BLACKBERRY
Rubus spp., family RosaceaeBlackberries grow wild throughout the United States, but commercial production is limited largely to Oregon and Washington with small acreages in California, Michigan, New York, New Jersey, Florida, Texas, and some other southeastern States. This acreage includes erect, semierect, semitrailing, and trailing blackberries, as well as boysenberries, loganberries, and youngberries. Production has decreased considerably from the 43,684 acres in 1959 (Darrow 1967), probably because of increased harvesting costs. In 1969, production from 6,850 acres in Washington and Oregon amounted to 41.7 million pounds valued at $6.9 million (USDA 1971).
Plant:
Cultivated and wild blackberries comprise a large but inexact number of species and hybrids. Bailey (1949*) stated that more than 400 species are known in North America. He listed eight species grown for ground cover or ornament and 31 species grown for the fruits. Many of the cultivated blackberries are hybrids.
Instead of grouping the plants according to species, most authorities group them according to growth habits. The prostrate or trailing blackberry, which may spread over brush or small shrubs in the wild state, is sometimes called "dewberry. " The erect untrained blackberry may reach a height of 10 feet.
The loganberry was considered to be a cross between the 'Antwerp' red raspberry and the 'Aughinbaugh' blackberry (Lewis and Cole 1909, Aspinwall 1911, and Logan 1955). Darrow at first (1918, 1937) considered it a kind of the Pacific Coast blackberry (R. ursinus Cham. and Schlecht.), but later he (1967) agreed that it was indeed the blackberry-raspberry cross.
The youngberry or Young dewberry is generally considered to be a cross between the 'Mammoth' and 'Mays' (syn.'Austin Mays').
Bailey (1949*) placed the loganberry and boysenberry under the subspecies loganobaccus Bailey of R. ursinus and stated that the youngberry is "probably a derivative of R. ursinus, perhaps of hybrid origin." Hence, boysenberry, loganberry, youngberry, and "dewberry" are grouped herein as blackberries.
Most blackberries have a biennial "cane" or stem rising from a perennial root system. The cane usually produces its growth the first year; the second year it bears fruit and dies back to the crown. A few thornless cultivars have been developed, but most cultivars bear stiff thorns (correctly prickles) to one-quarter inch along the branch and smaller ones on the stems and leaves. The leaves are usually deciduous, but on some cultivars they are persistent. The fruit clusters of the trailing blackberries are usually less numerous, more open, and ripen earlier than those on the erect blackberries.
The fruit consists of many one-seeded fleshy drupelets or carpers on the receptacle. In the blackberry, the receptacle, unlike that in the raspberry, is retained in the harvested fruit making it more firm than the raspberry.
Blackberry plants are usually set in rows (fig. 51). To facilitate harvest of the fruit, the vines are usually trained to a trellis or tied alongside uprights.
[gfx] FIGURE 51. - 'Lucretia' blackberries trained upright on individual posts.
Inflorescence:
The erect blackberry inflorescence is usually a cluster of 10 to 20 flowers, whereas the trailing blackberry is more likely to have 1 to 10 flowers in the cluster. Intercrossing has produced all variations of this cluster size in different types and cultivars. Also, there are many more flowers per square yard of erect than of trailing blackberries. Otherwise, the whitish flowers, 1 inch or more in diameter, are similar in size and shape. There are usually four white petals and 50 to 100 stamens clustered around and overshadowing about the same number of pistils (fig. 52). Nectar is secreted in a shallow nectar cup at the base of flower. Secretion begins just before the petals start to unfold and continues until petal fall (Percifal 1946).
Blackberry nectar and pollen are both quite attractive to pollinating insects, and the plants are a source of surplus honey for bees in some of the Southern and Pacific States. Pellett (1947*) stated that the honey was light-amber in color, had a good flavor, and was very thick and slow to granulate. Gates (19l7) indicated that some forms of blackberries are more readily visited by bees than others.
[gfx] FIGURE 52. - Longitudinal section of 'Olallie' blackberry flower, x 6, and individual floret, enlarged.
