Pruning Olives Hart

7/28/2019 Pruning Olives Hart

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^K D1 i v i s i o n of A g r i c u 1 t u r a 1 Sciencesv; \ U N 1 V E R S 1 T Y O F . C A L F O R N 1 A

H, T. HARTMANlt:.

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,r^KARL OPITZ R. M. HOFFMAN

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CALIFORNIA AGRICULTURALEXPERIMENT STATION BULLETIN 771


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Research has shown that . In nonbearing olive trees, any pruning retards vegetative growth, but sometraining is necessary to develop a strong trunk and a well-branched primaryscaffold system. Light summer pruning during the first several years willachieve that purpose.In bearing olive trees, pruning reduces yields in proportion to the removalof fruit-bearing wood. Limit all pruning to cutting with some definiteobjective:

To ease harvesting and spraying, to reduce disease and insect dam-age:

Remove dead wood, suckers, and watersprouts,Thin out dense, brushy growth in the fruiting area, andRemove excess scaffold branches.

To keep trees down to reasonable heights:Head back the upright and lateral branches,Cut back large limbs of trees grown too high.

Bearing olive trees may be pruned at any time of the year. In orchardsinfected with olive knot, prune in the summer to reduce spreading of thebacteria.

THE AUTHORS:H. T. Hartmann is Associate Professor of Pomology and Associate Pomologist in the Experiment

Station, Davis. Karl Opitz is Farm Advisor, Agricultural Extension Service, Tulare County. R. M.Hoffman was Farm Advisor, Agricultural Extension Service, Tehama County, when a portion ofthis study was made.

MAY, 1960


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Some pruning may helpOlive growers in California have used many different methods in pruning

their trees, both bearing and nonbearing. Such methods range from no pruningto very severe pruning. No specific procedures for training young trees aregenerally followed.

This bulletin reports research on:Methods for training young trees to induce early bearing and, at the same

time, develop a mechanically strong tree framework.Methods of pruning bearing trees to induce maximum yields over a period

of years consistent with large fruits, ease of harvesting, and insect and diseasecontrol.The practical findings of the research are summarized on pages 13 and 29.

CONTENTSPAGE

Review of Literature 4Experiments in Pruning and Training Young Olive Trees 7Experiments in Pruning Bearing Olive Trees 14Discussion 24Conclusions 29


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PRUNING OLIVESIN CALIFORNIA

H. T. HARTMANN KARL OPITZ R. M. HOFFMANREVIEW OF LITERATURE

California. Bioletti (1922) t in apruning study of young Mission olivetrees at Davis, California, concluded thatpruning retards the growth of olive trees,especially when they are young. He esti-mated that the excessive pruning some-times practiced on young trees retardstheir development as much as 90 per cent.He found that severe pruning of youngtrees delayed the onset of bearing by oneyear in comparison with unpruned trees.

Jacob (1934) studying young Mission,Sevillano, Ascolano, and Manzanilloolive trees at Davis, California, alsofound the same growth-depressing effectfrom pruning for the first three varieties.A single severe pruning of trees left un-pruned until they were five years old, hadabout the same depressing effect as fivelight annual prunings. For Manzanillo,however, trees lightly pruned annuallyfor five years developed faster than thoseleft unpruned. Trees left unpruned untilthey were five years old produced heaviercrops in the fifth season than did treeslightly pruned annually. The severelypruned trees did not produce a crop ofcommercial importance during the sevenyears records were taken.

In observing responses of young olivetrees to pruning, Opitz, in unpublisheddata, recommends the following proce-dure for training such trees in TulareCounty:

* Submitted for publication May, 1959.t See "Literature Cited" for citations referred

to in the text by author and date.

Suppress all lateral growth lower than12 to 24 inches from the ground by fre-quent pinching in the summer to developa straight, unbranched trunk.Where necessary, support the growingtree with a 5- to 6-foot grape stake.Remove or shorten branches that

might be injured or destroyed by culti-vation.

Allow all other growth to develop asit may.

Following the first cropor duringthe first fruiting season if the crop isheavylight annual pruning is sug-gested. This consists of removing shaded,weak, inside limbs and cutting back orsuppressing crossing and interferingbranches. Allow watersprouts to developif they are growing from a position thatwill not interfere with the developmentof a well-balanced tree. Pinch back andeventually remove unwanted water-sprouts. Encourage three to five frame-work branches to develop at well-spacedintervals beginning 12 to 24 inches fromthe ground.

