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PEAR
Pyrus spp., family Rosaceae

All of the important pears growing in the United States, referred to as the French or European types, belong to P. communis L., except a few hybrids such as the 'Kieffer' and 'Le Conte', which are crosses between P. communis and the fire blight resistant Chinese sand pear (P. pyrifolia (Burm. f.) Nakai) (Davis and Tufts 1941).

The estimated production of pears in 1971, was 701,120 tons, almost half of which (309,000 tons) were produced in California. Production in Washington was 165,400 tons and in Oregon, 174,000 tons. Production in other States was relatively insignificant. The total value of the crop was $63 million.

Plant:

The pear tree may live 100 years or more and if unpruned may reach a height of 50 feet. When grown in orchards, however, the trees are usually pruned to 10 to 20 feet. Its general appearance is similar to the apple although its limbs are usually somewhat less gnarled and more upright. It flowers in the springtime about the same time that apples flower or slightly earlier. The fruit is consumed fresh, canned, preserved, or pickled. The trees are usually spaced 20 feet apart in the orchard, except for dwarf trees, which are sometimes as close as 12 feet (Davis and Tufts 1941).

Although Hedrick (1921) stated that thousands of cultivars of pears are grown in Europe and the United States, the 'Bartlett', 'Williams', or 'Williams Bon Chretien', a European cultivar, is probably the most widely grown pear in the world (Griggs and Iwakiri 1954). Other important European cultivars are: 'Anjou', 'Bosc', 'Comice', 'Hardy', and 'Winter Nelis' (Magness 1937). According to Hedrick (1938*), the Europeans have listed more than 5,000 pear cultivars, the Americans, more than 1,000 cultivars. Hedrick considered the 'Kieffer' next in importance to the 'Bartlett', the 'Le Conte' about like the 'Kieffer' in quality but not quite as good. Today, 'Kieffer' is important only in the Eastern and Southern States where better quality pears cannot be grown because of fire blight (Batjer et al. 1967). The 'Winter Nelis', which was the standard winter pear in the United States, has been replaced in many places by the 'Anjou'. The relatively unimportant 'Pound' is grown primarily for its monstrous fruit (3 to 4 pounds each). Auchter and Knapp (1937*) showed a production of 210 bu/acre for 'Kieffer' pears versus 140 to 160 for 'Bartletts'.

Inflorescence:

Pear flowers are at least 1 inch in diameter, pure white, and in simple clusters (fig. 148). The flower is protogynous (the stigma of an individual flower is receptive to pollen before its anthers release pollen). The flowering on a tree usually lasts about a week. The flowers produce abundant pollen, which is highly attractive to bees (Tufts and Philp 1923), but the nectar is low in sugar content (Vansell 1946) and frequently fails to attract bees. When the flower opens, the style stands erect, the stigma is receptive, and the stamens are so bent inward that the unripe anthers are crowded together around the style but below the stigma (fig. 149). Later, they extend to the full height of the style and release their pollen. Unlike the plum and nectarine, the pear does not have a deep cup lined with nectar tissue, but only five small, slitlike openings in the flat top surface or disk area between the petals and stamens (Vansell 1942*). Vansell showed that the percentage of sugar concentration of pear nectar was quite low, for example, apple, 46.2 percent; peach, 28.9; plum, 25.8; sour cherry, 23.5; 'Winter Nelis' pear, 9.9; and 'Bartlett' pear, 7.9. He observed that bees frequently visited other blossoms for nectar but visited pear blossoms only for pollen.

Brown and Childs (1929) stated that a full-bearing need for 'Anjou' tree at 15 years of age may have as many as 8,000 fruit buds, each of which contains a cluster of at least seven perfect flowers. A single tree may therefore produce as many as 56,000 flowers, all of which are potential fruit producers. They estimated that 1.96 percent of the flowers could set and produce a satisfactory crop. Powell (1902) stated that if 6 percent of a moderately blooming tree set fruit, a heavy crop would result. Brown and Childs (1929) showed that a 7.1 percent set resulted in production of 12,851 lb/acre over a number of years.

