Asian Pears
James Beutel, UC Farm Advisor, Solano Co. 1990. Asian Pears. p.304-309 in: Advances in New Crops. Proceedings of the First National Symposium on New Crops held October 23-26, 1988 in Indianapolis, Indiana. J. Janick and J.E. Simon (eds.). 1990. Timber Press, Portland, Oregon.
Introduction
Asian pears comprise a large group of pears that are crisp in texture and, when mature, are good to eat as soon as harvested or for several months after picking if held in cold storage. This ready-to-eat feature may make them more acceptable to some people than European pears that are usually served when soft and juicy, which takes about a week to occur after removal from cold storage. Asian pears do not change texture after picking or storage as do European pears such as Bartlett or Comice. Often Asian pears are called apple pears because they are crisp and juicy like apples but with a different and distinctive texture. They also are called salad pears, Nashi (Japanese for "pear"), Oriental, Chinese or Japanese pears (Nihonnashi). All Asian pears today are selected seedlings or crosses made within the species Pyrus serotina.
Asian pears have been grown commercially in Asia for centuries. In Japan about 500,000 tons are grown and some fruit is exported to the United States in October and November. China and Korea also grow these pears for domestic consumption and export to the United States and Canada.
Most new Asian pear plantings in California are in Fresno, Tulare and Kern Counties. Older plantings are found in Placer and Sacramento Counties and limited new plantings are being made in the Sacramento Valley. A few plantings exist in Yakima and Wenatchee, Washington, and others found in Hood River and Willamette Valley in Oregon. In the last few years plantings of Asian pears were made in New Zealand, Australia, Chile, France, and the eastern and southeastern United States.
It is roughly estimated that 4,000-5,000 acres of Asian pears are planted in California, Oregon and Washington. Most trees are just beginning production since most recent plantings started in 1981. Since 1984 about 100,000 trees (500 acres) of Asian pears have been planted every year in California.
All Asian pear varieties will grow on Pyrus betulaefolia, P. calleryana, P. serotina, P. ussuriensis and P. communis (Bartlett, Old Home x Farmingdale, or Winter Nelis seedling) rootstocks. Usually P. betulaefolia is preferred for its vigor, large fruit and tolerance of wet soils. Its cold-hardiness varies with seed source. All rootstocks are satisfactory in California and the warmer winter areas of Oregon, but in Washington special cold-hardy P. betulaefolia strains are needed. In the Pacific Northwest, the Old Home x Farmingdale series (Old Home x Farmingdale #69, O.H. x F #87, O.H. x F #40) are preferred. This series has shown some resistance to pear decline and fire blight in that area. Most Japanese pear varieties are dwarfed about 50% on P. communis rootstock so California growers and nurseries prefer P. betulaefolia is used to prevent hard-end, a problem in some areas where P. serotina is used as a rootstock for Japanese pears. P. serotina or P. ussuriensis are cold-hardy to -40°F and could be used as an Asian pear rootstock in California but lack winter hardiness for most areas outside of California.
There is no standard accepted spacing for Asian pears on the West Coast of the United States. Plantings range from 7 ½ by 15 feet (380 trees per acre) to 15 by 20 feet (140 trees per acre ) depending on soil, rootstock, and grower preference. They generally approximate 200 trees per acre with spacing of 12 feet apart in rows and 17 to 18 feet between rows being a good planting pattern for long and short term production and minimum crowding of trees.
Large, ten-year-old, twelve-foot-high trees at Davis and Winters, California, cover a soil area of 150 to 225 square feet. Smaller dwarf-type 10-year-old trees on P. communis rootstock cover a soil area of 25 to 49 square feet. Space must be allowed around each tree for good light penetration and for use of orchard equipment. Thus, plantings of 145 to 200 trees per acre are recommended for vigorous selections and rootstocks--and for dwarf trees, 300 to 400 trees.
Asian pear varieties are partially self-fruitful but better crops are set where two or more varieties are planted together. In Fresno and Tulare counties, 20th Century or Shinseiki are known to set good crops when planted alone in large one-variety blocks. In areas with cooler temperatures at bloom-time, cross-pollination by European or Asian pear varieties will be necessary. Cross-pollinated fruit with seed tend to be larger and more uniformly round than fruit with few seeds due to inadequate pollination.
