r P^^ Vi*A ural Sciences UNIVERSITY OF CALIFORN COMMERCIAL APPLE GROWING IN CALIFORNIA E. C. KOCH . C. ALDERMAN D. S. BROWN CALIFORNIA AGRICULTURAL Experiment Station Extension Service CIRCULAR 538 CONTENTS Introduction 3 Establishing the orchard 4 Land selection and size of orchard 4 Land preparation 4 Laying out the orchard 4 Planting 4 Varieties 8 Pollination 8 Market demand 9 Variety descriptions 10 Rootstocks 14 Dwarfing rootstocks 14 Pruning and training 16 Management of the bearing orchard 18 Pruning 18 Cultivation 20 Cover crops 20 Fertilization 20 Irrigation 21 Thinning 21 Pre-harvest drop 22 Top-working 22 Frost protection 22 Insect and disease control 22 Harvesting, handling, and storage 23 When and how to pick 23 Handling methods and practices 23 Storage 23 Temperature 24 Controlled atmosphere 24 Storage-caused disorders 25 JUNE, 1966 THE AUTHORS: E. C. Koch is Farm Advisor, Santa Cruz County; D. C. Alderman is Extension Pomologist, University of California. Davis; D. S. Brown is Professor of Pomology and Pomologist, University of California, Davis. COMMERCIAL APPLE GROWING IN CALIFORNIA INTRODUCTION California grows about 8 per cent of the nation's apple crop of approximately 135,000,000 bushels. It usually ranks fourth among the states, preceded by Washington, New York and Michigan which together account for about 55 per cent of the country's annual production. A decrease of about 50 per cent in the national per capita consumption of apples has occurred during the last 50 years. In 1963, 27.0 pounds of apples per person were consumed in the U. S., 18.4 pounds of which were consumed fresh, and 8.6 pounds of which were processed. The con- tinuing demand for processed apples is of vital importance to the California apple industry, as 73 per cent of the state's crop is processed. Nearly all of California's fresh-market apples are consumed in the state, whose growing population accounts for the almost complete utilization of the state's domestic fresh-market apple crop, despite the declining per capita consump- tion nationally. The Oak Glen apple district in the San Bernardino Mountains has capitalized on the influx of population by marketing most of its crop at roadside stands in the district. CALIFORNIA APPLE ACREAGE, 1963 Bearing Nonbearing County or district Total acres* Total Watsonville 8,470 2,636 11,106 (Santa Cruz, Monterey, San Benito, Santa Clara) Sebastopol 9,871 1,335 11,206 (Sonoma, Mendocino, Napa) Sierra Foothills 1,817 517 2,334 (Butte, Nevada, El Dorado, Tuolumne, Kern, Shasta, Tulare) Southern California 893 94 987 (San Bernardino, San Diego) Other 1,172 243 1,415 Total 22,223 4,825 27,048 * From California Fruit and Nut Acreage, 1963, California Crop & Livestock Reporting Service, June, 1964. [3 ESTABLISHING THE ORCHARD Land selection and size of orchard Deep soils having good drainage are most important for optimum apple production, and soils containing claypans, hardpans, or underlain with gravel should he avoided. Heavy-textured surface soils are more difficult to work than loams or sandy loams, and they create more problems with crown rot. An adequate supply of good irrigat- ing water is necessary in most apple- producing areas. In certain sections (the Sebastopol district, for example) apples can be grown without supplemental irri- gation, but even in good dry-land areas supplemental irrigation will improve yield and tree vigor. A 20-acre apple orchard is probably the minimum size feasible for profitable production, although 40 acres is even more likely to be commercially practical. Production per acre in relation to the total size of the unit, and the costs of needed equipment, are key factors. A 20-acre unit yielding 10 tons per acre has been considered a marginal enterprise for the past 20 years. The better orchards in full production yield 15 to 25 tons an acre on the average, and some produce up to 40 tons per acre. Land preparation Crop land previously under irrigation should require little or no preparation before planting to the orchard. Sprinkler irrigation will reduce the need for exten- sive soil movement and leveling opera- tions, but grading and leveling is neces- sary for furrow, rill and border-check irrigation systems. Control of noxious weeds is best accomplished prior to planting. Where land has been cleared of timber, stump removal i> necessary for efficienl use ol mechanized equipment. Laying out the orchard A well-planned layout is important to all orchard operations. Once the trees are planted changes are almost impossible to make; therefore a good contour map should be prepared locating all proposed trees, pollinizers, roadways, pipelines, water