UNIVERSITY OF CALIFORN . *\ «? #^ ; ^$i iiuaioN t s ^ 1IF0RNIA " l.-Ti v '>* » Hudson T. Hartmai * f • KarlW.Opitz CALIFORNIA AGRICULTURAL mt Station Extension Service bbESMSz CIRCULAR 540 THIS CIRCULAR is intended for commercial growers interested in present or future olive production. All important aspects of such production are discussed, and references for more detailed information are given. This publication replaces former Manual 7 tz l-UMOOL i?-u^T\ JoLCNN $. f'iie: Distribution of olive acreage in California. Each dot represents 100 acres. Tulare County leads with 11,730 acres, followed by Tehama County with 4,938 acres and Butte County with 4,775 acres. (From California Crop and Livestock Reporting Service, 1964.) OCTOBER, 1966 THE AUTHORS: H. T. Hartmann Professor of Pomology and Pomologist in the Experiment Station. Davis; K. W. Opitz is Extension Subtropical Horticulturist, Agricultural Extension Service, Kearney Horticultural Field Station, Reedley. OLIVE PRODUCTION IN CALIFORNIA SECTION 1 ... the economic background ... a short history of olive production . . . importance of the crop . . . major varieties 3 SECTION 2 . . . getting started . . . choosing a site . . . preparing the land . . . planting and caring for young trees 12 SECTION 3 . . . botany . . . propagation . . . training . . . pruning. . . 17 SECTION 4 . . . setting a satisfactory crop . . . effects of controllable and noncontrollable influences on fruit set 33 SECTION 5 . . . production of the crop . . . cultural practices that will contribute to satisfactory long-term yields 39 SECTION 6 . . . pests and diseases . . . how to identify them. ... 50 (Glossary of Terms starts on page 60.) THE ECONOMIC BACKGROUND ... A SHORT HISTORY OF OLIVE PRODUCTION . . . IMPORTANCE OF THE CROP . . . MAJOR VARIETIES O uves are among the important tree fruits produced commercially in Califor- nia. About 2500 growers farm 32,270 acres of olives, and the annual crop value for a 5-year period ending in 1964 was about $9,405,600. In bearing acreage, olives ranked ninth in 1964, above plums, apples, and avocados, and just below apri- cots and pears. Commercial olive orchards are located mostly in the Sacramento and San Joaquin Valleys which, because of relatively cold winters and warm, fog-free summers, are more suitable for olive production than are the coastal regions or southern Cali- fornia. Yields are heavier and more regu- lar, and insect control is less difficult than along the coast. Many olive plantings were made along the coast and in southern California in the past, but there are no new commercial plantings in this area. However, the olive will grow in all parts of California except where winter cold may kill the trees. Beginnings of olive production in California Olives are grown commercially between about 30° and 45° north and south lati- tudes. The trees will not survive tempera- tures below about 10°F (-12.2° C), and most varieties are injured at 15°F (-9.4°C). They will grow vegetatively nearer the equator than 30° north or south latitude but are usually unfruitful, probably be- cause of insufficient winter chilling to in- duce flower formation. Olives were originally taken to the Western Hemisphere from the Mediter- ranean area by Spanish explorers who brought cuttings or seeds to South Amer- ica. Olive trees were first planted in Cali- fornia around 1800, when seeds or cut- tings were brought to Mission San Diego from Mexico by the Franciscan padres. The variety resulting from this early plant- ing at San Diego was named "Mission," and today it comprises about 30 per cent [3] Olive trees and production of olives, table olives, and olive oil in the leading olive-producing countries of the world. Country Total trees (1,000 trees)* Average trees per acre* Average total production per year (1,000 short tons) 1 960-63J Per cent of world production Average quantity of olives crushed (1,000 short tons) 1 960-63 1 Average Average production production for table use ! of olive oil (1,000 short (1,000 short tons) tons) 1960-63* , 1960-63t Spain Italy Greece Turkey Portugal Tunisia Morocco Syria Algeria France Argentina Jordan Yugoslavia Lebanon Libya U.S. A. (Calif.) Cyprus Chile Mexico Israel Egypt Peru Uruguay Australia Brazil Iran Japan Union of South Africa Iraq Malta Colombia 182 232 168.465 77,300 57,153 49,496 27,540 14,000 11,513 11,258 11,000 10,000 5,767 5,000 4,425 3,463 2,326 2,240 1,745 1,370 1,287 700 318 316 285 253 250 124 120 30 23 6 40 50 160 120 120 2478.7 2468 6 759 5 557 8 668. 0J 407 9 170 9§ 80 2 154 91 8 52 7 48 8 35 .8 48 5 38.95 54 9 30.9J 3 9 15 4§ 10. 7§ 11.0§ 2.2J 1.4 9 4 6 9 8 2 5 2.1 1.0 1.9 1 0.05 0.2 0.1 1 0.03 0.02 2414 2422 6 712 4 486 7 667.8 76.11 120.2; 7.2 39 7 42.4 30.11 6.1** 2.0 9.4 64 8 46.0 47 1 71 1 2 4 2 34 7 9 13 6 4 18.4 1.9 6 1 490 3 496.6 175 6 98 4 97 3 88 5 25 4 17 4 17.4 1.41! 8 9 1 5 8 8 3 8.5 1. 4 * F. A. O. Government Surveys, 1957. t F. A. O. Production Yearbook, 1963-64. t 1960 only. § 1960, 1961, 1962 only. 1 1960, 1961 only. || 1960, 1962, 1963 only. ** 1962, 1963 only. of the acreage of olives in California. Other commercial varieties currently grown here were introduced about 1875 from Spain and Italy, where they still are cultivated as standard pickling varieties. Numerous varieties were introduced be- tween 1850 and 1900 from Mediterranean countries, and much effort was given to testing them, chiefly for oil production. By 1875 the industry showed promise of becoming important in California agricul- ture, with about 11,500 trees in bearing. In 1910 there were about 958,000 such trees, but emphasis then shifted from oil to table varieties, and many orchards were grafted to the more profitable pickling- type olives. Since about 1925 the bearing olive acreage in California has been fairly constant, fluctuating around 26,000 acres. Acreage has been gradually increasing since World War II, however, and in 1964 there were 28,606 bearing acres and 3,663 nonbearing acres. The 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 production of 100 tons or less per year.) Olive produc- tion in the United States averaged 56,600 [4] 70- 60 to 50 z o 8 40 30 20 10 CALIFORNIA OLIVES- ACREAGE AND PRODUCTION 1915 20 25 30 35 40 45 50 55 60 Fig. 1. Bearing and nonbearing acreage and production of California olives. (From California Crop and Livestock Reporting Service.) tons per year from 1960 to 1964 — less than 1 per cent of the total world pro- duction. California supplies only about 6 per cent of the olive oil needed in the United States, and most of the remainder is im- ported from Spain and Italy. No orchards are planted for production of olives for oil only, because California cannot pro- duce it as cheaply as can the Mediterra- nean countries. Thus, olive oil production in California is largely a salvage opera- tion, utilizing small, cull, or frozen fruits. Imports of olive oil into the United States have remained fairly constant, averaging about 6,760,000 gallons annually for the period 1954-63. Spanish-green olives produced in Cali- fornia accounted for only about 11 per cent of those consumed in the U. S. during 1959-1963; the remainder was imported, mostly from Spain. This type of olive was not processed commercially in California until about 1935, and the annual produc- tion has not changed much since 1940, chiefly because of competition from the imported product. A limited market exists in eastern cities for fresh, uncured olives purchased for processing at home. Thus, California's olive industry is based on the production of canned ripe olives (black-ripe and green-ripe). The output of this product has increased from 2,300 tons in 1919 to 37,500 tons in 1964. Yield per acre for olives varies consid- erably throughout the state, depending upon district, age of trees, variety, and cultural care. From 1954 to 1964 the average bearing acreage of all varieties was 28,260, and the average marketable crop was 52,100 tons — an average yield per acre of 1.84 tons; heaviest yields are generally in Tulare County. With good care, California's olive trees start bearing during their third to fifth year, gradually reaching full production by the twelfth to twentieth year. Many groves decline in production after 40 to 50 years, usually because of overcrowding or poor fertilization, soil, and water man- [5 Table 1. Principal California bearing and nonbearing olive acreage (1964). County Bearing acreage Non- bearing acreage Total Sacramento Valley: Butte Glenn 4.686 1.092 315 841 803 4,357 299 711 13.104 234 912 171 327 513 137 359 230 9,572 12,455 568 1,198 47 697 89 169 4 47 581 4 894 43 75 99 353 2 20 13 2.158 4,775 1 261 Placer . . 319 Sacramento Shasta 841 850 Tehama 4 938 Yolo Yuba Total San Joaquin Valley: Calavaras Fresno 299 715 13,998 234 955 Kern Kings 246 426 Madera 866 Merced San Joaquin Stanislaus Tulare 139 379 243 11,730 Total Southern California: Los Angeles Riverside San Bernardino . . San Diego 2,763 4 1 15,218 568 1,202 47 698 Total All others 2,510 537 28.606 5 1 3,663 2,515 538 State total 32 2G9 SOURCE: California Crop and Livestock Reporting Service. agement. Closeness of planting, which af- fects the ultimate size of the tree, is an important factor in such decline (see page 15). Marketing olives California processor-canners (of whom there are about 14) handle the marketing of olives. Their output is chiefly canned ripe olives, but most processors also pack Spanish-green, chopped olives, and other types, and some also manufacture olive oil. A few grower-owned cooperatives market about half of the olives produced. There are several olive oil plants in Cali- fornia, although some do not operate every year. Processing olives and olive oil requires considerable capital and 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. Five varieties are commercially important The Manzanillo variety is grown on about 37 per cent of the bearing acreage in Cali- fornia (10,533 acres in 1964). Next in importance are Mission (9,356 acres), Sevillano (7,095 acres), Ascolano (833 acres), and Barouni (339 acres). In non- bearing acres in 1 964, Manzanillo led with 2,119 acres (about 58 per cent of the total) followed by Sevillano, Ascolano, Mission, and Barouni. In past years the value per ton of olives has increased considerably as fruit size increased. Therefore, varieties producing large fruits (such as the Sevillano and Ascolano) have been favored in new plantings, but the increased production of these varieties has caused a narrowing of the price differential favoring them. Most large processors now favor Manzanillo because it processes with the least diffi- culty, and because its fruit sizes sell more readily and are preferred by most con- sumers. In Tehama County, Sevillano is pre- ferred for new plantings and for top- working other varieties. In Butte County, Mission is chiefly grown. The packers in that area favor this variety but there are small acreages of all the other varieties, with Manzanillo increasing. In Tulare County, Manzanillo is considered the most suitable, with Sevillano and Asco- lano recommended for more limited plant- ings. Mission is not advised for new or- chards in the Tulare district. Each of the five commercial varieties will be discussed briefly below. (For a fuller discussion of varieties in California ask your Farm Advisor about University of California Agricultural Experiment Station Extension Service Bulletin 720, [6] Table 2. California production and imports of olive oil, Spanish-green olives, and canned ripe olives, 1944-1964. 1944 to 1949 1949 to 1954 1954 to 1959 1959 to 1964 Item Thousands of gallons* Olive oil: Average annual California production Average annual U. S. imports Per cent of U. S. consumption supplied by 774 2,375 24.6 1,324 8,777 13.1 5,963 (16,400 tons) None 100 549 7,117 7.2 1,098 12,088 8.3 8,720 (23,980 tons) None 100 461 6,650 6.5 1,796 11,854 13.2 11,200 (30,800 tons) None 100 249 6,919 3.5 Spanish green olives: Average annual California production Average annual U. S. imports 1,709 13,667 Per cent of U S. consumption supplied by 11.1 Canned ripe olives: (black ripe, green ripe) Average annual California production Average annual U. S. imports 12,189 (33,520 tons) None Per cent of U. S. consumption supplied by California 100 * A gallon is approximately equal to 5.5 pounds of olives. SOURCE: California Olive Association, "Statistics relating to the California Olive Industry," 1944-45 to 1963-64, April, 1965. Olive Varieties in California, which is out of print but available in many libraries.) Manzanillo. Trees are relatively low and spreading and fairly easy to harvest. Fruits process easily, are larger than those of Mission and have a much higher flesh- pit ratio. Oil content is high enough to warrant oil extraction of small size, frozen, or cull fruits. Fruit matures early enough in the fall to rarely be injured by frosts, but the trees are much more sus- ceptible to low-temperature winter injury than are those of other major varieties. Manzanillo is not likely to become badly infected with peacock spot disease (see page 57) , but it is very susceptible to olive Table 3. Production, utilization, and average returns to growers for California olives, 1959-60 to 1964-65. Canned ripe Crushed for oil Shipped fresh Other uses* Total production Crop year Tons Average return per ton Tons Average return per ton Tons Average return per ton Tons Average return per ton Tons Average return per ton 1959-60. . . 20,400 $276 2,300 $65 200 $148 3,900 $86 26,800 $229 1960-61... 44,300 203 7,800 54 800 214 12,900 57 47,800 157 1961-62... 26,100 217 7,800 61 700 206 9,200 79 44,000 160 1962-63... 37,700 262 5,700 67 600 166 7,800 95 52,000 214 1963-64... 39,100 245 7,500 50 600 221 9,600 94 57,000 193 1964-65... 37,500 165 6,200 61 700 223 9,400 55 54,000 135 Six-year average. 34,200 $228 6,200 $60 600 $196 8,800 $78 46,900 $181 1945-46 to 1950-51 average. $287 $140 $249 42,166 $227 * Other uses include California Spanish-green, Greek style, Sicilian style, chopped, sliced, and home cured. SOURCE: California Crop and Livestock Reporting Service. [7] mi|iiii|iii!jiiii|!iiiiiiii|iiiiiim name \\ 21 3J 4| . Si 6J ?| _&] . 9jL_ IJO Fig. 2. California's major olive varieties. Left to right. Sevillano, Ascolano, Barouni, Manzanillo, and Mission. knot (much more so than Mission); young trees or new grafts often become heavily infected with this disease, espe- cially when planted in or adjacent to orchards where infection is present. Mission. The fruit is fairly easy to proc- ess and its high oil content provides an alternative, though low-profit, product in years when oil production is necessary. Mission is most resistant to cold of any California commercial variety — some old trees survived temperatures as low as 8°F in the 1932 freeze — but its disadvantages tend to outweigh its advantages: the fruit is relatively small ("mammoth" or larger sizes are rare) and it has the lowest flesh- pit ratio of any commercial variety. Be- cause demand is usually for larger fruits, this must be met with other varieties. The fruit matures for pickling during late Oc- tober or November, when there is danger of freezing injury; if this occurs fruits shrivel and are no longer suitable for pickling, although they can still be used for oil. Mission trees tend to grow tall, and unless kept low by pruning they become difficult to harvest. While resistant to at- tacks of olive knot, Mission is quite sus- ceptible to infections of peacock spot. There appear to be several distinct strains of Mission. Sevi llano. Chief advantage of the Sevil- lano is its large-size fruit, for which a premium is paid. Its flesh-pit ratio is above both Mission and Barouni, but be- low Manzanillo and Ascolano. Oil content is not high enough to justify oil extraction. Fruit is usually harvested before danger of early frosts. Because the trees are not upright growing, fruits are relatively easy to pick. Most packers consider this variety more difficult to process and its quality somewhat lower than Mission or Man- zanillo, although with proper treatment a very satisfactory product can be ob- tained. Trees are susceptible to olive knot, but resistant to peacock spot. This variety is susceptible to three physiological disor- [8] > > ~5 _D 'c 1_ O ~5 u ~B "u 1_ £ £ o u C o D D -o q t3 "D O u Q. ^r ,_ O "55 ro E J^ tao 05 05 5-| |I 05 E 2 05 CJ H- — 2 -ZL — i_ 05 >, 00 — o'5. E-2 .£" a 2% , 05 .a .2 05 CO •0 -O 05 i- c go i O CO CO cz cz 05 05 *j E E '= Q. Q. cz 05 = 05 qj -E 05 O 05 — «" x: .. 05 05 05 — '*- a ffl Qfl V, 05 05 5, ^ .tZ -.9- " w .5- .2- c OT 2 cz •— x ^ c '? ,5 £ 05 E 05 cj 05 E - c/> 05^ CO 05 ™ '0 05 Q5 05 ai CO O. O. >? ro a a. 0. B- °- 05 CO Z3 j»: c ^t: v CZ ^. 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CN, CNJ CNJ 05 aim '£»• LO l~- 00 l~~ S?05 ■2'g ° CO csj CNJ OO CNJ co 1- 05 "• *^T3 ..* 05 >» ^-N »-■♦-> CO O 3 ■«* O Q.~ co cz cz OO OO ■=3 = ° ?8 © ce CO CO coi CO 10 CD O en CNJ LO CNI 00 oo CM C ^ CM a> CO CO 05 B O 2 LO 01 IO en 00 *d- O CNI CO QJ t-^ CN 00 00 CM 05 co _Q5 CO c/j CO en CO co 10 CO 0- LO CO 01 CO 0- co LO 00 00 1—1 05 bO c CO 05 CO LO CO oc CNJ r^ ^t LD CO a> en 00 CNJ r~ CO CN CO r>- CO >s "55 CO > 6 cz 'E cz CZ E a '8 TO IN TO _co CO i a C/j < TO 03 4.0 o < en o CD 0) 3.0 2.0 1.0 Manzanillo Mission Sevillano Ascolano 1950 51 52 53 54 55 56 57 58 59 60 6P ders: "shotberries," "split-pits," and "soft- nose" (page 56). Ascolano. Since these fruits are tender at maturity, extra care must be taken to avoid bruising during harvest and process- ing (this is probably why Ascolano is not more widely planted). Fruit is almost as large as Sevillano and has a high flesh-pit ratio (8.2:1), which, with its good qual- ity, makes this a fine table olive. Although canned ripe olives of this variety are gen- erally considered excellent, the fruits are not suited to Spanish-green pickling be- cause of "salt shrivel" during fermenta- tion. Although its oil content is almost as high as Manzanillo, the fruit is not used for oil extraction. Ascolano fruits gen- erally mature earlier than those of any other commercial variety, usually in late September or early October, so that frost damage is not a problem. Ascolano trees are relatively easy to harvest and are fairly resistant to peacock spot and olive knot. The trees are quite resistant to low-tem- perature winter injury. Barouni. Fruits of this variety are diffi- ... v cult to process commercially and the re- sulting product not as good as some other « varieties. Fruit is of good size, almost as large as Ascolano, but the flesh-pit ratio is relatively low (6.8:1); 200 to 600 tons of the crop are shipped fresh each year to eastern cities for home processing. In the northern part of the state, Barouni con- sistently bears very good crops, but in ^ southern California it is reportedly a shy bearer. This variety, the last to be planted in commercial acreages in the state, was introduced in 1905 from Tunisia by the USDA Division of Plant Exploration and Introduction. It was widely planted** throughout California from 1920 to 1925, * particularly in Butte County, but prac- tically no new plantings are now being made. Fruits mature for pickling during October or early November; trees are somewhat spreading and are easy to har- vest. Barouni is more susceptible to olive <" knot than is Mission, and in the 1932 freeze showed greater tree injury. [10] Fig. 3 (opposite page). Fluctuation in yields -of olives by variety, 1950 to 1962. Yields among varieties cannot be compared, as dif- ferent varieties are grown largely in different areas of the state. (From California Crop and Livestock Reporting Service.) 