UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA SOME EFFECTS OF THINNING ORANGE FRUITS E. R. PARKER BULLETIN 576 JULY, 1934 UNIVERSITY OF CALIFORNIA BERKELEY, CALIFORNIA CONTENTS PAGE Introduction 3 The time at which thinning might be most effective and profitable ... 5 Material and methods of experimentation 8 Results of the experiments 10 Effect of thinning Washington Navel oranges on the crop picked in the year of thinning (1930-31) 10 Effect of thinning Valencia oranges on the crop picked in the year of thin- ning (1930-31) 14 Effect of thinning Washington Navel oranges on the crop produced in the second season after thinning (1931-32) 14 Effect of thinning Valencia oranges on the crop produced in the second season after thinning (1931-32) 16 Summary of field and packing-house observations 18 Economic interpretation of data 19 Summary and conclusions 24 Appendix 27 SOME EFFECTS OF THINNING ORANGE FRUITS 1 2 E. E. PAEKEE 3 INTRODUCTION Orange growers in California are well aware that the size of the fruit harvested in different years varies greatly, and the returns which they receive for their fruit are influenced not only by the volume of their crop, but also, to a considerable degree, by the proportion of the most desirable sizes which they produce. Among the factors which affect the average size of the fruit is the size of the crop borne in the current crop year. Valuable information relating to the importance of this factor is afforded by comparisons of the average annual yield of oranges in California with the average size of the fruit harvested. Prior to the season of 1925-26 adverse weather conditions in some of the citrus-producing areas complicated such a study. However, from that time until the crop of 1931-32 was harvested, weather condi- tions favorable for fruit setting and development prevailed generally. During this period annual records of the average number of fruits per packed box of each variety shipped by the California Fruit Growers Exchange were compiled, and the data have been made available for the purpose of this study. 4 Since the records of size were obtained from a study of approximately 70 per cent of the total shipments, they are con- sidered indicative. These average sizes have been compared in figure 1 with the average yield in packed boxes per acre for the state for the respective periods. 5 Straight lines have been fitted to the data for both the Washington Navel and the Valencia varieties of oranges. All of the points pertaining to each variety fit reasonably well with the exception of the points made for the season 1925-26. In that year the average size of Washington Navels was somewhat smaller than one would expect from the distribu- i Eeceived for publication December 15, 1933. 2 Paper No. 287, University of California Graduate School of Tropical Agricul- ture and Citrus Experiment Station, Eiverside, California, s Assistant Horticulturist in the Citrus Experiment Station. 4 These data were furnished through the courtesy of F. O. Wallschlaeger, Treas- urer, California Fruit Growers Exchange. 5 This information was determined by dividing the total railroad shipments for the proper variety and year by the acreage estimates. The latter data were kindly furnished by E. E. Blair, California Cooperative Crop Eeporting Service, Sacra- mento. [3] University of California — Experiment Station tion of the rest of the points, and the size of Valencias was larger than would be expected in view of the yields obtained. Other factors may have had an unusual influence upon the growth during that season. A general coefficient of correlation of +0.82 was found between average size of crop and size of fruit for seven years. This correlation is a signifi- cant one. 6 150 160 170 180 190 200 210 220 230 240 250 260 s 1 1 1 1 n} '28 o V t •32 NO 2 ' Wash lngto i Nav els '28 '2&s • '30 °^ O >9 Vale ncias t\ '27 ^X 52 • sVale nciaa •31 v '29 Mean number of packed boxes shipped per acre Fig. 1. — The relation of size of crop of Washington Navel and Valencia oranges in California to the size of such fruit for the seasons 1925-26 to 1931-32, inclusive. The indicated date is the year of harvesting. The general relation between fruit size and the size of the crop har- vested suggests that attempts to influence the size of the fruits by artifi- cial thinning of fruits would be effective. This practice is not commer- cially employed and experimental evidence of its effect is meager. Waynick 7 , has reported the results of two experiments with Valencia oranges. From the first of these it was concluded that the removal of about half of the crop at the beginning of the harvesting season did not 6 Fisher, E. A. Statistical methods for research workers. 3d ed. p. 176. Oliver and Boyd, London. 1930. 7 Waynick, D. D. Effect of late thinning on growth of Valencia oranges. California Citrograph 14:509. 1929. Waynick, D. D. Does thinning affect the sizing of Valencias. California Citrograph 15:438. 1930. Bul.576] Some Effects of Thinning Orange Fruits 5 increase the amount of relative growth subsequently made by the rest of the fruit. In the second experiment about one-sixth of the total num- ber of fruits were removed from certain vigorous, productive seven- year-old Valencia trees about August 1. At harvesting the percentage of large fruits from the thinned trees was slightly larger than from the control trees. The crop was so reduced by the thinning, however, that a financial loss resulted from the practice. In the following year all trees set a heavy crop which appeared uniform in size. The results of small-scale experiments by Shamel and Pomeroy 8 indi- cate that it is possible to increase size of fruit somewhat by heavy thin- ning of small fruit, but the authors conclude that the practice seems impracticable. The present investigation was planned to give more detailed informa- tion on the effect of thinning oranges, particularly the young fruits of mature trees. Certain theoretical and practical aspects of the problem should be discussed before presenting the experimental data. THE TIME AT WHICH THINNING MIGHT BE MOST EFFECTIVE AND PROFITABLE Thinning of oranges would be done logically in years when the entire California production of any one variety is very large. At such times the larger sizes would, if the thinning produced the desired results, return enough extra money to more than offset the loss due to any pos- sible reduction in the tonnage picked. In addition to the knowledge of the condition of his own orchard, a knowledge of the condition of the crop of the state at the time thinning should be done would, therefore, be essential in determining whether or not a grower should perform this operation. Such information based upon a large number of local reports, is fortunately made available by the California Cooperative Crop Re- porting Service, Sacramento. Such reports are prepared for both the Washington Navel and the Valencia oranges at monthly intervals from May to November, inclusive. The weighted average estimates for the condition of the crop in the entire state for the years 1925 to 1931 are presented for each variety in table 1. In this table may also be found the mean yield per acre in packed boxes and also the mean number of fruits per packed box for each crop year. There appears to be a direct relation between the crop condition esti- mates and the yield per acre. The relative reliability of the estimates of different months may be 8 Shamel, A. D., and C. S. Pomeroy. Influence of numbers of leaves on growth of Washington Navel oranges. California Citrograph 17:394, 396. 1932. 