Pollination Requirements:
Some of the hybrids of blackberries are self-sterile, but many of the species are partially self-fertile (Darrow 1924, 1942, Darrow and Waldo 1948). Darrow (1967) stated that self-sterility is very widespread in wild blackberries, and he gave credit to bees for performing the necessary cross-pollination. Hedrick (1938*) called attention to the sterility in blackberries and noted that the pollen is frequently shrunken or otherwise malformed. Detjen (1916) also mentioned the variations in fertility of different blackberry groups and gave pollinating insects credit for transferring the pollen. Hartman (1923) considered most species self- fertile, but not all. He noted that insufficient pollination not only reduced the number of flowers that set but also resulted in imperfect fruit. Auchter and Knapp (1937*) mentioned that most cultivars are self- fruitful but some are self-unfruitful. Hooper (1912) pointed out that loganberries need insect pollination, and he recommended the keeping of hive bees for pollination in suburban gardens and fruit farms and where large areas of the same kind of fruits are grown. Shoemaker ( 1961 ) reported the commercial blackberry cv., 'Flordagrand', was selfunfruitful and that wild blackberries were suitable pollinators.
Whether the self-fertile cultivars are capable of pollinating themselves in the absence of pollinating insects has not been determined on all cultivars of blackberries. The structure of the blossom strongly indicates that insects are necessary to transfer the pollen from the appropriate anthers to all of the receptive stigmas if maximum production of highest quality berries is obtained. Hartman (1923) noted that the 'Mammoth' and 'Cory Thornless' cvs. of blackberries in Oregon were "more or less self-sterile and require cross-pollination. Insufficient cross-pollination of these not only reduces the total set but results in imperfect fruit. "
Shoemaker and Westgate (1966) stated that the 'Flordagrand' blackberry is self-sterile but can be pollinated with pollen from the native trailing type of blackberries, but the native plants must be growing "in quantity near the cultivated plants and overlapping must occur in bloom." The 'Oklawaha' cv. was developed precisely to provide a pollen source for 'Flordagrand' and to yield a marketable crop as well. The 'Oklawaha' sets no fruit with its own pollen but produces abundantly if cross-pollinated (Shoemaker and Westgate 1966).
Yields largely depend upon the degree of insect cross-pollination. Shoemaker and Davis (1966) stated that if a perfectly formed berry is to be obtained most or all of the pistils of the blossom must be effectively pollinated by some "mass" method such as the visits of honey bees. They recommended that colonies of honey bees be placed in or near the plantings just before bloom. They also recommended the planting of alternate rows of 'Flordagrand' and 'Oklawaha' to provide the supply of pollen for crossing. They concluded that in all of the trailing cultivars the yields depended on the degree of effective cross-pollination. Sherman and Westgate (1968) pointed out that differences in size of berries may be due to imperfect pollination.
The effective time period of pollen transfer within an individual flower, as well as between flowers of blackberries has not been determined. Most pollination probably takes place the first day the flower is open with the remainder occurring the second day, although flowers will stay receptive for 3 days in a greenhouse at 75 deg F. Petals will hang on for 4 days if the weather is cool, but they usually drop off the second or third day.
The USDA (1967) recommended the removal of all wild blackberry and raspberry plants in the vicinity of blackberry fields. From the standpoint of disease and harmful insect control, this is good advice but from the standpoint of cross-pollination and the production of the largest quantity of highest quality berries, it may be questionable if only one cultivar is in the field.
With recent development of mechanical harvesting, the need for firmer berries has been emphasized. Such berries are more likely to be obtained if they are adequately pollinated.
Pollinators:
There is little information on the pollinating insects of blackberries. Honey bees eagerly visit the blossoms if the weather is favorable and are credited with much of the cross-pollination that occurs. Bumble bees and various other wild bees also visit the flowers, but where the berries are grown commercially, there are not likely to be enough of these insects in the wild to provide the mass pollination desired for maximum crop production. Honey bee colonies can be moved to such fields as desired.
Pollination Recommendations and Practices:
Hooper (1913) and Shoemaker and Davis (1966) recommended the placement of colonies of honey bees in or near blackberry plantings, and the evidence is strong that commercial production would be enhanced by supplying adequate pollinating agents. Even selffertile cultivars can benefit by having bees transfer pollen to every receptive stigma of the blossom at the earliest possible moment. An adequate supply of pollinating insects should be highly remunerative both in volume and quality of berries produced.