'Other varieties. A number of varieties, * mostly from variety introductions in the early days of the industry, are found in scattered locations throughout California. Trees of strictly oil olives, such as the Nevadillo, Redding Picholine, Rubra, Pendulina, and Chemlali, have generally A been top-worked to large-fruited table varieties. Pickling varieties still found oc- casionally include Cucco, Lucques, Mac- rocarpa, Obliza, Polymorpha, Rouget, St. Agostino, and Santa Catarina. New introductions. Since 1900 the USD A Division of Plant Introduction 1 and Exploration has imported some 50 olive varieties from all parts of the world, and since 1946 the Department of Pomol- ogy of the University of California has imported about 50 varieties principally from the Mediterranean region. They are all growing and being observed, along y with selections from controlled crosses at the University's Wolfskill Experimental Orchards at Winters. c ■13 D 0) O i- 0) o _Q 0) 2?® l_«~ 2 o Jjj e= oo r-. oo oo oo .-* ii s »t h m in CO >- Q. O M CM CM CM -h « oe- < o c co o o < C -4— cu.2 wC- erag Bgat size cen OI^CO'ttmNlDOOIs omNcnccforooocD 0J SSfe-g- co n co oo ro J-." CD c: i— " i — «a- ■— < **■ CO CM CM M ^ < o c= CO '> CD oo d H— g> 2 coO ++ Q0->-- cd c: ^cDOoaor--CNjr-~-coor--~ 2 e>0~ o cd a> "> [--ocococococooor^ CM CM ■— 1 «T" ^2 -=£> , (O IB ^ ri Cfl CO *-■— <» 5 ■ h- Mn co o co CD l- Q. O • CM CM CM CM CM ^-" < c _o v> c/> m C= -1— Sn'~ *" ^ TO 15 Sj S OOOOOO.— " ^' CD ?Sfe¥ . W N ^- o. o ■ CM CM CM CM CM <— • < o c co rvi tz S C -1— a) >.2 oo O ++ ClC-h CD c re «! n o OOOLOTOOCOOOCT)-— i i£ a?w " C5OOCM00r-^CMC0*3-r~-- ^-1 CM •-! — « rt rf oo o ^h O oo /\ /^ in cm <» oioootncoOrHrt — ^t i/i cd rv co >-i 1 1 l- 1 1 1 1 | 1 LD OO O) -3 3 ro"- a. OCOCOCOlOCO-— r- oo ao — i co < oo ■a 3 TO o ■o CO 00 CO oo ■o _o _c CO T3 o • " m o J5 P <= CO uper- oloss, jmbo iant. lamm xtra I arge. lediui tanda ub-st cy- CS (S S: Ll. S: oc cr o> I- > . JZCO o to a;2 " o oo *" co a> = o E Q. >• "go .E E Ll. Q [11] GETTING STARTED . . . CHOOSING A SITE . . PREPARING THE LAND . . . PLANTING AND CARING FOR YOUNG TREES Climate and yield The best yields of Manzanillos are in Tulare, Fresno, Kings, and Madera coun- ties, while good yields of Mission can be obtained in certain areas of Butte County. Sevillano has produced well in parts of Tehama County and is preferred by grow- ers there. There are some olive orchards south of the Tehachapi mountains, but these are rapidly being lost to subdivisions and other more profitable uses. Insufficient winter chilling, hot, dry winds during bloom, and mild summer weather along the coast limits production in most of southern California. Because harvesting for pickling of most varieties occurs through October and well into November, it is important to avoid locations where early fall frosts prevail, as frost-damaged fruit is unsuitable for any processing other than oil extraction. Late spring frosts occasionally injure fruiting wood and inflorescences (see Glossary of Terms at back of this pub- lication), thereby reducing crops. Areas subject to poor air drainage, low winter temperatures, and late spring frosts, should be avoided. Water supply Commercial olive production in Califor- nia depends upon irrigation; without it production is light and erratic. Also, fruit size and quality is generally inadequate on unirrigated land. Olives grown for pickling require nearly as much water as citrus or deciduous orchards growing on similar soils. The usual amount applied on most central California olive soils is a total of 2V6 to 3 acre-feet per year applied when needed during the growing season. Because olives have a higher boron tolerance than other tree crops and a rela- tively high requirement for this element, irrigation waters carrying up to 3 ppm (parts per million) of boron may be used with safety. Nitrates over 40 ppm in the irrigation water may cause excessively heavy vegetative growth and irregular production. In general, olives tolerate more salinity than do most other tree crops. Waters too salty for general use may be safely ap- plied to olives provided salts do not accu- mulate in large amounts. Irrigation water high in sodium must be treated with gyp- sum to prevent structural changes in the soil that would interfere with adequate water penetration. Soils Olives grow well in a wide range of soil types. In central California, groves planted on soils rather high in clay, or underlain with hardpan, often yield better crops than those grown on deep fertile soil where vegetative growth may become excessive. Olives tolerate soils where many other tree crops fail, but prolonged wet soils or soils with a pH of 8.5 or more will cause poor tree growth. Thus it is desirable to avoid poorly drained or alkali soils. Olive trees grow well in soils relatively high in cal- cium and in boron. Transportation and marketing facilities Many olive growers sell their fruit to com- mercial packers or to buyers who in turn sell to canners, and many growers belong to cooperative canning organizations which process, pack and sell the olives. Canneries, or receiving stations operated by packers, are mostly located in the prin- cipal olive-producing areas (around Lind- say, Oroville and Corning) but some de- livery points are found in other parts of the state. Raw olives can be trucked at comparatively little cost for long distances and therefore it is not necessary to be close to processing centers — but it is im- portant to be reasonably close to an ade- quate harvest labor supply. [12] wt^\\) .*•■ Fig. 4. Effect of poor drainage on growth of olive trees. Center trees are in a low, poorly drained spot. Trees behind and to the left are in better-drained areas. Establishing the orchard For furrow or flood irrigation, properly graded and leveled land is essential. Land preparation will help determine the kind of irrigation system to install. Hardpan soil requires 36- to 48-inch-deep chiseling before planting; on rocky soils, or soils requiring extensive dirt moving, this should be done before leveling and plant- ing. Grading and leveling. For furrow irri- gation on hardpan soils, 0.2- to 0.6-foot fall per 100 feet of irrigation run is com- monly employed. If soil is of fairly uni- form texture and the furrows properly constructed, the ground can be leveled (without regard to moderate side-fall) to a good even grade for satisfactory water handling. Adobe soil may be more steeply graded, as long as the grade is uniform. Sandy soils are subject to erosion when graded to more than 0.3 foot per 100 feet of fall. If leaching is considerable, irriga- tion runs must be short; for medium- textured soils, 400 feet is about right. Rolling land with variable slopes is difficult to furrow irrigate, but improved sprinkler design has made possible more satisfactory water application without costly land moving, such as is involved in terracing. Application rates are deter- mined by the slope and the soil type. Installing the irrigation system. Careful planning and installation of the irrigation system, which is normally in and functioning before the first tree is planted, pays off with trouble-free water management. With furrow systems, a return-flow arrangement is often used. This permits more uniform water application, helps avoid over-irrigation, conserves moisture, and works well with the system of non- tillage commonly employed in central California. Tilled (cultivated) groves use the fur- row, the contour check, the check, and the square basin systems of irrigation, although sprinklers are occasionally em- ployed. The best use of sprinklers, how- ever, is in non-tilled (permanent sod or weed-free, chemically treated) orchards. With sod, or on coarse-textured soils, [13] Sample costs per acre to establish a Manzanillo olive orchard in Tulare Cou California— 1964. nty, Item Yield (tons). Pre-harvest cash, labor and field power: Land preparation Layout and plant Trees: 40 at $1.25 Irrigate Water at $6 per ac. ft Weed control Fertilize: Vi and 3 A man and tractor hrs.... Fertilizer: N at 12^/lb Pest control application— contract Pest control material Misc. labor: sucker, stake, rodents, etc Misc. material County taxes Office, car, operating capital, etc Repairs: irrig. system, equip, except tractor. Total pre-harvest cash and labor cost. Harvesting cost: Picking at $85 per ton... Hauling at $4.50 per ton. Total harvesting — 1st year 10.00 11 00 50.00 12.50 3.00 12.00 1.35 30 3.75 2.50 9.00 5.90 2.50 $123 80 2nd year 2 $15 00 4.50 12.00 1.35 1.20 3.75 1.50 9.00 3.50 3.00 $54 80 $17 00 .90 $17.90 3rd year 4 $15 00 6.00 12.00 1.35 2.40 3 75 1 50 9 00 4.50 3.50 $59 00 $34 00 1.80 $35 80 4th year $15 00 9.00 12.00 2.03 3.60 4.50 2.60 6 25 1.50 9.00 7.00 4.50 $76 98 $68.00 3.60 $71 60 5th year 12 $15 00 12.00 12.00 2.03 4.80 6.00 3.50 7.50 1.50 19.00 9.80 5.00 $98 .13 $102.00 5.40 $107.40 Total cash and labor cost. $123. $72.70 $ 94 80 $148.58 $205.53 Depreciation costs: Irrigation system ($200 cost) Buildings and equipment, except tractor ($100 cost). Tractor Total depreciation cost. $ 12.00 7.50 4.95 $ 24.45 $ 12.00 7.50 2.75 $22.25 $ 12.00 7.50 2.75 $ 22.25 $ 12.00 7 50 2.90 $ 22.40 $ 12.00 7.50 2.90 $ 22.40 Total cash and depreciation cost. $148 25 $ 94.95 $117.05 $170.98 $227.93 Interest on investment at 6%: Irrig. facilities at Vi cost ($100) Ruldings and equipment, except tractor on '/2 cost ($50). Tractor Land at $800 Interest on accumulated costs $ 6.00 3.00 2.25 48.00 Total interest on investment. $ 59 25 $ 6.00 3.00 1.25 48.00 12.45 $ 70.70 $ 6.00 3.00 1.25 48.00 19.99 $ 78.24 $ 6.00 3.00 1.30 48.00 26.90 $85.20 $ 6.00 3.00 1.30 48.00 32.68 $ 90.98 Total cost for year. $207 50 $165 65 $195 29 $256.18 $318 91 Credit for fruit at $200 per ton. $ 40.00 $ 80.001 $160.00 $240 00 Net cost for year. $207 50 $125.65 $115.29 $ 96.18 $ 78.91 Total accumulated cost $207.50 $333.15 $448 44 $544.62 $623 53 SOURCE: Karl W. Opitz and Burt B. Burlmgame. Mimeo. sheet, May, 1964. [ 14 Fig. 5. Left: orchard in permanent sod, using high-volume sprinkler heads. Right: non-tilled orchard under chemical weed control with low volume, movable, drag hose lines. large volume sprinklers can be used; on non-tilled, fine-textured soils, low-volume sprinklers are required. Orchards planted on steep or uneven terrain are best sprinkled with movable drag hose lines. Except in very porous soil, permanent over-the-tree sprinklers are generally un- suitable because their fixed pattern of pre- cipitation leads to under- or over-irrigated spots in the grove. If it is necessary to establish the orchard before the irrigation system is installed, trees may be basin-irrigated for a year or two, although the cost of hauling water is often more expensive than conventional furrows. When a drag hose system is em- ployed, "spits" or "spitters" (small, fixed sprinkler heads) rather than rotating sprinklers are used the first year or two. Laying out the orchard. Most Cali- fornia olive orchards are planted on the square. Many recently planted groves are double set with the intention of cutting back and eventually removing the interset or "filler" trees. (If filler trees are not re- moved, production will drop considerably after tree crowding commences). Stand- ard permanent planting distances vary from 30x30 up to 40x40 feet. Man- zanillo trees on shallow, infertile soil are planted closest together — Sevillanos, Mis- sions and Ascolanos fartherest apart. Some of the earlier-planted groves were set with 20 x 20 foot spacing, but this is much too close: yields from closely planted trees quickly decline, due to shad- ing out of bearing surfaces and to root competition. Planting the trees. Nursery trees are available in gallon containers or as field- grown, bare-root stock. With the latter, leaves are usually stripped off and the tree cut back to a single trunk without branches. If the bare-root tree is large, the primary scaffold limbs may be selected and cut back to stubs. Strongly cut-back trees suffer less shock, become more quickly adjusted to root loss, and start vigorous growth quicker in the spring than do trees not cut back heavily. Exposed roots require careful handling; they should be covered and kept moist at all times. It is best to set out bare-root trees in December, January or February when [15] Sample costs for producing Manzanillo olives in Tulare County, 1964. Based on a yield of 4 tons per acre. Man-labor at $1 .30 and $1 .50 per hour. Light wheel-tractor: cash cost $1.20 per hour; depreciation 55 cents; interest 25 cents. Sample costs Per acre Per ton Pre-harvest cash costs: Pruning: 40 trees at $1.30 $ 52.00 Brush disposal : contract 3.50 Fertilize: 1-man and tractor hr 2.70 Fertilizer: 40 lbs. N at 12^ 4.80 Irrigate: 7 times, 12 man hrs 15.60 Water: power to pump 3 acre-ft. at 6^ 18.00 Cultivate and furrow: 7-man and tractor hrs 18.90 Spray: \V% times, contract 2000 gal. at l!/ 2 *f 30.00 Spray material: Parathion + oil + Vi Bordeaux 18.00 Miscellaneous labor: 4 man and 1 tractor hrs 6.60 Miscellaneous material 4.00 County taxes 25.00 Office, car, operating capital, etc 27.40 Repairs, irrigation system, equipment (except tractor) 5.00 Total pre-harvest cash and labor cost $212.60 $ 53.15 Harvesting cost: Picking at $85 per ton $340.00 $ 85.00 Hauling at $4.50 per ton 18.00 4.50 Miscellaneous harvest 2 man and 1 tractor hrs 4 . 00 1 . 00 Total harvesting costs $362 00 $ 90.50 Total cash and labor $574.60 $143.65 Depreciation costs: Trees ($624 cost— 50 years) 12.48 Irrigation facilities: ($200 cost) 12.00 Tractor: 10 hrs. at 55^ 5. 50 Buildings and equipment ($100 cost) 7 . 50 Total depreciation cost $37.48 $ 9.37 Total cash and depreciation cost $612.08 $153.02 Interest on investment at 6%: Trees: on Vi original cost ($312) $ 18.72 Irrigation facilities: on Vi cost ($100) 6.00 Tractor: 10 hrs. at 25^ 2.50 Buildings and equipment on Vi cost ($50) 3.00 Land at $800 48. 00 Total interest on investment $ 78.22 $ 19.56 Total cost of production $690.30 $172.58 Cost per ton at varying yields. Yields, tons per acre 2 3 4 5 5 7 Cash and depreciation costs $216.54 $174 19 $153 02 $140 32 $131 85 $125 80 Total cost per ton $255 65 $200.27 $172 58 $155 96 $144 88 $136.97 SOURCE: Karl W. Opitz and Burt B. Burlingame, Mimeo sheet, May, 1964. [16] soil can be worked, but in heavy, wet, clay soils it may be necessary to delay bare- root planting until early March. Trees can be kept heeled-in, in trenches, until the soil works well. Container-grown trees may be planted anytime. Planting holes need only be large enough to accommodate the roots in a natural position — extra long roots can be pruned, and broken ones cut off. Trees should be set at the same depth they grew in the nursery. For a good start it is im- portant to firm the soil around roots as the hole is filled in, and to thoroughly soak soil around the newly planted tree. Never allow the newly planted tree to suffer from lack of moisture. A mulch of sawdust, straw, or sand helps prevent surface dry- ing and reduces necessity for frequent irrigation the first year after planting. Good weed control also helps the tree make a quick start by eliminating compe- tition for water and nutrients. Newly planted trees are protected with a coating of whitewash on the trunk or with impervious white paper wraps. News- paper or printers' mats also serve to pro- tect the trunk from sunburn. (See p. 27 for whitewash formulations.) Care of young trees. Good weed con- trol, fertilization as necessary, and ample irrigation provides conditions favorable for rapid growth and early bearing. Young trees are sometimes attacked by insects not normally considered olive pests, such as the false chinch bug and the soldier bug; these must be controlled, or growth suffers. The more serious insect pests on olives do not usually appear until the trees are of bearing age. (See p. 28 for methods of training young trees.) Intercropping the young orchard. If intercrops are grown, they must not be allowed to compete with the olives. Most vegetable crops, particularly tomatoes, potatoes, melons and strawberries are sub- ject to Verticillium wilt; cotton is also a host for Verticillium. Obviously these Verticillium-susceptible plants are un- satisfactory as intercrops. Soil previously planted to such crops should not be used for olives unless Verticillium-resistant rootstocks are employed. Of annual crops, corn, milo and other grains make the best use of the unused areas between tree rows. Citrus, or plums and peaches, or decidu- ous trees other than pomegranates conflict with olive cultural requirements and are not satisfactory as companion crops. Pomegranates tolerate conditions under which olives are grown, except that they are sensitive to the soil sterilants, Karmex® and simazine, which are used for weed control in non-tilled olive orchards. BOTANY, PROPAGATION, TRAINING, AND PRUNING Botany of the olive The olive is a broad-leaved evergreen tree capable of living more than a thousand years. The wood is resistant to decay, and if the top dies a new trunk will often arise from the roots. Trees are quite shallow- rooted even on deep soils. The thick, leathery leaves 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 europaea L. of the genus Olea. About 20 species of this genus are found in tropical and sub- tropical areas, but other than Olea euro- paea 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 (priv- et), Forsythia (Golden Bell), Jasminium (the jasmines), and Forestiera (Forestiera neomexicana — the California "wild olive"). Flowers of Olea europaea L. are borne on a paniculate inflorescence (see Glos- sary of Terms) arising in the axils of the oppositely arranged leaves; they are usu- ally produced on branches formed the previous season, but may arise from dor- mant buds 1 or 2 years old. Flowers are small and yellowish-white, with a [17] ^Jl% Fig. 6. 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: inflores- cences (flower clusters) shortly before and during bloom. [18] 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. Flowers are of two types: (1) perfect, containing both stamens and pistil; and (2) staminate, containing only stamens, the pistils being abortive and nonfunc- tioning. The relative proportion of perfect and staminate flowers varies with varieties and with the particular year. No purely pistillate flowers occur. In the perfect flower the pistil is large, almost filling the entire space within the floral tube; it is light green in the bud, and 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 plumose as it is with functioning pistils. The reason for the abortion of the pistil in staminate flowers is not clearly under- stood, but it is probably associated with water or nutritive deficiencies during the developmental period. Bud removal in early spring causes a decrease in the per- centage of pistil abortion in the remaining buds. Leaf removal up to within a month before full bloom causes pistil abortion; after this, defoliation no longer exerts an influence, the flower type apparently already being determined. 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 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 mesoearp, and the stone or pit, the endo- carp. The seed is within the endocarp. 