facilities, drainage and other features. The "square" planting pattern is a most popular and convenient system of plant- ing. The "quincunx" system is actually the square plan with a temporary or filler tree in the center of each square. The "rectangular" or "hedgerow" system is a modification of the square, with inter- plants in the rows in one direction. In the "hexagonal" (or "equilateral tri- angle") system all trees are equidistant, thus making more efficient use of space; adequate space should be allowed for mature trees as this system does not per- mit alternate tree removal in later years, as is possible with the quincunx or rectangular arrangements. On rolling land, cross-slope planting with the orchard laid out in blocks is much more feasible than the contour layout with spike rows. Planting Ideally, trees should be planted in Decem- ber, January, or February, and not later than early April. Holes for planting need not be larger or deeper than is necessary to accommo- date the roots in their natural position. Trees should be set in the orchard at approximately the same depth as they stood in the nursery. This depth can gen- erally be determined by the soil line on the trunks of the trees. [4 o SQUARE SYSTEM r\ b tO -^ I o o QUINCUNX rv r> o--- O o- -TV i o O jT> O o O- I o I I RECTANGLE O o- 5 I I ■O- I I 6 • be of use in Santa Cruz County, but may have a limited place in Mendocino County or climatically similar districts. Other promising varieties which have performed well outside of California but which have not yet been fully tested here include Julyred. Blaze, and Tydeman's Early Worcester ( Tydemaifs Red), which are earl) maturing varieties; Wayne, Niagara, and Spigold are recent intro- ductions from New York which have promise as dual purpose, mid-season varieties; Mutsu, a yellow apple of Japa- nese origin, resembles Golden Delicious but reportedly is less susceptible to russet and to shrivel in storage than is Golden Delicious. Rootstocks Most apple trees planted in California * are propagated by commercial nurseries. Seedling trees are grown from seed generally obtained from an apple-process- ing plant. The seedlings are budded to a desired fruiting variety and sold as 1- year-old whips or 2-year-old trees. Nursery trees are graded for sale accord- ing to the diameter of the trunk 2 inches above the bud union. The approximate height may also be listed: Diameter (inches) Height (feet) 11/16 and larger . . . 6 to 8 1/2 to 11/16 . . . . 4 to 6 3/8 to 1/2 3 to 4 1/4 to 3/8 2 to 3 The 1-year-old whips are preferred to 2-year-old nursery trees. Growers can make a better selection of scaffold branches and develop a better framework from whips than from 2-year-old nursery \ stock, as primary branching on whips will be initiated in the orchard rather than in the nursery row. Branches on 2-year-old stock are frequently deformed or poorly developed because trees are crowded in the nursery. The larger whips (1/2- to 11/16-inch diameter) usually perform better than smaller ones, growing more vigorously and developing a better selec- tion of laterals from which to form the framework. Dwarfing rootstocks. There has been an increasing interest in the use of dwarf- ing rootstocks to reduce labor and bring orchards into earlier commercial produc- tion. With smaller trees the primary saving in labor is the result of the reduc- [ 14 tion in ladder work for pruning, thinning East Mailing, or EM series, and the and picking. woolly apple aphid resistant Mailing- Two major groups of dwarfing root- Merton, or MM series. The most im- stocks, both of which were developed in portant of these rootstocks have been England, are being used. They are the classified into four vigor levels: Typical planting Vigor level Rootstocks intervals, in ft. Trees per acre Standard Standard seedlings, 25 x 25 70 EM XVI, EM XXV, to to MM 109 30 x 30 48 Semi-standard EM II, MM 104, MM 111 21 x 21 96 Semi-dwarf EM VII, MM 106 17 x 17 150 Dwarf EM IX, EM 26 15 x 8 363 Research work with these rootstocks growers. Because vital factors can vary has been carried on extensively in many with areas, further evaluation of these apple areas of the world, but in California rootstocks under California conditions is observations have been limited primarily needed before any firm recommendations to small trial plantings established by about them can be made. Dormant pruning. Fig. 5. (Below, left.) Tree before first dormant pruning. Fig. 6. (Below, center.) Same tree as in figure 5 after first dormant pruning. Fig. 7. (Below, right.) Same tree as in figure 3 after first dormant pruning. Scaffold branches are well distributed vertically and around the tree. Shoots