6 University of California — Experiment Station determined by the calculation of the coefficient of correlation between the estimates and yields. The results of such computation may be found in table 2. The closer the coefficient approaches unity the more perfect the corre- lation. In seven comparisons a coefficient of 0.66 should be indicative of TABLE 1 Estimate of Crops of Washington Navel and Valencia Oranges in California* with Mean Yield per AcREf and Mean Size of Fruits 1925-26 to 1931-32 Year of Per cent of a full crop in prospect Crop year affected Mean yield in packed boxes per acre Mean number of esti- mate May June July Aug. Sept. Oct. Nov. fruits per packed box Washington Navel oranges 1925 90 88 89 84 82 82 82 1925-26 104 4 194.8 1926 92 83 81 80 80 80 80 1926-27 124 178.1 1927 -1 70 68 67 67 68 69 1927-28 111.9 179.6 1928 96 95 92 93 93 94 94 1928-29 166.4 217.9 1929 85 77 70 58 58 56 57 1929-30 92.2 162.7 1930 95 95 87 84 83 84 84 1930-31 144.6 213 5 1931 87 74 74 74 73 75 76 1931-32 130 189 4 Mean 908 83.1 80 1 77.1 76.6 77.0 77 6 Valencia oranges 1925 88 88 87 84 82 82 82 1925-26 138.4 207.3 1926 93 91 84 84 84 86 86 1926-27 141 2 226.7 1927 -1 88 76 67 67 68 69 1927-28 106.8 207.6 1928 88 95 94 93 93 94 94 1928-29 166.4 249.7 1929 87 77 70 60 60 62 63 1929-30 105 2 212 3 1930 93 95 87 84 85 86 84 1930-31 147.3 239.6 1931 91 86 80 80 81 81 81 1931-32 145.8 232.5 Mean 90.0 88.6 82.6 78.9 78.9 79.9 79.9 * Data kindly furnished by Mr. R. E. Blair, Agricultural Statistician, California Cooperative Crop Reporting Service, Sacramento, California. t Total railroad shipments divided by total acreage. t Shipments of California Fruit Growers Exchange. Data courteously supplied by Mr. F. O. Wall- schlaeger, Treasurer. H Dashes indicate data are not available. the actual relation in 9 out of 10 cases, a value of 0.83 in 49 out of 50 cases, while as high as 0.87 is significant in 99 out of 100 cases. 9 All of the values are, therefore, significant with the exception of the estimate for Valencia oranges in May. Barring unfavorable weather conditions during the winter prior to harvest, it appears that the crop 9 Fisher, E. A. Statistical methods for research workers. 3d ed. p. 176. Oliver and Boyd, London. 1930. Bul.576] Some Effects of Thinning Orange Fruits 7 forecasts for June or later months would serve as reliable indexes of the size of the future crop. The estimates of the future crop may have an additional value in fore- casting with reasonable accuracy the size of fruit to be harvested in the future crop. Since a correlation coefficient of +0.82 was found between size of crop and number of fruits per packed box, as noted on page 4, and since the crop estimates are highly correlated with size of crop, it is TABLE 2 Coefficients of Correlation Between Crop Estimates for Various Months and Size of Crop and Size of Fruit Harvested for 1925-26 to 1931-32,* Inclusive Month of crop estimate Mayf June July August September October November. Coefficients of correlation* between percentage of full crop and Size of crop Washington Navels +0.810 +0.628 +0.619 +0.781 +0.786 +0.829 +0.838 Valencias 315 756 909 9(>6 977 974 971 Number of fruit per packed box Washington Navels +0.832 +0.795 +0.814 +0.881 +0.877 +0.893 +0.897 Valencias +0.365 +0.653 +0.661 +0.703 +0.755 +0.771 +0.759 * See text (page 6) for a discussion of reliability, t 1926-27 to 1931-32, inclusive. probable that the crop estimates are in turn correlated with average size of fruit. Using the available data, correlation coefficients have been de- termined between the monthly forecasts of the California Cooperative Crop Reporting Service and the size of fruit at the time of harvest. These coefficients are also reported in table 2. All of the coefficients are positive, and the standards of significance discussed above indicate that there is little probability that the relation between the two factors is due to chance. In general, forecasts made late in the season are more reliable than the earlier estimates, but these data suggest that the July and August estimates of the size of the crop provide a fairly good index of the size of Washington Navel and Valencia oranges in the future harvest. Apparently, information regarding general crop prospects can be obtained early enough to afford an idea whether large-sized fruit will be relatively plentiful or scarce, and consequently whether it will command a premium in the markets in any one year. Such knowledge would obvi- ously indicate whether an attempt to obtain larger sizes by the introduc- 8 University of California — Experiment Station tion of an additional cultural operation would be worth while, such as fruit thinning, should that practice prove effective. After determining the year in which the thinning might be profitable it is of course necessary to determine the stage of fruit development at which the operation should be carried out commercially in order to be effective. The physical effect of thinning might be expected to be greatest when done as early as possible after the blossoms have set. But to do the work before the June drop does not appear practical, because a heavy natural drop would make thinning undesirable by excessive reduction of the crop as a whole, or of the particular orchard. In view of the avail- ability of reliable estimates of crop conditions and the possibility of obtaining a desirable effect, the logical time to thin the crop appears to be immediately after the June drop. The experiments which are here- with reported were performed as soon as possible after that period. MATERIAL AND METHODS OF EXPERIMENTATION In the spring of 1930 there was a heavy set of both Washington Navel and Valencia oranges, followed by cool weather which resulted in a light June drop of young fruit. Seven orchards 10 were, therefore, selected for study at that time. These orchards are indicated in this paper by number. With one exception all of the trees were twenty-five to thirty-five years old, were normal, and were consistently good bearers. Orchards num- bered 1 to 3, inclusive, are of the Washington Navel variety. One of them was located in East Highlands on Hanford loam soil, another at Riverside on Hanford sandy loam, and the third at Corona on Yolo loam. All of these orchards bloomed normally in 1930. However, in orchard No. 3 a scattered amount of "off -bloom" fruit was probably set during the fall of 1929. In this orchard, this fruit was handled in the same manner as was the normal fruit which was set in the spring of 1930. The four Valencia orchards selected for study are numbered 4 to 7, inclusive. Two orchards were located in Corona, one on Yolo loam, and one on Yolo fine sandy loam, one was at Santa Paula on Eincon clay loam, and one at Riverside on Ramona loam. The Valencia orchard at Riverside was only thirteen years old in 1930. At each of the seven orchards an independent experiment of corre- sponding number was set up. In one part of each orchard approximately 30 trees were selected which were nearly equal in size, vigor, and amount 1( > Grateful acknowledgment is made to the owners and managers of orchards on whose property the experiments were carried out and to packing-house officials for their cooperation in these experiments. Among these are: The American Fruit Growers, Inc., L. V. W. Brown Estate, East Highlands Orange Company, and Messrs. A. C. Barnes, D. S. Bell, C. H. Calladay, E. Hagen, Joy G. Jameson, E. Jennings, F. J. Mueller, A. J. Neilson, and W. T. Webber. Bul.576] Some Effects of Thinning Orange Fruits 9 of fruit set. These trees were then grouped by rotation into three lots, A, B, and C, in such a way that each lot of about 10 trees was compar- able. Measurements were made of the circumference of the trunks at the smallest point to secure an index of the size of the trees. Thinning was done in July and August, 1930. In each experiment an effort was made to remove one-third of the crop from one lot of 10 trees, group A, and two-thirds of the crop from the trees of group B. The con- trol lot, C, was not thinned. The thinned fruits were snapped off at the button with the thumb while holding the fruit in the palm of the hand. They were