No proven guidelines exist on the closeness of pollenizers or the use of bees for Asian pears in California. It is suggested that every 4 to 8 rows of a single variety have a pollenizer row or that growers plant a block of 4 to 8 rows of a second variety adjacent to the first variety. Bees may be used at a density of one to two hives per acre. Early-blooming varieties Ya Li, Tsu Li and Seuri are compatible and should be planted together. Later-blooming varieties comprise most of the Japanese and hybrid varieties and selections. Notably Niitaka is pollen-sterile; Kikusui does not pollinate 20th Century; Seigyoku and Ishiiwase are poor pollenizers. Most other varieties pollinate each other. Too much pollination means more thinning of fruit is necessary for proper fruit sizing.
The early blooming Chinese varieties Ya Li, Tsu Li and Seuri bloom 10 to 14 days before Bartlett. In the San Joaquin and Sacramento valleys of California, these early blooming varieties are at full bloom in early to mid-March. They are the first pears to bloom and are most subject to frost damage. The earliest flowering Japanese variety is Chojuro which flowers at the same time as Anjou or Winter Nelis. Late flowering Japanese varieties are 20th Century and Okusankichi which reach full bloom with Bartlett. Most years the last third or half of Chojuro bloom overlaps the first third or half of the 20th Century bloom. Japanese and Chinese hybrids Shin Li and Dasui Li developed at the University of California bloom late in the Japanese flowering season. Thus, most Japanese pears overlap but rarely overlap Japanese or European pear varieties enough for good pollination in California. In Washington State it is reported that the early flowering D'Anjou variety is well pollinated by 20th Century and other Asian pears.
Asian pear trees like 20th Century are about as winter hardy as Bosc pears tolerating about -20°F but are less hardy than Bartlett and Anjou. Asian pear rootstocks' tolerances for winter cold are 10°F for P. calleryana, 0 to -10°F for P. betulaefolia and -30°F for P. communis and P. serotina.
Normally Asian pears are trained vase-shape in California. This is generally accomplished by heading nursery trees about 25 to 30 inches high at time of planting an selecting 3 or 4 main limbs the limbs the first year and heading these new limbs about 50% leaving 12 to 24 inches of growth depending on the length of the growth the first year. This will give 6 to 10 fairly low secondary limbs that are headed 30 to 36 inches long in the second dormant season. If trees are growing excessively then pruning should be reduced to encourage fruit spur development.
Most fruit are borne on spurs on 2 to 6 year old wood; however, the terminal bud on one year old wood will also set fruit from its very large cluster of flowers.. Older wood and spurs give smaller fruit than those on 2 to 4 year old wood. Pruning cuts and excess spurs should be cut off smoothly so stubs will not rub and damage fruit. Fruit sizes best on 1 to 3 year old spurs on wood 1 to 2 inches in diameter. Fruit on small lateral limbs and hanger wood sizes poorly. Pruning should encourage several limbs with wide angle branches off main scaffold limbs. Some limb spreading to open tree centers may be desirable. Pruning cuts should be made with the last bud facing down and out. This will force the new growth to develop more flat before turning upward. This encourages wider branch angles.
In many pear areas outside California, Asian pear trees are grown as central leaders similar to apple tree training. This is done with little or no heading of the tree and selecting wide angle limbs for framework limbs off the central leader. The final tree looks like a Christmas tree in shape. It is advisable to maintain individual tree spacing and avoid tight hedgerows for good fruit and long-lived, productive orchards. In New Zealand, most 'Nashi' trees are central-leader trained. In Japan, a flat-topped training system called "tanashitate" is used and trees are supported by cables and wire suspended from tall poles . This system is preferred for wind protection and to facilitate all the hand labor performed in Japanese pear production.
Trellis supported Asian pear orchards are sometimes used in California. The Tatura 'V' with about 4 main limbs on each side of the 'V' is the most common trellis system. Trellis costs of $2000-$3000 per acre add to establishment cost, but support trees well and expose fruit to sun for good color development.