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; blooming is generally 1 or 2 weeks earlier in the southern than in the northern sections. Grafting affinities and rootstocks Varieties of Olea europaea apparently can be intergrafted without difficulty, and can be successfully grafted on seedlings of other varieties. In grafting varieties of Olea europaea on seedlings of certain other Olea species — Olea ferruginea, Olea verrucosa, and Olea chrysophylla — the re- sults have not generally been good: trees may show considerable overgrowth at the graft union, produce excessive numbers of shotberry fruits, or may develop large numbers of yellow leaves; in many cases, the trees finally die. One combination among those tested — Sevillano on Olea chrysophylla — seems to produce normal, healthy trees, with adequate crops of fruit. However, Mission and Manzanillo varie- ties on this same rootstock produce trees with obvious incompatibility symptoms. Of five trees each of Mission, Manzan- illo, and Sevillano propagated on seedlings of Forestiera neo-mexicana, only one tree was still alive after 10 years. This tree was quite dwarfed, with about half the fruit produced being of the shotberry type. Attempts to graft varieties of Olea europaea on the ash (Fraxinus) and on the lilac (Syringa) produced plants which lived for several years, but with little new annual growth. The plants finally died. Studies at Winters, California, using three scion varieties and twelve different rootstocks over a 1 6-year period ending in 1965, gave results as follows: • The principal rootstock effect on the scion variety was in tree vigor. Rootstock influence noted in a given scion-rootstock combination did not necessarily hold true for a different scion variety on the same rootstock. • In two scion varieties, Mission and Manzanillo, own-rooted trees were more vigorous and yielded more fruit than did trees grafted on any of the rootstocks tested. In the Sevillano variety, however, this was not the case. Trees on certain [19] 4 i % Fig. 7 (above). Dwarfing effect due to a seedling rootstock. Left: own-rooted Mission tree. Right: Mission grafted on an Ascolano seedling rootstock. Both trees are 9 years old; measuring stick is 10 feet long. Fig. 8 (below). Left: Sevillano on Olea verrucosa rootstock. This type of overgrowth is usually found when O. verrucosa or O. ferruginea is used as rootstock. Points of swelling mark position of inserted scion buds. Right: Mission on Ascolano seedling rootstock. Scion portion of the tree was markedly dwarfed but the rootstock was making a strong growth, as evidenced by enlarged portion below graft union. \ [20] rootstocks were more vigorous than own- rooted trees. • Considerable variation in individual tree vigor was noted with different seed- ling rootstocks. Various degrees of dwarf- ing or invigoration of the scion variety oc- curred. Obtaining suckers from such root- stocks, and making cuttings from them, provides clonal rootstocks for a given va- riety which would allow some vegetative growth control. • Generally, no observable rootstock effect on fruit characteristics appeared, although trees on Olea ferruginea and O. verrucosa produced fruit with a reduced length-width ratio and with an increased percentage of fruit developing as shot- berries. Many instances of unexplainable tree behavior observed in California olive or- chards could be due to rootstock effects resulting from the variable influence of seedling stocks. For uniform, strong- growing, and high-yielding trees of the Mission and Manzanillo varieties, own- rooted trees started from cuttings would seem to be the most suitable. Ascolano on its own roots, started from cuttings, de- velops into strong-growing, productive trees. Where reduced tree growth is ac- ceptable for Sevillano, own-rooted trees 1 would be satisfactory; Sevillano cuttings root with difficulty. To obtain vigorous- growing uniform Sevillano trees, cuttings of a strong-growing variety such as the Mission could be suitable for the root- stock. When seedlings are used as a root- stock for any variety, variable tree per- formance can be expected. Propagation Olives do not produce the true variety from seed, hence they must be propagated by budding or grafting the desired va- riety onto a rootstock (seedlings, suckers, or cuttings) or by some other vegetative method such as cuttings or suckers. A full discussion of propagation will be found in Propagation of Temperate-zone Fruit Plants, Univ. of Calif. Agr. Exp. Sta. Cir. 471 (revised). Nursery stock. The first four methods listed below are the most important for starting olive trees. 1. Making hardwood cuttings of wood several years old; these should be 1 to 3 inches in diameter I Fig. 9. Mission olive nursery stock after 2 years in nursery propagated in two ways: Left: suckers with piece of old root or stem attached. Right: leafy cuttings. 21 2. Making leafy cuttings of 1- or 2-year- old growth. 3. Removing suckers with a root piece attached from the base of old trees and transplanting them to the nursery or or- chard. 4. Grafting or budding seedlings in the nursery. 5. Removing and planting knobby-type growth (ovuli) from the trunk of old trees. 6. Planting truncheons (large pieces of wood) horizontally 3 to 6 inches under soil surface. Propagation by hardwood cut- tings. This requires no special equip- ment but results are not always success- ful. It has the further disadvantage of re- quiring relatively large branches; if nu- merous cuttings are wanted it involves removal of much fruiting wood. (If you can find an orchard being pruned heavily in late winter or early spring, you can use pruning wood from it, if wood is prepared immediately after cutting.) Do not use wood infected with olive knot, or new trees will have this disease. Do not try to start Sevillano trees by this method, as the cuttings are very difficult X I Cm- M % Wl • to root. Root-promoting chemicals, such as indoleacetic acid or indolebutyric acid, increase the rooting percentage and pro- motes more root formation. Directions. Prepare cuttings in late Jan- uary or early February from wood 3 or 4 years old, and from 1 to 2 inches in di- ameter. Cut into 1-foot lengths and re- move all leaves. Use care not to get the polarity of the cuttings reversed — they must be planted right side up. Soak the basal few inches of the cut- tings for 24 hours in a fresh solution of indoleacetic or indolebutyric acid (root- promoting chemicals) at a strength of about 13 ppm (1/20 gram in 1 gallon water, or a level Va teaspoon in 8 gallons of water). Dissolve the chemical in a small amount of alcohol (isopropyl, methyl, or ethyl) before adding to the water. Next, bury cuttings in slightly damp (not wet) sawdust for about 30 days in a building where the temperature will be from 60° to 70° F; during this time root initials develop at the base of the cuttings. After the 30-day moist storage period, plant cuttings in a well-prepared nursery soil, with about one-eighth of the cutting above ground. Frequent irri- gations during summer are essential. Propagation by leafy cuttings. Many cuttings can be prepared by this method without removing an excessive amount of fruiting wood from trees. However, it has the disadvantage of re- quiring glass- or plastic-covered beds or greenhouse mist propagation facilities — and, preferably, provision for maintain- ing bottom heat. To obtain a high percentage of well- rooted cuttings they should be treated with a root-promoting chemical, prefer- ably indolebutyric acid. This type of cut- ting must be handled under greenhouse conditions after having rooted or losses will be heavy. After cuttings are properly hardened-off they can be lined out in the Fig. 10. Hardwood olive cuttings after 1- year's growth in nursery. Mission variety. Left: check (no treatment). Right: cuttings soaked 24 hours in indoleacetic acid at 13 ppm, followed by storing in moist sawdust at 65° F for 30 days before planting. [22] Fig. 1 1. Effect of concentration of indolebutyric acid on rooting of Ascolano olive cuttings after 8 weeks under intermittent mist in a perlite and peat moss rooting medium. Upper, left to right: control, 500 ppm, 2000 ppm. Lower, left to right: 4000 ppm, 7000 ppm, 10,000 ppm. nursery row. Some nurserymen prefer to transplant rooted cuttings into gallon cans and grow them 1 to 2 years until they are large enough to plant in the orchard. Directions. Make the cuttings in June or July from wood of the previous sum- mer's growth, using fairly vigorous shoots growing in full sun in the tree's upper por- tions. Discard the succulent terminal few inches of each shoot. Cuttings should be about 4 or 5 inches long, with the basal cut just below a node. If rooted under mist, retain 4 to 6 leaves at the top of the cutting (in a closed frame two leaves are sufficient). Keep cutting- wood and cuttings damp at all times. Dip the basal ends of the cuttings for 5 seconds in a 50 per cent alcohol solution of indolebutyric acid at about 4,000 ppm. (Add an equal amount of water to 95 per cent alcohol to obtain approximately a 50 per cent alcohol solution. Dissolve a level l A teaspoon of the crystals in 3 J /3 fluid ounces of the 50 per cent alcohol solution. This will be enough to treat several thousand cuttings. Isopropyl, methyl, or ethyl alcohol may be used). Place cuttings in flats containing a rooting medium of perlite and peat moss 1:1, sand and peat moss 1 : 1 or, prefera- bly vermiculite and perlite, 1:1. If inter- mittent mist propagation facilities are [23] available the cuttings should be rooted un- der these conditions. Even difficult-to-root Sevillano cuttings can be started by this method if they are taken in midsummer. If mist-propagation facilities are not avail- able, keep cuttings covered with glass at all times and water them frequently (but not excessively) to maintain high hu- midity. Protect them from the full sun. Provision for bottom heat under the cut- tings, using electric soil cables, is de- sirable but not essential. Cuttings usually root in 8 to 12 weeks, and can then be transferred to pots or gallon cans. Keep them under high hu- midity for a time to allow plants to be- come adjusted to the new environment. Cuttings well rooted by midwinter can be hardened-oiT in the flats in which they were rooted, and then transplanted to the nursery row by mid-March. If they are well irrigated and lightly fertilized with nitrogen through the summer, nursery trees large enough to set out in the or- chard may be obtained by late fall. Fig. 12. Typical Manzanillo olive nursery trees 1 year after being started as leafy cut- tings under mist. Cuttings started on November 28 and transplanted to the nursery on March 23; trees dug the following December 3. Propagation by the use of de- tached suckers. This simple method of starting new trees requires no special equipment — all that is necessary is a source of large trees originally propagated on their own roots, which produce an abundance of suckers from the base. The suckers are sometimes planted directly in the orchard, but it is preferable to grow them for a year in the nursery. One haz- ard here is that the suckers coming from the mother tree may be from the root- stock of a grafted tree, in which case the new trees must later be budded or grafted to the variety desired. Directions. In February or March re- move suckers from the old tree, using an ax or sharpened heavy shovel to take a piece of the old root about 3 inches in diameter 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 1 year in the nursery, trees are usu- ally large enough to set out in the orchard. Propagation by grafting or bud- ding seedlings. It is said that olive trees on seedling roots are longer-lived and less likely to blow over in heavy winds than are trees started from cut- tings. No formal experimental evidence supports this belief, however, and in Cali- fornia excellent orchards have been pro- pagated by both methods. Starting trees from seedlings is generally slower than using cuttings. Directions: germination of seeds. Secure seeds in October from fruits of Mis- sion, or preferably Frantojo or Chemlali variety. The seeds are planted about l /i- inch deep in a seedbed; when seedlings are several inches high they are trans- planted to nursery rows and grown until they are large enough to bud or graft (this usually requires 2 years). To facilitate germination, the pits are cracked, or the tip ends are clipped. Germination can also be hastened by soaking uncracked pits in concentrated sulfuric acid — this causes partial disinte- gration of the pit and allows the seedling to emerge more readily. Pits of the Red- ding Picholine variety are soaked in acid [24] for 24 hours, then washed thoroughly in running water for 2 hours and planted. The acid-soaking period may be different for different varieties. Treated seeds ger- minate in about 6 weeks; untreated seeds require 5 to 6 months. A cold-storage stratification period does not seem neces- sary for germination of olive seeds. EXTREME CAUTION should be taken to avoid contact with skin or eyes when using con- centrated sulfuric acid. Some nurserymen have as sources of seedlings large Chemali, Mission, or Man- zanillo trees, under which volunteer seed- lings can be pulled up each year after rainy periods during the winter, thus sav- ing the trouble of germinating seeds. Such seedlings are usually grown another year in the nursery before grafting or budding. Grafting or budding seedlings. Seed- lings may be grafted in the nursery, using the side graft method shown (fig. 13), in late February or early March. The tops above the graft should be cut back about a month after grafting. In Italy, olive seed- lings are successfully grafted in great quantities using a miniature form of the bark graft. (See circular 471 referred to \ Fig. 13. Propagation of the olive by a side graft method. A: cuts in stock and scion. B: scion inserted into stock, and graft union tied with plastic tape. C: graft after 1 -year's growth. D: section cut through graft union. on page 21, or Cal. Ag. Ext. Service OSA number 65, Grafting Olive Trees. See these also for information on bark grafting. ) The seedlings may be budded in March, after the bark starts "slipping," using the T or shield-bud method. The disadvantage of budding as compared with grafting is the possibility of losing the bud "eye." If the bud eye, or shoot, dies the stock must be rebudded. A graft, however, has sev- eral growing points and loss of a single bud from the scion will not be serious. 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 be- fore budding is helpful in getting the buds to "take." Grafted or budded seedlings are usually grown in the nursery for 1 or 2 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 an olive tree or orchard. This can easily be done by bark grafting. Directions. Top-grafting can be done at any time from early March to late April. Select three to five well-spaced primary scaffold branches, cutting them off near the trunk but leaving a smooth place to graft. Cutting the branches low eliminates considerable water-sprout growth and starts the tree at a desirably low height. With large branches it is necessary to use enough scions (spaced 3 or 4 inches apart around the trunk) to obtain satisfactory healing of the stub. One to three branches should be retained as "nurse" or "safety" branches to be removed during the fol- lowing year or two; other non-grafted branches can be removed at the trunk, at grafting time or a year later. Stubs should be grafted not more than 3 or 4 hours after the limbs are cut back, using the bark-graft method with three or four scions in each stub; if branches are quite large more scions are necessary. Use scion wood of the desired variety, col- lected at the time of grafting from trees with good fruit and bearing characteris- tics. Scions should be Va - to Vi -inch diam- eter, obtained from wood 1 or 2 years old. Remove leaves immediately and keep scion sticks continually moist and cool in [25] • >■ vC, Fig. 14 (above). 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 wtih budding rubber. Ordinary dormant buds may be used, rather than twig-buds. It may be necessary to notch or girdle the seedling just above the inserted bud to force it into growth. ^ Fig. 15 (below). Bark graft for top-working olives. A: side of scion resting against wood of the stock; B: side view of scion. C: opposite side from A. Right: scions in place, held by two flat-headed wire nails (%-inch, 20-gauge) driven through the scion. After grafting, all cut surfaces are thor- oughly covered with grafting wax. Sometimes a longer more slanting cut can be made on the scion, which can then be inserted between the bark and wood of the stub without cutting bark. H • t ABC ■ [26] mm I v i w ! . ■ s ■ Fig. 16. Mature olive tree top-grafted to a different variety by the bark-graft method. Branches whitewashed to prevent sunburn. Nurse branches will be removed after 1 or 2 years. damp burlap or peat moss. Scions ready for insertion should be about 5 inches long, with 2 nodes (4 buds) above the stub. A formal comparison was made be- tween 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. It is important that all exposed cut sur- faces be thoroughly covered with grafting wax immediately after grafting, using hot wax or a commercial asphalt-emulsion grafting preparation. (The latter will wash off if rains occur before it dries.) Grafting wax often cracks after application; if this happens, graft unions should be rewaxed immediately. After waxing, whitewash scions, branches, and trunk of each tree. This facilitates healing of the graft union Fig. 17. After large olive trees have been top-grafted, black polyethylene sheeting or heavy brown wrapping paper can be wrapped and tied around base of trunk to prevent sucker growth. by reducing temperature, and prevents death of exposed wood from sunburning. Commercial, prepared, whitewash com- pounds, such as Tre-Co-White or Tree- Trunk- White are available. A good, ready- to-use whitewash spray formula consists of 10 pounds of zinc sulfate, 50 pounds of lime, and 1 pound of casein or Z-l spreader per 100 gallons of water. A longer-lasting formulation, which requires several days advance preparation, is quicklime (CaO), 5 pounds; salt, Vi pound; wettable sulfur, Va pound. Add salt and sulfur while lime is slacking. Age whitewash mixture for several days before using, and dilute to a consistency easy to apply with a brush. If grafts grow vigorously and become 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. Vigorous sucker and water-sprout growth usually follows top-working. These [27] •• mmmmmM. shoots should be removed from around the scions but can be left on the trunk for a time during the summer to nourish the tree and to protect the bark from the sun. Head them back, however, to prevent ex- cessive growth. Withhold nitrogenous fer- tilizers from newly grafted trees for 2 or 3 years, but continue irrigation, although the water requirements are considerably less because of the reduced leaf area. During the year or two after grafting, remove the nurse branches and prune the grafts lightly and judiciously to select the limbs that are to be retained permanently. Cut back the other grafts gradually to per- mit the stub to heal over. When the graft- ing wound heals, the excess grafts are re- moved. The grafted branches usually bear fruit the third season after grafting. Moving large trees In mature orchards where the trees have been planted too closely together (e.g., 20'x20'), considerable benefits in in- creased yields may be obtained by re- moval of about half the trees — as alternate trees in each row. In such cases, the trees can be pulled out, moved to a new loca- tion, and replanted, and can be in bearing again by 3 or 4 years. For such an oper- ation to be a success the primary scaffold branches should be pruned back heavily to reduce leaf area; the digging and mov- ing should be done during winter months, preferably during cloudy weather. After replanting, the trees must be thoroughly watered and irrigations continued through the summer. Training and pruning olive trees 1 Young olive trees are pruned to: • develop a good structure without an unnecessary delay in production • provide a mechanically strong trunk and scaffold framework for sustain- ing heavy crops and resisting strong Fig. 18. Transplanting mature olive trees. Above: trees shortly after being moved to a new location. Below: trees cut back and ready to be replanted. (Photographs courtesy B. E. Glick & Sons, Corning, California.) 