taken in order without regard to location or condition, except that an effort was made to break up clusters. Records were kept of the time necessary for the operation and of labor costs. After thinning the crop of each tree, the removed fruits were counted ; a subsequent count of the harvested fruit showed that somewhat less than the desired one-third or two-thirds of the fruit was removed in the thinning process. The actual percentage of the fruit removed in thinning is consequently used. Measurements of every tenth fruit removed showed them to be very uniform in size and to average about 1.5 inches in diame- ter on various lots of trees. There were no significant differences be- tween the averages of the size of the normal-bloom fruit on various groups of trees at the beginning of any one experiment. The methods by which the effect of thinning was determined are as follows : At the time of harvesting the crop of 1930-31, the fruits from each tree were kept separate until their total volume was determined to an accuracy of Y 10 of a field box (4.5 pounds). The number of fruits harvested from each tree was determined and the diameter of every tenth fruit was then measured. The measurements so obtained for the fruits from each tree were grouped into frequency distributions. These were generally normal and of such a pattern that it is felt that a good sample was obtained. Each tree average was therefore regarded as an absolute figure. The average of these individual-tree averages was taken to represent the average size of the fruit of the trees in any one treat- ment group. After the measurements were taken, the fruits from all trees of each group in an experiment were combined. In most of the experiments each group of fruit was then graded as a unit in the pack- ing-house. In addition to the observations which were made in the year of thin- ning it was also possible to obtain similar data for the crop produced by several of the experimental orchards in 1931-32, the season following that in which the thinning was done. The crop year 1931-32 was also favored with satisfactory growing conditions and good crops. The orch- 10 University op California — Experiment Station ards observed during the second season were Nos. 1 and 2 among the Washington Navels, and Nos. 5, 6, and 7, among the Valencias. It was not possible, however, to obtain the packing-house data for the fruit of the experimental trees in orchard No. 6. RESULTS OF THE EXPERIMENTS Although the results of each of the seven experiments need not be discussed separately, it is desirable that they be made available in suffi- cient detail so that they may be studied and interpreted by the reader. Only in this way can the effects of variety and the special conditions appertaining to each experiment be evaluated. The data for each experi- ment are therefore presented in tabular form. Attention will be directed to the more important conclusions to be drawn from the individual experiments. Effect of Thinning Washington Navel Oranges on the Crop Picked in the Year of Thinning (1930-31). — It may be seen from table 3, that the thinning of fruit of the Washington Navel variety during the month of July, 1930, caused an increase in the average size of the fruit picked from each of the three experimental orchards. Columns 6 and 7 of table 3 show the exact amounts of the increase. One exception to this generalization was observed. This was in the lightly thinned group of experiment No. 3. In all other instances the increase in size of fruit due to thinning is significant, since it is at least three times its probable error. The general tendency of all the other experiments strengthens the conclusion that thinning as practiced caused an increase in the size of the harvested fruit, and that this effect was a function of the severity of the practice. In the single exception cited, the lightly thinned group in experiment No. 3, it is apparent from column 2 of table 3 that a strictly comparable lot of trees was not used for this group. The trunk measurements show that the trees are considerably smaller than those of trees used as con- trols or of those trees which were heavily thinned. This suggests that a factor, such as decreased leaf area per orange, as indicated by the experiments of Shamel and Pomeroy, 11 may be operative in limiting the growth of fruit. Columns <§ and 9 of table 3 show that an additional effect of thinning was a significant reduction in the volume of the crop of Washington Navel oranges harvested in the year in which the thinning was done. The amount of the reduced yield was related to the extent to which the trees were thinned. It is evident that the increased size of the fruit on 11 Shamel, A. D., and C. S. Pomeroy. Influence of numbers of leaves on growth of Washington Navel oranges. California Citrograph 17:394, 396. 1932. Bul. 576] Some Effects of Thinning Orange Fruits 11 TABLE 3 Effect of Thinning Washington Navel Oranges in 1930 on the Crop of 1930-31 Num- ber of trees Average trunk cir- cumference, inches Number of oranges per tree* Percent of fruits re- moved Diameter of fruit harvested Average diameter, inches Treatment Before thinning Harvested Increase over check, inches / * 3 4 5 6 7 Experiment No. 1 (thinned July 18-19, 1930; harvested January 27-28, 1931) Check Lightly thinned.. Heavily thinned. 21.75±0.02 1,045.8 20.94±0.04 934.8 22.51±0 02 1,231.3 ,045 8±56.8 575.9±26.0 29.3 696.6±15.7 43.0 2.63±0 02 2.80±0.03 2 84±0.02 00 17±0 04 0.21±0.03 Experiment No. 2 (thinned July 22-23, 1930; harvested February 19-20, 1931) Check Lightly thinned ... Heavily thinned. 27.62±0 06 1,293.7 26 20±0.06 1,175.2 27.37±0.05 1,367.1 1,293.7±59.2 924.5±33.3 21.3 620 2±35.0 45 4 2 61±0 02 2.68±0.02 2.77±0.02 0.00 0.07±0.02 15±0 03 Experiment No. 3 (thinned July 29-30, 1930; harvested February 28 and March 1, 1931) Check Lightly thinned.. Heavily thinned 25.75±0 06 21.82±0.12 25.14±0.05 1,282.1 1,397.0 1,325.4 282.1±49.2 049.3±22.9 24.9 610.7±32.9 53.9 2 55±0 02 2 52±0 02 2 68±0.02 0.00 -0.03±0.03t 13±0 03 Table 3 (Continued) : Cols. 8 to 16. Field boxes per tree Num- ber of oranges per packing box Per cent of size of all fruit harvested Per cent of grade of all fruit harvested Treatment Number harvested Reduc- tion in per cent of check 200 per box and larger 216 and 252 per box 288 per box and smaller Fancy Choice Stand- ards, culls, and "ponies" 8 9 10 11 12 IS U 15 16 Experiment No. 1 (thinned July 18-19, 1930; harvested January 27-28, 1931) Check Lightly thinned.. Heavily thinned 7.01±0.32 4.59±0.16 5.37±0.10 0.0 218.3 39.5 37.8 22.7 87.5 9.4 34.5 187.5 59.2 28.8 12 88.5 8.1 23 4 186.6 61 28.6 10.4 91 6.2 3 1 3 5 2.8 Experiment No. 2 (thinned July 22-23, 1930; harvested February 19-20, 1931; Check Lightly thinned... Heavily thinned 7.89±0.33 6.16±0.27 4.26±0 20 230.2 27.9 40 2 31.9 64 1 22.9 21.9 218.3 35 4 39.8 24.8 68.1 19.9 46.0 205 4 44.3 37.5 18.2 67.2 20 6 13 12 12.2 Experiment No. 3 (thinned July 29-30, 1930; harvested February 28 and March 1, 1931) Check Lightly thinned... Heavily thinned. 9.17±0.60 7.84±0.41 5.00±0 24 219.5 36 2 37.8 26 86.1 10 1 14 5 224.5 34.7 32 2 33 1 80.8 12.6 45 5 205.8 49 5 30 1 20 4 86.4 10 5 3.1 Excluding drops. From 10 to 45 drops were counted under each tree, on an average, at time of harvest. 