Chapter 7: Small Fruits and Brambles


Chapter 7: Small Fruits and Brambles


BLUEBERRY
Vaccinium spp., family Ericaceae

The blueberry industry in the United States is concerned primarily with three distinct types of blueberries: highbush, lowbush, and rabbiteye. In the lowbush type, the two most common species are V. angustifolium Ait. and V. myrtilloides Michx. The highbush type developed mainly from V. australe Small and V. corymbosum L. (Goheen 1953). The rabbiteye type consists of one species, V. ashei Reade. Some hybrids, relatively unimportant in the United States, have been considered as a halfhigh group. Darrow (1966) stated that there were millions of clones - covering tens of thousands of acres from New Hampshire to West Virginia - of segregates of highbush-lowbush hybrids that are called lowbush. Numerous other species of minor importance are mentioned in the excellent book on blueberries by Eck and Childers (1966).

The 1964 United States Census of Agriculture reported 43,114 acres of blueberries in 20 States, with production of 46 million quarts of berries valued at $15 million. However, Darrow and Moore (1962) stated: "Although the blueberry crop from all cultivated varieties had a value of more than $13 million in 1960, the total value of the industry in the United States is much greater, as wild blueberries are harvested in several widely separated areas." Further on they continued: "About 150,000 acres of native blueberries in Maine are given some care." Eck and Childers (1966, p. 5) stated: "At present more than 100,000 acres of the lowbush species are under cultivation in the United States. Two-thirds of this acreage is harvested annually, and one-third is burned over each year." These statements would indicate that the 1964 United States Census of Agriculture data dealt only with tilled acreages, whereas the wild or burned over acreages were in addition.

This would indicate that about 200,000 acres may be concerned to some degree with blueberry production in the United States.

The bulk of the lowbush berry crop comes from plants to which some attention is given, such as burning over the area every 2 to 3 years, treating with insecticides and herbicides, fertilizing, and providing insect pollination. In recent years, more attention has been given to the care and harvesting of the lowbush type than formerly. By contrast, the bulk of the highbush and rabbiteye blueberry crop comes from plants that receive intensive cultivation.

Plant:

Lowbush blueberries may be less than a foot tall, but highbush types may grow to 30 feet. With one exception, the plant is grown only for its fruit, the delicious blue-black berry, l/4 to 1 inch in diameter. The evergreen blueberry (V. ovatum Pursh), which grows along the Pacific coast, not only yields berries, but florists also use its branches of green leaves as ornamentals. The lowbush blueberry plant develops from an individual fertile seed but spreads as a single clone by underground growth to form a colony as much as 40 feet across. Most seeds develop as a result of crossfertilization, giving rise to thousands of different kinds in the field. The highbush and rabbiteye develop as individual isolated plants with one to several stems and an oval canopy of growth above.

Before the arrival of the white man on this continent, the Indians intermittently burned over the lowbush blueberry growth, their only effort at cultivation of this plant. Burning prevents overgrowth of other plants and promotes new growth by the lowbush blueberry. Unfortunately, it also destroys many pollinating insects.

Starting in 1906, highbush blueberry selections were taken from the wild and crossed and back-crossed to form improved cultivars and an intensively cultivated crop (Coville 1937). The rabbiteye blueberry, which is a southern type, has also recently been included in the intensively cultivated crops.

The fruit of a few wild highbush species, for example, V. alto- montanum Ashe and V. membranaceum Dougl., are handpicked. The berries from the lowbush plants are harvested with hand rakes. Berries from the cultivated highbush and rabbiteye types are handpicked or mechanically harvested.

Inflorescence:

The blueberry inflorescence is usually a raceme on the last several inches of a branch (fig. 53). In the mountain blueberry (V. membranaceum Dougl.), the flowers are borne singly or in palrs on the feat axis.

The white or pink petals of the flower are united to form a tubular or bell-shaped corolla, 1/4 to 1/2 inch long, that hangs open end downward before pollination (fig. 54). After the flower is pollinated, it points skyward (Oldershaw 1970). Eight to ten stamens are inserted at the base of the corolla, around a much longer style that is receptive only on its tip. Pollen is released through pores on the end of the anther, during the period of stigma receptivity. Nectar is produced in the base of the corolla; after fertilization, the ovary matures into the many-seeded blueblack berry that ripens 2 to 3 months after flowering. The berry may contain as many as 65 extremely small seed, which do not interfere with the fruit's palatability. In fact, Barker and Collins (1965) stimulated seedless fruit development with gibberellic acid, but the product was a bland fruit with only half of the expected amotlnt of sugars present. Berry size increases with seed number (Eaton 1967, Brewer and Dobson 1969a, b).

