CHERRY
Prunus spp., family RosaceaeCherries grown commercially in the United States include sweet cherries (P. avium L.); tart, sour, or pie cherries (P. cerasus L.); and Dukes (probably P. gondouinii (Poit. & Turp.) Rehder). The mahaleb (P. mahaleb L.) and the mazzard, a wild or seedling form of P. avium, are used as rootstock upon which the fruiting types are grafted. The mahaleb is used much more extensively than the mazzard (Howe 1926, USDA 1967).
In 1970, 121,650 tons of sweet cherries, including Dukes (usually grouped with the sweet cherries), were produced, primarily on the West Coast. Oregon produced 40,000 tons; Washington, 25,800; California, 25,400; and Michigan, 21,000 tons. There were 118,640 tons of tart cherries produced - 79,000 in Michigan and 18,200 tons in New York. Several other States produced smaller amounts of both kinds.
The value of the 1970 sweet cherry crop was $43.2 million, compared to $17.9 million for the tart cherries.
Plant:
The deciduous cherry tree does not thrive where summers are long and hot, yet the blossoms are susceptible to injury by cold spring weather (Cullinan 1937). For these reasons, the growing areas are limited to the more northerly States, except for some areas of high altitude and temperatures moderated by large bodies of water such as the oceans or the Great Lakes.
The trees are planted at various distances apart but most commonly 20 feet for tart cherries and 25 to 32 feet for sweet cherries. They are usually planted at equal distances apart, except when the contour or hedgerow systems are used (Griggs 1970*).
When hedgerow planting is used in California, the trees are placed 6 feet apart in the row and the rows are spaced 4 feet apart. The pollenizer trees are placed at every eleventh location in every other row, offset by five trees, about one pollenizer for each 20 recipient trees (Ryugo and Mikuckis 1969).
Inflorescence:
When in bloom the cherry tree displays white, faintly fragrant flowers in clusters of two to five on short lateral spurs on the many branches (fig. 71). The five petals of the flower are oval, white, and rather widely spread. There is a single upright pistil and about 30 loose stamens (fig. 72). The sweet cherry flower is about an inch across, the tart cherry slightly smaller. The flower remains open 7 to 8 days. When the flower opens the stigma is receptive, but the anthers are closed. Anthers begin opening shortly after flowers open and continue into the second day (Knuth 1908*, p. 703; Srivastava and Singh 1970). Nectar is secreted on the inner surface of the receptacle. Eaton (1959) stated that pollination on the first day after anthesis was much more effective than pollination on the second day, and he stressed the importance of the earliest possible pollination particularly in cultivars such as 'Schmidt'.
Both pollen and nectar are attractive to insects, particularly bees, throughout the day if weather permits. The sweet cherry nectar is much richer in sugar (55 percent sugar) than the tart cherry nectar (28 percent) (Vansell 1942*). Pellett (1947*) stated that in California the cherry is one of the best fruit trees for honey production. Because of the time of year that cherries bloom, colonies are frequently not sufficiently strong to store surplus amounts and cherry honey is practically unknown. There are usually few other floral visitors except honey bees, although Nevkryta (O.M.) (1957) reported that only 60 percent of the insects on flowering sweet cherries were honey bees.
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FIGURE 71. - Fruiting branch of cherry, showing spurs and clusters of flowers.
FIGURE 72. - Longitudinal section of a 'Bing' cherry flower, x 7.Pollination Requirements:
The sweet cherry was shown by Gardner (1913), Anonymous (1926), Overholser and Overley (1931), Crane and Brown (1937), and Way (1968) to be self-sterile or self-unfruitful, and, furthermore, the most important cvs., 'Bing', 'Lambert', and 'Napoleon' ('Royal Ann'), were shown to be interincompatible. This interincompatibility continues to be a problem (Griggs 1970*), although Lapins (1971) reported that the 'Stella' cv. was a self-compatible sweet cherry, derived from a radiation-induced self- fertile selection obtained from England.