12 University op California — Experiment Station the trees which were thinned did not compensate in volume for the reduced number of fruits which were harvested from those trees. From the data that have been referred to, it is difficult to determine what the increase in size may mean in relation to commercial packing- house sizes. This can be determined by comparing the results of grading the fruit in the packing-house after it has passed through the ordinary procedures of temporary storage and handling which are performed there. The fruit was graded into Fancy (first grade), Choice (second grade), Standards (third grade), culls (unmarketable fruit), and "ponies" (extremely small unmarketable fruits). The size of fruits in each of these grades was determined. Summaries of the results of this grading process are given for the Washington Navels of 1930-31 in table 3. Column 10 of the table shows that thinning produced a difference in the average size of all grades (including those not packed), which could be readily measured in the packing-house. The results of sizing the fruit in this way are similar to those obtained by measuring every tenth fruit harvested per tree and averaging the results for each tree, as given in column 6. They do not, however, provide an index of the reliabil- ity of the measurement. It may be asked whether the average increase in diameter of fruit was obtained at the expense of any one size of fruit or whether the size of all fruit remaining on the tree is increased by the process. That the latter was the case is indicated by the summary of the packing-house size data for each lot of fruit in the individual experiments as given in columns 11, 12, and 13 of table 3. The percentage of all fruits that packed 200 or fewer per packing box (size 200 or larger) increased in each of the three experiments in relation to the extent of thinning. The percentage of medium-sized fruits (216 and 252 per box) decreased slightly, and that of small-sized fruits (288 or more per box) decreased more markedly as a result of thinning. Only the one exceptional group in one experiment, which has been discussed above (page 10), is contrary to this general tendency. The conclusion is that thinning affected all the fruits left on the tree to some extent. Another problem of practical importance is the effect of the thinning process on the percentage of fruits of various grades. Data on this ques- tion are presented in columns 14, 15, and 16 of table 3, for the Washing- ton Navels in the crop year in which the thinning was done. The type of grading varied at various packing-houses, but for the purpose of this presentation the data are reduced to three grades : Fancy, Choice, and one classification including those grades which were not packed, namely, Standards and culls and "ponies". The percentages given are compa- Bul.576] Some Effects of Thinning Orange Fruits 13 TABLE 4 Effect of Thinning Valencia Oranges in 1930 on the Crop of 1930-31 Num- ber of trees Average trunk cir- cumference, inches Number of oranges per tree* Per cent of fruits re- moved Diameter of fruit harvested Average diameter, inches Treatment Before thinning Harvested Increase over check, inches 1 2 3 4 5 6 7 Experiment No. 5 (thinned August 20-21, 1930; harvested July 17, 1931) Check Lightly thinned... Heavily thinned. 25.74±0.03 26. 72=1=0. 04 26.43±0 04 1,015.1 1,073.2 1,149.2 1,015. 2±62. 8 0.0 797.6±42.3 25.7 713.5=1=26.5 37.9 50±0.01 53±0.01 55=1=0.01 0.00 0.04=1=0.02 0.05±0.02 Experiment No. 7 (thinned July 19, 1930; harvested June 20, 1931) Check Lightly thinned... Heavily thinned 22. 92=1=0.03 903.8 23.84±0.03 878.8 23 71=1=0 04 993.1 903.8=1=47.1 0.0 676.1±35.1 29.9 521.9±33.5 47.5 41db0 01 46±0.01 50±0.01 00 0.05=1=0.02 0.09±0.02 Experiment No. 6 (thinned August 13-14, 1930; harvested June 13, 1931) Check Lightly thinned... Heavily thinned. 21.50±0.03 1,529.6 20.94±0.05 1,417.2 22.13=1=0 05 1,683.0 1,529.6±61.2 0.0 1,090.8±52.9 23 931.1±40.5 44.7 41±0.02 48±0.02 49±0.02 0.00 0.08=1=0. 03 08±0.03 Experiment No. 4 (thinned July 26, 1930; harvested July 7, 1931) Check Lightly thinned... Heavily thinned. 25. 39=1=0. 02 23.80±0 05 24.35±0.03 1,348 6 1,326.7 1,389.1 1,348. 6±41. 2 980.2±38.5 718.8±25.8 25 Of 50. 0t 43=1=0.01 51=1=0.01 61±0.02 0.00 0.08±0.01 18=1=0.02 Table 4 {Continued) : Cols. 8 to 16. Field boxes per tree Num- ber of oranges per packing box Per cent of size of all fruit harvested Per cent of grade of all fruit harvested Treatment Number harvested Reduc- tion in per cent of check 200 per box and larger 216 and 252 per box 288 per box and smaller Fancy Choice Stand- ards, culls, and "ponies" 8 9 10 11 12 13 14 15 16 Experiment No. 5 (thinned August 20-21; harvested July 17, 1931) Check Lightly thinned... Heavily thinned. 7.43±0.45 6.21±0.34 5.83±0.22 0.0 251.3 13.7 46.9 39.4 65.6 27.9 16.4 245.2 18.1 42.0 39.9 66.2 29.2 21.5 243.7 18.9 44.9 36.2 63.6 28.7 6.5 4 6 7.7 Experiment No. 7 (thinned July 19, 1930; harvested June 20, 1931) Check Lightly thinned... Heavily thinned 4.43±0.22 3.50=1=0.18 2.90±0.18 0.0 264.1 11.3 43.8 44.9 75.2 19.8 21.0 251.8 17.7 45.8 36.5 75.8 18.0 34.5 233.1 27.6 46.6 25.7 75.5 20.7 5.0 6.2 3.8 Experiment No. 6 (thinned August 13-14, 1930; harvested June 13, 1931) Check 8.07±0.28 6.54±0.19 5.62±0.17 0.0 19.0 30.4 X Lightly thinned.... Heavily thinned.. Experiment No. 4 (thinned July 26, 1930; harvested July 7, 1931) Check Lightly thinned... Heavily thinned. 7.10±0.22 5.48±0.22 4.40=1=0.15 0.0 263.7 8.5 47.6 43.9 63.2 30.9 22.8 247.1 13.2 54.5 32.3 63.1 32.2 38.0 231.6 28.0 49.9 22.1 60.0 35.1 5.9 4.7 4.9 * Excluding drops. t Estimated. { Dashes indicate data not available. 14 University of California — Experiment Station rable for only one experiment, and not between experiments. It may be observed that within the various experiments the thinning proc- ess did not show a consistent effect on the proportion of fruit of any one grade. Apparently its effect on the crop is reflected only in the size and amount of fruit harvested. Effect of Thinning Valencia Oranges on the Crop Picked in the Year of Thinning (1930-31). — The results obtained with the experimental thinning of Valencia oranges in 1930 from the crop in the same year, 1930-31, are presented in table 4. In each of the four experiments thin- ning resulted in an increased size of fruit, whether interpreted by means of the average size of fruit of each tree in each experimental group, as in columns 6 and 7, or by the packing-house sizes for all the fruit from each group as a whole, as in column 10. The effect of thinning was greatest when it was most severe. The increased size of fruit was not sufficient to offset the effect of the reduction in the number of fruits, however, and columns 8 and 9 show that the volume of crop harvested was reduced by the practice. The average increase in size of the fruit was apparently due to an effect of thinning on all remaining fruits, for columns 11, 12, and 13 show that the percentage of large sizes was in- creased, and that there was no consistent change in the percentage of medium sizes, while there was a decrease in that of small sizes. As in the case of Washington Navels, thinning of Valencia oranges had no effect on the proportion of fruit from any one orchard which graded Fancy, Choice, or lower at the packing-house. Apparently it effected only the size and numbers of fruits harvested. Effect of Thinning Washington Navel Oranges on the Crop Produced in the Second Season After Thinning (1931-32). — The crops harvested in 1931-32 were observed from two of the orchards of Washington Navel oranges which had been thinned during the summer of 1930. The data are presented in table 5. A striking increase in the number of oranges harvested from the dif- ferently treated groups of each experiment was observed. Hand thin- ning of the previous crop caused a very pronounced increase in the number of oranges produced by the next succeeding crop (columns 1 and 2 of table 5) . This increase is positively related to the extent of thin- ning in the two trials. From the data of columns 3 and 4 it is seen that the average size of fruit harvested in 1931-32 from the thinned trees was less than that picked from the checks. However, this decrease was not sufficient to offset the larger number of fruits, and a considerably larger volume of fruit, as measured in field boxes, was picked from the thinned trees, as shown in columns 5 and 6 of the table. Bul.576] Some Effects of Thinning Orange Fruits 15 ~5 If o-a CD Ah Standards, culls, and "ponies" GO J c O O,. >> o (3 - "o3 §1 11 01 p-i ooxg °° O S CM „Q CO o T5 h fl 2 v- 03 ag OS » 03 so 00 Number of oranges per packing box t^ QJ 0) (-. t< 01 a 0> o X! 13 Increase in per cent of check «o 11 >0 0) >• o3 "3 'o a? a 03 Q 11 0> C 68 h ■><■ 13 o I" 1 so *8 1 > 03 -C '3 Increase in per cent of check ®* C o> | "o3 0> u H ^ 1^ 00 Csj p CM <* «* 03 o -r ,— 1 CO TO CO lO cr CO "5 i-O >o CO o ■^ ■* « 03 ^ ~ lO oo CO CO p ■>*l CO CO CM CM CO r CO CO "* "* ^ co o C-q CM ■* l> C o CM o c~ »o o 1^ CO m CM CM P »o o o o 4 + 4 0C l>. t^. t> as CO CO o O o o + 4 ■r o CM CM o o o c^ o o o o -t 4 OS 5C CM p CM o m lO CO co o cc CI -*i cc CO 4 + 4 CM CO »o S o- CO CO oc 1-1 t: a P p 1 — J3 t | ,5 c £ a CO CM CM OC cm -I- CO CO CO CO ■>»< CM co m CO CO oo CM CO t>- CO i-H CM o o CM t~- CO t^ CO o> O c "5 CO CO rt' CM ■* a + CO a- CO ■* CO CM o o 4 4 O co CO O CO t^ O O a ° ° o o 4 4 1^ o .