not selected as scaffolds were merely stubbed to provide additional leaf surface in next growing season. '^■dSLJ&z Pruning and training During the firsl I years of the orchard the primary aim in pruning is to develop a lice shape thai \\ ill lend itself to eco- nomical culture. The ideal tree should have three primary scaffold branches originating from the trunk, and two secondary scaffold branches arising from each primary. These six secondary branches are the main framework from which fruiting branches will grow. First year summer pinching. Growth <>l well-placed shoots for use as scaffold limbs max be encouraged by depressing the growth of other shoots. Removing the tip inch or two of shoots not well located for permanent limbs is called "pinching." It should usually be done from about mid- April to mid-May, or when shoots are 1 to 8 inches long. Pinching shoots on weak trees is not recommended. The first dormant pruning is done in winter following the first summer's growth. Three primary scaffold branches are selected at this time, and these should be -paced about equally around the trunk, preferably with a vertical spacing of 4 to 6 inches between them. Good vertical spacing promotes strong crotches which are le^< likely to develop pockets of rot later on or to split out from heavy crops and wind. The primaries generally need not be headed back, except to achieve a balance in growth among them. Three well-spaced primary branches cannot always be obtained the first year. If two good limbs are available, they may be headed hack to about 18 inches from the trunk to suppress their develop- ment until a third scaffold can he selected al the end of the second growing season. With an occasional tree it will he neces- sary to cut laterals back to one bud and defer scaffold selection until the next year. Such trees will generally grow vigorously and will benefit by summer pinching din- ing the second grow ing season. Second year dormant pruning. Five to seven secondary branches per tree, usually two on each primary scaffold, should be selected in the second dormant season. Well-chosen secondaries should be directed partially outward. New growth from such branches will fill in laterally, giving the tree a well-shaped framework. Secondary limbs should be left full length and not headed back, unless it is necessary to maintain balance with the primaries or other secondaries. Any forked tips may be thinned out to a single terminal. If a primary scaffold branch is overly vigor- ous it can be retarded by heading hack to balance with I he resl of the tree. Upright-growing sucker shoots should be removed. Most trees will produce 4 short Fig. 8. Tree after first dormant pruning, with scaffolds headed hack lor balance ami spreaders holding branches apart. [16] / / By the fourth dormant pruning, tree training has been largely completed. From here on pruning should be done in such a manner as to permit the best de- velopment of the crop. The tree should be thinned out and the remaining branches cut to side limbs, as was done in the third dormant pruning. A moderate number of small shoots should be left in the center of the tree for fruit-bearing wood. Adequate thinning out of branches and fruiting wood will maintain a well- distributed bearing area throughout the tree and reduce excessive spread and breaking of branches. i / / %~. f C 1 i 1 1 j / J f — J Fig. 9. Tree prior to second dormant pruning. laterals and spurs during the second year, and these should not be immediately re- moved as they provide shade and some early fruit. Third and subsequent dormant sea- son pruning. Third-year training con- sists of thinning out unwanted branches and cutting others to desirable side limbs. Secondary branches often form fruit spurs during the third growing season, but on young trees fruit buds may form at the tip of unpruned shoots. [17] mmm*. Fig. 10. Same tree as in figure 9 a with spreaders in place to sepa limhs and direct them outward. fter pruning, rate scaffold V "\ Same tree as in figures 9 and 10, but branches lightly beaded to shorten unusually long or vigorous secondaries and to maintain balance among them. Light heading may also be needed to remove tips of shoots infected with mildew. Fig. 12. Tree before third donna pruning. MANAGEMENT OF THE BEARING ORCHARD By about the fifth summer after planting most apple varieties produce enough fruit to be considered a bearing orchard. The cultural practices recommended in the following sections are a means of main- taining satisfactory crop yield and quality. Pruning Tree- proper!) cared for during their formative period will be well shaped and mechanically able to support heavy