Pruning studies of bearing olive treesat Corning, California, were reported byMerrill and Condit (1928). Twelve-year-old Sevillano trees received annuallyminimum, medium, and heavy pruning.Annual yields per tree over a three-yearperiod were : 70 pounds for the minimumpruning, 67 pounds for the medium prun-ing, and 35 pounds for the heavy prun-ing. In regard to fruit size over the (\'three-year period, the heavy pruning re-

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suited in an average of 51 per cent"colossal" and "super-colossal" olives,medium pruning in 50 per cent, andminimum pruning in 39 per cent of thesesizes. However, in considering thepounds of olives of these sizes produced,the heavy pruning yielded an average of14.2 pounds per tree per year, the me-dium pruning, 25.3 pounds, and theminimum pruning, 20.1 pounds. In otherwords, the percentage of the larger oliveswas higher in the heavily pruned trees,but due to the low total yield, the num-ber of pounds was much less. Merrilland Condit concluded from this experi-ment that heavy pruning reduced thetotal yield as well as the yield of thelarger-sized olives.Moore (1945) reported upon the re-

sults of a four-year pruning experimentwith mature Manzanillo olive trees atLindsay, California. Starting with largetrees that had received no pruning forthe previous 12 years, three pruningmethods were used: (1) trees prunedevery year in February, (2) trees prunedat two-year intervals in July, and (3)no pruning. The results are summarizedin table 1.

Conclusions drawn from this studywere that the yields were reduced in thepruned trees about in proportion to theamount of pruning, and that fruit sizewas not appreciably affected by pruning.

Spain. Although the pruning practicesvary from one district to another, fromthe standpoint of maximum productionthe amount of pruning is excessive byCalifornia standards. The severe pruningin the unirrigated Spanish groves maybe justified, however, because water lossfrom the tree must be reduced duringperiods of drought and because heavypruning may be needed to stimulate newshoot growth since little nitrogenous fer-tilizers are used. Fungicidal sprays arerarely used, and the heavy pruning prob-ably helps control such diseases as pea-cock spot (Cycloconium oleaginum) andMacrophoma. In Spain it is believed thatfruit sizes are improved by heavy prun-ing (Opitz, 1956).

Pruning tends to be lighter in theprovince of Granada than in Jaen andCordoba. Trees in certain regions ofGranada do not receive any pruning;such trees have made exceptionally largegrowth and have yielded heavily (Diaz,

Table 1 . Results of four-year pruning experiment in Tulare County,Mature Manzanillo olive trees. Data of Moore (1945).

TreesprunedannuallyTrees prunedtwice infour years

Treesnotpruned

Average annual yield per tree (lbs)Average annual yield per acre (lbs) (based on

30 X 30 foot spacing)Average per cent of fruit in top three size gradesAverage per cent of fruit "petites" and "culls"Comparison of average values of crop per ton,based on 1941 grade prices (dollars)

Gross value of crop per acre per yearApproximate total time of pruning labor per tree during

the four-year period (hrs)Approximate average time of pruning labor per acre

per year on basis of 48.4 trees per acre (hrs)Reduction in crop value per acre per year due to

pruning (dollars)

227.3

11,00152.617.0

131.25721.94

4',

51.4

74.68

232.0

11,22946.023.7

121.25680.75

3',

39.3

115.87

254.2

12,30352.021.0

129.50796.62

5]


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1954). However, in much of the largerproduction areas in Spain the trees arepruned annually or biennially.

Italy (Opitz, 1957). Many olive or-chards in Italy receive little or no prun-ing, and the trees become very large;on the other hand, in some areas ofItaly, probably the most drastic pruningprocedures in the world are used. Vari-ous rather detailed pruning systems havebeen developed to limit tree size, regu-late bearing, and to compensate for lackof rainfall.

Specific recommendations (Savastano,1934) advise that newly-planted trees notyet in bearing should be pruned verylightly, while young trees which have juststarted bearing should also be prunedlightly, just enough to shape the tree,aiming at a strong, easily accessible treeof large framework. The full grown treeshould be pruned moderately each year,enough to insure adequate light for theremaining branches and to correct faultsin growth. When the trees are old orhave ceased to bear well, they must bepruned more heavily. Old, uselessbranches should be eliminated, withyoung, newly-formed shoots taking theirplace. This should be accompanied byabundant organic and inorganic fertiliza-tion. Pruning alone cannot replace fer-tilization.