The attitude toward the pollination of tart cherries has changed over the years. Crane (1925), Dujardin (1921), Hooper (1924), and Schuster (1925) stated that the tart cherry was self-sterile or nearly so. Einset (1932) said that there was a continuous range from complete self- fruitfulness to complete self-unfruitfulness. Roberts (1922) and Marshall et al. (1929) said the blossoms were self-fertile and that insect pollinators were not needed. Murneek (1930) said they were self-fertile but benefited from insect pollination in unfavorable seasons. However, Hootman (1931, 1933) showed that only 4 percent of screened blooms (of 'Montmorency' cv.) produced fruit as compared to 49 percent that were hand pollinated. Lagasse (1928) and later Vansell and Griggs (1952*) stated that the commercially important tart cherry cultivars are self- fruitful if enough pollinizing insects are available, but better crops can be expected if the orchard contains more than one cultivar. The knowledge is now fairly well accepted that all of the important tart cherry cultivars will set fruit with their own pollen, but only after it is transferred by some outside agency from the anthers to the stigma.
The amount of fruit set expected on cherries has been mentioned by various research workers. All concede that set of every blossom is undesirable. Shoemaker (1928) reported a range of 13 to 60 percent with an average of 35 percent set of sweets, 21 to 42 percent with an average of 33 percent for tart cherries, and 10 to 53 percent with an average of 20 percent set for Dukes. As previously mentioned, Hootman (1931) obtained 49 percent set of hand-pollinated 'Montmorency' tart cherries. Gardner (1913) stated that 50 percent of the sweet cherry flowers should set. Griggs et al. (1952*) reported an overall average for several seasons of good crops at 21 to 32 percent set. Griggs (1970*) stated that self- fruitful cultivars of sweet cherries may be undesirable if they tend to set too heavily. Also, the fruit fails to develop adequate size without expensive thinning practices.
Luce and Morris (1928) stated that if the cherry blossom is not pollinated, the fruit develops to the size of a garden pea, then drops to the ground.
Tukey (1925), Free and Spencer-Booth (1964), and numerous others have reported decreasing production with increased distance from the pollenizer row of sweet cherries.
In summary, all cherries are basically incapable of automatic self- pollination. Tart cherries will set fruit if the pollen is transferred from anthers to stigma of the same flower but will set more fruit if other cultivars are interplanted in the orchard. Compatible cultivars can only be determined by tests (Griggs 1953*). Sweet cherries, with the exception of the 'Stella' cv. (Lapins 1970), will not set fruit with their own pollen, only with pollen of certain other cultivars.
Way and Gilmer (1963) showed that healthy trees are important in the set of cherries. When they used pollen from trees infected with tart cherry yellows disease, fruit set was only 25 to 90 percent of that with pollen from healthy trees. Such pollen would either decrease production or create a demand for more insect pollinators.
Pollinators:
Wind is not a factor in cherry pollination, as has been clearly and repeatedly established over the years (Roberts 1922, Burtner 1923, Murneek 1930, Claypool et al. 1931, and Brown 1968). Most researchers and growers give the primary credit for the pollination of cherries to honey bees. A heavy pollinator population is needed and flowering occurs too early in the year for other insects to be plentiful. Hendrickson (1922) stated that as early as 1894 a government report showed that a cherry crop near Vacaville, Calif., was greatly increased when several colonies of honey bees were placed in the orchard. Morrill (1899) also reported that bees increased cherry production. Gardner (1913) was the first to establish scientifically the need for pollination, and he stressed the importance of bees. This was supported with further research by various others, including Wellington (1923), Tuft and Philp (1925), Hooper (1930). Claypool et al. (1932), Weiss (1957), Skrebtsova and Iakovlev (1969), Eaton (1959), and Brown. 21
The fact that possibly only one pollen grain is needed to pollinate a cherry flower would indicate that repeated bee visits may be unnecessary, providing the pollen grain is compatible and successful fertilization of the ovule ensues. To play safe, the grower should insure the transfer of many pollen grains to the stigma. Tart cherry pollen may come from the same flower or the same tree, although greater benefit is usually derived if pollen comes from another cultivar. Sweet cherry pollen must come from another - and compatible - cultivar; therefore, a high degree of bee activity on the tree and between trees is required to adequately pollinate the crop.
