride). Applications of so-
dium chloride in amounts equivalent to
that in the manure caused typical "soft-
nose" fruit symptoms to develop. How-
ever, this condition failed to appear in
1950 in the trees treated with manure or
ammonium nitrate. In 1951, a heavy crop
year, "soft-nose" appeared in the entire
orchard, but was especially noticeable in
trees having had heavy applications of
nitrogen in 1950 both as manure and am-
monium nitrate.

Split-pit. This trouble is also found
largely with the Sevillano variety and is
a serious problem in some years. The pits
split gradually along the suture during
fruit growth, resulting in a bluntly flat-
tened type of fruit, which can be easily
distinguished by its external appearance.
Although the fruit is of normal size and
seems to process satisfactorily, it makes
a poor product because the pit comes
apart when the fruit is eaten. The cause of
this trouble is not clear, probably being
due to some particular group of environ-

[55]

9 • •

Common fruit defects found in olives. Upper left: "soft-nose." Upper right: "split-pit." Lower
left: "shotberries." Lower right: Spray injury due to summer oil applied in excessive amounts or
during hot weather.

mental conditions occurring at a certain
stage in the growth of the fruit. Some
growers believe it appears when the or-
chard soil is allowed to become dry in
the early stages of fruit growth and then
the trees are heavily irrigated.

Parasitic diseases

Three diseases of commercial impor-
tance at present affect olives in California.

Two are fungous diseases, Cycloconium
oleaginum Cast., commonly called "Pea-
cock Spot," and Verticillium alboatrum
R. and B. The other is a bacterial disease,
Bacterium savastanoi E.F.S., known gen-
erally in California as "Olive Knot."
These diseases are found in the chief
olive-producing areas of the state, but
orchards can be found that are free of all
of them.

[56]

Peacock spot. This disease, well
known in the Mediterranean countries,
has been observed in California for over
50 years. It is commonly found on the
Mission variety, occasionally on Man-
zanillo, and to a lesser extent on Sevillano,
Barouni, Ascolano, and Nevadillo.

Outbreaks seem to be associated with
years of above-average rainfall. Infection
is most prevalent on leaves in the lower
parts of the tree and in the interior parts
of the orchard, where exposure to sunlight
and air movement is at a minimum. The
disease was of little commercial impor-
tance before 1940 in California, but in
outbreaks since 1941 the productiveness
of some trees has been reduced by as much
as 20 per cent due to partial defoliation.

Infection and development of the
disease in healthy leaves occurs during
the rainy season (November through
May), with symptoms appearing from 2
weeks to 3 months after infection. Moder-
ate temperatures and abundant moisture
in the form of rain or fogs are favorable
to this organism. In central California the
activity of this disease organism is low
throughout the hot, dry summer months.
During this period it exists in diseased
leaves on the tree.

What to look for. Typical leaf symp-
toms are shown in the color photo on page
32. Usually found on the leaf blade, they
may also occur on the leaf petiole, fruit,
and fruit stem. Lesions almost always
develop on the upper surface of the leaf,
first appearing as inconspicuous, sooty
blotches and later developing into dark
green to black circular spots from % to
% inch in diameter. A faint yellow area
is sometimes found in the leaf tissues
around the spot. As the lesions expand,
the rest of the leaf becomes yellow and
finally it drops from the tree.

What to do. The successful preven-
tion of infection by protective fungicides
depends largely upon timely applications
of the spray. Orchards seriously affected
should be sprayed as soon as possible
after fruit is harvested for pickling. The

most satisfactory fungicides to use are
either a 3 per cent lime-sulfur or a 10-10-
100 Bordeaux mixture. The latter material
will have a more lasting protective effect
and is preferred if the spray cannot be
applied until November.

Verticillium. This fungous disease,
which has appeared in recent years in
California olive orchards, has been ob-
served since about 1900 in peach, apricot,
and almond orchards, where it is com-
monly known as "black-heart." It is due
to a soil-borne fungus that infects the trees
through the root system. It is very likely
to be found in soil that is or has recently
been planted to such crops as potatoes,
tomatoes, cotton, or some other truck
crops. Mature trees seldom die from this
disease, but nursery stock or trees up to 3
or 4 years of age may be killed.