France (Bonnet, 1944). Recommen-dations for pruning bearing olive treesstate that the pruning should be done an-nually, making small cuts rather thanresorting to heavier pruning at longerintervals. Suckers and dead or weakbranches should be removed and long-growing branches should be shortenedto induce growth of new shoots near themain scaffold branches.Algeria (Rebour, 1944). The vigor

of the mature tree is the basis for thepruning recommendations. Weakly-grow-ing, nonfruitful trees receive a fairly

strong pruning so as to invigorate theremaining branches. With trees of aver-age vigor and normal fruitfulness, onlya moderate pruning is recommended. Forunfruitful, excessively vigorous trees,light or no pruning is advised. A lighttype of pruning is recommended for treesgrown under irrigation and in soils thatare rich and well fertilized. Under non-irrigated conditions it is pointed out thatafter a heavy crop has set, a heavy prun-ing may have to be done to allow thetrees to conform to the limited watersupply in the soil.Morocco (Briand et al, 1949). It is

advised that in no case should pruningbe excessive; this is especially true withtrees coming into bearing, as it will re-tard fruit production. In pruning treesto obtain fruitfulness, it should be re-membered that the olive produces mostof its fruit on wood which grew the previ-ous year. Generally, this wood producesfruit only once and after that it is usedto support future branches that will bearfruit. In addition, the most fruitfulbranches are those of average vigorwhich are horizontal or hanging down.The upright growing branches tend toremain vegetative. Sucker and water-sprout growth also is unproductive andshould be removed.The quantity of fruit-bearing wood to

be left on the tree depends upon the vigorof the tree. The higher the fertility ofthe soil, the greater the fertilizationgiven, and the more irrigation wateravailable, the less severe the pruning willneed to be. It is recommended that thepruning be done annually.Greece (Anagnostopoulos, 1953).

Annual pruning is considered necessaryto reduce the tendency toward alternatebearing. Winter pruning is recom-mended, coinciding with harvest, to re-move shoots most heavily loaded withfruit. The most fruitful shoots are be-lieved to be those making an annualgrowth of about 12 inches with internode

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lengths of about ^ to l 1/! inches. This pruning. Summer pruning may be useddesirable type of fruiting shoot can be to reduce transpiration of unirrigatedobtained by adjusting the amount of trees in years of excessive drought.

EXPERIMENTS IN PRUNING AND TRAININGYOUNG OLIVE TREESMethods

Objectives in these studies were thedevelopment of methods of trainingnewly-planted olives in such a way asto produce trees with a strong, well-shaped trunk and primary scaffold sys-tem and, at the same time, not appre-ciably delaying growth and the onset ofbearing.The earlier studies of Bioletti (1922)

and Jacob (1934) showed generally thatany pruning of young olive trees tendedto retard growth and delay bearing, andthat such effects are more pronouncedas the pruning becomes more severe.Summer pruning, therefore, seemed tooffer the most promise as a method oftraining the trees by eliminating un-wanted shoots and, at the same time,removing a minimum amount of wood.All pruning of the young trees in thisstudy was therefore done as summerpruning; removed were small shootswhich would have developed into unde-sirable branches.

Trees of the Mission variety, propa-gated as rooted cuttings, were used. Thenursery trees, as straight whips, wereplanted at the California AgriculturalExperiment Station Orchard, Winters,in April, 1949, spaced 35 x 35 feet apart,in a very deep and fertile Yolo silt loam.Temporary trees were planted in the cen-ters of the 35-foot squares, but the spac-ing was sufficient so that these trees didnot interfere with the experiment. Cleancultivation was maintained throughoutthe experiment, with three to five flood-type irrigations given each year duringthe summer months. Watering was more

frequent during the first three years,being applied in small flood basinsaround each tree. No fertilizers were ap-plied throughout the course of these ex-periments since leaf analyses showed thetrees to be adequately supplied withmineral nutrients.