crops. Apple trees normally produce their crop on long-lived spins originating as laterals from shoot wood at least 2 years old. Some varieties such as Rome Beauty. Golden Delicious, and Jonathan may pro- duce additional fruit on the tips of last year's shoots. The primary consideration in pruning bearing trees is to maintain a proper balance between vegetative growth and fruit production. Excessive growth b\ the young tree is usually produced at the expense of fruit production, while over- bearing is accompanied b\ less growth L8 •y* •V*^ Vi n lfiiliI«Mifi^ Fig. 13. Same tree as in figu pruning. JfeilSS 12 aft< and, if continued, loss of vigor. On the ideal mature tree, shoots average at least 10 inches of new terminal growth per shoot each year. Thus the tree increases and maintains its fruiting area while producing satisfactory annual crops. With most trees that have received regular pruning previously there is little necessity for more than a light thinning and cutting back of the upper branches to laterals; this will prevent the tree from getting too high for economical spraying and picking operations. It is desirable to provide ladder spaces for pruning, thin- ning and harvest operations. The center of the tree should be kept fairly open with varieties for which fruit color is an important factor; if this has // 1 / H It Fig. 14. Same tree as in figure 13 after a few additional light thinning- out cuts. Any advantages of the ad- ditional thinning are debatable, par- ticularly in relation to the time required to do it. Spreaders at this age of tree are of limited value, ex- cept when used to help force a scaf- fold outward (as illustrated by the branch on the left turning inward in figure 13). been neglected for several years it is best to thin out surplus branches over a period of two or more seasons. Heavy removal of branches can upset the balance of the tree and expose scaffold branches to sun- burn damage. Any heavy pruning will encourage a large amount of vegetative growth. Old bearing trees producing small fruit will benefit from heavy pruning, which stimulates new shoots and fruiting spurs. [19] In the Pajaro Valley and with the Yel- Cover CfOpS ow Newtown variety particularly, mildew n , . iii . • Lover crops are used nlection is reduced by pruning out in i fected tips in the dormant and even in the growing season. Whenever a limb larger than an inch in diameter must be removed, the cut should be made as close as possible to the branch from which the limb arises so as not to leave a stub. Large pruning wounds should be protected with some covering in order to exclude rot-causing fungi. For this purpose commercial preparations may be used. Bordeaux paste is a good temporary covering. A more permanent covering consists of combining Bordeaux powder with paint. An excellent formula is: 1 gallon "orchard contour" paint or similar formula, 1% gallons boiled linseed oil, and 7 pounds of Bordeaux powder ("one- package" Bordeaux). Cultivation Orchards are cultivated to (1) reduce noxious weeds and plant competition; (2) facilitate subsequent orchard opera- tions, such as irrigation, harvesting, brush removal or spraying; (3) in- corporate cover crops and fertilizers; (4) prepare seedbeds for cover crops; and (5) to aid in the absorption of water where certain orchard operations have produced an impervious soil condition. Cultivation should not be any deeper than is necessary to accomplish the various objectives listed above. Tillage does not reduce water loss, except by killing weeds which use water. Unneces- sary cultivation, especially when the soil is wet, increases the costs of operation and may cause definite injury through soil compaction and damage to soil struc- ture. (See University of California Agri- cultural Experiment Station Extension Service Circular 486, Essentials of Irri- gation and Cultivation of Orchards.) r crops are used to (1) improve water penetration; (2) fix nitrogen (leguminous cover crops only) ; (3) im- prove the general physical condition of the soil; and (4) reduce soil erosion on sloping land. Non-leguminous cover crops such as mustard, rye, oats and barley are planted alone or in combination with a legume; vetch and Canadian field peas are two of the most common leguminous species, and either can be used alone. Where volunteer covers of weeds and grasses are adequate, growers would be wise to fertilize this natural cover rather than to spend money in purchasing cover crop seed. Planted cover crops are fall seeded and disked under in the spring. They should not be allowed to grow late in the spring because they will compete with the trees for nitrogen and water. In non- irrigated