What to look for. The disease may
occasionally attack the entire tree, but it
is usually confined sharply to one side or
even to only one branch. Usual symptoms
are the sudden collapse of one or a few
branches, which may be followed within a
few weeks by the successive collapse of
other branches. Very small trees often
wilt and die all at once. Usually the symp-
toms appear in May or June but some-
times do not occur until midsummer. The
most striking evidence of verticillium in
olives is the persistence of the dead leaves
and flowers, which usually remain on the
tree throughout the summer. In olives the
typical internal symptoms are not present.
There is no brown discoloration of the
wood such as is characteristic of verti-
cillium on other plants.

What to do. Avoid planting young
olive trees in soil that has recently been
planted to such susceptible crops as toma-
toes, potatoes, or cotton; avoid also in-
terplanting such crops in young olive
orchards. Since infection takes place un-
derground in the root system, it is impos-
sible to control the disease with fungicide
sprays. Branches killed by this disease
should be pruned away carefully and
burned.

[57]

Olive knot. This disease is wide-
spread throughout the Mediterranean
countries. It was first observed in Cali-
fornia in 1893. A severe outbreak oc-
curred in Butte County about 1920 and in
Tehama County in 1930 and 1932. Since
then it has become widespread in olive
orchards throughout the Sacramento and
San Joaquin valleys.

Mission is the most resistant variety
to this disease, followed by Ascolano,
with the Manzanillo, Sevillano, and Neva-
dillo very susceptible. In Tulare County
Manzanillo is much more susceptible to
this disease than Sevillano.

The olive knot bacteria are abundant
in knots with live tissue and are exuded
to the surface of the knots and spread
downward on the branches by rains. New
infections occur largely during the long
rainy periods of midwinter, but the knots
do not appear until spring. Wounds of
some sort are appearently necessary for
infection. These may be freezing cracks,
pruning wounds, scars from dropped
leaves or flower clusters, and injuries
from ladders or from cultivation and har-
vesting implements.

The spread of the disease about the tree
is due to dissemination of the bacteria
over the surface of the branches, and not
to internal translocation of bacteria

Bacterium savastanoi (Olive Knot) injury on
olive twigs.

through the conducting tissues. The in-
fection may be spread to adjacent trees
by wind-borne rain. Spread of the disease
over longer distances is believed to be
due to infected pruning tools or to
diseased nursery stock.

What to look for. The presence of
this disease is very conspicuous, existing
in rough, roundish galls or swellings,
sometimes 2 inches or more in diameter,
on twigs, branches, trunks, roots, or even
on leaf petioles and fruit stalks. Galls are
likely to develop on the fruiting shoots in
the spring following winters in which low
temperature causes defoliation and other
injury to the twigs. The disease may kill
much of the fruit-bearing area.

What to do. There is no adequate
control at present for this disease in Cali-
fornia. Two approaches are possible, how-
ever: (1) removal of all knots from the
tree in order to reduce sources of infec-
tion; and (2) application of preventive
sprays to reduce new infections. For badly
infected trees the removal of all knots
would be impractical as it would involve
eliminating all the branches. Where only
a few knots have appeared in an orchard,
their removal is desirable to prevent fur-
ther spread of the disease.

After the knots are cut out, paint the
exposed surface with a disinfectant such
as a mixture of 1 part Elgetol to 4 parts
alcohol, or a mixture of 1 part Bordeaux
paste to 2 parts asphalt emulsion graft-
ing wax. Experiments have shown that
several applications of an 8-8-100 Bor-
deaux mixture during the winter months
reduces the number of new infections.
The first application should be made in
the fall before the rainy season begins.
This method may be too costly to use on
a commercial scale as a regular practice.

Since one of the chief methods of
spreading this disease is by pruning dur-
ing the rainy winter months when active
bacteria are present, all pruning in an
infected orchard should be done during
the dry summer months, when there is
little likelihood of spreading the disease.