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All Asian pear varieties except 'Shinko' may develop fireblight (Erwinia amylovora). Asian pears are as susceptible to fireblight as most European pear varieties. Experienced growers usually spray antibiotic fireblight materials (Strepyomycin, Terramycin or copper) during the bloom period and later in the spring when conditions for fireblight infections are favorable, namely when average daily temperatures exceed 60°F and rain or dew occurs on the flowers. Antibiotic sprays for fireblight should be made in April and May and after harvest. Do not use the high rate of streptomycin on the varieties whose name ends with "sui". These varieties (examples include Hosui, Kikusui, etc.) can develop severe leaf burning at the high rate. Frequent removal of diseased (blighted) limbs to control fireblight is necessary most years. When removing fireblight strides, make cuts 1 1/2 to 2 feet below the strike area. Fireblight bacteria can be spread to uninfected wood with pruning cuts. Frequent sterilization of the pruning shears is important. Because the disinfectant solutions will corrode pruning tools, wash and oil the pruning tools at the end of each day. Diseased wood should be removed from the orchard prior to bloom.
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In areas with a cold spring seasons, Asian pears will get bacterial canker (Psuedomonas syringae).
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When trees are planted too deep in the soil they may die of crown rot (Phtyophthora sp.)
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In Japan, black spot (Alternaria kikuchiana) is extremely damaging to fruit requiring bagging to protect certain yellow-skinned varieties but black spot disease is not known to exist in the United States.
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Scab is a problem in Japan, but is not the same scab species found in California on Bartlett pears and apples.
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Codling moth (Carpocapsa pomonella)is severe on Asian pears, requiring 3 to 4 well-timed sprays at or near full dosage for control of this serious pest. Materials in these sprays are the same as used for apples and domestic pears. Thinning clusters to single fruit also reduces codling moth infestation on fruit.
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Pear psylla (Psylla pyricola)can cause sticky fruit and requires at least one delayed dormant spray.
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Many types of stink bugs and plant bugs cause injury as hard, tan-colored spots under the flesh of Asian pears.
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Two-spotted spider mites are serious on Asian pear trees especially if the trees become water-stressed. Mite sprays before harvest and frequent irrigation are essential for control of two-spotted and European red mites.
Trees require frequent irrigation to produce large fruit sizes; however, high vigor makes fireblight harder to control and fruit tender to pick. Avoid over irrigation on poorly drained soils. Excess moisture will induce iron deficiency, which turns the leaves yellow. Needs for nutrients is similar to other fruit trees. Iron deficiency is common in some soil types. Acidifying the soil with soil sulfur or sulfuric acid will help to overcome this problem. Dwarf rootstocks will require more nitrogen than vigorous rootstocks to maintain tree vigor.
All Asian pear varieties require heavy thinning to obtain good fruit size, to insure annual cropping, and to avoid limb breakage. All thinning is done by hand since chemical thinning is not reliable or reasonably effective. Some growers blossom-thin, by cutting off by hand all but 2 to 3 flowers per cluster. Most growers wait for fruit to set and then cut off all but 1 or 2 fruits per spur. This first fruit thinning is best done before the first codling moth spray and can be done by cutting off the fruit with clippers or small hand shears. A second follow-up thinning before the second codling moth spray is necessary on hard-to-size varieties to remove pears not properly thinned the first time. The best thinning usually requires two times to effectively leave no more than four to six inches apart. Thinning up to 30 days before harvest can benefit size, but early thinning is essential for annual bearing and good fruit sizes. Thinning will require up to a half-hour per tree on younger trees and one hour plus on older trees. Trees four to five years old can size fruit if they have about 100 fruit per tree after thinning is finished. In Japan, 500 to 700 fruit are recommended on large bearing trees or 50,000 fruit per acre.
Harvest season in California is from mid-July through September with a few earlier or later varieties. In Washington State and Japan fruit are harvested August, September and October. Most growers determine harvest date by fruit taste and color. Sugar content over 12.5% usually is adequate and fruit pressure of 8 to 11 pounds seems satisfactory. Fruit pressure is not as good a measure of maturity in Asian pears as it is in European pears. The color of russett-type fruit changes from green to brown, and the ground color of green fruit changes from green to yellow. Color and sugar content best determine time to harvest. Some green Chinese and hybrid types do not change color much at maturity. All Asian pears must be carefully handled to minimize bruising and brown marks and stem punctures. Over-mature fruit quickly show roller bruises, fingerprints and other signs of handling at harvest. Under-mature fruit are poor in flavor and ruin the market for Asian pears. Any fruit that has Ya Li as a parent should be harvested by September 1 in California. Later harvests of this fruit may develop brown flesh in storage. At least three color picks are necessary to get mature, quality fruit from most varieties in the central valley of California.