[gfx] FIGURE 148.- Branch of pear tree in full flower.
FIGURE 149. - Longitudinal section of 'Bartlett' pear flower, x 9.

Pollination Requirements:

The classic research by Waite (1895, 1899) established the principles of fruit pollination and clarified the need for pollination insects on fruit. In particular, he showed that the 'Bartlett' pear was self-sterile in Virginia and only set good crops when other cultivars were grown nearby so that bees could bring compatible pollen to its flowers. This basic pollination principle for pears was shown by Swayne (1824) (see also, Chittenden 1914), but it was largely forgotten until Waite's research. Close (1903) also showed that neither 'Kieffer' nor 'Angouleme' set fruit on bagged flowers. Fletcher (1907,1911) showed that both 'Kieffer' and 'Bartlett', if planted in solid blocks in West Virginia and Michigan, yield poorly if not properly pollinated. Florin (1925) found that 'Bartlett' were self-sterile in Sweden. Powell (1902) recommended the interplanting of pollinizer cultivars with the 'Kieffer'. Kraus (1912) advised growers in Ohio to plant 'Anjou', 'Clairgeau', 'Howell', or 'Kieffer' with 'Bartletts' for cross-pollination.

Luce and Morris (1928) reported that the 'Bartlett', 'Bosc', 'Anjou', and 'Winter Nelis' were partly or entirely self-sterile in the Wenatchee, Wash., area. However, rumors began to develop that 'Bartletts' might not require cross-pollination and considerable controversy developed on the subject. Weldon (1918) reported that large solid plantings of 'Bartletts' in California produced satisfactory crops. Tufts (1919), after a study of fruit production from hand-crossed flowers and from commercial orchards, concluded that all 'Bartlett' orchards should be provided with facilities for cross-pollination, that is, supplied with other varieties and bees. Westwood and Grim (1962) showed that 'Bartlett' yields were inversely related to distance from the pollenizer.

Kinman and Magness (1935) stated that the setting of fruit by all important pear varieties is aided by cross-pollination under some if not all conditions in the Pacific States. Magness also admitted that in some areas in some years 'Bartlett' sets good crops where no provision was made for pollination but that in other years heavier crops might be expected if pollination were provided. Davis and Tufts (1941) also considered the 'Bartlett' varying from almost completely self-sterile in the Sierra Nevada foothills of California to only partially self-sterile under interior valley and coastal conditions. Under these latter conditions, orchards planted solidly usually produce satisfactory crops. Griggs and Iwakiri (1954) finally showed that it was not the area where 'Bartletts' grew but the conditions under which they grew that determined their fruitfulness. They showed that the inclination of 'Bartletts' to produce parthenocarpic fruit determines its need for cross-pollination. This was supported by Bulatovic and Konstantinovic (1962); Wellington (1930); Reinecke (1930); Griggs and Vansell (1949); Konstantinovic and Milutinovic (1968); and Griggs et al. (1951).

If the orchard is well cared for, it will set a commercial crop of parthenocarpic fruit in many of the main pear-growing areas. If conditions are not good for parthenocarpic set, cross-pollination by bees will insure set of the crop. Parthenocarpic fruit, being seedless, is more desired by the consumer, although Reinecke (1930) showed that such fruit does not keep as well as pollinated fruit.

Stephen (1958) showed that when 'Bartlett' trees were caged for several seasons, the amount of fruit that set declined rapidly in succeeding years whether the tree was caged without bees or with bees alone without a bouquet of blooms from other varieties. The first year, there was no apparent difference. The second year, production in the cage containing only bees declined 58 percent. The following year, production was down by 92 percent. Stephen believed that the ability to produce fruit-set parthenocarpically decreased as time increased after the tree was cross-pollinated. These studies indicate that parthenocarpic fruit may be produced satisfactorily in some parts of Western United States, although, as Griggs (1970*) indicated, fruit set could be increased by interplanting pollinizers and using an ample supply of bees.