The number of bee visitations per number of flowers that would provide this service is unknown, but considering the time a bee spends in a flower and the number of stigmas that need to be pollinated, the recommendation of one honey bee for each 100 (muskmelon) flowers (McGregor et al. 1965) might be a conservative recommendation on berries. Such a rate of bee visitation might require the placement of several strong healthy colonies of honey bees per acre in the field at flowering time.
LITERATURE CITED:
ASPINWALL, B.
1911. THE OREGON BOGANBERRY Oreg. State Hort. Soc. 26th Ann. Mtg., pp. 77-78.DARROW, G. M
1918. CULTURE OF THE BOGAN BLACKBERRY U.S. Dept. Agr. Farmers' Bul. 998, 24 pp.____ 1924. DEWBERRY GROWING. U.S. Dept. Agr. Farmers' Bul. 1402, 28 pp.
____ 1937. BLACKBERRY AND RASPBERRY IMPROVEMENT. U.S.. Dept. Agr. Yearbook 1937: 496-533.
____ 1942. BLACKBERRY GROWING. U.S. Dept. Agr. Earmers' Bul. 1399, 18 pp.
____ 1967. THE CULTIVATED RASPBERRY AND BLACKBERRY IN NORTH AMERICA; BREEDING AND IMPROVEMENT. Amer. Hort. Mag. 46(4): 203-218.
____ and WALDO, G. F.
1948. GROWING ERECT AND TRAILING BLACKBERRIES. U.S. Dept. Agr. Earmers' Bul. 1995, 34 pp.DETJEN, L. R.
1916. SELF-STERILITY IN DEWBERRIES AND BLACKBERRIES. N.C. Agr. Expt. Sta. Tech. Bul. 11, 37 pp.GATES, B. N.
1917. HONEY BEES IN REBATION TO HORTICULTURE. Mass. Hort. Soc. Trans. Pt. 1: 71-88.HARTMAN, H.
1923. THE CANE FRUTT INDUSTRY IN OREGON. Oreg. Agr. Expt. Sta. Cir. 48, 28 pp.HOOPER C. H.
1913. THE POLLINATION AND SETTING OF FRUIT BLOSSOMS AND THEIR INSECT VISITORS. Jour. Roy. Hort. Soc. 38: 238-248.LEWIS, C. I., and COLE, C. A.
1909. CULTURE OF SMALL FRUITS. Oreg. Agr. Expt. Sta. Bul. 105, 29 pp.LOGAN, M. E.
1955. THE LOGAN BERRY. 20 pp. M. E. Logan, Oakland, Calif.MCGREGOR, S. E, LEVIN, M. D., and FOSTER, R. E.
1965. HONEY BEE VISITORS AND FRUIT SETTING OF CANTALOUPS. Jour. Econ. Ent. 58: 968,-970.PERCIFAL, M. S.
1946. OBSERVATIONS ON THE FLOWERING AND NECTAR SECRETION OF RUBUS FRUTICOSUS (AGG.). New Phytol. 45: 111-123.SHERMAN, W. B., and WESTGATE, P. J.
1968. BLACKBERRY PRODUCTION IN FLORIDA. Fla. Agr. Ext. Serv. Cir. 325,12 pp.SHOEMAKER, J. S.
1961. POLLINATION REQUIREMENTS OF FLORDAGRAND BLACKBERRY. Fla. State Hort. Soc. Proc. 74: 356-358.SHOEMAKER, J. S., and DAVIS, R. M.
1966. BLACKBERRY PRODUCTION IN FLORIDA. Fla. Agr. Ext. Serv. Cir. 294,20 pp._____ and WESTGATE, P. J.
1966. OKLAWAHA BLACKBERRY. Fla. Agr. Expt. Sta. Cir. S-159, Leaflet.UNITED STATES DEPARTMENT OF AGRICULTURE.
1967. GROWING BLACKBERRIES. U.S. Dept. Agr. Farmers' Bul. 2160,10 pp._____ 1971. FRUITS. PART 1. NONCITRUS BY STATES 1969-70 U.S. Dept. Agr. Statist. Rptg. Serv. CRB FRNT 4-1 (5-71),22 pp.