Beekeepers sometimes obtain honey crops from blueberries (Firmer and Marucci 1964). Both nectar and pollen from blueberries are attractive to bees although some cultivars are more attractive than others (Brewer 1970, Wood et al. 1967). The reason for this difference has not been determined but should be given more serious study. Incorporation of the attractive factor in new cultivars could increase berry production.

[gfx] FIGURE 53. - Branch of highbush blueberry in flower.
FIGURE 54. - Longitudinal section of 'Tifblue' rabbiteye blueberry, x 12. A, Individual anther, x 17; B, cross-section of ovary, x 12.

Pollination Requirements:

Properly pruned and nurtured highbush or lowbush blueberry plants growing under favorable conditions are capable of setting almost 100 percent of their blossoms. A set of 80 percent is required to yield an excellent commercial crop of highbush blueberries - 50 percent for lowbush - but Karmo (1957) stated that many growers do not get over 10 to 20 percent set.

Aalders and Hall (1961) and Wood (1968) found considerable self- sterility and some cross-sterility in lowbush blueberries. More specifically, Hall and Aalders (1961) found that over 5 percent of the lowbush plants were male-sterile and that 45 percent produced less than abundant pollen or practically none. With so much sterility and pollen scarcity, it becomes evident that free transfer of pollen between plants is essential to maximum fruit production.

Early in the study of blueberries, Coville (1910) stated that pollination was effected by some insect. Later, Coville (1921) observed that when blueberry flowers were pollinated with their own pollen, and fruit was obtained, the berries were smaller and later in maturing than when pollen came from another plant, and some plants were almost completely sterile to their own pollen. Bailey (1937), Beckwith (1931), Lee (1958), Phipps (1930), Phipps et al. (1932), Shaw and Bailey (1937), Schaub and Bauer (1942), and Shaw et al. (1939) also concluded that cross-pollination was a requirement for good blueberry production. This was further confirmed by Meader and Darrow (1944,1947) and Wood (1965). Eck and Childers (1966) stated that the rabbiteye blueberry is so nearly self-sterile that compatible cultivars must be interplanted. Morrow (1943) showed that even when eelfing occurred the cross- pollinated flowers produced more seeds and were larger and earlier in maturing than those produced from selfed flowers. Boller (1956) and Darrow and Moore (1962) recommended that at least two cultivars be included in every planting to provide adequate cross-pollination possibilities.

Insect pollination is essential for maximum blueberry production. Failure to produce good crops is frequently the result of poor pollination (Firmer and Marucci 1963). Chandler (1943) stated that growers frequently blame frost for their low yields when in reality poor insect pollination is the cause. The plants set more fruit, larger fruit, and set it earlier when there is adequate cross-pollination.

The blossom is well adapted for insect pollination, with its fragrance, its nectaries at the base of the corolla, and its receptive stigma and heavy pollen, both so placed in the narrow throat of the corolla that the bee must come in contact with each when foraging. The structure and position of the blossom--hanging downward with the 10 stamens forming a tight circle around the pistil, which extends beyond them-- ideally facilitates cross-pollination. A mere touch of the blossom will dislodge some of the pollen and cause it to fall downward, but the likelihood is small that it will land on the stigma of its own or another blueberry blossom, unless it falls first upon a bee's hairy body and is then transferred to the stigma. If pollination does not occur, the pistil continues to elongate until it extends beyond the corolla, which enhances its possibility of contact with pollinating insects.

Stigma receptivity may last 5 to 8 days (Merrill 1936, Moore 1964, and Wood 1962). However, if pollination does not occur within 3 days after the flower opens, fruit set is unlikely (Chandler and Mason 1964).

Knight and Scott (1964) made cross-pollination studies in the greenhouse with four cultivars under cool and warm conditions. They reported that warm temperature hastened pollen tube growth and improved fruit set. They also found that cross-pollinated fruit ripened earlier than selfed fruit. They concluded that the larger, earlier berries and increased percentage of fruit set from cross- as compared to self- pollination indicated that growers would be economically just)fied in promoting cross-pollination.

As soon as fertilization occurs, the flower begins to lose attractiveness and development of the ovary begins.

Merrill (1936) and Merrill and Johnston (1939) erroneously concluded that blueberries were self-fruitful, and they encouraged growers to plant single cultivars in solid blocks. This advice, which was still being given as late as 1959 (Johnston 1959), seriously curtailed maximum blueberry production in Michigan for years (Martin 1967).