Three treatments were used initially,with 11 tree replicatestwo summer-pruned (A and B) and one unpruned(D). The training objective for the two-pruned plots was to develop three to fivewell-placed primary scaffold branchesarising from the main trunk, spaced oneto three feet from the ground level, well-separated up and down the trunk, anddirected outward equally around the tree.In treatment B (see figure 1) a stakewas driven into the ground beside thetree with sticks nailed to the stake later-ally upward, to which the primary scaf-fold branches were tied so as to directthem to the desired position. In treatmentA this was not done.In an additional treatment (treatmentC), no pruning was given any of thetrees until they came into bearing (afterthe fourth growing season) . At that timethese trees were pruned rather drasticallyin an attempt to train them in one opera-tion by removing excess primary scaffoldbranches, with the remaining branchesconstituting the permanent primary scaf-fold system (see figure 2).

Table 2 shows the dates of pruning, thetime consumed, and the dry weight ofprunings removed for each of the treat-ments during the first five years, at whichtime the primary scaffold system wasconsidered to be permanently established.

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ResultsFigure 3 shows the difference in ap-

pearance of the primary scaffold systemafter four years' growth between treestrained by summer pruning (treatmentsA and B) and unpruned trees (treatmentD).

Table 3 gives trunk cross section areameasurements over a 10-year period ofthe trees maintained under the differenttypes of training. Table 4 gives the fruityields per tree during a six-year period,from 1953 to 1958, inclusive.

Vegetative growth of the trees was re-tarded even by summer pruning. In 1958,at the end of the study, trees receivingonly a light summer pruning during theirfirst four years of growth averaged 1154sq. cm. in trunk cross section area whiletrees trained by receiving one heavypruning after four years of growth aver-aged 1829 sq. cm. and entirely unprunedtrees averaged 1867 sq. cm.

Large yield differences among the vari-ous pruning treatments did not occur.

Fig. 2. Below: Methods used to develop a primary scaffold system in previously unpruned treesby cutting out unwanted scaffolds after trees started bearing (Treatment C). Top row: Typicaltrees before pruning. Bottom row: Same trees following pruning. After four years' growth.


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Table 3. Effect of three methods of pruning on vegetative growth asmeasured by trunk cross section area. Mission olives. Winters, California.Trees planted April, 1949.

Trunk cross section areaMeasurements made at end of growing season Differences requiredfor significanceDate Trained by

summer pruningduring first fouryears(treatments A & B)sq. cm.

Trees trainedby heavy pruningafter four seasons'growth(treatment C)

sq. cm.

Unpruned(treatment D)sq. cm.

at 5 per centlevel

at 1 per centlevel

1949 131869

2788541154

19841612971829

16

3822246814561867 343

195019511952195419571958 480

Fig. 3. Comparison of primary scaffold system of typical trees trained by summer pruning(Treatments A and B, top row) with unpruned trees (Treatment D, bottom row). After four years'growth.


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Table 4. Yields per tree from the fifth to tenth year, inclusive, of Mis-sion olive trees trained by four different methods. Winters, California.Trees planted April, 1949.

YearTreatment ASummer prunedduring firstfour years.

Lateral branchesnot staked

Treatment B

:

Summer prunedduring firstfour years.

Lateral branchestied to stakes

Treatment C

:

Untrained untilfourth year(1952), thentrained byheavy pruning

Treatment D:Unpruned

Difference requiredfor significance

at 5 per centlevel

at 1 per centlevel

pounds17953 17 27 33 29 23

1954 85 99 115 130 45 621955 61 79 74 88 11 321956 236 266 262 287 27 781957 174 214 138 110 22 661958 307 338 302 231 79 109

Totalsix-yearyieldper tree 880 1023 924 875

UJCL\-

or

OCOQ-z.3OCL

IQ

300

200

100

Treatment A

1953 1954 1955 1956 1957 1958Fig. 4. Comparison of annual yields for trees receiving different pruning treatments. A

Trees trained by annual summer pruning during the first four years. BSame as A but primaryscaffold branches tied to stakes to direct growth. CTrees unpruned until the end of the fourthseason's growth, then trained by removal of excess primary scaffold branches. DTrees un-pruned. Mission olives, Winters, California.

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As shown in figure 4, the unpruned treesin the earlier years of the experimentout-yielded the pruned trees, but not toa great extent. In the latter portion ofthe period under study the pruned trees,even though smaller, according to trunkdiameter measurements, outyielded theunpruned trees. Thus, in comparing thetotal yields over the six-year period, dif-ferences among the four treatments werenot large.