In other parts of the United States, 'Bartlett' should be interplanted with other cultivars and provided with bees. Evidently insect cross- pollination is essential for some cultivars in all areas (Hutson 1925, van Laere 1957) and for all cultivars in some areas. Where 'Bartletts' produce fruit parthenocarpically, the presence of other cultivars and bees can be an insurance in marginal seasons, and, during favorable seasons, tend to increase the number of seeded fruit. Lewis (1942) showed that parthenocarpy can be induced in some cultivars by frost. Steche (1959) showed that cross-pollination by honey bees trebled the crop when compared to the weight of fruit from self- or non-pollination.

Pollinators:

Waite (1895, 1899); Johnston (1927); Overholser et al. (1944); and Vansell (1942*, 1946) mentioned numerous species of insect visitors to the pear flowers, including hymenoptera, diptera, coleoptera, and other major groups. Like the other observers, Vansell (1942*) found that the honey bee was the most important visitor of all. In an orchard adjacent to uncultivated brush and timberland, which should have provided an abundant supply of insect visitors, honey bees accounted for more than 62 percent of the visitors to the flowers over two seasons even though there were few colonies of honey bees in the area. Vansell pointed out that although blowflies accounted for 23 percent of the visitors, they were of little value as pollinators, and concluded that honey bees were "practically the only distributors of pear pollen." He noted also, as did Scullen and Vansell (1942) Smith and Bradt (1967*), Stephen (1958), and Tufts and Philp (1923), that the bees showed a strong preference for pear pollen but weak interest in the nectar, which had a concentration of only 4 to 25 percent sugar and which influences the bee foraging behavior (Free and Smith 1961).

Pollination Recommendations and Practices:

Most growers of 'Bartlett' pears in California make no attempt to interplant pollenizer cultivars or to increase the local pollinating insects although the evidence indicates that they would benefit at times by doing so. Growers in other areas, and of most other cultivars should provide for cross-cultivar pollination and arrange to some degree for placement of honey bee colonies in or near their orchards. The colonies should be strong, sheltered from cold wind, exposed to the warm sun, provided with clean water, and protected from pesticides - a standard operation in the pollination of most fruit crops.

The number of visits by insect pollinators to pear flowers for optimum cross-pollination has not been determined. The pollinator population should be sufficiently heavy on cultivars that require cross-pollination that the bees are forced to forage on many blossoms to obtain a load of food. Waite (1895, 1899) recommended that there be honey bees in the neighborhood or at least within 2 or 3 miles, and that each large orchardist should keep bees. Root (1899) recommended that hives should be within one-half mile of the orchard. Fletcher (1900) stated that the keeping of bees by the grower might become necessary. Hooper (1935) advised growers to have one or more hives of bees in the vicinity of the orchard. Tufts (1919), Davis and Tufts (1941), Stephen (1968), Brown and Childs (1929), Vansell and DeOng (1925), and various others recommended that one colony of honey bees per acre be scattered throughout the orchard. Batjer et al. (1967) and Luce and Morris (1928) recommended one strong colony per two acres. Corner et al. (1964) recommended two colonies per acre of pears.

LITERATURE CITED:

BATJER, L. P., SCHOMER, H. A., NEWCOMER, E. J., and COYIER D. L.
1967. COMMERCIAL PEAR GROWING. U.S. Dept. Agr., Agr. Handb. 330, 47 pp.

BROWN, G. G., and CHI1DS, L.
1929. POLLINATION STUDIES OF THE ANJOU PEAR IN THE HOOD RIVER VALLEY. Oreg. Agr. Expt. Sta. Bul. 239, 15 pp.

BULATOVIC, S., and KONSTANTINOVIC, B.
1962. THE ROLE OF BEES IN THE POLLINATION OF THE MORE IMPORTANT KINDS OF FRUIT IN SERBIA. In 1st Internatl. Symposium on Pollination Proc., Copenhagen, Aug. 1960. Commun. 7, Swedish Seed Growers' Assn., pp. 167-172.

CHITTENDEN E. J.
1914. POLLINATION IN ORCHARDS. Ann. Appl. Biol. 1 (1): 37-42.

CLOSE, C. P.
1903. REPORT OF THE HORTICULTURIST. In 14th Ann. Rpt. Del. Agr. Expt. Sta. for year ending June 1902: 89-108.