1 See: University of Calif. Ag. Expt. Sta. Cir. 537, Pruning Olive Trees in California. [28] Fig. 19. Left: well-trained, 3-year-old Mission olive tree pruned to a single trunk, with three well-spaced primary scaffold branches. Right: the same tree 2 years later. A strong trunk and a low-headed scaffold system not likely to break as the tree grows older has been developed. winds without limb breakage through- out the tree's lifetime. Bearing olive trees are pruned to: • help obtain satisfactory yields of good quality fruit for many years • facilitate harvesting and spraying op- erations for insect and disease control • prevent deterioration of the trees and reduction in yields as they grow older. Young trees. Olive nursery stock in gal- lon cans, or balled and burlapped, can be planted with no pruning other than re- moval of suckers or badly placed branches. Bare-rooted trees should be cut back to 24-30 inches from the ground. During the first growing season, three laterals, well distributed around a single trunk and spaced within 12 to 24 inches from the ground, are retained and the re- maining branches, especially suckers from the base, kept removed. By going over the young orchard several times during the summer much can be done at little ex- pense to create a desirable framework and eliminate unwanted branches before they make much growth. During the second, third, and fourth growing seasons, pruning should consist of removal of suckers and watersprouts from the base of the tree, as well as broken branches or those crossing over in unwanted positions. Pruning should be kept at a minimum, although an attempt should be made to develop a satisfactory system of scaffold branches — excessive cutting increases the age at which young olive trees come into bearing. During the first few years, little or no wood should be removed from the upper portion of the tree. After trees come into bearing (from 3 to 5 years of age) an- other phase of pruning is required to de- velop a secondary scaffold system. This consists of about three permanent branches arising from each of the three primary scaffolds spaced around the tree so as to form a strong supporting frame- work for the fruiting top and side branches. It is best to develop this sec- ondary scaffold system, and to thin out unwanted branches over a period of sev- eral years. Heavy thinning out of branches in any one year causes trees to become so strongly vegetative that they stop bearing until fruiting wood again develops. Bearing trees. Olive fruits are usually borne laterally along shoots of the previ- ous season's growth, the bearing area be- ing a more or less hemispherical "shell" 2 to 3 feet deep around the tree's periphery. Few fruits are borne inside this shell — that is, closer to the trunk. For maximum 29] Fig. 20. The natural fruit-bearing area of the olive is a shell (shaded area) around the tree's periphery. Highest yields can be expected if this shell is kept as large as possible and close to the ground for easy harvesting. crops, pruning should be designed to pro- mote a continuing supply of new fruiting wood and to keep this bearing region vigo- rous and with a maximum leaf area. This is impossible if the trees are planted too close together, in which case excessive shading reduces the bearing surface to the top, the south half, and perhaps the upper sides of the east and west halves of the tree — and this reduces yields. Cutting out the top in order to let light into the center and north portion of the tree will not solve the problem, as this merely eliminates fruiting wood from one portion in an attempt to produce it in another. Moderate annual pruning is necessary in mature, bearing olive trees for the fol- lowing reasons. ( 1 ) Stimulation of prun- ing helps to maintain growth of new fruit- ing shoots. (2) There is a continuing production of dead or dying unfruitful twigs caused by shading out in the fruit- bearing shell; these twigs should be thinned out to admit more light, facilitate harvesting and spraying, and reduce the chance for insect or disease infestation. (3) After the tree occupies all the space allotted to it (with allowance for good light conditions on all sides) moderate pruning is necessary to hold it to the de- sired size. High harvesting costs require that trees be kept relatively low to facilitate picking. After the tree's fruiting top has reached about 15 to 18 feet, judicious pruning can hold it at that level. During annual prun- ing a special effort is made to remove or cut back upright growing branches in the center of the tree which tend to raise the height of the top fruiting surface. Continuing unchecked growth, espe- cially where trees are planted fairly close together, gradually results in the shading out and death of fruiting wood on the sides and confines the bearing surface to the tops. These factors cause decreased yields. If trees have been planted too close together (20' x 20', for example) pruning does little for obtaining satisfactory yields. Removing some trees to provide ample sunlight will improve production. Severe pruning is sometimes required. Older trees (especially Mission) may grow to such heights that it is impossible to harvest fruit in the tops. In such cases a severe heading back of upright branches is required, followed by an annual cutting back of branches tending to grow out of reach. Neglected orchards having had little or Fig. 21. Well-shaped and well-spaced olive trees capa- ble of bearing heavy, easily harvested crops. [30] no pruning for many years sometimes re- quire a rejuvenation type of pruning. In addition to removing dead wood and broken or crossing branches, upright and laterally growing main scaffold branches are cut back to about half their length 8 to 10 feet from the ground; these cuts should be made just above smaller lateral branches if possible. Excessive scaffold branches should be removed. New growth forced out by this heavy pruning needs to be thinned out during the following few years to space new branches properly. When such heavy cutting is practiced, nitrogen fertilizers should be withheld for a year or two to reduce excessive sucker and water-sprout growth. If much bark area is opened to direct sunlight, white- wash should be applied to avoid sunburn- ing and death of the tissues. When well-spaced scaffold branches have been established and all unnecessary branches eliminated, severe pruning should be avoided, as continued heavy pruning of irrigated olive trees reduces production markedly without a sufficient increase in fruit size to offset reduced yields. Instead, a maximum fruit-bearing shell, reaching almost to the ground around the entire tree, should be encour- aged. When olive knot is present, pruning should be done in summer to guard against spreading the disease. If pruning must be done in winter, tools should be disinfected frequently. A satisfactory solu- tion for this consists of Clorox ( 1 part to 10 parts of water) plus a small amount of household detergent to facilitate wetting the surfaces of the pruning tools when they are dipped. In orchards having a definite alternate bearing pattern some benefits may be ob- tained by doing a portion of the pruning just after fruit set of the "on" year. When it becomes apparent that the tree is going to bear too much fruit, some of the small branches and twigs carrying large num- bers of fruit can be cut off, using care to avoid removing branches bearing only a few fruits. The objective is to remove as much fruit as possible while removing a minimum number of leaves. Brush from pruning should be shredded or hauled out of the orchard. Brush should not be burned in the orchard because this injures the trees. Pruning of frost- damaged olive trees After cold winter weather (15° to 17° F) excessive leaf fall, bark cracking, and oc- casionally death of limbs occurs. Heavily pruned trees are more susceptible to cold damage than are lightly pruned (or un- pruned) trees. The effect of foliage loss from freezing injury is similar to that of severe pruning. New growth from unin- jured buds appears in abundance during late spring. If trees are cut back too soon following a damaging freeze, it is likely that some limbs will be removed that may have recovered and become fruitful the following season. Experience and experimental evidence show that the best treatment for frost- damaged olive trees is to leave them un- pruned until the following June or July, by which time the necessary corrective cuts can be readily determined. At the same time, trees suffering from olive knot may also be pruned with safety (the chief pruning then to be done is cutting out dead and diseased limbs). Young trees are more sensitive to cold than are older trees. If temperatures are likely to drop to 23 °F or below, the trunks may be wrapped with an insulating covering for protection. Fruit growth Olive fruit exhibits a cyclic growth pat- tern, the first stage being one of rapid growth followed by a second stage in Au- gust and September when size increase is slower. The third stage, in autumn, is again one of rapid growth and coincides with the color changes — from green to straw tc red to black. Because the value of olive fruits increases markedly with size, it is best to delay the harvest of can- ning olives to take advantage of this rapid increase in fruit size. But it is unwise to delay harvest to the point where the proc- essing qualities of the fruit are affected, or where damage from early frosts is likely. Recommended harvest maturity standards developed for the industry are given on page 48. [31] JUNE JULY AUG. SEPT. OCT. NOV DEC. JAN. Fig. 22. Fresh weight, moisture, oil, and dry matter other than oil of Mission olives. (Based on an average of 100 fruits.) Fruit size increase in autumn comes mainly from increased moisture content of the fruit, so if the trees lack soil mois- ture during this period the expected in- crease in fruit size cannot occur. If there is high transpiration and low soil moisture the leaves withdraw water from the fruits, causing them to shrivel. Therefore it is important that the trees are amply (but not excessively) supplied with water for several weeks just before harvest. About August 1 accumulation of oil in the fruit begins; this increases gradually through fall and winter and reaches its maximum in late December or January as fruits become completely black. Vegetative growth Vegetative shoot-growth in the olive com- mences about the first of April in Califor- nia and continues until about the middle of October. Growth rate is fairly uniform, with no abrupt flushes of growth as in citrus. Vegetative growth starts when an appreciable number of hours over 70°F are experienced daily, and ceases when there are no hours above this temperature. [32 SETTING A SATISFACTORY CROP . . . EFFECTS OF CONTROLLABLE AND NONCONTROLLABLE INFLUENCES ON FRUIT SET Olive trees often fail to set a satisfactory crop even though they are well cared for and make excellent vegetative growth. Part of the problem is that of alternate- bearing; the trees exhaust their nutrient reserves with a heavy crop and are unable to produce the year following. It is also quite common for some orchards to set little or no fruit each year for several years, although causes for such nonbearing are not clear. The influence of cultural methods on yields is probably secondary to influences of climate in the long run, and thus weather conditions are probably the most fundamental forces affecting yields. An important time in the setting of an olive crop is from about February 1 to July 1. From March 1 to 15 the first microscopic evidence of flower formation in the buds may be observed. Following this is a rapid development of the floral parts, with extension of flower clusters; full bloom occurs about 8 weeks after initiation of the floral parts. Coinciding with this is the beginning of vegetative growth (about April 1). Obviously, a heavy drain on the tree's food reserves occurs during this period, and trees in top condition are therefore more apt to pro- duce good crops. One of the causes for poor fruit set in some orchards in certain years is the lack of enough perfect flowers — orchards have been observed where practically the entire bloom was composed of staminate flowers. These result from an abortion of the pistil, occurring sometime during the develop- ment of the floral parts, which may be caused by a deficiency of water, mineral nutrients, carbohydrates, or by some im- balance of hormones during floral devel- opment (March, April). Other factors that may influence fruitfulness in the olive are discussed below. Temperature Olive trees in California are unfruitful unless they are exposed to a certain amount of cold during the winter period. In experiments at Davis, half of a group of young, bearing Mission 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, but the outdoor trees bloomed and fruited normally. Effect of duration of exposure to natural winter chilling temperatures on inflorescence production of Manzanillo olives. Treatment* Buds forming inflorescences! Lateral buds growing vegetativelyj Per cent Greenhouse control: 2 hours below 45°F 0.0 0.0 Partial chilling: 1240 hours below 45°F... 6.1 1.6 Out-of-doors all winter: 1852 hours below 45°F... 73.4 0.4 * Treated plants were 4-year-old trees in containers. t L.S.D. at 5% level = 19.5; at 1% level = 29.5. t Differences not significant at 5% level. Some olive varieties seem to require more winter-chilling than others for good flower production. At Davis, Ascolano and Sevillano required from 1 700 to 2000 hours below 45 °F during the winter to produce a normal set of inflorescences. Mission, Barouni, and Manzanillo pro- duced a few inflorescences with less chill- ing (about 1300 hours below 45 °F). Azapa and Rubra produced some inflor- escences with only about 600 hours below 45 °F. However, all varieties produced the maximum number of inflorescences with the maximum amount of winter chilling provided. In microscopic examinations of the buds no flower parts were observed until late winter. (Chilling is not essential for vegetative growth to take place) . [33] Along with winter-chilling the presence of leaves on fruiting shoots is necessary for inflorescence formation. This is shown in the following table and it emphasizes the importance of preventing tree defolia- tion. Effect of defoliation at beginning of chilling period on percentages of buds forming inflorescences, and of buds growing vegetatively, on 3-year-old Manzanillo olive trees grown in containers. Treatment Buds forming inflorescences* Buds growing vegetativelyt Per cent Out-of-door trees, com- pletely defoliated Out-of-door trees, half defoliated: Defoliated half 0.0 1.7 83.4 0.0 84.3 65.0 24.0 Foliated half 1.0 Greenhouse trees, intact control 0.0 Out-of-doors trees, intact control 1.0 * L.S.D. at 1% level = 30.0. t L.S.D. at 1% level = 16.7. SOURCES: Hackett, W. P. and H. T. Hartmann, "Morpho- logical development of buds of olive as related to low temper- ature requirement for inflorescence formation." Bot. Gaz. 124: 383-87. 1963. Hackett, W. P. and H T. Hartmann. "Inflorescence forma- tion in the olive as influenced by low temperature, photoperiod and leaf area." Bot. Gaz. 125: 65-72. 1964. Olives in California usually bloom from about May 1 to June 1, depending upon season, variety, and location. Damage to the crop from spring frosts is rare during bloom — average dates for the last killing frost are: Oroville, March 17; Corning, March 8; Orland, March 4; and Lindsay, March 19. (But there have been years when unopened buds were damaged by cold spells in late March or early April.) The occasional occurrence of hot, dry winds during the blooming period has been associated with poor sets of fruit. Winds occurring during June, when there is a period of natural drop of the young fruit, may increase the amount of fruit dropping. In California, fruits still on the tree by July 1 will as a rule continue on to maturity. In a statistical study of yields of Sevil- lano olives in Tehama County in relation to temperatures during certain periods in the winter (1951 through 1960), the fol- lowing conclusions were drawn: Years with January mean tempera- tures approaching the 50°F level are likely to be years of poor olive pro- duction unless the temperatures in the immediate post-January period are cool enough for flower-bud de- velopment. Intermediate yields can be expected in years with only mod- erately low January temperatures and moderate to high temperatures in February and early March. High- est olive yields are most likely when both January and February tempera- tures are cool. In Tehama County, where in most years January temper- atures are cold enough to favor some flower bud initiation in olives, the temperatures of February and early March are also critical in relation to the number of flowers formed and the ultimate yield. Soil moisture The fact that practically the entire olive acreage in California is irrigated is argu- ment for the benefits of this practice. Irri- gation results in increased yields because it helps produce new fruiting wood, in- creases fruit set as well as fruit size, and prevents shrivelled fruits. If normal winter rainfall has been in- sufficient so that trees may be suffering from a lack of moisture during the critical spring period, one or two pre-bloom irri- gations are advisable. Experiments show that insufficient soil moisture during the spring floral development period not only causes abortion of the pistils in the flower, but also causes a reduction in the number of inflorescences and flowers formed. This effect of low soil moisture on fruit set and yields is further borne out by an irrigation experiment conducted in the spring of 1951 in a Sevillano orchard at Corning. In that year, March and April were extremely dry, with only 0.2 inch of rain falling from about the first of March until April 28 (the normal amount of rainfall expected then is about 5 inches). Three adjacent experimental plots were [34] ■'":. f Fig. 23. Typical inflorescences from experimental olive trees grown in containers and exposed to different soil moisture conditions in early spring. A: continuous ample soil moisture during floral development period. B: soil moisture deficiency during a 1-week period at an early stage of flower development. C: moisture deficiency for 1 week during an intermediate stage. D: moisture deficiency for 1 week at a late stage. E: soil moisture deficiency during entire period of floral development. established. No. 1 had one irrigation on April 1; No. 2 had one on April 14; No. 3 had no irrigation until after bloom. All three plots had about 1.9 inches of rain from April 28 to May 7. The unirri- gated plot was thus without water during most of the time the flower buds were forming, from March 1 to April 28. The effect of the three different irrigation treatments on the crop was determined by making counts of the number of fruits per 100 inflorescences, and by obtaining yield records per tree at harvest. Showers occasionally fall during olive- Effect of pre-bloom irrigation on fruit set and yields of olives with low spring rainfall, Sevillano variety, Corning (thirty trees per plot)*. Plot 1 . . Plot 2.. Plot 3.. Date of first irrigation April 1 April 14 After bloom Fruits per 100 inflorescences 2.7 2.3 1.4 Yields per tree (lb.) 101 113 65 * Rainfall was 0.2 inch from March 1 to April 28; normal is 5 inches. blooming, 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 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 no significant differ- ences. The sprinkling seemed to have no adverse effects under the conditions of this test. Mineral nutrients Nitrogen. Nitrogen fertilizers should be applied early enough so that they will be absorbed by the tree by March 1. Appli- cations of commercial fertilizers are usu- ally made in late December or January, and manures applied the previous fall. Nitrogen applications are essential to sus- tained production. This is due, in part, to the necessity of stimulating growth of fruiting wood. There also is evidence that nitrogen applied several months prior to [35 bloom results in increased fruit set, espe- cially in the shallow soils of Butte County. In fact, some growers in that area are cautious about applying too much nitro- gen for fear of causing excessive fruit set and developing an alternate-bearing con- dition. Olive trees in deeper and more fer- tile soils are not so responsive to changes in the nitrogen fertilization practices. Boron. One of the symptoms of boron deficiency in olives in Butte County was unfruitful trees. Some trees appeared to blossom and set fruit normally, but most of the immature fruit dropped during July and August. Such trees would be expected to have a boron content of 14 to 15 ppm in the leaves. However, severely affected trees (having a boron leaf content of 7 to 13 ppm) produced few if any blooms. Potassium. Potassium deficiency in olives causes marked reduction in yields due to resultant lack of new vegetative growth, failure to produce a satisfactory bloom, and reduction in fruit size. Other than the mineral nutrients men- tioned above, there is no evidence of min- eral deficiency in California soils sufficient to result in reduced friut set and yield in olives. Carbohydrates Little can be done to increase the carbo- hydrate level in the tree other than to maintain a heavy, vigorous leaf area. This can be accomplished by irrigation, nitro- gen fertilization, wide spacing of the trees, minimum pruning and control of the fun- gus disease, peacock spot, which infects leaves and causes them to drop. 