DiscussionAny severe pruning of young olive

trees will retard growth and delay theonset of bearing; how, then, can a treebe developed with a strong, well-shapedprimary scaffold branch system whileholding pruning to a minimum? Suchpruning seemed most reasonably done assummer pruning; removing unwantedbranches when they were only severalinches long would be the least severe typeof pruning that could be accomplished.However, in this study even such lightpruning, practiced only during the firstfour years of growth, retarded treegrowth in comparison with unprunedtrees. Such growth differences were stillevident after the tenth year.One purpose of this type of minimum

pruning was accomplished, however ; thesummer-pruned trees had a strong, well-

shaped system of primary scaffoldbranches, as shown in figures 3 and 5.None of the summer-pruned trees blewover in winds or had branches break offat the ground level. In the unprunedtrees, however, this was an importantdetrimental factor. Forty per cent of theunpruned trees in this test either blewover in winds or had one or more of themain branches break off at the ground.As the main branches of unpruned treesenlarged (as shown in the lower part offigure 3) , they pushed against each otherand had a tendency to break off in strongwinds.

There were no striking differences be-tween the behavior of summer-prunedtrees which had scaffold branches tied tolateral stakes, and that of summer-prunedtrees with branches not so tied. In threeof the six years yield records were taken(1955, 1956, and 1957), trees withlateral branches tied had significantlyhigher yields at the five per cent levelthan trees with branches not tied. Thisincreased yield may possibly be due tothe better spacing of the scaffoldbranches with less crowding of the fruit-ing area as the trees became older. Itis rather doubtful, however, that enoughbenefit would accrue from this rathertime-consuming procedure to justify itsuse, especially in developing a large or-chard.

Fig. 5. Appearance of typical trees trained by three different methods of pruning after 10years of growth. Left: Tree trained by summer pruning during first three years. Center: Treeunpruned during first four years then trained by removing unnecessary primary scaffold branches.Right: Unpruned tree.


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The unpruned trees outyielded thepruned trees in the first four years ofbearing; this trend, however, was re-versed during the latter years of thestudy. The unpruned trees, althoughlarger (as measured by trunk diameter)than pruned trees, had such a dense topgrowth due to the relatively large num-ber of primary scaffold branches, thatexcessive shading soon occurred; muchof the top growth became unfruitful, anddeveloped a considerable amount of deadtwigs. This may explain the decreasedyields of the unpruned trees toward theend of the study in comparison with thepruned trees which, with fewer scaffoldbranches, would not develop an over-crowded condition in the top of the treeas soon as the unpruned trees.The method of training given in treat-

ment C, in which the trees were allowedto develop unpruned until after theirfourth growing season and then weregiven a fairly heavy pruning to shapethe tree, gave better results than ex-pected. The inhibition of growth due toearly pruning was not encountered andthe heavy pruning at the onset of bear-ing was not especially detrimental, eitherin future vegetative growth or in yields.Yields may have remained high, in spiteof the removal of a considerable portionof the top fruiting surface, because oftwo reasons : ( 1 ) thinning out of the topavoided the dense, overly-crowded con-dition which occurred in the unprunedtrees, and led to increased fruitfulnessand (2) an actual stimulation of fruitsetting due to a decrease in the top-rootratio. This latter situation has often beennoted previously in top-grafting olivetrees, where a nurse branch is retained.Removal of all the fruiting top of the treeexcept the nurse branch usually resultsin a very heavy fruit set on the nursebranch, due probably to the greatly in-creased supply of moisture and availablenutrients from the entire root system tothe one nurse branch.

The nature of the trunk and primaryscaffold system in treatment C, after theheavy pruning, was far from satisfactory,however, as shown in figures 2 and 5.The several main branches coming di-rectly from the ground in later years,after enlargement, will tend to pushagainst each other and to break off inwinds.

Conclusions1. Any pruning of young, nonbearing,

olive trees will retard vegetative growthin comparison with unpruned trees. Eventhe very minimum type of summer prun-ing, as practiced in this study, reducedgrowth.

2. Some training of the young treesduring the first few years is necessaryif a strong trunk and a well-branchedprimary scaffold system is to be devel-oped. An unpruned olive tree developsas a bush rather than a tree and theprimary scaffold branches thus developas enlargements of the suckers arisingat ground level. As the tree becomes olderthese main branches enlarge, pushagainst each other, and tend to break off,either in winds or from a heavy fruitload.