All Asian pear varieties should be harvested carefully into padded picking buckets or boxes and handled gently in the packinghouse. They have tender skin that bruises, discolors and blackens a day after rough handling during picking and handling. Rough handling during picking can cause many stem punctures. Many growers believe Asian pears are harder to handle than firm peaches and believe they are not suited to large, fast-moving packinghouse lines. Fruit is best field-packed from picking containers to packing boxes or trays.
In the packinghouse, placement of fruit on wide, slow-moving, smooth, clean belts will distribute fruit to packers who "eye-size" fruit and place them into plastic pack trays used to hold fruit in containers going to market. Fruit should be padded within boxes using "bubble pads" or paper-covered excelsior pads to prevent rolling while in transit.
Fruit are packed either two layers deep in "cherry" lugs or flats. Fancy large fruit (12, 15, 16, 18 and 21 sizes -- 3-4 inch diameter) are packed in single-layer 11 to 12 pounds of fruit in "cherry" boxes. Medium-sized fruit are packed in two-layer boxes as sizes 48 or 50 (3 inch diameter), 54 or 56 (2-7/8 inch diameter), and 60-64 (2-5/8 inch diameter), with fruit weight of 21 to 24 lbs. Imported Japanese fruit are packed in 20-kilo cartons similar to tray-pack apples and are 3-1/2 to 4 inch diameter.
Fruit of some varieties can be stored at 32°F for one to three months without problems. After 2 ½ months Hosui and Shinko fruit gets spongy, shows some storage rot, and after four months may show internal breakdown in the core area. Less mature fruit get spongy sooner than fully mature fruit. At room temperature of 70°F, the fruit begins to soften or get spongy after 14 to 21 days. Storage problems include shrivel of skin, spongy fruit, internal browning of core and skin blackening. Storage diseases vary but Botrytis and penicillium are common. For benefits of controlled atmosphere storage of Asian pears see Produce Fact Sheet.
In the early 1980s, demand and prices for Asian pears increased greatly due to the increasing population of Asian people in the United States and Vancouver, Canada. These prices were about $1.50 1b. wholesale and thus stimulated new planting of Asian pears in California beginning in 1982. As these early planting began producing pears, prices declined moderately. In the late 1980s with annual supplies of about 600,000 to 800,000 packed boxes, prices ranged from a low of $6.00 per box to a high of $20 per box. Large (3-4 inch diameter) fruit sold for three times as much per box as small fruit (2 ½ inch diameter). Well colored, sweet (13% sugar) fruit brought better prices than greenish-skinned fruit. Approximate prices for #1 and fancy grade fruit in August and September were $10.00 to $16.00 per 24 lb. Box of 30 to 36 fruit, about $10.00 per box of 42 to 48 fruit and $6.00 to $8.00 per box for 60 to 64 fruit. One layer trays or "cherry" boxes of 12 to 20 fruit weighing 11-12 lbs. sold for about $10.00 each.
Yields of Asian pears are lower per acre than for Bartlett or Bosc because heavy fruit thinning is necessary to get sizes the market demands and pays for with premium prices. Orchards may produce a few pears the third year, better in the fourth season but yields in the fifth to seventh years range from 200 to 400 packed boxes per acre. When trees are full-sized (12 feet wide and high) at age 10-14 years old, yields may reach 800 to 1,000 packed boxes per acre of 3 to 4 inch diameter pears. Higher yields are possible but sizes will be too small for good market prices.
Production costs approximate $2, 500 to $3, 000/acre which is greater than Bartletts because of high costs to thin fruit and higher picking costs. Packing costs per box will be similar to fancy grade pears or apples.
Asian pear varieties are numerous with over 25 known in California and hundreds of varieties known in the Orient. Selection of the better varieties for planting and future sales is a problem for all involved with this crop. The more important varieties available in California are discussed with some ripe dates indicated for Davis, California. In Fresno, ripening will be 7 days earlier; in Oregon and Washington, about 21 to 30 days later.
There are 3 types of Asian pears. They are 1) round or flat fruit with green to yellow skin, 2) round or flat fruit with bronze colored skin and a light bronze russet, 3) pear shaped fruit with green or russet skin. Varieties are listed in order of ripening.
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Ichiban Nashi - An early maturing, large, brown fruit ripening in mid-July ahead of Shinseiki, Shinsui and Kosui. Fruit appears to have tender skin subject to injury during harvest and packing.