The inability of blueberries to set commercial crops in the absence of pollinating insects is now well established in different areas and under different conditions. However, Darrow (1966) stated that much more information seems to be needed on pollination of both lowbush and highbush blueberries. This is still true.

One of the major problems in highbush blueberry pollination is that the bulk of the commercial plantings consist of solid clonal blocks, which afford little opportunity for cross-pollination. For most efficient pollination and highest production, such blocks should be interplanted with compatible cultivars. The selfsterile rabbiteye must be interplanted with compatible cultivars.

Pollinators:

There has been considerable lack of opinion in the past as to which pollinating agent is most effective in pollinating blueberries (White and Clark 1938). In Massachusetts, Beckman and Tannenbaum (1939) recorded more bumble bees (46 percent) than honey bees (38 percent) on blueberry blossoms. In Michigan, Merrill (1936) stated that both bumble bees and honey bees played a major part in blueberry pollination, but he considered bumble bees the primary agents. Wood (1961) stated that the importance of honey bees as a supplement to native bees had not been clearly established in Canada. Filmer and Marucci (1963) noted that bumble bees are good pollinators of blueberries in New Jersey, but their numbers fluctuate so they are not reliable. Later Marucci (1966) conceded that bumble bees and other wild bees were inadequate. Numerous references show that modern agricultural practices have greatly reduced the bumble bee population in many areas. Other native pollinators are usually insignificant. Brewer et al. (1969a) showed that neither airblasts nor vibrations gave a commercial fruit set for either 'Jersey' or 'Rubel'. The only recourse for adequate pollination in the absence of native pollinators is to move honey bee colonies to the blueberries.

Boulanger (1964) and Boulanger et al. (1967) noted that there were too few native pollinators to set an adequate crop in many fields in Maine, and they recommended the introduction of honey bees. Darrow and Moore (1966) also stated that, in general, native bees are inadequate and should be supplemented with one to five strong colonies of honey bees per acre. Dorr and Martin (1966) stated that the scarcity of bumble bees and other bees in Michigan blueberry plantations had previously been an important factor in limiting optimum production. They recommended both the placement of honey bee colonies in the field and bumble bee conservation practices. Eaton and Stewart (1969b) and Oldershaw (1970) mentioned the wellknown fact that bumble bees frequently "burglarize" the blossoms by cutting a hole in the base of the corolla and stealing the nectar without contributing to pollination. Honey bees frequently visit these holes so their pollinating efficiency is also reduced. Helms (1970) attributed these holes to honey bees which he - we believe erroneously - considered to be "parasites."

With the populations of bumble bees decreasing as a result of various agrotechnical factors, the repeated results of various researchers previously mentioned as well as others (Eaton and Stewart 1969a, Filmer 1963, Filmer and Swift 1963, Hansson 1969, Karmo 1958, 1966, 1972, and Marucci 1965) plus practical experience strongly indicate that the value of the honey bee has gradually become fairly well recognized in most areas as the primary pollinator of blueberries. Some questions not conclusively answered about the honey bee include the appropriate number, strength, placement, and various problems of management of the colonies to be used.

The number of colonies per acre recommended by various researchers varies and lacks strong supporting data. Wood (1971) reported no increase in perfect seeds per berry when up to eight colonies per acre of lowbush blueberries were used. Brewer et al. (1969b) compared berry production and seeds per berry with colonies per acre. They obtained 160 ounces of berries with 4.9 seeds per berry per plot in fields not supplied with bees; 290 oz with 23 seeds per berry per plot in the fields supplied with two colonies per acre; and 335 oz with 28 seeds per berry in plots of a field supplied with five colonies per acre. Yet, for unexplained reasons, they stated that slightly more than two strong colonies per acre will provide an adequate pollinating force.

Marucci (1966) recommended one colony per 2 acres of highly attractive cultivars, one colony per acre of 'Weymouth', and two colonies per acre of less attractive cultivars such as 'Coville' and 'Earliblue'. Lathrop (1950, 1954) recommended one strong colony per acre on small acreages. Darrow and Moore (1966) recommended one to five strong colonies per acre. Increased production of lowbush blueberries has been shown with up to 10 colonies per acre (Boulanger 1966).

Howell et al. (1970, 1972) introduced honey bees into cages with blueberries at 0, 25, 50, and 100 percent of full bloom. They concluded that 25 percent of full bloom is the latest time for bees to be added to insure maximum yield.

According to E. C. Martin (personal commun., 1973), there was a rather dramatic acceptance of the information on the value of bees to blueberries in Michigan following publication of papers by Martin (1966) and Dorr and Martin (1966). Within 3 years, growers of 9,000 acres of blueberries were using between 12,000 and 15,000 colonies of honey bees (Mich. Agr. Expt. Sta. 1970), and this activity was primarily responsible for that State being the leading producer of blueberries. He stated that two colonies per acre has become the accepted optimum for commercial growers, and some growers were convinced that higher numbers of colonies per acre were economical.