orchards, it is advisable to disk in the cover crops as soon as possible to- ward the end of the rainy season. On the steeper slopes in the foothill and mountain areas where there is danger of soil erosion, most apple orchards are maintained under a system of sod culture or trashy cultivation. For more deailed information on cover crops in orchards, see University of Cali- fornia Agricultural Experiment Station Extension Service Circular 466, Ferti- lizers and Covercrops for California Orchards. Fertilization A statewide recommendation for the fertilization of apples cannot be made because of variations in soil, moisture and temperature within and between the various districts. As a general rule, how- ever, trees will show a response to nitro- gen; this should be applied annually at the rate of % to 1% pounds of actual nitrogen per mature tree. [20] Phosphorus deficiency has not been found in California apple orchards to date. Phosphates are used with nitrogen to stimulate cover crop growth. Occasional trees and some orchards have been found deficient in potassium, and correction may sometimes be made by heavy applications of potassium sul- fate, which should be trenched or drilled into the soil about 6 inches deep, using 10 to 25 pounds per tree. It may require a year or two for tree response to become evident. Minor element needs must be de- termined on a local basis and treated accordingly. Your local Farm Advisor should be consulted when a deficiency is noted or suspected. Irrigation Good irrigation replaces moisture re- moved from soil by growing plants before they show stress. Thus, satisfactory irri- gation for apples requires some knowl- edge of the amount of water the trees remove from the soil. The relation be- tween soil type and climate affects the amount and frequency of irrigation. Apples have been raised successfully under dry-land conditions in the cooler coastal areas of California on good, deep soil. Optimum yields, however, are closely associated with optimum soil-water rela- tions. Medium-sized trees growing in the warm section of the Sierra foothills use nearly twice as much water annually as do large trees growing in the cool coastal belt, and differences in summer tempera- ture and humidity contribute to these variations. Approximately half of the total seasonal water consumption occurs during July and August. Factors which tend to limit depth of root distribution will also affect the need for more frequent irrigations. Texture of the soil is also important: sandier soils, which have lower water-holding capacity, require more frequent irrigation than do heavier loams. Sharply stratified surface soils and subsoils, impervious layers of hardpan or rock, or shallow water tables, limit root activity and create difficult problems in orchard management. Irrigation programs vary according to orchard location and soil type, and each grower must learn the requirements of his own land. Diligent use of a shovel, soil auger or soil tube is a highly recom- mended method of determining the moisture conditions surrounding the tree roots. Soil moisture measuring instru- ments, such as tensiometers and gypsum blocks, are also helpful. On fairly flat land, apple orchards may be irrigated by the use of furrows, con- tour checks, strip checks, square checks, or sprinklers. On rolling foothill lands the sprinkler system, while expensive to install, is far more efficient than contour furrows and results in better distribution of water. Sprinkler irrigation has become a common practice in most apple-growing areas of the state because it does not inter- fere with the propping necessary for trees producing heavy crops. On heavy soils any irrigation system which tends to result in a wet-soil condition around the trunk for extended periods may promote crown rot. On such soils furrow irrigation may therefore be preferred to sprinklers. Thinning Fruit thining is well recognized as one of the most important orchard operations. It results in improved fruit size and uni- formity, promotes regular bearing, re- duces limb breakage, assists in maintain- ing general tree vigor, and decreases the labor of handling the crop at harvest time. Historically, apples have been thinned by hand, usually following the natural June drop, when the fruits are between the size of a cherry and a walnut. With most varieties, the small apples are re- moved from their stems, leaving the stems attached to the spurs. Growers generally [21] strive to thin their crop to one fruit per cluster, with 6 to 8 inches between fruits. If the crop is light to begin with, it is practical to leave two fruits per cluster with most varieties. In recent