-H CO o o CM o o 4 CO CO o o o d 4 4 CO •*»< a> co CM CM o o O0 CO -*l CD lO O 452 1±33 700.0±36.7 934.5±34.7 c c c a c z I 1 e IS i g i -S ^ o © w «< 16 University of California — Experiment Station The smaller size of the fruit from the thinned plots is reflected in the packing-house data of average number of oranges per packing box, column 7. The decrease in size of fruit was apparently due to an effect upon all fruits, for columns 8, 9, and 10 show that the percentage of large sizes was decreased, while those of medium and small sizes was increased by the thinning. The percentage of fruit in experimental orchard No. 1 which packed Fancy, Choice, etc., was not altered by the procedure. In orchard No. 2, however, there was a tendency for a lowered grade of fruit. This was due to a larger proportion of "ponies." Effect of Thinning Valencia Oranges on the Crop Produced in the Second Season After Thinning (1931-32). — In three experimental orch- ards it was possible to study the effect of the original thinning of Valen- cia oranges on the crop following that in which the thinning was done. In the case of two of these, all the observations heretofore discussed were made, but in the case of experimental orchard No. 6 it was not possible to obtain the packing-house data. The summaries of the studies are recorded in table 6. With the exception of experimental orchard No. 7, the results were in general agreement with those obtained from the Washington Navel orchards in the crop year following that in which the thinning was done. The quantitative results with Valencias are not as striking, however. Reference to table 6 shows that thinning caused an increase in the num- ber of oranges harvested per tree, columns 1 and 2. Although the average diameter of oranges, columns 3 and 4, was slightly less than that of fruit from the check trees, the number of field boxes picked was greater, as indicated in columns 5 and 6. As far as the packing-house data go they indicate that thinning in the previous year caused a reduction in the percentage of large sizes and an increase in that of small sizes, with very little change in that of medium-sized fruits, columns 8, 9, and 10. There was no consistent effect of thinning upon the percentages of fruits in the various packing-house grades, as indicated in columns 11, 12, and 13 of the table. The performance of experiment No. 7 was not consistent in all respects with that of the other experiments during the 1931-32 season. A hypo- thetical explanation may account for that fact, namely, that the normal check yield for this plot in 1931-32 was 27 per cent greater than in 1930-31, whereas the normal check yields of all other plots observed were almost equal or were less in the season following thinning than in the season in which thinning was done. This orchard was only thirteen years old at time of thinning, an age which is less than that at which small sizes are usually a serious problem. Also, the general health and Bul.576] Some Effects of Thinning Orange Fruits 17 « o s W o o CO M 3a ol *.£ 03 3 ft «^> 8 'o O e* >> o 03 En - ■8-8 .81 03 > -I PM oo ^ o3 CM g H o ^3 t, o3 ag OJ 00 Number of oranges per packing box i^ 8 01 a =3 5 "3 Increase in per cent of check c© 11 »o T3 0) 1 > u A '3 (4 u a Q o >- o O o> Q o ""«*■ l 03 13 -G > 0) GO 1 I 1 > .4 '3 u Increase in per cent of check e<* - a> o <* o en oo •* ^ ■* N o oo Ol Ui CM -r* tjh ■»*< ta co O oo ■>* io ■* -H -H -H 41 -H o «? 41 -H -H IO CO CO -H -H 4H O OO •* 1 s •« ■- ^ 00 >o CM lO Ui Ui *n CO o H >-l CM 1-1 w* i-H t^. o oo CM CM CM 00 00 00 -* .-H Tfl r- co CO CO CO lO ■* -^ «o Ui Ui ,_, Ui OJ 00 O OS 00 "1 "**< CO (M -1— -t o 00 00 o T 7 -* T-l CM o o o 4 -H CD CM Ui >o Ui Ui © © o o -H 4 o © S8 o o o o o o o o o 4 4! Si Tt< CO Ui Ui CM CM CM o t^ O c O CO 1 t^ t^ © cc 00 CM c< 4 -H -H o- oo r^ CM t^ oc oo oo a p c ] ■s ^ >» ^ c 3 S ■£ M a) L k! ft I I I I I I I I I I I I I I I I I I I I I CM CO CO CO o o o -H -H OS Of) OS CO 1—1 CO r» oo o o o o -H 41 ^ O! N CO N CO N H N lO O^K BPQ 18 University of California — Experiment Station vigor of the grove visibly improved from 1930 to 1932, a condition which may have resulted in an increased yield. As thinning would gen- erally be done when the yield is high and, on the average, be followed by a year of lower yields, this orchard is not as favorable as many for the experiment, for it would not have been considered a good possibility for commercial thinning. That it was included among the groves studied is fortunate, however, for it emphasized the likelihood that orchards would respond in varying ways to the thinning of their fruits. SUMMARY OF FIELD AND PACKING-HOUSE OBSERVATIONS The following conclusions are apparent from observations of the results of the three experiments with Washington Navel oranges and the four with Valencia oranges. In the case of healthy, mature trees of both varieties, there was a definite tendency for thinning of young fruit soon after the normal June drop, in a year of large crops, to result in an increase in the size of the remaining fruit. This increase was greater with more severe thin- ning. The greater average size was probably due to an increase in size of all the fruit remaining on the tree, rather than to an increase of size of any one class of fruit. In spite of the larger average size of the fruit harvested, fewer boxes of fruit were picked from the trees which were thinned than from the control trees. Thinning apparently did not affect the proportion of fruit in the various packing-house grades. In the year following that in which the thinning operation was car- ried out, there was a definite tendency for the thinned trees in the older, healthy orchards to mature a larger volume of fruit than did the control trees. The fruit from the treated trees was smaller than the fruit from the controls. It is probable that all of the fruit on the trees was affected by the thinning procedure in the previous year. In three of the four experiments for which packing-house data are available for 1931-32, there was no effect of thinning on the proportion of fruit placed in the various grades. In one case, however, there was a lowering of grade, owing to an increase in the number of unmarketable small sizes which are classed as "ponies". The effect of thinning in the previous year on the number and size of fruits harvested was more marked in the case of Washington Navel oranges than in that of Valencia oranges. A possible increased effectiveness of the thinning procedure on fruit sizes is suggested by the responses observed. It seems likely that the ability of the trees whose fruit was thinned to mature a larger crop in the following season might be put to practical use by thinning for two or more consecutive seasons. Under such conditions it is possible the Bul.576] Some Effects of Thinning Orange Fruits 19 average increase in size of fruit might be greater in the second season than in the first, provided equal numbers of fruits were left on the