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Shinsui - An early maturing, brown fruit with reasonable size, ripening in mid-July after Ichiban Nashi and before Shinseiki. Tree is extremely vigorous requiring special training to spread the tree shape.
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Kosui - A small, flat, bronze russet, early maturing, sweet fruit with a tender skin that ripens in mid-July. A strong growing tree with leaves sensitive to 2-spot spider mites and many sprays.
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Shinsieki - A round, yellow skinned, firm fruit that is early-maturing (late July) plus it stores well up to three months. In appearance it resembles 20th Century but is larger in size. Fruit holds on the tree well and is often color-picked four times per season.
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Hosui - A very large, juicy, sweet, low acid, bronze-skinned pear that ripens in early August. The tree is extremely vigorous on P. Betulaefolia and has a wild, loose growth habit. This is a very popular new variety in Japan and California. It is usually very susceptible to fire blight.
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Kikusui - A flat, yellow-green, medium - sized fruit with excellent flavor but a reputation for having tender skin and poor color. It ripens in mid-August but fruit has preharvest drop problems.
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Yoinashi - A large, brown-skinned fruit with excellent flavor. It ripens in mid-August with 20th Century but sizes much better.
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20th Century (Nijisseki) - This is the best flavored and most popular Asian pear in Japan and California. It originated in Japan in about 1900 and was responsible for the high popularity of pears in Japan. It is round, yellow-skinned, easily bruised, but stores well up to six months. The fruit is more difficult to size than other varieties. It should not be grown on P. Communis rootstock because it is badly dwarfed. The fruit ripens in mid-August. It grows well on P. betulaefolia, P. calleryana, and P. serotina. Old trees need spur removal and rejuvenating pruning to maintain fruit size.
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Chojuro - An old, firm, brown-to orange-skinned, flat-shaped, highly productive variety is losing popularity because it is not as juicy as many newer varieties. It matures in mid-August, bruises easily but stores for five months. It must be picked when first yellow-brown in color or fruit is subject to severe bruising and skin discoloration.
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Shinko - The fruit is large and round to slightly flattened with a beautiful bronze-russet skin. Fruit flavor is excellent in hot climates but the fruit stores poorly and tree growth and vigor decline severely as the tree ages. It is very upright in growth habit. The tree is well shaped and extremely productive. It matures during the first week of September and appears to be nearly resistant to fire blight.
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Nitaka - A very large, firm, brown-russet fruit. It is noted for its large size, average flavor and high production. The tree is dwarfed severely on P. communis and vigorous on P. betulaefolia. Fruit ripens in early September and stores two months. The flowers are pollen-sterile but it sets well when cross-pollinated with most varieties.
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Ya Li - A popular Chinese variety, is pear-shaped, has green skin and is quite tender to bruising. It is an early blooming variety that needs cross-pollination by other early flowering varieties like Tsu Li and Seuri. The flavor is sweet and milder than other varieties. It is the most important pear variety in China. It stores well.
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Tsu Li - A large, football-shaped, green fruit of only fair quality. It has long storage life (six to ten months) and gets better the longer it is stored. The fruit ripens in early to mid-September and develops a greasy feel on the skin. It must be pollinated by Ya Li.
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Dasui Li and Shin Li - New patented U.C. hybrids, very large fruit, greenish to yellow in color. They ripen in late September and early October and store well at 32 degrees F. Trees are extremely vigorous and pollinate each other. For good crops, limited pruning is essential. They grow well on P. betulaefolia or P. communis roots.
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Berkeley, B. 1985. Asian Pears. Fowler Nursery, Newcastle, CA.
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Beutel, J.A. 1985. Asian Pears. Washington State Hort. Proc., Wenatchee, Washington.
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Beutel, J.A. 1987. Asian Pears. Pomology Dept. Publication, UC Davis, Davis, CA.
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California Tree Fruit Agreement. 1987. Pear, plum, peach and nectarine annual reports. California Tree Fruit Agreement, Sacramento, CA.
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Griggs W. And B. Iwakiri. 1977. Asian pear varieties in California. University of California DANR Publication #4068, Oakland, CA.
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Sunset Magazine. 1984. The New Crunch Pears. Sunset Magazine 84:72-75.
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Van der Zwet and N. F. Childers. 1982. The Pear from Varieties to Marketing. Horticultural Publications, Gainesville, FL.