CORNER, J., LAPINS, K. O., and ARRAND, J. C.
1964. ORCHARD AND HONEY BEE MANAGEMENT IN PLANNED TREE FRUIT POLLINATION. Brit. Columbia Dept. Agr. Apiary Cir. 14, 18 pp.

DAVIS, L. D., and TUFTS, W. P.
1941. PEAR GROWING IN CALIFORNIA. Calif. Agr. Ext. Serv. Cir. 122, 87 pp.

FLETCHER, S. W.
1900. POLLINATION IN ORCHARDS. N.Y. (Cornell) Agr. Expt. Sta. Bull 181, pp. 361-386.

______ 1907. POLLINATION OF KIEFFER AND BARTLETT PEARS. Mich. State Hort. Soc. 37th Ann. Rpt.: 36.

______ 1911. POLLINATION OF BARTLETT AND KIEFFER PEARS. In Va. Agr. Expt. Sta. Ann. Rpt. 1909 and 1910 pp. 212-232.

FLORIN, E. H.
1925. [PEAR POLLINATION.] Meddel. Perm. Kom. Eruktodlingsforsok. Sweden. No. 5, pp. 38. From 1925 Expt. Sta. Rec. 53(7): 641. [In Swedish.]

FREE, J. B., and SMITH, M. V.
1961. THE FORAGING BEHAVIOUR OF HONEYBEES FROM COLONIES MOVED INTO A PEAR ORCHARD IN FULL FLOWER. Bee World 42: 11-12.

GRIGGS, W. H., and IWAKIRI, B. T.
1954. POLLINATION AND PARTHENOCARPY IN THE PRODUCTION OF BARTLETT PEARS IN CALIFORNIA. Hilgardia 22(19): 643-678.

______and VANSELL, G. H.
1949. THE USE OF BEE-COLLECTED POLLEN IN ARTIFICIAL POLLINATION OF DECIDUOUS FRUITS. Amer. Soc. Hort. Sci. Proc. 54: 118-124.

______ IWAKIRI. B. T.. and DETAR. J. E.
1951. THE EFFECT OF 2, 4-5 TRICHLOROPHENOXYPROPIONIC ACID APPLIED DURING THE BLOOM PERIOD ON THE FRUIT SET OF SEVERAL PEAR VARIETIES AND ON THE SHAPE, SIZE, STEM LENGTH, SEED CONTENT AND STORAGE OF BARTLETT PEARS. Amer. Soc. Hort. Sci. Proc. 58: 37-45.

HEDRICK, U. P.
1921. THE PEARS OF NEW YORK. 636 pp. N.Y. State Dept. Agr. 29th Ann. Rpt., v. 2, part 2. J. B. Lyons CO., Albany.

HOOPER, C. H.
1935. PEARS - THEIR POLLINATION, THE RELATIVE ORDER OF FLOWERING OF VARIETIES, THEIR CROSS-FERTILIZATION AND THE INSECT VISITORS TO THE BLOSSOMS. Jour. Sol-East. Agr. Col. [Wye, Kent] 36: 111-118.

HUTSON, R.
1925. THE HONEYBEE AS AN AGENT IN THE POLLINATION OF PEARS, APPLES AND CRANBERRIES. Jour. Econ. Ent. 18: 387-391.

JOHNSTON, S.
1927. POLLINATION, AN IMPORTANT FACTOR IN SUCCESSFUL PEAR PRODUCTION. Mich State Hort. Soc. 57th Ann. Rpt., pp. 196-199.

KINMAN, C. E., and MAGNESS, J. R.
1935. PEAR GROWING IN THE PACIFIC COAST STATES. U.S. Dept. Agr. Farmers' Bul. 1739, 40 pp.

KONSTANTINOVIC, B., and MILUTINOVIC, M.
1968. [INFLUENCE OF BEES ON YIELD INCREASE IN SOME APPLE AND PEAR VARIETIES.] Savremena Poljoprivreda 16(2): 161-166. [In Serbo-Croation, English summary.]

KRAUS, E. J.
1912. THE POLLINATION QUESTION. Oreg. Agr. Expt. Sta. Cir. Bul. 20, 7 pp.