trees. This phase of the problem has not been investigated. ECONOMIC INTERPRETATION OF DATA To attempt to interpret the results of these experiments in a manner which will determine the economic value of the thinning procedure is difficult and hazardous. It is felt that the use of experiments in several orchards has given a rather reliable idea of the responses which might be made by trees subjected to thinning in other years. However, the prices received for fruit in the years of study may be very poor criteria of the prices which will be received in the future. Under present economic con- ditions it is obviously impractical to repeat the experiments each year in order to establish average price levels and the differentials paid for fruit of various sizes and grades. These criteria would be essential to predict financial returns accurately. It appears desirable, however, to give some illustration of the possible effect of thinning upon returns, even if that be inadequate for purposes of precise prediction. The following somewhat hypothetical study has, therefore, been made. The returns of each experiment for which packing-house records could be obtained, have been calculated in the following manner : The actual prices which were paid for California oranges of each size and grade in certain years were studied. The years for which the returns were used are 1926-27 to 1931-32, inclusive. It should be noted that the price level during the early part of this period was high. During this six-year period there were three very large crop years in which thinning might presumably have been done; these years of large crops alternated with years of somewhat smaller crops. The gross returns during these years are those actually paid for fruit delivered to the packing-house by one of two cooperative packing-houses, the Monte Vista Citrus Associa- tion in Riverside, or the Upland Citrus Association in Upland, and are believed to be representative of average prices paid for the respective seasons. The series of prices used for the Washington Navel oranges are given in table 8 of the Appendix', and for the Valencia oranges in table 9. The hypothetical gross returns based on these prices have been calculated for each group of each experiment for which packing-house data are avail- able. In view of the effect of thinning on the yield the year after the thinning was done, the returns for that year have also been calculated. The complete packing-house data upon which these calculations are 20 University of California — Experiment Station to o a o to s < O w Eh < w Eh p £ j ID 1 ft PH «5 p ti ft < N £ ^ £. to M CO o Eh P w p o ^ & to « p P !i J § o pq g to 2 N W pq H Eh ft <5 1 W Eh Ph . c_> P [x| m £ fa i p o p to Ph ^ <5 10 n fc Eh P5 P Eh g pel P CO m W in S < o &f 3 u H B g w W W Eh a; ,C CO o"C a; C £ 4i Lightly Heavily thinned thinned O 3 Is XJ >> 1! .S s 03 a * o js S CO CO O CO CSS >>*0 > s 03 fl K5 ~' CD bfi.g 35 o CD o bo _e '3 a o co a o 3 a) CO CD s 1 CSS CM CC CSS > 5 03 Pi ^•5 ^4 o CD o t— CN CO CM os o3 a ffi5 M.S 35 o CD O a o ^ 3 * .2 £-3 Ph d o 1" "5 CD |e a 1 3 * k: O" j. OO 00 CD 1 « 1 b- CC tr. OO CD m o- j: CO ■- 1 t- o- I> e> en 1 cq rH o 1 *^ »-i a> © CC t- co CC C ** iH cs- CC vn a o~ cs- CO 1-1 ^h CM CC (N cs- fN 1 '-' CSS CM CC OJ 00 h* 1 rtc CD l 3 CC CO ce CO o> i-h O oc LC 1 « IC CC 1 °° T-l Tf 1—1 ■^ "* "* >o o> »c CO 00 CO o> t^ CC or 1 s o ^ "* Tfl m »> CN e> CO Tt< c CC CI CO CD CC co en >- CD OC lO c in CSS u? 1 T* U5 r-j 00 ifl t>. 3 co ~ 1 »H 1 *4 oc CI CC CC »c >o t^ oc m t- O t" t--. <-H EC 1 M 1 CS 1 CM t^ U0 1 ?* co p 1 •>* C3- CO CO o o ° l> CN b- :." rH (M 1 CM CO l~- 1 S t^ «3 OS c t^ OO CC OC CO CN OO CO m CN 1 N 1 es »H 1 CS o -* ■"*" to 1 M OC CN CO CM •>* •> CO r^ ^H "# iH 1 es b 1 b D b c P c Si b c °P b C D fc. C •1 Sf c p - P P P P pC -a t 'r .C CO a ^_ R a +- 03 CD O R s C c > s C c c- >> C3 R 5 s ! i Es t- R B 5 c >H ^ PC >■ >■ PC ^ > t> m ff c V c b DT3 a a 03 > c- CC < o c co C S ? -a 5 Bul.576] Some Effects of Thinning Orange Fruits 21 «*- o o'C S3 oj > 5 OS C K5 3^ 8 U C Is 1! o §1 1 GG o co > fl ©•- #8 II 35 /4 o CD o M c '3 A "3 H O | a> CO T3 03 § CO .T3 " o> > c os a W3 35 03 O ."3 o> > a >/9 35 J4 u a> O s O 111 *•§ ° ill <*> O "os T3 a, > O tH_ •r cj s Is -2 fa cS 0> i- C O .1 = o IO IO O •"*( -h IO xf CO t- O co | eo s oi I io ti to | © os oo t» iq © - Tt< e* IO CM 00 W N a -*i CM C» •O CO I 00 OJOOIC- CM i-l I CO CO r-H C- iO "*< © i-H OO o» co^e- cm eo i to co eo to t^ t© t CO ■* CO I t- f-H O I tH to »-i 00 M cj io o t>. t- "■f •<* oo co co I to ■* eo B- <-H 0O | © ■* 05 I M CO * I N io io © oo ^ m is io I fq x** co ob cm co to co co | e- O » | N O0 CO I T* •>»< © I ** cm to en r-~ a> c- io » m io © u» co to o •* oo eo CM I CM h | N ^h I CM CO CM | 18 CM^HICO CO CM I IO t>. © t© IO N N «■* CO I ** io o to * » d io oo eo CM I CM ^H I CM rH I M CO »^ I "# CO CO I «l lOCMIt- cm to eo os cx) e» o cm em e t» M eo to O 115 N N rt I N H I M rt I N OO GO I IO © CO 00 CO i-H IO CO ■«*< o o> ir- on GO CO CO IO to o CM to em •O "<}< en IO i>- U-, °> «*-i ^ >H bO C 31 1 3 53 03 "o "eS e3 eS CD Oi 22 University of California — Experiment Station based are presented in tables 10, 11, 12, and 13, in order that the reader may determine the effect of other prices than those given, upon returns for fruit in the various experiments. In table 7 are presented the gross returns received per tree for fruit delivered to the packing-house door from each of the groups of each experiment, assuming that the thinning had been done in the large crop years 1926-27, 1928-29, or in 1930-31, the year in which the operation was actually performed. A further assumption is necessary, namely, that the same crops would have prevailed in each of these periods, and would have been followed by the same after-crop as was actually observed in 1930-31 and 1931-32, coupled with the observed response to thinning. The hypothetical returns may be seen to vary greatly for each experi- mental orchard in the three periods. This variation has had a pronounced effect upon the relative returns from various treatments in each orchard. The cost of the thinning operation, although it has not been deducted, should be kept in mind while considering these computations. In these experiments the work was done by intelligent and active help. At each orchard a new crew was broken in. Increased care was used over that which would be employed by a grower because the thinned fruits were put in a picking sack for measuring. Under these conditions the average time of thinning was close to 1 hour per tree. A slight reduction of this time might be possible under commercial conditions. It is believed rea- sonable to regard a charge of 30 cents per tree as the cost of the opera- tion. Charges for picking and hauling, which are variable, have not been made. In general, table 7 indicates that under the conditions from which comparisons are drawn there is a tendency for thinning to cause a reduc- tion of gross returns in the year of thinning. This appears to be true of both varieties of oranges. The few scattered exceptions to this generaliza- tion are weakened by lack of consistency between the returns for lightly and heavily thinned trees in the same experiment. When the theoretical returns are considered for the season after that in which the thinning was done, a different result is obtained for each of the three periods studied. In the second year there is a pronounced ten- dency for the thinned trees to return more money than the unthinned control trees. This tendency is shown in every instance except that of the lightly thinned trees in experiment No. 7. This particular experiment in which the trees performed differently from the others, has already been discussed (page 16). When the gross returns for the year of thinning and the subsequent year are totaled for each experiment in which the data could be obtained, it is found