The proper pollinator population is not easy to establish. Griggs et al. (1952*) counted 30 to 40 bees per sweet cherry tree that had been in production several years. The number of colonies per acre necessary to provide this population was not given. Skrebtsova and Iakovlev (1959) spoke of "saturation pollination" of cherries, but their data indicated that even with their maximum of 3.8 colonies per hectare (less than two colonies per acre) maximum set of all flowers was not achieved.
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21 Brown, K. BEES FOR SWEET CHERRY POLLINATION- UNDER WILLAMETTE VALLEY FONDITIONS. Polk County (Oregon) Agr. Ext. Serv. Agent, 2 pp. 1969. [Mimeographed.]Pollination Recommendations and Practices:
Schuster (1925) recommended one strong colony for each 1 to 2 acres "if the stands are strong." Tufts and Philp (1925) recommended at least one colony per acre. Marshall et al. (1929), Murneek (1930), Philp (1930, 1947), and Stephen (1961) concurred with the one-colony-per-acre recommendation. Hooper (1930) recommended that colonies be placed in the orchard during flowering. Brown (1968)22 recommended four to five colonies per acre for his area of Oregon, the colonies placed in groups on each 5 to 10 acres of the orchard. Eaton (1962) stated that strong colonies should be brought into the sweet cherry orchard on or before the day the first flowers open, because placement in the orchard even 1 day late could result in a reduced crop. Auchter and Knapp (1937*) recommended one colony containing 7 to 9 pounds of bees to every 3 to 4 acres but conceded that many growers use one colony for each acre or two. Coe (1934) and EIoffman (1965) urged the use of bees but did not designate the concentration. Nevkryta (A. N.) (1957) recommended four to five colonies per hectare (about two colonies per acre). Skrebtsova and Iakovlev (1959) recommended "saturation pollination" of the orchard, and showed that with 3.8 colonies per hectare, 15 percent of all flowers set fruit but with 2.8 colonies only 13 percent set. Luce and Morris (1928) recommended one colony per acre. Schuster (1925) also reported, "It is becoming the practice for cherry growers either to keep their own bees or to hire stands of bees during the blooming season." To take advantage of this needed cross-pollination between cultivars, various planting plans of trees in the orchard were recommended, ranging from one pollenizer and nine recipient trees to a 1:1 ratio. This recommended usage of bees barely seems to be accepted by the growers. Kelly (n. d.) reported that during 1959 - 63, tart cherry growers in Pennsylvania spent only 28 cents per acre for pollination fees; when colonies were rented, the fee was $4.50 per colony. Considering the pollination needs of this crop and the apparent lack of effort expended by these growers, one is not too surprised at his statement: "In the last decade sour cherry production and growers have both declined 31 percent." However, pollination is probably not the only reason for this decline. In a similar study made in Michigan on 37 tart cherry farms, Kelsey (1964) reported that growers paid an average of $1.33 per acre for bee pollination. The number of colonies of honey bees utilized, for which there was no remuneration, was not disclosed. In general, most cherry growers make some attempt to have bees present in their cherry orchards at flowering time. Frequently, if bees are rented and there are 2 or 3 days of good weather for bee flight, the tart cherry grower is ready for the bees to be removed. The number, strength, and placement of colonies necessary to provide 50-percent set of cherry flowers (Gardner 1913, Hootman 1931) is not known but should be determined. Also, the difference in the need of bee pollination between sweet and tart cherries should be determined. For highest production of cherriesÑthe setting of the maximum number of blooms for greatest production of sizeable fruitÑcross- compatible cultivars that flower at the proper time must be interplanted in sweet cherry orchards, and possibly also in tart cherry orchards, although large solid blocks are known to produce satisfactory crops. For highest production of either sweet or tart cherries as many as five strong colonies of honey bees per acre should be placed on each 5 to 10 acres just before flowering time. The colonies should contain 600 in2 or more of brood and 7 to 9 pounds of bees.