[58]

REFERENCES

Anagnostopoulos, P. TH.

1951. The XIII International Congress of Olericulture 1(5). Greece.
Bioletti, F. T.

1922. Pruning young olive trees. California Agr. Exp. Sta. Bui. 348:87-110. (Out of print.)
Brooks, R. M.

1948. The relative incidence of perfect and staminate olive flowers. Amer. Soc. Hort. Sci. Proc.
52:213-18.

Drobish, H. E.

1930. Olive thinning and other means of increasing sizes of olives. California Agr. Exp. Sta.
Bui. 490:1-20.
Everett, H. P.

1942. Progress report on olive die-back. California Agr. Ext. Service Leaflet (Butte County).
(Mimeo.)

Hansen, C. J.

1945. Boron content of olive leaves. Amer. Soc. Hort. Sci. Proc. 46:78-80.
Hartmann, H. T., and R. M. Hoffman.

1950. Tests on girdling olive trees. California Agriculture, February.
Hartmann, H. T.

1951. Time of floral differentiation of the olive in California. Bot. Gaz. 112:323-27.
Hendrickson, A. H., and F. J. Veihmeyer.

1949. Irrigation experiments with olives. California Agr. Exp. Sta. Bui. 715:1-7.
Jacob, H. E.

1934. The effect of pruning in the training of young olive trees. California Agr. Exp. Sta. Bui.
568:1-26.
Johnston, J. C, and E. C. Moore.

1941. Olive orchard fertilization. Progress Report. Tulare County Farm Bureau Olive Committee.
King, J. R.

1938. Morphological development of the fruit of the olive. Hilgardia 11 :437-58.
Lelong, B. M.

1890. The Mission olive. California State Bd. Hort. Ann. Rpt. 185-89.
Merrill, Grant.

1941. Olive fertilization tests in Tehama County. 20th Technical Conference California Olive
Assn. Proc.
Opitz, Karl, and A. Shultis.

1949. Tulare County olive harvesting survey, 1948. California Agr. Ext. Ser. Leaflet. (Mimeo.)
Scott, C. E., H. Earl Thomas, and Harold E. Thomas.

1943. Boron deficiency in the olive. Phytopath. 33 :933^11.
Stinson, T. E., Jr.

1951. New trees from old. Pop. Mechanics Magazine 95:81-85.
Tufts, W. P.

1939. Pruning deciduous fruit trees. California Agr. Ext. Cir. 112:1-62. (Out of print.)

ACKNOWLEDGMENTS

Appreciation is expressed to Mr. Henry Everett, Mr. Robert Hoffman, and Mr. Karl
Opitz of the California Agricultural Extension Service for their assistance in obtain-
ing much of the information included in this publication. Thanks is also given to the
many growers and packers who have kindly co-operated in carrying out many experi-
mental plots, as well as to the California Olive Association for assistance in obtain-
ing data concerning the industry.

Various research workers in the other olive-producing countries of the world have
been most generous in supplying information concerning olive-production in their
countries. Grateful appreciation is also expressed for their co-operation.

[59]

In order that the information in our publications may be more intelligible, it is sometimes necessary
to use trade names of products and equipment rather than complicated descriptive or chemical
identifications. In so doing, it is unavoidable in some cases that similar products which are on the
market under other trade names may not be cited. No endorsement of named products is intended
nor is criticism implied of similar products which are not mentioned.

Cooperative Extension work in Agriculture and Home Economics, College <y; Agriculture, University of California, and United States Department of Agriculture
co operating. Distributed in furtherance of the Acts of Congress of May 8, and June 30, 1914. J Earl Coke, Director, California Agricultural Extension Service.

5m-4,'53(A2291)AA

THIS MANUAL..

contains information of interest to anyone who is cur-
rently operating an olive orchard, or who is considering
going into the business of producing olives in California.
The material in the manual covers practically every phase
of olive production, from the economic factors involved,
to the diseases and pests that threaten the trees and fruit.

Selling price $.7284

State sales tax 0216

Total price /. $.75