that under the price structures of 1926-27 and 1927-28, Bul.576J Some Effects of Thinning Orange Fruits 23 thinning in 1926 might have returned a slight profit under some condi- tions even after the 30-cent charge for thinning labor is deducted. Al- though the average return from the thinned trees is slightly greater than from the unthinned, the variation between the lightly thinned and heavily thinned plots is such that one could not be certain whether a particular plot would be profitable under the conditions of those years. In the next two seasons, 1928-29 and 1929-30, the prices paid for fruit were such that the theoretical total gross return for the two years was, in all cases except one (experiment No. 7), greater from the trees which had been thinned. This appears to be due to a larger differential in prices between large and small oranges in 1928-29 as compared with 1926-27. The returns of this second period are increased partly, particu- larly in the case of the Washington Navels, by a slightly lower differ- ential for 1929-30, as compared with 1927-28. In both of these two years of high prices the price ranges for fruit of various sizes favored thinning. In the season in which the thinning was actually done, 1930-31, and the year following, 1931-32, the total gross returns from the experi- mental trees were such that no definite conclusion concerning the effect of thinning on gross returns could be established. In each experiment one of the thinned plots returned slightly more money than did the unthinned trees. However, when the cost of thinning is deducted, the return from fruit on the thinned trees is found to exceed that from the unthinned trees in only two out of eight cases. In these two cases the average margin of profit is less than the average loss in the other six cases. In these years the probability is low that an additional mature orchard would show a profitable return as a result of thinning. Prices in these two seasons were characterized by lower levels, particularly in 1931-32. In two of the three periods for which hypothetical returns have been calculated, thinning in the first season could not be regarded as a surely profitable procedure. In one two-year period, 1928-29 and 1929-30, it did return a theoretical profit. By reference to table 1 it may be seen that crop-condition reports for the year 1928 were very high and that they were correlated with total crop produced. Likewise, the mean size of fruit was smaller than for any other year studied. These factors, which produced in 1928-29 a pronounced gradient in prices between large and small-sized fruit, were coupled in this study with a high gen- eral price level in 1929-30, with little differential between the prices paid for large and small fruit. Apparently these two years were ideal for the practice of fruit thinning. Sufficient data are not available to indicate whether such a situation is likely to occur frequently. 24 University of California — Experiment Station SUMMARY AND CONCLUSIONS The experiments discussed above indicate that the thinning of young oranges after the June drop will cause an increase in the year of thin- ning in the average size of fruit produced by mature, thrifty, produc- tive orange trees in California. Because of the decrease in the number of fruits harvested from thinned trees, the total volume of fruit has been less than in the case of unthinned trees. The price ranges that have been studied hypothetically have been such that the differential in favor of large-sized fruit has not been sufficient to offset the effect of the de- creased total volume of crop in the year of thinning, and a financial loss would be usually anticipated in the first year as a result of thinning. In the second season after the thinning was done, however, an in- creased number of fruits matured on previously thinned trees. Al- though the mean size of such fruits was smaller than on the unthinned trees, the total volume of fruit was greater. In general, with the prices studied, an increased return from the thinned trees over the unthinned trees resulted in the second season. In two out of three periods of two years each, the first year of which was a large crop year, the increased hypothetical return as a result of thinning just about balanced the losses resulting in the year of thin- ning. The net result for the two-year period was, therefore, almost nil. In one two-year period, however, 1928-29 and 1929-30, the price struc- ture was such that the responses obtained as a result of thinning fruits in orchards of the type discussed above were theoretically profitable. The price levels which were studied were much higher than those which have existed since 1932. With lower average prices the differen- tial between large and small sizes in large crop years may or may not be greater than with high prices. The general commodity price level has an important bearing on this ratio. In the year after thinning a price differ- ential based on fruit size is not desired for most favorable results. How- ever, in years following a large crop in which the thinning is presumably done, it seems probable that the total production of the industry would be smaller and that, in general, a smaller actual price differential would exist. In the light of these findings it seems unlikely that thinning of orange fruits will become a general practice. This is particularly true since certain additional factors, not taken into account in this investigation, must be considered by the individual grower. One of these is the possi- bility of a crop failure in all or in part of the citrus areas of California. If the individual grower were not affected at the time of such disaster he would lose or gain as a result of thinning, according to whether the Bul.576] Some Effects of Thinning Orange Fruits 25 general crop failure occurred in the year he thinned or the year follow- ing. If, on the other hand, the farmer lost all or a part of his crop along with that of many other growers, his loss would be greater than other- wise as a result of thinning, and his loss would be the greater if the crop failure occurred in the year following thinning. It seems unlikely, there- fore, even if a grower did have a grove which would respond satisfac- torily to thinning, that he would perform this operation unless he were located in a favorable place in relation to frost, winds, etc., and had a long record of regular crop production. Given all of the conditions just mentioned, however, it is possible that some groves with a history of large crops of unprofitable small-sized fruit might be thinned with good results. No other type of grove should be subjected to this treatment in view of present knowledge of the effect which present and future returns for oranges of various sizes and grades may have upon the economic results of such thinning. Bul. 576] Some Effects of Thinning Orange Fruits 27 APPENDIX TABLE 8 Value of Fruits of Washington Navel Oranges on the Trees, for the Seasons 1926-27 to 1931-32, Inclusive, and Mean Value for Groups of Seasons Mean of Mean of Number 1926-27, 1927-28, of fruits per 1926-27 1927-28 1928-29 1929-30 1930-31 1931-32 1928-29, 1929-30, packed box and 1930-31 and 1931-32 Fancy grade, returns per orange in cents 80-100.. 126 150 176 200 216 252 288 324-344 360-392 2.64* 2.36 1.99 1.70 1 50 1 39 1 14 0.81 0.49f 45 2.60 2 45 2.42 2.22 1 99 1.80 1 54 1 19 0.60f 54 4 30 3 30 2 41 1.60 1.02 75 47 0.35 0.21 14 38 87 40 36 28 22 07 83 45f 65 1 70 1 30 0.93 79 69 63 53 43 0.32f 0.23 81 0.72 71 0.71 70 0.66 0.60 0.52 39 10 3 00 2.32 1.78 1.36 1 07 0.92 71 53 0.34 0.27 1.93 1 85 1 84 1.76 1.66 1.56 1.40 1.18 81 0.64 Choice grade, returns per orange in cents 80-100. 