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22 Brown, K. POLLINATION OF ROYAL ANN (A-10) IN THE WILLAMETTE VALLEY. Polk County (Oregon) Agr. Ext. Serv. Agent, 4 pp. 1968. [ Mimeographed.]LITERATURE CITED:
ANONYMOUS.
1926. CROSS POLLINATION OF THE WINDSOR VARIETY. Amer. Fruit Grower Mag. 46(3): 26.BURTNER J. C.
1923. LATEST CHERRY POLLINATION STUDIES. Better Fruit 182: 5 - 6, 23 - 24.CLAYPOOL, L. L., OVERLEY, F. L., and OVERHOLSER, E. L.
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1931. WASHINGTON SWEET CHERRY POLLINATION STUDIES IN 1931. 27th Ann. Mtg. Wash. State Hort. Assoc. Proc. December 1, 2, and 3 at Yakima, Wash., pp. 171-174.COE, F. M.
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1937. IMPROVEMENT OF STONE FRUITS. U.s. Dept. Agr. Yearbook 1937: 724 - 737.DUJARDIN F.
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1965. POLLINATION AND FRUIT DEVELOPMENT OF TREE FRUITS. N.Y. (Cornell) Agr. Ext. Serv. Bul. 1146, 8 pp.HOOPER, C. H.
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HOOTMAN, H. D.
1930. RECENT DISCOVERIES IN POLLINATION METHODS AND PRACTICES AND THEIR INFLUENCE UPON GREATER YIELDS OF DESIRABLE FRUIT. Md. Agr. Soc. Farm Burl Fed. Rpt. 15,170-182; also in Md. State Hort. Soc. Proc. 33: 24-36.____ 1933. THE IMPORTANCE OF POLLINATION AND THE HONEYBEE IN FRUIT YIELDS. Mo. State Hort. Soc. Proc. 1930/1932: 59-67.
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1926. RELATIVE MERITS OF MAZZARD AND MAHALEB ROOT-STOCKS FOR CHERRIES. Amer. Soc. Hort. Sci. Proc. 23d Ann. Mtg., pp. 53-55.KELLY, B. W.
[ n.d. ] FACTORS RELATED TO THE COST OF PRODUCING CHERRIES IN PENNSYLVANIA, 1959-1963. Farm Mangt. 20, (Pa. Agr. Ext. Serv.), 17 pp.KELSEY, M. P.
1964. THE COST OF GROWING TART CHERRIES IN THE VARIOUS AREAS OF MICHIGAN AND HOW THEY WERE DETERMINED. Mich. State Hort. Soc. 94th Ann. Rpt., pp. 90 - 94.
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1971. 'STELLA', A SELF-FRUITFUL SWEET CHERRY. Canad. Jour. Plant Sci. 51: 252-253.LUCE, W. A., and MORRIS, O. M.
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1957. [DISTRIBUTION OF APIARIES FOR POLLINATING CHERRIES.] PchelovodstVo 34(4): 34-38. [In Russian.] AA-373l58.NEVKRYTA, O. M.
1957. [INSECT POLLINATORS OF WILD AND CULTIVATED CHERRY IN THE UKRAINE.] Zbirn. Prats Zool. Muz. 28: 49-61. [In Ukrainian, Russian summary.] AA-418/65.OVERHOLSER, E. L., and OVERLAY, F. L.
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1970. FLORAL BIOLOGY, FRUIT-SET, FRUIT-DROP, AND PHYSICO- CHEMICAL CHARACTERS OF SWEET-CHERRY (PRUNUS AVIUM L.). Indian Jour. Agr. Sci. 40: 400-420.STEPHEN, W. P.
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