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. This has sometimes re- sulted in definite increases in the percent- age of perfect flowers, fruit set, and yields. In girdling, a strip of bark about V^-inch wide is removed from most of the pri- mary scaffold branches on the tree (a grape-girdling knife does this very rap- idly), and the girdled area is covered immediately with a grafting compound. This is most effective when performed on young, vigorous trees, but it has several disadvantages and is advisable only as a last resort in getting trees to set a crop. In orchards infected with olive knot it is quite likely that the bacteria will become established in the girdling cuts unless cuts are immediately covered with hot grafting wax, then with a Bordeaux-mixture paste, and finally with an asphalt-emulsion graft- ing compound. Bordeaux paste applied di- rectly to the girdling cut causes consider- able injury to the tissues and is not ad- vised. Alternate bearing The physiological basis for this condition is the fact that flowering and fruiting "ex- hausts" the tree considerably. A heavy r crop removes much of the various carbo- hydrate materials, organic nitrogenous substances, and other essential nutrients from the tree so that adequate stored-food reserves are not available for production of a crop the following year. The best method for preventing alter- * nate bearing is the prevention of exces- sively large crops. Because the olive has an erratic bearing behavior it is difficult to predict excessive fruit set, which can- not be determined until about the first to the middle of June. Therefore the only practical way to prevent an excessively heavy crop is to thin out some of the young fruits after they have set. This must » be done early, preferably in June. Such thinning is done only with heavy crop sets; once a regular bearing pattern is established thinning can be discontinued, perhaps for several years. There is no clear-cut evidence that al- ternate bearing can be overcome by prun- ing, but it is possible that if pruning can be delayed until late June of the "on" year, it may lessen the alternate-bearing tendency. Pruning is not as effective as fruit thinning in overcoming alternate bearing, however, because leaves as well as fruit are removed. This type of pruning /, should be "detailed" rather than simply the removal of large branches. Efforts should be made to cut off shoots heavily laden with fruits, and to ignore shoots bearing only a few fruits: the object is to remove as many fruits as possible while [36] removing only a minimum number of leaves. No fertilizer practice can be relied upon to eliminate alternate bearing in olives, although nitrogen fertilization may increase production without greatly changing the long-term patterns of fluctu- ating yields — patterns which are similar to those of unfertilized orchards. On the other hand, excessive applications of nitrogen in winter or early spring may cause a heavy fruit set and initiate an alternate-bearing pattern. (This is espe- cially true in Butte County.) Fruit thinning Apart from possible alleviation of alter- nate bearing, the benefits of thinning ex- cessive sets of fruit are: (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 breakage, (7) production of more fruiting wood for the next season's crop, and (8) increased yields over the years. The disadvantages of thinning are the cost of the thinning operation and the re- duction in total yield the year thinning is done. Increased fruit size will not offset the reduced number of fruits, therefore the premium paid for larger fruits must be enough to overcome decreased yields. In general, thinning will not pay unless trees are definitely overloaded. With ex- cessive fruit set, however, thinning may be profitable because it increases to can- ning size fruit that otherwise would have to be sold for oil. Spray thinning. Experiments and grower experience since about 1954 have shown that spray thinning of olives with naphthaleneacetic acid (NAA) is a useful tool for regulating the size and quality of the crop. Naphthaleneacetic acid has been registered by the USDA as a fruit thin- ner on olives when used at the rate of 1 50 ppm and applied Vi to 2Vi weeks after full bloom. This approval was given on the basis of no tolerance at time of har- vest. Best results from NAA are obtained if sprays are applied when fruits are about 15 22 30 6 JUNE JULY Fig. 24. Fruit growth of olives during the summer on unsprayed control trees (dotted line) and on trees spray-thinned with NAA (naph- thaleneacetic acid). Final fruit size on thinned trees was about 30 per cent greater than from unthinned trees. Vs-inch to %6-inch in cross diameter, which is generally from about May 27 to June 5. Timing is critical: spraying too early may remove too much fruit; spray- ing too late will not take off enough. A concentration of 150 ppm of NAA, plus enough household detergent to cause good wetting of the leaves, has given the best results. (NAA at 100 ppm plus \Vi per cent light summer oil may also be used). High air temperatures (above 100°F) during and just after spray application have tended to accentuate the thinning effect. Addition of oil has also resulted in increased removal of the fruits. A com- bination of oil additive plus high air tem- peratures may cause excessive thinning, especially if the orchard's soil moisture is low. Fruits of all the commercially grown varieties of olives except Sevillano have been thinned by applications of NAA. The thinning action is greater on heavily loaded trees than on trees bearing a light set of fruit. NAA seems to accentuate the naturally occurring June drop of young olive fruit. The chief effect in spray thin- ning is to remove a portion of the fruit, with remaining fruit reaching a greater size than that attained by fruit on similar unthinned trees. The size increase of the remaining fruit is directly proportional to the amount of fruit removed. There is [37] some evidence that trees showing a sub- stantial thinning effect will, during the next year, produce a heavier crop than will unthinned trees. When olive trees are used as ornamen- tals it is often undesirable to have them fruit at all. Sprays of naphthaleneacetic acid at the same concentration used for fruit thinning (100 to 150 ppm) if applied at full bloom will usually prevent fruit setting. If the bloom is prolonged — over 7 days — two sprays, one toward the be- ginning of bloom and one near the end, may be necessary to prevent fruiting. Tender ornamentals growing under or near sprayed trees should be covered dur- ing spraying to prevent injury to them; drift of the spray onto nearby properties should also be avoided. Hand thinning. Trees should not be thinned unless they are overloaded. Ex- perienced growers know the maximum fruit set their trees can carry while still maintaining satisfactory fruit size at ma- turity: this is approximately three to five fruits per foot of twig, depending on such factors as age and vigor of trees. Thinning should be done as early as possible for maximum benefits; mid-June to July 10 is the preferable time; reduc- tion of alternate bearing is obtained only with such early thinning. Later thinning (late July or August) causes increased fruit size for the remaining fruits, but total reduction in yield is proportionately increased. The following points should be observed : 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 five or six olives can be removed at one pull. Try to leave an average of three to five olives per foot of twig. Unless enough fruits are removed, thinning will not be useful. To check results, leave overloaded un- thinned trees near the thinned ones, at least for the first trials. Pollination The need for cross-pollination in olives has long been debated here and in other olive-producing countries. Experimental work in Italy showed that most varieties examined were self-sterile, a few were self-fertile, and some were partially « self-fertile, and so the planting of pollini- zer varieties was recommended. In Portu- gal, however, hundreds of acres of iso- lated olive orchards of one variety some- times produce excessive crops. In Cali- fornia many large orchards of a single variety have produced satisfactory crops, , although some of the highest and most consistent yields are in orchards where two varieties are interplanted. Investigations with Ascolano, Manzan- illo, and Sevillano olive varieties showed that chances of fertilization and fruit set are much greater after cross-pollination than after self-pollination. Pollen-tube growth usually is faster following cross- pollination than after self-pollination, and more pollen tubes can reach embryo sacs before the sacs degenerate. Despite long-standing contradictory views regarding the benefits of mixed va- rieties in olive orchards, studies at Davis and Winters have shown that cross-pol- lination of varieties does increase fruit set in some years. In parts of California the olive crop is poor in some years, even when conditions seem favorable for pol- lination and fruit set. Temperature is a possible factor in olive fruit set, because individual varieties have particular tem- perature requirements and temperatures affect pollen-tube growth. Generally higher temperatures are more favorable than low. However, in cross-pollinations with Sevillano pollen, cool conditions were better. Higher tem- peratures increase the incompatibility re- actions of Sevillano, and pollen tubes more frequently become blocked some- where between the stigmas and embryo sacs. Of the three varieties tested, Sevillano appeared to be the most self-incompatible and Ascolano the least so. t Growers contemplating planting of new orchards of two varieties may find it prof- itable to interplant them, especially if orchards of other varieties are not nearby. It facilitates harvesting operations to plant varieties in groups of four rows each. [38] Delayed harvest Olive trees excessively loaded with fruits often fail to produce fruit of sufficient size by October to justify harvesting them for canning olives. Consequently fruits are allowed to remain on the trees until January or February and are then har- vested for oil. Such late-harvested trees produce little if any fruit the following year. Trees with a light to moderate crop, however, produce fruits large enough to be harvested in October for canning. These early-harvested trees have usually been observed to return a satisfactory crop the following year. It was thought from this that late harvesting itself was detrimental to the set of a subsequent crop, but experiments in two Mission or- chards in Butte County failed to bear out this conclusion. Adjacent groups of trees in the same orchard, and bearing approxi- mately the same amount of fruit, were harvested early (October), medium (De- cember), and late (February); yields the following year were practically the same in each of the three plots, and similar results were obtained yearly for 4 years. The lack of a subsequent crop with heavily-loaded, late-harvested trees is perhaps due simply to alternate bearing: such 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. PRODUCTION OF THE CROP . . . CULTURAL PRACTICES THAT WILL CONTRIBUTE TO SATISFACTORY LONG-TERM YIELDS Fertilizers Nitrogen. This is the main fertilizer with which olive growers need be concerned. It has been so beneficial in increasing yields that most growers annually apply about Vi to 2 pounds of actual nitrogen per tree. Nitrogen can be applied as animal ma- nures, or as one of the chemical fertilizers listed in table on page 43. Fertilizers should be chosen on the basis of which of them will supply a pound of nitrogen at the lowest cost. When manures are used as a source of nitrogen they should be applied in the fall, as the nitrogen in them is slowly available to the trees. Commer- cial fertilizers are best applied in late De- cember or January, because fruit bud dif- ferentiation, floral development, and fruit setting occur in the olive from March 1 to June 15, and the fertilizers should be applied early enough so that they will be available to the trees during this time. Concentrated organic nitrogen (urea) fertilizers have been applied experimen- tally to olives at the rate of 12 pounds per 100 gallons as foliage sprays during floral development (March 1 to April 15). Leaf analyses showed that the olive ab- sorbs nitrogen in this form through the leaves. In some experiments fruit set has been increased over that of non-fertilized trees, but benefits have not usually been sufficient to justify the increased cost of this method of application. Nitrogen fertilizers have been applied to large olive trees experimentally as high as 30 pounds of ammonium nitrate per tree (10 pounds of actual nitrogen) on clay soils in Tulare County without caus- ing injury. However, it is uneconomical to practice continued heavy applications of nitrogen fertilizers to olives, because ni- trogen in the tree, as determined by leaf analysis, never exceeds about 2 per cent of the dry weight of the leaves — thus in- dicating that there is a maximum amount the tree will absorb (additional nitrogen may be leached out of the soil and wasted). Conversely, the nitrogen level of olive trees apparently seldom or never goes below about 0.9 per cent of the dry weight of the leaves. Average orchards in good condition have a nitrogen content in leaves of about 1.5 to 1.8 per cent. If leaves are dark green and the new shoot growth is 8 to 20 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 [39] growth of at least 8 inches per year, it is likely that trees are deficient in nitrogen and would respond to fertilizer applica- tions. Chemical soil analyses are not a reliable means of judging the fertilizer re- quirements of trees, because they do not allow for the tree's ability to absorb the elements from the soil — nor is it possible to get a soil sample representative of the entire orchard. Leaf analysis is a much better method, although fertilizer require- ments probably can best be judged by the trees' response to test applications. Some growers believe that applications of nitrogen during the summer cause in- creased fruit size, but experimental work with nitrogen fertilization of olives and other fruit crops has not substantiated this. Two 4-year nitrogen fertilization ex- periments were conducted with Manza- nillo olives in Tulare County from 1937 through 1940. One was in an orchard in poor condition with trees 24 x 24 feet apart; the other in an orchard in fair con- dition with trees 30 x 30 feet apart. In addition to the "control" of no nitrogen, two different amounts were added as shown immediately below. Yield of fruit per tree for the 4-year period is also shown in the text table below. The main responses to fertilization in these experiments were increased tree growth, with a large increase in bearing surface, and setting of more fruit. Fruit size was not increased; with some heavy sets, size decreased proportionately as set increased. No particular difference in time of fruit maturity was reported. In orchards having a high level of nitro- gen fertilization, marked responses such as obtained with nitrogen-deficient trees would not be experienced by further in- creases in nitrogen applications. In similar tests in Tehama County with Sevillano olives the following conclusions were drawn: yield and income tended to increase with each year of nitrogen appli- cation; fertilizers induced better bud de- velopment and additional growth, so that the effect of annual applications was cumulative. Sizes (expressed on a percentage basis) were reduced by nitrogen fertilizers, but the greater total yield resulted in greater production of larger sizes. Percentages of culls in fertilized olives were higher than in non-fertilized, and this seemed to be associated with a vigor- ous, rank type of growth. No marked dif- ference in pickling quality or flavor was apparent in olives from trees with or with- out nitrogen fertilization. Experiments with nitrogen fertilizers in Butte County (1952 through 1956) led to the following conclusions: Under the low- fertility conditions of the foothill soils, Mission olives responded markedly to ni- trogen applications by increased fruit set and yields. Reduced fruit size accom- panied increased nitrogen levels because of increased numbers of fruits per tree. Increased levels of nitrogen retarded fruit maturity. Oil content of fruit was not as- sociated with nitrogen level of the tree. Unfertilized trees had significantly smaller leaves than did those receiving nitrogen. In the Corning district, Sevillano trees having more fertile soil