3. The system of allowing the tree togrow unpruned until it comes into bear-ing, then developing the primary scaf-folds by removing the excess branchesseems suitable as far as rapid tree growthand fruitfulness is concerned but it is un-likely to result in a satisfactory perma-nent trunk and scaffold system.

4. The system of light summer pruningduring the first several years of treegrowth resulted in an entirely satisfac-tory trunk and primary scaffold system.While even this minimum pruning re-duced tree growth as well as yields duringthe first four years of fruiting, such treeslater yielded more heavily than the un-pruned trees.

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EXPERIMENTS IN PRUNING BEARING OLIVE TREESThree general methods of pruning

bearing trees have been practiced inCalifornia:Heavy pruning, in varying degrees

of severity, given annually or moreoften, every other year, or every thirdor fourth year. The proponents of thismethod believe that heavy pruning willsecure larger fruit size, heavier fruit sets,and easier harvesting and pest control.

Light pruning, consisting only in theremoval of dead wood, suckers, andwatersprouts, done annually or once inseveral years.No pruning except perhaps the re-

moval of broken limbs and suckers. Ad-vocates of the latter two methods believethat yields are reduced by heavier prun-ing without sufficient increase in fruitsize to offset the yield reduction.To determine which of these three

types of pruning would result in the mostprofitable crops over a period of yearswhile maintaining the trees in a healthycondition, two experimental plots receiv-ing such treatments were established in1946 in irrigated orchardsone nearCorning in Tehama County, and one nearOroville in Butte County. In addition,five plots were established in TulareCounty in 1949, also comparing maturetrees receiving heavy, light, and no prun-ing.The general plan of the Corning and

Oroville experiments was to use a uni-form block of trees and prune one thirdof the trees severely each year, one thirdmoderately, while one third received nopruning. These tests were conducted forsix years, although the severe pruningtreatment was discontinued after thefourth year. Individual tree yields wererecorded each year and commercial sizegrades of the fruit from trees receivingthe different types of pruning were ob-tained. By using these data, together with

the price paid growers per pound of fruitin the various size grades, the gross re-turns per tree could be calculated.Corning experiments

This plot was established at the May-wood orchard, about 5 miles southwestof Corning on Tehama gravelly loam soil.Sevillano trees, about 50 years oldplanted 30 x 30 feet apart, were used.This orchard had an average annual pro-duction of 2.6 tons per acre from 1944to 1949. For some years prior to the es-tablishment of this experiment the treeshad received a rather light annual prun-ing.

The plot of severely-pruned trees con-sisted of 21 trees running north andsouth through the entire orchard. Themoderately-pruned plot contained 27trees in a row adjacent to the severelypruned trees. There were 27 trees in the

TYPICAL EXPER

Fig. 6. Tree in the "severely-pruned" plot.

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unpruned plot and these were in a rowadjacent to the moderately-pruned trees.The trees were pruned in late winter

or early spring as shown in figures 6, 7,and 8. The approximate amount of woodremoved per tree is shown as well as theappearance of the trees after pruning.While the severely pruned tree in figure6 is not cut back as heavily as somegrowers prune their trees, the object inthis case was to thin out the dense growthsufficiently so that sunlight could pene-trate easily to all parts of the interiorof the tree. Some fairly large cuts weremade, especially the first year. Thissevere pruning treatment was discon-tinued after four years due to the obvi-ously large reduction in yields. Themoderately-pruned trees were cut justenough to remove dead wood, suckers,and watersprouts from the interior ofthe tree and, in addition, the fruiting areaaround the outside of the tree wasthinned out to some extent. No large cutswere made. The trees in the unpruned

block were not cut at all during the six-year period.

Except for the different types of prun-ing, the trees were all treated alike, receiv-ing the same amount of nitrogen fertilizerand were irrigated in the same manner.

During harvest, the fruit from eachindividual tree was weighed separatelyand the entire crop from each of the threeplots was graded in a commercial sizegrader.

Yields, during the six-year periodfrom 1946 to 1951, are given in table 5and shown in figure 9. At the end offour years, when the severe-pruningtreatment was discontinued, the treeswhich were pruned severely had pro-duced an average of 83 pounds of fruitper tree per year. The moderately-prunedtrees produced 111 pounds, while thetrees receiving no pruning produced 120pounds. At the end of six years, the aver-age annual yields for each of these groupswere 96, 115, and 122 pounds, respec-tively.