years the advent of chemical thinning agents has provided growers with an economical means of partially thinning their crop. In the Watsonville district, Yellow Newtown and red De- licious can be thinned using naphthyl- acetamide (NAAmide) at 40 parts per million at 70 to 80% petal fall. In the Sierra foothills, Golden Delicious and Stayman Winesap can be thinned with NAAmide at 50 parts per million at 80 to 90% petal fall. NAAmide is not used on red Delicious in the Sierra foothills due to the fact that it tends to produce pigmy apples. Naphthaleneacetic acid (NAA) sometimes causes overthinning and some flagging of the foliage and stunting of the shoot growth; it is used in the Sierra foothills on Golden Delicious and red Delicious at 15 parts per million 2 to 3 weeks after full bloom. Recently the insecticide, 1-naphthyl N-methylcarba- mate (Sevin®), was found to act as a thinning agent. It has been used success- fully on most varieties in California at 1% pounds 50 per cent wettable powder per hundred gallons of water 10 to 20 days following full bloom. Sevin® and NAAmide have not caused overthinning on healthy trees. It is usually necessary to do some supplemental hand thinning following chemical thinning, but the total cost of thinning is still greatly reduced. Apples may be left in clusters of two during the supplemental thinning and still attain satisfactory fruit size. Pre-harvest drop Dropping of apples immediately preced- ing and during harvest may result in considerable loss. With most varieties, this drop may be materially reduced with hormones containing napthalene- acetic acid or its derivatives. These preparations are available under a num- ber of different trade names (directions for their use and application are printed on packages and should be followed exactly) . They are applied a few days before harvest or as soon as dropping is evident. The period of effectiveness usually ranges from 5 to 20 days. Top-working Grafting or budding is commonly used to establish a variety on seedling root- stock by nurseries. Growers may use the same techniques to convert an orchard to a new or more desirable variety, or to provide additional pollinizers. Frost protection Since the larger apple-growing areas of the state are at low altitudes and relatively near the coast, frost danger to blossoms and young fruit is infrequent, and few growers are prepared to heat their orchards. At altitudes of 3,000 feet or higher, spring frosts may do considerable damage or even destroy the crop one year out of four or five. With such a frequency of loss it is seldom economically sound to attempt to provide frost protection. INSECT AND DISEASE CONTROL Information on insects and diseases of apples is available al your Farm Advior's Office. Good control of these [tests is vital to the health of the tree and the production of marketable fruit. Spray schedules for such control prepared annually by the Agricultural Experiment Station and the Agricultural Extension Service of the University of California are also available at your Farm Advisor's Office. Five to seven sprays are generally required through- out the season. I 22 1 HARVESTING, HANDLING, AND STORAGE When and how to pick Statewide minimum maturity standards have been established for most com- mercial varieties. Flesh firmness, soluble solids in the juice, and ground color of the skin are criteria that may be used to set a standard. The County Agricultural Commissioner in each county enforces maturity standards in his particular county, and in apple-growing sections he is equipped with refractometers, pressure testers, and color guides for determining fruit maturity. He will on appointment test fruit for growers. If a variety com- plies with the standards for two of the three maturity criteria the commissioner releases it for harvest. The standards require that fruit ripen to reasonable dessert quality, have a satisfactory appearance, and be free from excessive shriveling during storage and marketing. However, being minimum standards, they permit apples at the be- ginning of the season to be harvested considerably in advance of optimum ma- turity for top quality. Such early harvest can adversely affect their acceptance as dessert apples, resulting in lowering of the early-market price in most seasons. When apples are harvested at minimal maturity, the total tonnage from any given orchard is less than if harvest is delayed until a more advanced maturity is reached. Apples of low maturity are still growing, and a delay in harvest of 2 or more weeks can result in a gain in tonnage of as much as 20 per cent. (Brown, Dillon S. and Edward C. Koch, Yield Gain by Delayed