conditions and less subject to leaching rainfall showed much less response to added nitrogen; after withholding nitrogen fertilizers for 3 years, leaf analyses showed the nitrogen level to be still within the normal range. No consistent immediate response in fruit set or yields was generally found. Table 7 gives the results obtained from this study. Orchard No fertilizer Orchard I (24' x 24') (poor condition) 18 pounds Orchard II (30' x 30') (fair condition) 161 pounds One pound of Two pounds of nitrogen per nitrogen per tree per year Yield 141 pounds 323 pounds tree per year 186 pounds 367 pounds [40 Table 6. Effect of nitrogen fertilizer applications on yields per tree and leaf nitrogen. Mission olives at Palermo. Pounds of fruit per tree and per cent leaf nitrogen Treatment 1955 1956 1957 lb. per cent lb. per cent lb. per cent Control 1.3 9.3 21.2 19 5 (123) (152) (1.43) (148) 48.8 171.6 196.2 225.7 (123) (1.42) (162) (1.60) 60.8 98.4 106.2 105.4 (1.06) Vt lb. nitrogen per tree in February ] and [ (1.49) Yi lb. nitrogen per tree in June J 1 lb. nitrogen per tree in February (1.53) 3 lb. nitrogen per tree in February (171) Difference required for significance at: 5% level 13.8 18.5 54.5 72.9 30.5 40.9 1% level Response of olive trees to nitrogen fer- tilizers is likely to be rapid and pro- nounced when the nitrogen level in the trees is low (1.2 per cent or less in leaves) . In gravelly, shallow hillside soils low in organic matter and subject to heavy, leaching rains the natural nitrogen con- tent is low and added nitrogen soon dis- appears. Under such conditions, a pro- nounced response of olive trees to nitro- gen fertilizers would be expected. This would be the case year after year, because added fertilizers tend to be lost by leach- ing, and the low level of organic matter in the soil would not be conducive to a natural build-up of soil nitrogen. How- ever, in heavier and deeper clay soils on level ground, nitrogen would tend to be more stable because of higher organic content and less leaching. Even with no added nitrogen the level in the trees tends to remain adequate for some years; hence, lack of immediate response to one nitro- gen application, or to withholding of one application, is not surprising. Maintaining olive trees at an optimum nitrogen level under the soil conditions found in the Tulare and Tehama valley floor olive districts is relatively simple. Soil nitrogen there does not fluctuate ap- preciably, and the only problem is that of occasionally adding nitrogen to maintain trees at an optimum nitrogen level. Even at initially high nitrogen levels, however, trees will gradually lose nitrogen after several years and should receive applica- tions before leaf nitrogen drops below ap- proximately 1.5 per cent. Maintaining proper nitrogen level under conditions such as those in Butte County is more difficult and is likely to be a major problem of the olive grower. Shallow, gravelly soil with low organic matter and fertility, coupled with heavy leaching due to the rolling topography and high rain- fall, causes a rapid loss of soil nitrogen and a need for annual additions of nitro- gen fertilizer. Potassium. The paragraphs on potas- sium and boron deficiencies apply mainly to Butte County; except in isolated in- stances there is no record of deficiency of these elements in the other olive-produc- ing areas in California. In 1947, olive trees in the Wyandotte area of Butte County showed leaf symp- toms later identified as being caused by potassium deficiency. Analysis of these leaves showed them to contain 0.1 per cent potassium on a dry-weight basis. Pre- vious extensive work by Lilleland and Brown in orchards in different parts of California had established the average po- tassium level for olives as ranging from 0.8 to 1.0 percent. In experiments in a potassium-deficient olive orchard in Butte County, single mas- sive applications of potassium sulfate (25 to 50 pounds per tree) increased potas- sium content in leaves the following year, eliminated the development of dead areas in leaves, and caused a leaf color change [41] lO oo to OO c > c- lO *> coi- 1 CD oo *-< r— • CS CNl CO II! -= > Q. 00 0>n2 lO o o C3 ir to CT) to co CNI CT tO CT) CO O to ct> r-» — i co tr CNI •**■ 2 to to to tr O O .c CO IT) io cr> to co cni c: LO ~^ to to to to *-< CNI CO oo o ^-> c- ) o «r 5 to CT) r- r- 1 — r- si s.« *- OiO x: w .5? LO to ^-> ^H «J CT) CO co to == CT) o o O CT O —i co to co r~~. to tc tf to ID CT) to CT) — I c > CT) CO T3 cz to "3- to tr O —< co .^ 3 IT) tO CO to c: OO CNI to OO p-h to tJ ii: CT) to to to tc o -^ to to OO o c CNI CO CNI CNI es/ CN -w ^\ •"■ s| C/> O T3 O. to to co CNI CNI to O CO cnj tr co «=r >- CT) Fruit set (fruits per 100 inflores- cences) to to CT) o -a- co to oo •- tt tc CT) OO to r- OO to CT) oo r-» cni r- CNI oo c >> ■ — CO -Kf *f if co ^ '£. r-H r-l' ,-,' — o o o .^C < to 53 to LO CT) o o CT) tC CNI OO rt to r~. to r~ o ,-■ ^ —. 1-1 O O Q TO CD O cr CO o co '5 Of) E 00 "ro o >. t— CO CZ 3 2 c: ct: CD 3 % CD '5 co CO — , c CX 3 .E — CD CD CD = 1 *- > > O) CD CD CO <= z .E o — — _ z O ' . -O Z C u -Q c£ -Q — £ tfc from light green to normal dark green. The response from this single application continued to be evident for several years. Fertilized trees showed increased shoot growth, fruit size, and yields in compari- son with unfertilized trees. Yields per tree for the unfertilized olives over a 4-year period averaged 36 pounds per year, while trees receiving 50 pounds of potassium sulfate at the beginning of the trial pro- duced 152 pounds of fruit per year. Po- tassium-deficient, unfertilized trees pro- duced 20 per cent canning size fruits (standard grade or larger) in the first year, 19 per cent the second year, and 5 per cent the third year. Trees receiving potassium fertilizer produced 78 per cent canning size fruit the first year, 62 per cent the second year, and 33 per cent the third. Boron. For a number of years olive trees in the Wyandotte area of Butte County exhibited the following symptoms, diag- nosed as being caused by boron defi- ciency: (1) Short, branched growth in For differences in the leaf symp- toms of potassium- and boron-defi- cient trees see page 51. 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; the new terminal buds die and addi- tional branching occurs. (2) Limb die- back in severe cases, sometimes dying back to main trunk. (3) Small leaves with brown, scorched tips, and with an inter- mediate golden-yellow area between dead tips and green basal portion. There are no dead areas along lateral margins, as with potassium-deficient leaves. (4) Thickened and corky bark, sometimes having a rough, blister-like appearance. (5) Mis- sion trees affected have a high percentage of defective fruits, locally termed "mon- key-faced." (6) Reduced yields due to early dropping of fruits before harvest. Experimental injections of copper, man- ganese, boron, and zinc salts directly into limbs of affected trees were made in the spring of 1941, but response was obtained only with boron. Later tests showed that [42] Table 8. Comparison of some common forms of nitrogen-containing fertilizers. Fertilizers Nitrogen Phosphate per cent Potash Approximate amount required to supply 1 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 10.0 3.0 3 2.4 12.0 8.0 2.0 5.0 6 3 6.3 3 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. Figures are averages and useful only for estimates. the same response was obtainable by ap- plying borax to the soil under the trees at 1 pound per tree. There is a correlation between the se- verity of the symptoms and the boron content of the leaves. Trees showing severe deficiency symptoms have a boron con- tent of 7 to 13 ppm; mild symptoms, 14 to 15 ppm; doubtful range, 16 to 18 ppm; normal boron content, 19 ppm and over. 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 Vi to 1 pound per tree. With the exception of a few iso- lated cases, definite response of olives to boron applications has been found to occur only in the Butte County olive dis- trict. Leaf analyses from trees in well- maintained orchards in other commercial areas have shown they are in the normal range for boron, but it is possible for de- ficiencies to develop in the future. There is no evidence that olive trees in California will respond to fertilizers other than nitrogen and (in Butte County only) potassium and boron. Orchards do not re- spond to fertilizers containing these ele- ments if trees already have enough. Irrigation Most of the world's olive trees grow in the Mediterranean basin and receive virtually no irrigation. In California, however, all commercial olive orchards are irrigated. Olives tolerate considerable drought and high temperatures because their leaves are relatively small and leathery and have a protective cuticle on the upper surface that tends to reduce water loss; the hairy undersurface also slows transpiration. Stomata, while numerous on the lower surface, are sunken and have small open- ings. For good crops of canning-sized olives, irrigation comparable to that re- quired by most other tree crops is essential. Experimental work in California shows that olives react to a lack of readily avail- able soil moisture just as other trees do: growth rate of the fruit declines when soil [43] Fig. 25. Boron deficiency symptoms in Mission olives. Upper: defective fruits (commonly termed "monkey-face" fruits). Lower: twig dieback; the death of the terminal growing point with subsequent branching is characteristic of this trouble. [44] moisture is deficient, and insufficient mois- ture during blooming and fruit setting causes crop failure. Insufficient water in the growing season any time after the crop sets may result in shriveled fruit. Growers are particularly concerned with providing ample moisture as harvest approaches in order to gain the maximum fruit size; however, excessive water sometimes re- sults in a soggy, poorly aerated soil which causes root losses, interferes with ade- quate water uptake, and contributes to fruit shrivel. If too much water is applied during the growing season, withholding water until soil moisture approaches the permanent wilting percentage helps re- store normal root activity. After cold, wet winters it is important not to aggravate high-moisture conditions by applying water too early in the spring. Alternate middle irrigation will help to prevent over- wet conditions. Trees suffering from drought do not tolerate winter cold as well as do trees having an adequate mois- ture supply to the roots. There is no optimum nor best soil mois- ture content for fruit-tree growth. Experi- ments with many kinds of tree crops show that water is used with equal ease through- out the entire range of soil moisture — that is, between field capacity and permanent wilting percentage. Water taken by trees from the soil is almost entirely given off through the leaves by transpiration, the rate of which is affected by soil moisture, sunlight, tem- perature, humidity, and wind. Large, healthy trees use more water than small ones, because of greater leaf area. The amount of fruit does not materially affect the amount of water used, as the main water demand is from leaves. Because the olive is an evergreen it uses water through- out the year, although much less in winter than in summer. Total water used by comparable trees will not be greater on a sandy than on a clay soil, if both soils are fertile and have readily available water at all times — al- though on sandy soils water must be ap- plied more frequently and in smaller amounts than on clay soils. On shallow, hardpan soils, trees require more frequent irrigation (in smaller amounts) than they do on deeper soils. Moisture-measuring devices (such as tensiometers and gypsum blocks) are a help in deciding when to irrigate. In or- chards with a cover crop of some deep- rooted, broad-leaved plants such as Malva or Melilotus, the appearance of the plants helps determine the soil moisture condi- tions: when they wilt, the trees need more water. Soil moisture conditions can be de- termined accurately after a little experi- ence by means of a soil auger or tube. To be certain that soil has sufficient moisture, it is best to irrigate before all the trees need water — if some get too much water while the majority of them are being cor- rectly irrigated, cut water away from those over-irrigated. Benefits derived from good irrigation practices are cumulative and may take two or three seasons to appear, but an irrigation procedure that provides ample, though not excessive, soil moisture at all times will help produce and maintain healthy trees. Poor irrigation practices cause low yields, small fruit, poor fruit quality, and stunted trees. To avoid shriv- eled fruit, considerably more water (by means of more frequent irrigations) should be applied during the hot periods normally experienced in July, August and September. Shriveled fruits regain their turgor after irrigation, but may shrivel again during processing and make a poor- quality product. Poor drainage Olives do not grow well where surface or subsurface drainage is poor. Trees in such locations are stunted, with numerous dead twigs, small yellowish-green leaves, poor yields, and prematurely ripe fruit. Eventu- ally, adverse root conditions may cause the trees to die. Olives cannot be success- fully grown with such poor drainage, and the best way to avoid it is to carefully determine the drainage characteristics of the orchard site prior to planting. Soil management Cover crops will help to maintain or im- prove soil structure, increase water pene- tration, and prevent erosion. Good soil structure helps speed the infiltration of [45 water applied to the soil and provides con- ditions favorable to tree-root penetration. Root channels formed by the cover crop provide a means for rapid movement of water into the soil, but cover crops do not provide a substitute for careful soil han- dling. Cultivation when soil is too wet puddles many soils so badly that it takes years of good care to repair the damage — and working too dry a soil may have a similar effect. The use of any kind of heavy equipment on moist soils also re- sults in compaction and lowered infiltra- tion rates. In California's interior valleys, cover cropping does not increase the moisture- holding capacity of soil as it may in cool, humid climates. (In experiments at Davis, moisture-holding capacity of the soil re- mained unchanged after 25 years of cover crops.) Cover crops may have great value on slopes subject to erosion: a plant cover reduces the puddling effect of rain drops beating on the soil, and acts as a sponge to collect and distribute water so that the soil can absorb it more easily. The cover also tends to hold the soil in place and to reduce the amount of washing by the part that does flow away. Although soil nitrogen may be in- creased in cool, humid regions by legumi- nous crops, experiments carried out in California's hot, dry interior valley failed to show any measurable nitrogen increase with summer or winter legumes. Commer- cial fertilizers still must be relied upon to achieve and maintain the desired nitrogen level in the soil of California's olive- growing areas. Some of the benefits of cover crops can be obtained by working organic mate- rial — sawdust, straw, or manures — into the soil. With sandy or medium-textured soil, straw causes a decrease in soil nitrates because bacteria needed for cellulose breakdown utilize available nitrates, which thus become unavailable to the trees. (Clay soils are more apt to be well- supplied with nitrates and putting strawy materials into them is less likely to affect tree growth.) Extra amounts of nitrates applied with organic matter help alleviate nitrogen deficiency. Cover crops utilize nitrogen while grow- ing, particularly after being incorporated into the soil by disking, and extra amounts of nitrogenous fertilizers may then be nec- essary for adequate growth and fruitful- ness of the trees. Cover crops also use much soil moisture. If they grow in sum- mer, additional irrigation water is needed. A few of the annual cover crops used are ( 1 ) the winter legumes — yellow clover (Melilotus indica), the vetch and bur clovers; (2) the summer legumes — cow- peas, soybeans; (3) the winter non-le- gumes — mustard (Brassica nigra), rye, barley and volunteer weeds; and (4) the summer non-legumes — orchard grass, Su- dan grass and annual weeds. Perennial weeds such as Bermudagrass, Johnson grass, nut grass and morning glory rob the trees of needed nutrients and moisture and tend to choke out more desirable cover. They should be elimi- nated — and this requires persistent efforts. Sod culture Many olive growers in the Sacramento Valley utilize permanent sod culture, ad- justing fertilization and irrigation to satisfy the needs of trees and sod. Well- constructed, permanent furrows are estab- lished before planting. If sprinklers are to be used, the orchard is leveled sufficiently to eliminate pockets where water might collect, and then grasses are sown. Grass is kept low by mowing or (occasionally) letting livestock graze it. If animals are used, it is important that water and salt be properly placed to avoid injury to trees when the animals move around. If the animals start to browse the olive trees they should be taken out of the orchard. With sod culture cultivation expense is nil, the root system undisturbed, erosion controlled, and orchard operations may be carried on soon after irrigation or rains. However, sod culture is inadvisable if water or nitrogen is limited. Perennial rye grass or native grasses and weeds make satisfactory sod. Tillage Conventional cultivation practice is to disk-in volunteer weeds before they use much moisture and nutrients. This usually [46] involves disking, floating or harrowing, and furrowing out after every second or third irrigation during the summer; weed cover is allowed to grow in winter. The soil is disked and floated prior to spraying or harvesting if the weed cover interferes with these operations. Because most of the olive tree's roots are in the first 2 or 3 feet of the soil, even in deep soils, deep cultivation or subsoil- ing can destroy much of the root system. Frequent cultivation compacts the soil and reduces movement of water and air into it. Where olive trees grow on shallow or rocky soil, eliminating tillage allows tree roots to completely penetrate the available soil mass. Non-tillage Because of water costs and disadvantages inherent with tillage, many growers in central California eliminate weeds with weed oils, such as Karmex® or simazine. The costs of a weed-spray rig and prepara- tion of soil prior to chemical herbicide applications make the first year's costs higher than with tillage, but after weeds are controlled, costs are generally less — sometimes only half as much as with con- ventional tillage. These herbicides are safe if proper dosages are used and materials carefully applied, but it is essen- tial that weed oil be kept off the fruit. If spray mist gets on the fruit, it will impart an unremovable off-flavor to the canned product. Check with your local Farm Ad- visor or Agricultural Commissioner if you plan to use any herbicide other than those mentioned above. Many herbicides cannot be safely used in or near olive orchards. Harvesting the crop Harvesting olives represents 50 to 70 per cent of the total production labor cost, and 30 to 40 per cent of the gross returns from the crop. In general, the bigger the trees and the smaller the yield, the greater the expense