NTAL TREES, SEVILLANO VARIETY, CORNINGThe approximate amount of wood removedper tree per year is shown

Fkj. 7. Tree in the "moderately-pruned" plot Fig. 8. Tree in the unpruned plot.[15]


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Table 5. Average yield of mature olive trees under three methods ofpruning during a six-year period. Corning and Oroville, California.

Severeannual pruning Moderateannual pruning No pruningDifference required

for significanceYear

at 5 per centlevel

at 1 per centlevel

poundsSevillano variety, Corning

1946 146838122

83

1639813547

111

16810715749

120 18

194719481949Four-year average 24

1950 43*199*

96

67178

115

52200

1221951

Six-year averageMission variety, Oroville

1946 15914

1925

20213947

1948 183 204 2321949 72 82 120

Four-year average ... 107 121 142 32 44

1950 174* 158 1871951 126* 145 167

Six-year average 121 131 154Pruning was discontinued in the severely-pruned plots following the 1949 harvest.

200

Pruning discontinued in"severe" plot after 1949 harvest

1946 1947 1948 1949 1950 1951

Fruit size, as seen in table 6, increasedslightly with severity of pruning. Theaverage size index (see footnote, table 6)of the fruit during the six-year period was6.654 for the severe pruning, 6.466 forthe moderate pruning, and 6.361 for fruitfrom unpruned trees. Table 7 also showsthis trend: 67.3 per cent of the fruitsfrom severely pruned trees were "giant"or above in size, whereas the unprunedtrees had 58.3 per cent of their fruits"giant" or above. On the basis of theactual amount of fruit produced per tree,however, over a four-year period the un-pruned trees produced 70.3 lbs. of fruit

Fig. 9. Average annual yields of Sevillanoolive trees under three pruning treatments dur-ing a six-year period. Corning.

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'"giant" or above in size, moderatelypruned trees 62.0 lbs. "giant" or above,and severely pruned trees 55.7 lbs."giant" or above. Although there was anincrease in fruit size on a percentagebasis with increased severity of pruning,the decreased yield nullified this benefit.As shown in table 7, the annual gross

income during a four-year period, cal-culated on an acre basis, was $575.50 forthe severely-pruned trees, $717.50 forthe moderately-pruned trees, and $826.50for the trees receiving no pruning. Thisamounted to a loss of $251 per acre peryear for trees severely pruned, and $109per acre per year for trees moderatelypruned. This loss was due primarily to areduction in yield caused by the removalof fruiting wood.The values of the fruit in the various

size grades as given in table 7 are aver-ages of the prices paid to growers atCorning for Sevillano olives during theyears 1946, 1947, 1948, and 1949.

Oroville experimentsThis plot was established at the Noel

Graves orchard in the Wyandotte areaof Butte County, about 7 miles southeastof Oroville. Mission trees, about 35 yearsold and planted 30 x 30 feet apart, wereused. This orchard, on Aiken clay loamsoil, produced an average of 1.7 tons offruit per acre from 1940 to 1949 and hastended strongly toward alternate-bear-ing. The trees had previously received alight annual pruning for a number ofyears.

This pruning experiment was estab-lished similar to the one at Corning.Three methods of pruning were usedsevere, moderate, and no pruning, withten trees in each treatment. The threeplots were situated adjacent to each otherwith all conditions, other than the typeof pruning, being maintained the same.About 65 pounds of prunings were re-moved per tree each year from the

Table 6. Effect of severity of pruning on fruit size, expressed as sizeindex,* under three methods of pruning during a six-year period.

Severe Moderatepruning pruning

6.735 6.6706.402 6.3286.769 5.8527.049 6.9877.039 6.7505.932 6.206

No pruning

Sevillano variety, Corning19461947..1948194919501951

Six-year average ...

Mission variety, Oroville194619471948194919501951

Six-year average ....

6.654

1.2403.4951.0692.7251.9002.080

2.085

6.466

7.0806.2755.5907.1776.3655.676

6.361

1.235 1.2643.118 3.1381.079 1.0522.650 2.6152.210 1.7301.490 1.870

1.964 1.945

* Size index is calculated by multiplying the percentage of fruit in each size grade by the following arbitraryfactors, then adding the results. (Standard0.02, medium0.03, large0.04, extra large0.05, mammoth0.06,giant0.07, jumbo0.08, colossal0.09, super-colossal0.10).17


18/32

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Pruning Olives Hart

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