126 150 176 200 216 252 288 324-344 360-392 2 03* 1.75 1 55 1.41 1 24 1 16 0.90 55 0.49t 0.45 1.99 2 09 2.14 2.02 1.88 1.67 1 43 1.19 60t 0.54 2.68 2.27 1.85 1.20 77 53 0.28 18 15 14 1.97 80 1 81 0.61 2 03 53 1 96 0.50 1 92 46 1 87 43 1 73 35 1 55 31 1 19t 0.18 65 23 35 37 42 0.44 45 0.43 37 34 0.24 0.10 1.74 1 54 1 31 1 04 82 71 51 35 0.27 0.27 1.44 1.09 1.16 1 47 1.42 1.32 1.18 1 03 0.68 0.64 Third classification, returns per pound in cents Standards Culls, rots, and "ponies" 2 159 500* 2.614 500* 682 0.500' 3 136 500* 1.091 0.500* 0.477 300* 1.311 500 3 076 0.400 * Estimated. t Estimated. Originally packed as Standards. 28 University of California — Experiment Station table 9 Value of Fruits of Valencia Oranges on - the Trees, for the Seasons 1926-27 to 1931-32, Inclusive, and Mean Value for Groups of Seasons Mean of Mean of Number 1926-27, 1927-28, of fruits per 1926-27 1927-28 1928-29 1929-30 1930-31 1931-32 1928-29, 1929-30, packed box and 1930-31 and 1931-32 Fancy grade, returns per orange in cents 80-100.. 126 150 176 200 216 252 288 324-344 360-392 2.70* 2.70 2.41 1.96 1.47 1.15 81 47 0.22f 0.21 4.54 3.27 2.89 2.81 2.61 2.34 2.02 1.99 1.34 0.61 3.24 3.40 2.79 2.20 1.57 1.08 0.59 0.34 0.17 0.16 3.56 3.28 2.95 2.94 2.80 2.67 2.26 1.85 1.11 1.64 2.33 2.19 1.66 1.28 0.95 0.80 0.55 39 0.22 0.11 2.45 1.76 1.28 1.91 0.66 0.60 0.41 0.31 0.25 0.13 2.76 2.76 2.29 1.81 1.33 1.01 0.65 0.40 0.20 0.16 3 52 2.77 2.37 2.22 2.02 1.87 1.56 1.36 0.90 46 Choice grade, returns per orange in cents 80-100.. 126 150 176 200 216 252 288 324-344 360-392 2.24* 2.24 1.81 1.62 1.22 0.96 0.59 0.36 0.22f 0.21 2.47 2.20 2.23 2.29 2.18 2 03 1.66 1.42 0.91 0.61 2.10 2.24 1.91 1.66 1.11 0.83 0.41 0.25 0.09 0.16 1.34 1.65 2.15 2.25 2.18 2.11 1.72 1.28 67 64 1.04 1.99 0.78 0.62 50 45 0.31 0.16 06 0.11 76 0.81 0.61 0.52 0.39 33 0.22 0.17 0.14 0.13 1.79 1.82 1.50 1.30 0.94 75 0.44 0.26 12 0.16 1.52 1.55 1.66 169 1.58 0.96 57 0.46 Third classification, returns per pound in cents Standards Culls, rots, and "ponies" 0975 0.568 2.927 1.393 0.755 341 341 0.541 341 0.650 0.341 0.757 0.417 2.219 0.692 * Estimated. t Estimated actually packed as Standards, and calculated returns are on basis of Standards. Bul.576] Some Effects of Thinning Orange Fruits 29 TABLE 10 Statement of Grades and Sizes of Fruits Harvested from Thinning Experiments with Washington Navel Oranges, in the Year of Thinning, 1930-31* Number Experiment No. 1 Experiment No. 2 Experiment No. 3 of fruit per packed box Check Lightly Heavily thinned thinned Check Lightly thinned Heavily thinned Check Lightly thinned Heavily thinned Average number of fruits per tree, Fancy grade 80-100.. 126 150 176 200 216 252 288 324-344 360-392 3.1 28.0 53.9 113 2 158.5 189.2 153.6 77.5 54.8 42.8 10.2 56.2 67.0 86.4 87.0 94.1 53.7 24.3 11.8 13.2 12.1 64.9 78.2 111 5 115.4 115.6 61.6 23.8 15.8 10.6 0.9 6.1 42.0 74.9 101.7 194.3 147.0 158.2 87.8 1.5 10.7 52.7 81.7 84.9 162.1 100.8 93.6 45.8 0.0 3 5 14.6 48.1 59.8 64.7 98.2 56.0 46.1 17.8 0.0 1.4 14.9 66.7 140.7 159.8 238.0 145.8 198.5 25.6 10.1 2.4 22.3 51 1 110.8 133.7 175.6 130.9 168.6 54.7 21.7 0.9 15 2 61.8 88.0 84.2 84.4 75.5 63.0 15.2 7.9 Average number of fruits per tree, Choice grade 80-100.. 126 150 176 200 216 252 288 324-344 360-392 0.8 1.4 0.8 1.7 10 1.3 0.2 9 2.3 4.2 3.4 7.3 5 8 4.6 0.8 1.1 5.0 5.6 4.7 18.2 19.1 14.3 3.5 6.7 6.0 5.7 4.5 37.5 28.3 24.6 17.1 22.1 18.3 9.1 9.2 44.6 27.3 19.5 13.3 18.7 14.1 7.4 6.3 48.4 30.1 23.2 10.8 15.4 16.5 6.0 5.6 74.7 44.3 25.7 38 1 12.1 15.4 32 3.7 25.7 15 8 5.2 16 23.9 10.9 2.4 2.5 31.7 13 6 7.0 9.1 25 7 4.8 9 0.6 0.0 0.0 0.0 8.8 8.7 0.0 1.4 3 5 9.4 8.5 5.6 15 2 5.6 5.3 3.8 Average number of pounds per tree Standards. . Culls, rots, "ponies". 4.1 3 2.5 2.3 2.7 41.4 28.3 3.9 19.7 2.6 19.0 4.8 * The number of trees in each group of each experiment is 10, except in the check and lightly thinned groups of experiment No. 3, which contain 11 and 7 trees, respectively. 30 University of California — Experiment Station TABLE 11 Statement of Grades and Sizes of Fruits Harvested from Thinning Experiments with Washington Navel Oranges in the Year Following Thinning, 1931-32* Experiment No. 1 Experiment No. 2 Number of fruits per packed box Check Lightly thinned Heavily thinned Check Lightly thinned Heavily thinned Average number of fruits per tree, Fancy grade 80-100.. 126 150 176 200 216 252 288 324-344 360-392 57.9 70.7 86.0 83.0 61.7 55 7 41.9 14 5 7.1 6.1 13 40 8 92 8 106 8 95 4 91 82 9 26 1 13 2 10 4 26.4 53.1 92.2 137.2 127.5 125.6 118.1 37.7 19 1 17 2 28.3 63 1 43.6 23 4 12 8 7.0 2.6 1.4 4 0.1 22 1 68.6 67 1 54 8 38.8 37.8 12 5 6.9 1.1 5 10.1 39.3 56 5 57 3 45 6 45.4 14 8 13 8 3 6 1.4 Average number of fruits per tree, Choice grade 80-100. 126 150 176 200 216 252 288 324-344 360-392 20 2 31.7 34.9 29.5 30.1 45 2 34 5 14 6 11 5 3 5 2 8 11 30 4 49 4 53 82 1 69 43 8 25 7 5 8 2.7 9.4 35 56 6 59.4 97.4 84.1 45 8 34 11.0 52 9 49 23 2 16.1 25.4 21.9 9 6 1 34 8 62.6 50 4 43 5 34.9 23 10 5 4 6 8 0.1 29 1 37.0 51 9 54.9 48 9 26.9 14 3 3 4 5 Average number of pounds per tree Standards Culls, rots, "ponies' 16.8 10.7 27.4 10 .6 34 6 12.8 22.7 22.3 28.7 54 27.9 51.2 2 is 8. The number of trees in each group of experiment No. 1 is 10, and in each group of experiment No. Bul. 576] Some Effects of Thinning Orange Fruits 31 TABLE 12 Statement of Grades and Sizes of Fruits Harvested from Thinning Experiments with Valencia Oranges, in the Year of Thinning, 1930-32* Number Experiment No. 4 Experiment No. 5 Experiment No. 7 of fruit per packed box Check Lightly thinned Heavily thinned Check Lightly thinned Heavily thinned Check Lightly thinned Heavily thinned Average number of fruits per tree, Fancy grade 80-100 1 1 3.6 27.1 45 3 157.3 271.5 124.5 136.7 26.1 0.0 0.2 3.7 30 60.0 239.4 126.2 89.6 62.3 6.9 11.5 56 3 72.2 137.1 108.0 21.5 69.9 1.4 0.0 0.3 7.2 26.3 59.7 158.5 181.8 97.9 45.9 23.4 0.0 0.8 10.1 23.9 61 5 136.8 99.0 118.1 49.5 12.0 0.0 1.0 8.2 7.1 68.8 124.7 99.2 90.9 37.9 13.7 0.1 0.2 6.6 18.3 36.4 60.1 164.6 65.1 100.8 2.6 1.1 9.9 30.9 55 9 71.7 169.6 62.5 72.7 0.0 0.0 126 150 1.6 11.3 176 35.2 200 49.2 216 57.3 252 95.7 288 32 5 324-344 28.2 360-392 .... 0.2 Average number of fruits per tree, Choice grad B 80-100 0.1 2.1 4.2 23.1 73.7 90.5 48.7 101.9 43.2 0.0 0.2 1.2 7.6 25.5 21.6 142.2 41.9 62.0 13.0 0.0 0.2 2.3 22.7 56.2 55.7 89.7 20.5 27.0 4 6 0.1 0.1 0.4 8.4 23.1 35 9 48.7 99.2 33.7 6.1 0.3 0.4 1.9 11.9 27.9 45 39.9 71.1 21.1 5.8 0.1 0.1 1.3 16.6 29.5 47.6 35.9 55 5 13.8 3.2 0.0 0.2 0.2 2 4 3.2 13.2 25 27 5 28 7 19.2 0.1 0.4 1.0 4 4.8 17.2 26.1 25.4 23 4 9.9 2 126 .. 0.4 150 2.0 176 6.6 200 7.3 216 17.1 252 20 2 288 13.7 324-344 12.8 360-392 5.8 Average number of pounds per tree Standards Culls, rots, ponies" 11 7 4.9 8.5 2.8 7.7 2 4 \ 13.5 J 8.3 13.6 | 15 4 6 1.0 6.7 1.6 2.3 * The number of trees in each group of experiments Nos. 4 and 5 is 10, while in each group of experi- ment No. 7 the number is 12. 32 University op California — Experiment Station TABLE 13 Statement of Grades and Sizes of Fruits Harvested from Thinning Experiments with Valencia Oranges, in the Year Following Thinning, 1931-32* Experiment No. 5 Experiment No. 7 Number of fruits per packed box Check Lightly thinned Heavily thinned Lightly Check thinned Heavily thinned Average number of fruits per tree, Fancy grade 80-100.. 126 150 176 200 216 252 288 324-344 360-392 9.2 50 6 57.5 180.4 153 6 107.9 32.4 12.0 0.0 11.2 43.2 64.1 193.5 167.1 107 9 33 9 18.4 0.1 14.8 39.7 54 5 102.9 173.5 135.8 38 4 11.7 3 4.2 27.6 61.6 188.7 212.0 111.2 58.2 18.7 0.1 0.8 2.7 20.4 393 181 5 211.4 97.4 88.0 17 5 0.0 3 2.7 22 3 55 7 190.7 216.8 107 2 85.9 22.7 Average number of fruits per tree, Choice grade 80-100.. 126 150 176 200 216 252 288 324-344 360-392 2 3.4 13.6 39 5 63.6 92.7 10.6 9.4 0.0 1 2.9 13.9 63.1 104.5 149.9 54 21.4 0.0 0.0 0.2 2.1 13.0 50.6 91.6 137.7 15.5 16.0 0.1 0.8 4.9 9.1 23.5 32.8 12.3 11.2 3 5 3.1 9.7 19.3 29.7 16 4 13.0 0.2 11 3.4 10.0 23.8 38.8 13 4 11.1 Average number of pounds per tree * The number of trees in each group of experiment No. 5 is 10, and in each group of experiment No 7 is 12. 10m-8,'34