of picking the fruit. Excessive amounts of brushy growth, dead limbs, large weed growth, smut from black scale infestations, and rough ground add to the picking expense. Picked fruit begins to lose moisture immediately. When picked during hot, sunny weather, boxed fruit should be set in the shade while waiting to be hauled away. Unshaded picked fruit sunburns and will be graded as culls. Rough han- dling causes bruises and loss of grade. A few growers harvest their fruit me- chanically, using oscillating tree shakers and catching frames. More developments may be expected in this field. Canning olives Olives are harvested for pickling in Cali- fornia from mid-September to mid- November depending on variety, local conditions, and needs of the canneries. Optimum harvesting time is determined by the color and texture of the olive. In order to get the greatest amount of large fruit, harvesting should be delayed until olives reach maximum size. When the crop is large, it may be necessary to spot- pick — first the ripest fruit, and then the remainder; some growers pick over the grove several times, taking only the large, mature fruit each time. Some overloaded trees may be left until the latest possible time to pick for canning or (in the case of Manzanillos and Missions) to harvest sub- standard fruit for oil. Over-mature or badly bruised fruit fre- quently develop spoilage during process- ing. To get the best returns from harvested fruit, it should be delivered to the cannery as soon as possible. Olives kept too long in boxes or bins after harvesting start "sweating"; this may cause deterioration during processing. Maximum time be- tween picking and brine storage should be not more than 14 hours, therefore long- distance hauling presents an important problem. Some processors do their long- distance hauling at night, while others provide brine storage close to supply cen- ters. Low temperature injury to canning fruit. To avoid freeze damage to fruit, the pickling-olive harvest is usually con- cluded before November 10. Fruit from overloaded trees may not attain maturity [47] HARVESTING AND HANDLING OLIVES FOR CANNING An olive is considered immature if it will not yield a characteristic white juice under moderate pressure between thumb and finger. Manzanillo olives should be picked when an even pale green color with a minimum of whitish spots visible, to and including a straw color. During the first half of the season the olives may show a light red blush covering not more than half of any olive; blush is undesirable during the second half of the season. Mission olives should be picked when an even, pale green color with a mini- mum of whitish spots visible, to and including a dark red color; during late season dark red olives are undesirable. Sevillano olives should generally be picked when straw colored. During the first half of the season the olives may show a slight blush if confined to the shoulder on the stem end; no blush is permissible during the second half of the season. Ascolano olives should be picked when an even, pale green with a minimum of whitish spots to and including a straw color. o o- o The break between early and late season is considered to occur (on the average) : Mission Manzanillo Sevillano Ascolano Sacramento Valley Nov. 5-10 Oct. 20-25 Oct. 20-25 San Joaquin Valley Nov. 5-10 Oct. 16-21 Oct. 22-27 Oct. 15-25 •o o -o Growers should be permitted to start picking when no more than about the following per cent of the first fruit delivered will be immature: Mission and Manzanillo 20 per cent Sevillano and Ascolano 1 5 per cent The grower should be stopped from making further deliveries of any variety when more than 10 per cent of the fruit delivered is overripe. Olives should be of good color, shape and quality, and in good condition for pickling. Olives should be free from • damage by bruises, hail, frost or wind • spray residues • scale or scab (scars) • clusters, leaves, dirt and other foreign substances. After harvest, olives should be placed in the shade and protected against direct sunlight. All canning olives should be delivered to the processor on the day harvested. (Prepared by Industry Harvest Standards Committee sponsored by the California Olive Association.) [48 TO LOWER HARVEST COSTS Prune and space trees to encourage the natural spreading tendency of most olive varieties. Remove dead and interfering branches to facilitate picking and encourage the production of higher-quality fruit. Adopt cultural methods to permit tree skirts to come within a foot or two of the ground. Use weed-control implements designed to avoid contact with tree or fruit. Teach pickers to use both hands, and to pick toward the container. Moving the hands together rather than independently results in more rapid, careful picking. Ascolanos require careful picking lest they bruise. Manzanillos may be "milked" off if the picker learns to avoid stripping the leaves and twigs along with the fruit. Have pickers climb to the highest point for the fruit with each new set of the ladder, and then pick coming down. Greater picker efficiency may be obtained if the grower manages the picking crew himself, or has an experienced foreman do so. by this time. This condition may be avoided by spray-thinning such trees in late May or early June, or by hand-thin- ning them before the last of June. The average date of the first killing frost is November 14 at Lindsay, November 26 at Oroville, and December 3 at Corning. Freezing temperatures of 25° to 28 °F (-3.9° to -2.2°C) for an hour can cause fruit damage consisting 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. If the temperature has dropped below 27° to 28 °F during a still night, the fruits should be allowed to warm up gradually before they are touched. Fruit temperatures can drop considerably below their freezing point without ice crystals forming, but if the fruits are shaken or jarred at this time they may freeze immediately. Frost damage varies among orchards and may not become apparent until after processing, when the olives become mealy and soft. There seems to be no difference among varieties in regard to the freezing point of their fruits, although small fruits freeze more quickly than large ones. Green fruits are more susceptible to freez- ing injury than are the red or black. Olives that have been frozen are perma- nently injured; they 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 but can be harvested for oil later in the winter. Temperatures of 32° to 36°F can cause "chilling injury" to olive fruits, resulting particularly in the development of dark- ened tissues around the pit, with poor flavor after processing. All fruits subjected to these temperatures should be examined carefully for evidence of such damage. During the latter part of the harvesting period, another type of fruit shrivelling Size grades of canning olives Fruits must reach a certain mini- mum size at harvest, depending upon variety, or they cannot legally be used for canning. Minimum sizes are: Mission and Manzanillo Standard Obliza Medium Ascolano, Barouni, and St. Agostino Extra large Sevillano Mammoth [49] often occurs in which fruit cells are not injured and canning quality is usually un- impaired. Such shrivelling may develop when there are low night temperatures and strong, drying winds; then, loss of water from leaves exceeds uptake of water by the roots, with the consequent with- drawal of water from the olives, shrivel- ling them. However, if this is followed by low transpiration conditions (such as cloudy, rainy, or foggy weather) with higher temperatures, fruit regains 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 fruit on heavily loaded trees. Oil olives. If fruits in October and November are not large enough for can- ning, they can remain on the tree until mid-December or mid-February, by which time they are usually black and have max- imum oil content. Although the fruits will probably be shrivelled and perhaps frozen this does not impair their value for oil extraction. (In California, returns from oil olives are much lower than from can- ning fruit.) Oil olives may be harvested by hand- picking or by spreading canvas sheets under trees and beating limbs with poles to cause the fruit to drop — but this is not desirable as it tends to break off fruiting twigs and causes openings in the bark through which olive-knot bacteria can enter. Beating poles may also cause the spread of olive knot through the orchard. Mechanical devices, such as tree shakers, are used to some extent in California to facilitate the harvesting of oil olives. In some countries small rakes are used to strip fruit from the branches. PESTS AND DISEASES . . . HOW TO IDENTIFY THEM (This section on insect pests was prepared by E. M. Stafford, Professor of Entomology, except for the discussion of nematodes prepared by M. W. Allen, Professor of Hematology, and the discussion of biological con- trol of olive scale, prepared by C. B. Huffaker, Professor of Entomology.) Insect pests The three principal pests which confront olive growers are olive scale, oleander or ivy scale, and black scale. In some parts of California, growers use the term "olive scale" to designate oleander or black scale. However, the term can properly be applied only to the olive parlatoria scale, which is found from San Diego County to Tehama County, with occasionally heavy infestations in the San Joaquin Valley from Bakersfield to Modesto. Oleander and black scales are commonly found in all olive-growing regions of California. See Pest and Disease Control Pro- gram for Olives (available from the University of California Agricul- tural Extension Service, or your Farm Advisor) for all chemical control measures. Olive scale (Parlatoria oleae [Colvee]). Often a grower finds olive scale for the first time during harvest. The sharply out- lined dark purple spots caused by the scale appear in marked contrast with the yellow-green background of the ripening fruit (page 51). What to look for. The adult female scale has a small gray covering somewhat less than %6-inch long. The cover is cir- cular 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 deformed and darkened. When infestation is heavy the scales [50] 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 Olive parlatoria scale. Purple spots appear on green and red fruits at harvest. (See page 50.) [51] Cjl JB^H| * ^ *> Oleander scale. Green spots remaining on the dark, ripening fruit are caused by this insect. (See page 54.) Peacock spot. Black spots first appear on the green leaves causing them to turn yellow and drop. (See page 57.) Fig. 26. Olive fruits at harvest severely damaged by olive (Parlatoria) scale. settle on the fruit as soon as it is formed in the spring, and this commonly results in a badly deformed olive at harvest. In early June the scales make their character- istic dark purple spots on the small fruit; these tend to fade as the fruit grows rapidly, so that a grower cannot survey his orchard for the presence of olive scale by looking for purple-spotted fruit in mid- season. By mid-August the young, small (and difficult to see) scales may be on the fruit without causing any change in color. What to do. The best control of olive scale is obtained from thorough spray treatments to control eggs and young scale of the first brood (late May to July 1). Experience has shown that best control has resulted from thorough drenching of the tree. This has been true when spraying with hand-operated guns, oscillating- nozzle boom sprayers, or blower-sprayers. If spraying is not completed by July 1 the remainder of the application should be delayed until July 15 to August 1, at which time another brood of eggs and young will be present. (In early July the scales are adults and therefore are more difficult to kill.) To avoid possible injury to trees, spray oils should not be used when the tempera- ture is over 90°F. Oil-spray injury (espe- cially when an excessive amount of oil is used) appears on the fruit as small dark spots, or raised corky tissues, where oil has penetrated the lenticels of the fruit. Lenticels of fruit sprayed with oil in July or August are usually a little darker and more noticeable than those on unsprayed fruit. This cannot be seen on black ripe olives — it is most easily seen on olives pickled by the green-ripe process, al- though it does not affect the quality of the canned olives. Olives to be used for green or green-ripe processing should not be sprayed with oil after about August 20. Biological control of olive scale. Two species of insect parasites of olive scale introduced here in recent years have become well established. The Persian Aphytis, Aphytis maculicornis (Masi), introduced in 1952, now occurs through- out the range of olive scale in California. A more recent introduction, Coccopha- goides utilis Doutt, has not spread as rapidly but is now (1965) well established in all major olive-growing districts of Cali- fornia although not in all groves. Orchard trials employing Aphytis to control olive scale met with varying suc- cess during the period 1953-1960. In cer- tain olive orchards Aphytis held olive scale below economic levels year after year; in others it failed to exert satisfac- tory control. Limited colonization of Coccophago- ides in 1957 and 1958 resulted in its estab- lishment in two olive orchards in Madera and Fresno Counties. With both parasite species working together, olive scale was brought under excellent control within two years in these two orchards. Addi- tional orchards subsequently colonized with Coccophagoides and already having Aphytis, have also exhibited consistently excellent control. Increased colonization of Coccophagoides (4,500,000) since 1961 has resulted in a marked increase in the number of growers employing this method of olive scale control. Commercial olive acreage now under biological con- trol in the San Joaquin Valley is approxi- mately 1,500 acres (1965). Portions of [53] large acreages in the Sacramento Valley are also under biological control, and the parasites have also undoubtedly reduced the rate of invasion into uninfested acre- ages. As Coccophagoides continues to spread throughout the olive districts of the state the achievement of fully reliable biolog- ical control of olive scale (as good as is obtained by use of chemicals) should greatly reduce the necessity for using chemicals. It is reasonable to expect that a much greater proportion of the total acreage could be placed under this con- trol program, with large savings to the industry. It is not as easy to establish Coccophagoides in the groves as it was to establish Aphytis, but with time, patience, and proper techniques this transition can be made with little risk of substantial eco- nomic losses. 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 (page 52). What to look for. The whitish covering of the adult female oleander scale may be slightly larger than Mo-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 numbers on the leaves of the lower inside part of the tree. Oleander scales have the ability to deform the fruit greatly. Extremely heavy infestations may reduce the oil con- tent as much as 25 per cent. What to do. Natural enemies of the ole- ander scale may keep this insect at a low level for many years. In some regions and in certain years chemical control becomes necessary. 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 vigor and productivity of the trees. What to look for. Black-scale adult Fig. 27. Black scale on olives showing various stages of development. Younger scales on the leaves with "rubber," and adult stages on the twig. (Photo by E. M. Stafford.) females are from %2- to about ^io-inch long, and are dark brown or black with a very tough outer skin. 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 ("honeydew") which supports the growth of a black fungus. The scale's feeding often so weakens the trees that many leaves drop and the next season's crop is reduced. Before reaching maturity, most of the scales move to the twigs to com- plete their growth. What to do. Well-pruned trees are less apt to harbor black scale; sunlight, high temperatures, and prolonged hot weather may greatly reduce infestations. In the northern part of the interior valley of California black scale is often held in check by natural enemies. This is espe- cially true where sprays for other olive insects and diseases are not necessary or are not regularly applied. In this area [54 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, and once started the grower may thereafter have to depend on chemical control. How- ever, it is usually not necessary to spray olives more than two consecutive years for control of black scale anywhere in the interior valley. Greedy scale {Aspidiotus camelliae Sign.). This insect may easily be mistaken for oleander or olive scale. The shell covering is more conical, however, and there is a small black spot to one side of the center; the body is yellow. Control measures as for olive scale are used. Red scale (Aoinidiella aurantii [Mask.]) . This important citrus pest is often found on olives in southern California. The fe- male adult has a thin, circular shell about Mc-inch in diameter. The body color is reddish and shows through the scale shell. Control measures as for olive scale are used. Thrips. Western flower thrips Franklini- ella occidentalis (Perg.), and Chirothrips aculeatus (Hal.) occasionally damage olives in California, and the damage is sometimes severe enough to require treat- ment. Parathion treatment for scale con- trols thrips if applied during bloom, but special permission from the local County Agricultural Commissioner is required, as this treatment destroys bees that might be working during bloom. Grasshoppers. These insects cause se- vere damage to olive fruit, but the amount of fruit attacked does not usually warrant control. 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 and as a result the twigs may break at these holes. The beetles normally breed in dead wood, chiefly madrone, oak, and old grape canes, and elimination of such wood is probably all that is necessary to prevent severe attacks. 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 Fig. 28. American plum borer. Above: adult moth. Below: larval stage which causes the in- jury. (Photos by R. M. Hoffman.) 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 Vs- inch long and black with a whitish pattern on the back. It breeds on unhealthy trees or olive prunings. In areas where this in- sect is a pest, cut olive wood should be burned. 