Boulanger (1966) compared blueberry production in fields where the colonies were shifted from one field to another every few days (rotated) with fields where the colonies were left in the field throughout the period of bloom (static). The fields were supplied with 3.5, 4.5, 7.9, and 10 colonies per acre. Production varied considerably between fields and years and within treatments, but the highest yield, 80 bu/acre, was obtained from the field that contained 10 static colonies per acre. Nevertheless, he concluded that colony rotation held promise as a future management practice. Karmo (1961) also showed that colony rotation increased blueberry production. However, Karmo (1972) suggested that the bees be present for 4 to 5 days during the peak of bloom then moved to later blooming fields for more efficient use of the bees.

Sharp (1970) reported increased efficiency in pollination by the bees when the colonies were rotated. The theory involved in this shifting of the colonies is that the first day or so after a colony is reoriented the bees forage only near the hive. This subject has not been sufficiently explored to determine if the extra effort is worthwhile. Filmer and Marucci (1963) considered one bee visitor per square yard of lowbush blueberries in full bloom on days of good weather as adequate. When the population goes below this level, they recommended supplementing the local supply of pollinators with honey bees. Eaton and Stewart (1969a) showed that some colonies of honey bees collected much more blueberry pollen than other similar colonies. The genetic inheritance of this character has not been studied although other studies have shown that the tendency to collect specific pollens is inherited.

The greatest benefit in blueberry pollination seems to be derived when there are aufficient pollinators to distribute the pollen freely, not only from anthers to stigma of self-fertile flowers, or between plants of a cultivar some of which may be self-sterile, but also between self- sterile cultivars (Hall and Aalders 1961). As Eck and Childers (1966) pointed out, when the bee population is high, the more attractive blossoms become pollinated and fall rapidly, forcing the bees to work sooner on the less attractive blossoms; thus, the higher the bee concentration the more efficient the bees become.

Pollination Recommendations and Practices:

The recommendations for the supplemental use of honey bees on blueberries range from less than one colony to five colonies per acre. Frequently, the lower recommended number seems to stem from the beekeeper's reluctance to overstock an area from the standpoint of honey production or colony buildup. The actual usage varies from none to three, and State averages of honey bee colony rentals for blueberry pollination are less than one colony per acre.

Evidence indicates that the grower would profit most, in terms of quantity and quality of berries produced, earliness of harvest, and greatest percentage harvest at first picking, if the highest possible bee population were maintained at flowering time. This might mean five or even 10 colonies per acre; doubtless under most conditions it should be greater than one or two.

Most growers make some attempt at having honey bees in or near their fields; however, this supply is seldom adequate. During optimum bee flight weather, there should be sufficient colonies to provide several bees per square yard of highbush plants in full bloom and at least one bee per square yard of lowbush plants.

LITERATURE CITED:

AALDERS, L. E., and HALL, I. V.
1961. POLLEN INCOMPATIBILITY AND FRUIT SET IN LOWBUSH BLUEBERRIES. Canad. Jour. Genet. and Cytol. 3: 300-307.

BAILEY, J. S.
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BARKER, W. G., and COLLINS, W. B.
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BECKMAN, W., and TANNENBAUM, L.
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BECKWITH, C. S.
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BOILER, C. A.
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BOULANGER, L. W.
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____ 1966. BLUEBERRY POLLINATION IN MAINE. In North Amer. Blueberry Workers' Conf. Proc., Apr. 6-7. Maine Agr. Expt. Sta. Misc. Rpt. 118: 34-36.

____ WOOD, G. W., OSGOOD, E. A. and DIRKS, C. O.
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BREWER J. W.
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____ and DOBSON, R. C.
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____ and DOBSON, R. C.
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DOBSON, R. C., and NELSON, J. W.
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DOBSON, R. C., and NELSON J. W.
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CHANDLER, F. B.
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____ and MASON, I. C.
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COVILLE F. V.
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DARROW, G. M.
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____ and MOORE, J. N.
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____ and MOORE, J. N.
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DORR J., and MARTIN, E. C.
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EATON, G. W.
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____ and STEWART, M. G.
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____ and STEWART. M. G.
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FILMER, R S.
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____ and MARUCCI, P. E.
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____ and MARUCCI, P. E.
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____ and SWIFT, F. C.
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GOHEEN, A. C.
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HANSSON, A.
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