Harvest. Califor- nia Agriculture 11(9) :6, 1957.) More Gravenstein and Yellow New- town apples are canned or otherwise processed than are sold fresh. Standards for fresh apples do not apply directly to those sold for processing. However, top quality in processed apples or apple products comes only from fruit harvested at optimum maturity, so processors desire fruit of more advanced maturity than is required for the fresh market. Picking should be done in such a way as to avoid bruising and stem punctures. Apples should be grasped in the palm of the hand and removed from the fruit spur with a quick, upward turn of the wrist. A straight pull will usually result in pulling the stem out of the fruit or the spur from the tree. Apples should be transferred carefully from picking con- tainers into boxes or bins. Varieties such as Golden Delicious and Bellflower re- quire extra careful handling. Handling methods and practices Most commercial apple growers have re- placed field boxes with pallet bins in recent years. The bins are used for har- vesting and for storing of fruit until ready for final packing and shipment. After picking, apples should be put under cover immediately. Picked apples left in the orchard ripen faster than those remaining on the tree, and uncovered fruit is subject to heat injury. Because apples at harvest time seem to be hard, there is a tendency to handle them in a rougher manner than more perishable soft fruits. While not particularly visible at packing time, injuries resulting from rough handling do show at marketing time — or on the retail shelves. Such in- juries detract from eye appeal at the time of purchase and may make the fruit dis- tasteful. Storage All fresh fruits are alive and remain so during storage and marketing. Being alive they respire, combining sugar and [23] other constituents stored in them while on the tree with oxygen from the air to produce carbon dioxide and energy (heat) . The reactions are extremely com- plex and lead ultimately to fruit de- terioration. Cold storage is used to retard these deteriorating effects and to reduce decay from pathogens and shrivel from water loss. The best storage temperature is generally the lowest the fruit will with- stand without freezing, though certain apple varieties such as Yellow Newtown will not tolerate storage temperatures quite that low. Deterioration may also be retarded by controlled-atmosphere storage, in which carbon dioxide, oxygen, and temperature and humidity are controlled in gastight rooms. Apples are one of the most important fruits stored on a tonnage basis, and the average time of storage is considerably longer than for other fruits. Cold storage is critical to proper handling and market- ing, although storage time may be short for an early variety like Gravenstein. Temperature. For most varieties, 30° to 31°F is the recommended storage temperature. This is 1.5° to 2.5°F above the average freezing point (28° to 28.5°F) of most apples and is normally safe for modern storage rooms. In older rooms with limited air distribution, 30°F is unsafe because of variability of tem- perature at different locations within the room. Some apple varieties such as Yel- low Newtown develop physiological dis- orders that impair storage life and marketability if held at the above tem- peratures. At 38° to 40°F, however, such storage disorders may not be an economic factor; unfortunately, such an elevation in temperature results in faster deteriora- tion which greatly shortens storage life and marketability time. Because the raised temperature may have almost as serious consequences in relation to marketability as does the physiological [2 disorder, a storage temperature of ap- proximately 36°F is often used. The storage life of apple varieties largely depends on harvest maturity, elapsed time and temperature between harvest and storage, rate of cooling in storage and, sometimes, cultural factors. Mature apples usually have the greatest storage potential. Essentials for rapid cooling and good cold storage are ade- quate refrigeration capacity, rapid air circulation, and proper stacking to per- mit good exposure of fruit to cold moving air. Controlled atmospheres. Controlled- atmosphere storage may offer important gains in extending the market life of certain apple varieties. Only apples of good quality, proper maturity and high storage potential should be placed in controlled-atmosphere storage. Yellow Newtown and Mcintosh varie- ties were the first to receive controlled- atmosphere storage because of their sus- ceptibility to low temperature disorders. By elevating their storage temperature to approximately 40°F, and altering the composition