LAERE, O. VAN
1957. [THE EFFECT OF BEES ON THE SETTING OF TREE FRUIT.] Maandbl. van de Vlaamse Bieenb. 42(7): 188-193. [In Dutch.] AA-274/58.

LEWIS, D.
1942. PARTHENOCARPY INDUCED BY FROST IN PEARS. Jour. Pomol. and Hort. Sci. 20(1-2): 40-41.

LUCK, W. A., and MORRIS, O. M.
1928. POLLINATION OF DECIDUOUS FRUITS. Wash. Agr. Expt. Sta. Bul. 223, 22 pp.

MAGNESS, J. R.
1937. PROGRESS IN PEAR IMPROVEMENT. U.S. Dept. Agr. Yearbook 1937: 615-630.

OVERHOLSER, E. L., OVERLEY, F. L., and ALLMENDINGER, D. F.
1944. PEAR GROWING AND HANDLING IN WASHINGTON. Wash. Agr. Expt. Sta. Pop. Bul. 174: 30-35. 292

POWELL, G. H.
1902. KIEFFER PEAR POLLINATION. REPORT OF THE HORTICULTURIST. Del Agr. Expt. Sta. Ann. Rpt. 13: 121-124.

REINECKE, O. S. H.
1930. THE RELATION OF SEED FORMATION TO FRUIT DEVELOPMENT OF THE PEAR. So. African Jour. Sci. 27: 303-309.

ROOT, A. I.
1899. BEES NEAR BY ALMOST A NECESSITY TO SUCCESSFUL FRUIT- GROWING. Gleanings Bee Cult. 27: 56.

SCULLEN, H. A., and VANSELL, G. (A.) H.
1942. NECTAR AND POLLEN PLANTS OF OREGON. Oreg. Agr. Expt. Sta. Bul. 412, 63 pp.

STECHE, W.
1959. [EFFECT OF POLLINATION BY BEES ON YIELD AND FRUIT FORMATION IN THE PEAR FONDANT DE CHARNEU.] Erwerbsobstbau 1(7): 132-134. [In German.] AA-315/60.

STEPHEN, W. P.
1958. PEAR POLLINATION STUDIES IN OREGON. Oreg. Agr. Expt. Sta. Tech. Bul. 43, 43 pp.

SWAYNE, G.
1824. ON FERTILIZING THE BLOSSOMS OF PEAR TREES. London Hort. Soc. Trans. 5: 208-212.

TUFTS, W. P.
1919. POLLINATION OF THE BARTLETT PEAR. Calif. Agr. Expt. Sta. Bul. 307: 369-390.

TUFTS W. P. and PHILP, G. L.
1923. PEAR POLLINATION. Calif. Agr. Expt. Sta. Bul. 373, 36 pp.

VANSELL, G. H.
1946. BEES AND PEAR POLLINATION. Oreg. State Hort. Soc. Proc. 37: 51-53.

______and DE ONG E. R.
1925. A SURVEY OF BEEKEEPING IN CALIFORNIA AND THE HONEYBEE AS A POLLENIZER. Calif. Agr. Expt. Sta. Cir. 297, 22 pp.

WAITE, M. B.
1895. THE POLLINATION OF PEAR FLOWERS. U.S. Dept. Agr. Div. Veg. Path. Bul. 5, 86 pp.

______ 1899. POLLINATION OF POMACEOUS FRUIT U.S. Dept. Agr. Yearbook 1898: 167-180.

WELDON, G. P.
1918. PEAR GROWING IN CALIFORNIA. Calif. State Commr. Hort. Monthly Bul. 7: 219-410.

WELLINGTON, R. A.
1930. POLLINATION OF PEARS AND SMALL FRUITS. N.Y. State Hort. Soc. Proc. 75th Ann. Mtg.: 216-220.

WESTWOOD, M. N., and GRIM, J.
1962. EFFECT OF POLLINIZER PLACEMENT ON LONG TERM YIELD OF ANJOU, BARTLETT AND BOSE PEARS. Amer. Soc. Hort. Sci. Proc. 81: 103-107.

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