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. Larvae of the moth attack soft, spongy tissue such as that of tree wounds, grafts, and olive-knot tissue; from such tissue larvae may continue feeding into healthy tissue and thus girdle fairly large limbs. Nematodes. The root-lesion nematode, Pratylenchus vulnus Allen and Jensen, attacks the roots of olive trees in several areas of California. Infested trees may be characterized by 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. Larger roots of infested trees have symptoms of longitudinal cracking of the root cortex, and the area under- neath these cracks is darkened and ne- crotic — the necrotic lesions are typical of the attack of the root-lesion nematode, and nematodes are normally present in [55] Fig. 29. Left: longitudinal cracking on olive roots typical of injury due to the root-lesion nematode, Pratylenchus vulnus. Right: uninjured roots. root tissue immediately adjacent to the dead area. Nematodes also attack and fre- quently kill small feeder roots. The citrus nematode, Tylenchulus semipenetrans Cobb, has attacked olive roots in a few localities in California where the trees were adjacent to, or planted on, land previously occupied by citrus. Information about the effect of citrus nematode infestations on olives is not available, but infested trees sometimes lack vigor, and their root systems are characterized by considerable disintegra- tion of small feeder roots. Root-knot nematodes, Meloidogyne spp., sometimes attack olive roots, caus- ing the formation of galls or knots on the roots; heavily infested roots cannot carry on their normal functions. Infested trees may have reduced vigor and show symp- toms of decline. There are no known methods of controlling nematode infes- tations on the roots of established olive trees. Pre-planting soil fumigation, and use of nematode-free planting stock, are the best known methods for avoiding nematode injury to young trees. Non-parasitic defects Shotberries. This trouble is most preva- lent with Sevillano and Manzanillo. Shot- berries are undersized, round-shaped fruits which occur more frequently in some years than in others. The fruits de- velop 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. This is possibly a form of par- thenocarpy, with enough stimulus present at the post-bloom stage to cause fruits to set. The seed fails to develop normally, however, and without it the fruit also fails to grow to its normal size. Many of the undersized fruit drop early, but some ad- here until maturity. No method of bring- ing such fruits to normal size is known. Soft-nose. Sevillano variety is particu- larly susceptible to this non-parasitic trouble, which does not appear until late in the season, during or at the end of the harvesting period. The fruit colors first at the apex end; this is followed by a shrivelling and softening. This trouble (which is more prevalent in years of heavy crops) varies in intensity from one orchard to another, and some growers think that it may be correlated with heavy nitrogen fertilization practices, especially when nitrogen is applied as manure. In 1950, a light crop year, tests were made using heavy applications of poultry ma- nure (500 pounds per tree) and amounts of ammonium nitrate equivalent in nitro- gen, on different groups of Sevillano trees. Soft-nose failed to appear either in the trees treated with manure or with am- monium nitrate. In 1951, a heavy crop year, soft-nose appeared in the entire or- chard, but was especially noticeable in trees which had heavy applications of nitrogen in 1950 both as manure and am- monium nitrate. Split-pit. This trouble occurs largely with Sevillano variety and is a serious problem in some years. The pits split gradually along the suture during fruit growth, resulting in a bluntly flattened type of fruit. Although the fruit is of normal size and seems to process satis- factorily, it makes a poor product because the pit comes apart when the fruit is eaten. The cause is not clear, but probably lies in environmental conditions occurring at a certain stage in fruit growth. Some growers believe it appears when the or- chard soil is allowed to become dry before [56] Fig. 30. Olive knot galls on olive shoots caused by infection with the bacterial organism, Bacterium savastanoi, E.F.S. pit hardening and the trees are then heavily irrigated. Parasitic diseases Three diseases of commercial importance affect olives in California. Two are fun- gus diseases, Cycloconium oleaginum Cast, (peacock spot), and Verticilliwn al boat rum R. and B. The third is a bac- terial disease, Bacterium savastanoi E.F.S. , known generally in California as "olive knot." These diseases are found in all the olive-producing areas of the state, but orchards can be found where one or more of the diseases does not occur. Peacock spot. This disease has been ob- served in California for over 60 years. It is commonly found on Mission, and to a lesser extent on Sevillano, Barouni, Asco- lano, Nevadillo, and Manzanillo, in the order named. Outbreaks are 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. Peacock spot was of little commercial importance before 1940 in California, but since then the productiveness of some trees has been considerably reduced due to partial de- foliation from the disease. Infection and development of the dis- ease in healthy leaves occurs during the rainy season (November through May), with symptoms appearing from 2 weeks to 3 months after infection. Moderate temperatures and abundant moisture in the form of rain or fogs are favorable to this organism, whose activity is low in hot, dry summer months; during this period it exists in diseased leaves on the tree. What to look for. Typical leaf symp- toms are found mostly on the leaf blade (page 52) but may also occur on the leaf petiole. Lesions develop on the upper sur- face of the leaf, first as inconspicuous, sooty blotches and then developing into dark green to black circular spots from Vs - to 3 /8 -inch in diameter. A faint yellow area is sometimes found in the leaf tissues [57] around the spot; as lesions expand the rest of the leaf becomes yellow and finally it drops from the tree. What to do. Successful prevention of infection depends largely upon spraying. Orchards already seriously affected should be sprayed as soon as possible after fruit is harvested for pickling. Pruning to ad- mit sunlight helps somewhat to reduce peacock spot. Olive knot. This disease, first observed in California in 1893, is now widespread in olive orchards throughout the Sacra- mento and San Joaquin valleys. Mission is most resistant to this, followed by Asco- lano, Sevillano, and Manzanillo, in the order named. Olive knot bacteria are abundant in knots with live tissue; they move to the surface of the galls and then spread down- ward on the branches by rains. New infec- tions occur largely during long midwinter rains, but galls do not appear until spring. Wounds of some sort are apparently nec- essary for infection — these may be freez- ing cracks, pruning wounds, scars from dropped leaves or flower clusters, and in- juries from ladders or other equipment. Spread of the disease about the tree is due to dissemination of bacteria over the surface of branches, and not to in- ternal translocation of bacteria through conducting tissues. Infection may be spread to adjacent trees by wind-borne rain; spread over longer distances is be- lieved due to infected pruning tools or dis- eased nursery stock. What to look for. The disease is marked by rough, roundish galls or swell- ings, sometimes 2 inches or more in di- ameter, on twigs, branches, trunks, roots, or even on leaf petioles and fruit stalks. Galls are likely to develop on fruiting shoots in the spring following winters in which low temperature caused defoliation and injury to twigs. The disease may kill much of the tree's fruit-bearing area. What to do. No adequate control for this disease is known. Two approaches are possible, however: removal or killing of galls to reduce sources of infection, or preventive sprays to reduce new infec- tions. For badly infected trees, removal of all knots would be impractical as it would mean removing all the branches. Where only a few galls have appeared in an orchard, their treatment is especially important to prevent further spread of the disease. Since one of the chief methods of spreading olive knot is by pruning during the rainy winter months when active bac- teria are present, all pruning in an in- fected orchard should be done during the dry summer months, when there is little likelihood of spreading the disease. Verticillium. This fungus disease has appeared in olive groves in California since about 1942, although it has been observed since about 1900 in peach, apri- cot, and almond orchards, where it is commonly known as "blackheart." Verti- cillium wilt, which has become the most serious disease affecting olives in central California, is caused by a soil-borne fun- gus infecting trees through their roots. It is likely to be found in soil that is, or has been, planted to potatoes, tomatoes, cot- ton, or other truck crops. Trees of all ages are killed or rendered worthless by this disease. Due to the large increase in cot- ton acreage and consequent rise in soil inoculum it is not safe to set out new groves in much of Tulare County unless they are on resistant rootstocks (the same is true of replants in established or- chards). The University of California is screening many hundreds of seedlings and has found some highly resistant to this fungus, and eventually recommenda- tions will be made on rootstocks best suited for Verticillium-infested soils. What to look for. The disease may at- tack the entire tree, or it may be confined sharply to one side or even to only one branch. Usual symptoms are the sudden collapse of one or a few branches, and this may be followed within a few weeks by collapse of other branches. Small trees often wilt and die all at once. Symptoms usually appear in May or June but some- times do not occur until midsummer or later. The most striking evidence of Ver- ticillium wilt in olives is the persistence of dead leaves and flowers, which usually remain on the tree throughout the sum- mer. In olives the typical internal symp- [58] J? MSWM i£te,: li#= ll|||# i: JRSS « ■fe: - Fig. 31. Common fruit defects found in olives. Upper left: soft-nose. Upper right: split- Lower left: shotberries. Lower right: spray injury due to summer oil applications. pit. toms are not present and there is no brown discoloration of the wood such as is characteristic of Verticillium in other plants. What to do. Avoid planting young olive trees in soil that has recently been planted to such susceptible crops as tomatoes, po- tatoes, or cotton; avoid also interplanting such crops in young olive orchards. Since infection takes place underground in the root system, it is impossible to control the disease with fungicidal sprays. Branches killed by this disease should be pruned out after midsummer. 59 GLOSSARY OF TERMS Alternate middle irrigation — watering every other middle between the tree rows, reversing the pattern at each subsequent irrigation. Axil — the upper angle between a twig or petiole and the stem from which it grows. Bud-eye — the growing bud occurring on the shield piece used in propagation by budding. Calyx — outermost flower whorl. Cambium — a layer of dividing cells between the phloem and xylem which causes growth in diameter. Capitate — abruptly enlarged; forming a head. Carpel — a floral leaf, bearing ovules, frequently along the margins of the leaf. Chlorosis — loss of chlorophyll in leaves or parts of leaves. Corolla — petals, collectively; the conspicuous flower whorl. Cortex — primary tissue of stems or roots, bounded on the inside by the phloem and the outside by the epidermis. Cotyledon — seed leaf — a part of the embryo. Cuticle — a waxy layer on the outside of epidermal cells. Detailed pruning — type of pruning in which many small cuts are made rather than the removal of a few large branches. Drupe — a simple fleshy fruit, derived from a single carpel, in which the exocarp is thin, the mesocarp fleshy, and the endocarp stony. Embryo sac — a structure inside the ovule in which the embryo originates. Endocarp — inner layer of fruit wall (pericarp). Endosperm — a nutritive tissue in the ovule, formed within the embryo sac of seed plants. Exocarp — outermost layer of the fruit wall (pericarp). Field capacity — all the water a soil will hold after it is drained. Indolebutyric acid — an organic acid, having growth-promoting properties, which is quite active in stimulating development of adventitious roots on stem cuttings. Inflorescence — flower cluster. Inoculum — source of infection by organisms. Lenticels — structures in the outer layer of the bark and fruit through which gases may pass. Lesions — areas of dead tissues on stems or roots. Locule — cavity of the ovary of the flower in which the ovules occur. Mesocarp — middle layer of fruit wall (pericarp). Milked-off — picking fruit in groups, using both hands, rather than removing them individually. Necrotic — dead plant tissue. Node — slightly enlarged portion of the stem where leaves and buds arise. Ovary — enlarged basal portion of the pistil (in the center of the flower) which be- comes the fruit. Ovule — a rudimentary seed, developing in the ovary. Own-rooted trees — those propagated by rooting cuttings; having no graft union. Paniculate — referring to a panicle; an inflorescence, the main axis of which is branched, and whose branches bear loose flower clusters. Parthenocarpy — the development of fruit without the union of sperm and egg cell in the embryo sac. Perfect flower — a flower having both stamens and pistils. An hermaphroditic flower. Perlite — a gray-white material of volcanic origin; it is crushed and screened to small particle sizes, then expanded by heating to high temperatures. It is widely used as a rooting medium for cuttings. Permanent wilting percentage — the soil moisture content at which plants cannot obtain water readily. [60] Phloem — conducting tissue in stems and roots just outward from the cambium layer, through which organic nutrients move downward. Pistil — central organ of a flower consisting of an ovary, style, and stigma. Pistillate flower — a flower having a pistil but no stamens; a female flower. Plumule — the first bud or shoot of an embryo. Polarity — the exhibition of different characteristics at opposite ends of an axis. Pollen tube — a structure arising from a germinated pollen grain which grows from the stigma through the style to the embryo sac in the ovule. Puddle — harmful alteration of soil structure due to cultivation when wet. Radicle — that portion of the plant embryo which develops into the seed root. Salt shrivel — olive fruits shrivelling when stored in salt brine. Scion — piece of stem used in grafting from which the upper portion of the new grafted plant will arise. Stamen — the flower structure consisting of the anther (pollen-bearing organ) and the stalk or filament. Staminate flower — a flower having stamens but no pistil. A male flower. Stigma — receptive portion of the style to which the pollen adheres. Stomata — small openings in the epidermis of leaves and stems through which gases may pass. Style — slender column of tissue which arises from the top of the ovary through which the pollen tube grows downward to the ovary. Suture — the junction, or line of junction, of contiguous parts. Sweating — moisture developing on fruit surfaces when they are stored in boxes. Verm icu lite — a micaceous mineral which has been exposed to very high tempera- tures giving it a fluffy characteristic. When graded to small particle size it is useful as a rooting medium for cuttings. Xylem — a conducting tissue in stems and roots just inside the cambium through which water and inorganic nutrients move upward. REFERENCES Baldini, E., and F. Scaramuzzi. (Editors) 1963. Olive da Tavola. (Table Olives). Edagricole. 318 pp. Bologna. Bradley, M. V., W. H. Griggs, and H. T. Hartmann 1961. Studies on self and cross pollination of olives under varying temperature con- ditions. California Agriculture 15(3) :4-5. Brown, D. S., R. S. Campbell, and W. R. Schreader 1962. Temperature and olive yields. California Agriculture 16(6) :7-8. Foytik, J. 1960. Trends and outlook — California olive industry. Univ. of California Agr. Exp. Sta. Cir. 492. Hackett, W. P., and H. T. Hartmann 1963. Morphological development of buds of olive as related to low-temperature requirement for inflorescence formation. Botanical Gazette. 124:383-87. 1964. Inflorescence formation in the olive as influenced by low temperature, photo- period, and leaf area. Botanical Gazette. 125:65-72. Hartmann, H. T. 1946. The use of root-promoting substances in the propagation of olives by soft- wood cuttings. Proc. Amer. Soc. Hort. Sci. 48:303-08. 1949. Growth of the olive fruit. Proc. Amer. Soc. Hort. Sci. 54:86-94. 1951. Time of floral differentiation of the olive in California. Botanical Gazette. 112:323-27. 1952. Spray thinning of olives with naphthaleneacetic acid. Proc. Amer. Soc Hort Sci. 59: 187-95. [61] 1953. Effect of winter-chilling on f'ruitfulness and vegetative growth in the olive. Proc. Amer. Soc. Hort. Sci. 62: 184-90. 1958. Some responses of the olive to nitrogen fertilizers. Proc. Amer. Soc. Hort. Sci. 72:257-66. 1958. Rootstock effects in the olive. Proc. Amer. Soc. Hort. Sci. 72:242-51. Hartmann, H. T., and P. Papaioannou 1951. Olive varieties in California. Univ. California Agr. Exp. Sta. Bui. 720. Hartmann, H. T., and J. G. Brown 1953. The effect of certain mineral deficiencies on the growth, leaf appearance, and mineral content of young olive trees. Hilgardia 22(3) : 1 19-30. Hartmann, H. T., and I. Porlingis 1958. Effect of different amounts of winter-chilling on fruitfulness of several olive varieties. Botanical Gazette 119(2) : 102-04. Hartmann, H. T., M. Simone, R. H. Vaughn, and E. C. Maxie 1959. Relation of fruit maturity at harvest to quality of black-ripe processed olives. Proc. Amer. Soc. Hort. Sci. 73:213-28. Hartmann, H. T., and C. Panetsos 1962. Effect of soil moisture deficiency during floral development on fruitfulness in olives. Proc. Amer. Soc. Hort. Sci. 78:209-17. Hartmann, H. T., K. Uriu, and O. Lilleland 1966. Olive Nutrition, in Fruit Nutrition, Chapter X, pp. 252-61. New Brunswick, N.J.: Horticultural Publications. Hartmann, H. T. and F. Loreti 1965. Seasonal variation in rooting leafy olive cutting under mist. Proc. Amer. Soc. Hort. Sci. 87:194-98. Hartmann, H. T., and Karl Opitz 1966. Pruning olive trees in California. Univ. of California Agr. Exp. Sta. Cir. 537. Hendrickson, A. H., and F. J. Veihmeyer 1949. Irrigation experiments with olives. Univ. of California Agr. Exp. Sta. Bui. 715. Huffaker, C. B., C. E. Kennett, and G. L. Finney 1962. Biological control of olive scale, Parlatoria oleae (Colvee), in California by imported Aphytis machlicornis (Masi) (Hymenoptera: Aphelinidae). Hil- gardia 32(13) :541-636. Informations Oleicoles Internationales (Revue Officielle de la Internationale d'Oleiculture.) Direction Generates de la F.T.O. Madrid. Quarterly publication. King, J. R. 1938. Morphological development of the fruit of the olive. Hilgardia 11(8) : 437-58. Loreti, F., and H. T. Hartmann 1964. Propagation of olive trees by rooting leafy cuttings under mist. Proc. Amer. Soc. Hort. Sci. 85:257-64. Marsico, D. F. 1955. Olivicultura y elayotecnia. Solvat, 582 pp. Barcelona. McKenzie, H. L. 1952. Distribution and biological notes on the olive parlatoria scale, Parlatoria oleae (Colvee) in California. California State Dept. Agr. Bui. XLI: 127-38. MORETTINI, A. 1 966. Olivicoltura (Olive culture) . 2nd ed. Ramo Editorale degli Agricoltori, Rome. Pansiot, F. P., and H. Rebour 1961. Improvement in Olive Cultivation. Rome: F.A.O. Agricultural Studies No. 50, 249 pp. Scott, C. E., H. Earl Thomas, and Harold E. Thomas 1943. Boron deficiency in the olive. Phytopathology 33:933-41. [62] Stafford, E. M. 1 949. Control of olive scale in California with parathion. Jour. Econ. Entom. 42 : 656. Wilhelm, S., and J. B. Taylor 1965. Control of Verticillium wilt of olive through natural recovery and resistance. Phytopathology 55:310-16. Wilson, E. E. 1935. The olive knot disease: its inception, development, and control. Hilgardia 9 (4) :233-64. Wilson, E. E., and H. N. Miller 1949. Olive leaf spot and its control with fungicides. Hilgardia 19( 1) : 1-24. 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