of the atmosphere, chilling- injury symptoms were avoided. Recently, attention has been given to varieties such as Delicious that can be stored at low temperatures. Some of the construction require- ments^ — -in addition to those called for in conventional storage rooms — are: (1) gas tightness, (2) provision for removing excess C0 2 from the atmosphere, (3) pro- vision for ventilation to control oxygen level, (4) adjustment to changing atmos- pheric pressures, and (5) provision for maintenance of very high relative humidity required by the longer storage period. Precautions in the operation of con- trolled-atmosphere rooms are highly im- portant as the atmosphere in them will not support human life. The size of a controlled-atmosphere room is also im- portant: once the room is opened, its APPROXIMATE REQUIREMENTS FOR CONTROLLED- ATMOSPHERE STORAGE OF APPLES* Variety Per cent C0 2 1 D er cent O2 Temperature, F Mcintosh .... . . . 2 to 5 2 to 3 38 Delicious and Golden Delicious . . . 1.5 to 3 2.5 to 3 30 to 32 Baldwin, Jonathan, Rome Beauty, Stayman Winesap . . . . lto5 2 to 3 30 to 32 Yellow Newtown . . . 5 to 8 2 to 3 51, Storage of Apples, Pears and Grapes. 38 to 40 (Prepared by Clay- * From p. 614, chapter pool, L. L. and Nelson, K. Davis.) ASHRAE Guide and Data Book, 1964. American Society of Heating, Refrigeratin g and Air-Con ditioning Engineers, Inc., 345 East 47th Street, New York 17, New York. contents should be marketed or utilized within a few weeks. A service is now available in which a generator delivers an atmosphere of de- sired composition to a storage room which need not be as gastight as those rooms in which fruits lower the atmos- pheric oxygen by respiration. Economic considerations determine the commercial use of different controlled-atmosphere methods. Storage-caused disorders. Scald is a serious disorder affecting apples in stor- age. It first appears as traces of light mottling on the greener surfaces of the fruit. Darkening becomes more severe with elapsed time and will extend to red colored surfaces. Ordinarily, scald affects only the skin, but in severe cases may extend into the flesh. It develops rapidly at warm temperatures, and apples with light scald in storage may be severely scalded during marketing. Immature fruit is susceptible to scald. Bitter pit is characterized by small sunken spots on the fruit surface. They are most prevalent near the blossom end and usually near the surface. At first, they show as small water-soaked areas that shrink and turn brown as water is lost from them, and end up as brown localized areas of dead tissue. Yellow Newtown, Delicious, Golden Delicious and Gravenstein are susceptible. The problem is most severe when apples are picked on the immature side, and may be worse in light-crop years when fruits are large. Internal browning is associated with the Yellow Newtown apple grown in the coastal area of California and is char- acterized by brownish streaks radiating into the flesh from the core. Susceptibility varies between years and orchards. It can be controlled by storage at 40°F, but because of the short storage life at this temperature a compromise tempera- ture of about 36°F is ordinarily used. With controlled-atmosphere storage, how- ever, the higher temperature can be used. To simplify the information, it is sometimes necessary to use trade names of products or equip- ment. No endorsement of named products is intended nor is criticism implied of similar products not mentioned. 25 Co-operative Extension work in Agriculture and Home Economics, College of Agriculture, University of California, and United Stales Department of Agriculture cooperating. Distributed in furtherance of the Acts of Congress of May 8, and June 30, 1914. George B. Alcorn, Director, California Agricultural Extension Service. 20m-6,'66(F9254)V.L. ^i J^ -0r* Sfc*S' £#8S& BLACK BOXES *■ Agriculture has them too Both manned and unmanned vehicles sent into space are equipped with "black boxes" that record or transmit in- formation needed by space scientists who hope to explore other planets. Not as glamorous perhaps, but equally important to our country's welfare are the measuring devices used by agri- cultural scientists to gain knowledge that will improve conditions on our own planet. From information in such "black boxes" will come better farming methods, better foods and fibers, better living. The agricultural sciences offer rewarding careers for qualified young men and women who would have a part in making the future better. Write for the booklet AGRI- CULTURE-OPEN DOOR TO YOUR FUTURE. Agricultural Publications University Ha!! University of California Berkeley 4, Calif. *