Compendium of Raspberry and Blackberry Diseases and Pests, Second Edition

Introduction The Genus Rubus Blackberries and red and black raspberries are members of the family Rosaceae, along with apples, apricots, cherries, pears, plums, peaches, and strawberries. They are in the diverse genus Rubus with hundreds of other species, and while the center of origin is in China, they are native to all continents except Antarctica. The common name for Rubus spp. in eastern North America and Europe is bramble, while in western North America the term caneberry is more common. The genus Rubus is divided into 12 or 13 subgenera, depending on which classification system is used; raspberries are classified into the subgenus Idaeobatus and blackberries are classified into the subgenus Rubus (formerly Eubatus), which is further divided into 12 sections (Fig. 1).

Most Rubus spp. are colonists of habitats disturbed by either natural causes (e.g., fires, glaciers) or human activities (e.g., logging, farming). The aggressive colonization of open ground by species such as R. armeniacus has led to their being declared noxious weeds in some countries. Most species with edible fruit are found in mid-­successional temperate climates (e.g., at the edge of a forest or along a stream). While blackberries and red and black raspberries are the most widely grown commercial Rubus cultivars, nearly every region of the world where Rubus spp. are native has developed thriving regional industries based on their local species. A few examples include Morá (R. glaucus) in Andean South America; wineberry (R. phoenicolasius),

Korean black raspberry (R. coreanus), and trailing raspberry (R. parvifolius) in Asia; and cloudberry (R. chamaemorus) and arctic raspberry (R. arcticus) in the far northern regions of Eurasia and North America.

Cultivated blackberries are derived largely from species in the taxonomic sections Allegheniensis, Arguti, Rubus, and Ursini. Since most of the cultivated types of blackberries are derived from hybrids among two or more species, most of them do not have a species epitaph and are designated as Rubus subgenus Rubus (or Rubus subgenus Eubatus in older literature). In addition to the interspecific crosses in their background, polyploidy, apomixis, and a highly variable phenotypic response have made it difficult to classify blackberries into distinct biological species.

The one cultivated exception to this is the group of cultivars derived from the European cutleaf blackberry (R. laciniatus).

The trailing R. laciniatus ‘Evergreen’ was once widely grown in Europe and the United States. Eventually, a thornless sport was found and named ‘Thornless Evergreen’ and it soon dominated the western North American industry despite the fact that it commonly reverted to a thorny type when injured or when shoots sprouted from roots. ‘Everthornless’, which was derived from a cell culture of the L1 thornless layer of ‘Thornless Evergreen’, is genetically thornless and therefore does not revert to thorny canes when injured.

Red raspberries, while commonly designated as R. idaeus, are sometimes separated into the European R. idaeus and the North American R. strigosus; although it is difficult to distinguish

Fig. 1. Relationships between various Rubus spp. (Cour­tesy M. P. Pritts; Used by permission)

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between them based on morphology, and they freely hybridize.

Black raspberries (R. occidentalis) are in the subgenus Idaeobatus with red raspberries.

Chromosome numbers in Rubus spp. range from 2n = 2x = 14 to 2n = 18x = 126, including odd ploids and aneuploids. The chromosomes are small, 1–3 µm long, with a nuclear DNA content for the diploid species ranging from 0.56–0.59 pg. While manual counting is the most reliable method of determining the ploidy level in Rubus spp., flow cytometry has proven to work well to differentiate ploidy level, if not the precise number of chromosomes. Most raspberries are diploid; blackberries range from diploid to dodecaploid, with all erect and semi-­erect blackberries being 4x and the trailing cultivars ranging from 6x to 12x.

Red and black raspberries have been hybridized to produce purple raspberries that are sometimes designated as R. × neglectus. Purple raspberries are vigorous, productive, and large fruited, but the distinctly flavored fruit is typically soft. Raspberries often produce mutations or offspring that are yellow fruited (e.g., cultivar Anne). These yellow-­fruited raspberries are identical to red raspberries in most ways. Blackberries and red raspberries also have been hybridized to produce cultivars Boysen, Logan, and Tayberry, among others, and these are often termed “hybrid berries” and sometimes designated as R. loganobaccus. Cultivar Logan, in turn, was often used as a parent in the development of trailing blackberries and most, therefore, have red raspberry somewhere in their ancestry.

Fig. 2. Blackberry fruit on the plant, showing the absence of the receptacle where the fruit has abscised. (Cour­tesy B. Strik; © APS)

Fig. 3. Blackberry fruit cut open, showing the receptacle in the fruit. (Cour­tesy B. Strik; © APS)

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Growth and Morphology in the Genus Rubus Blackberries are distinguished from raspberries not only by being more vigorous but by the morphological trait of whether the torus/receptacle remains with the fruit when picked (blackberry) (Figs. 2 and 3) or with the plant, leaving a hollow center in the picked fruit (raspberry) (Figs. 4 and 5).

The primary progenitor species for the cultivated Rubus spp. are perennial plants with biennial canes. In these species, vege­ tative canes called primocanes are produced the first year, and after a dormant period, they are called floricanes. Primocanes of these progenitor species generally require a winter dormant period of about 800–1,600 h of chilling (at 0–7°C; 32–45°F) for raspberries and 200–900 h for blackberries to satisfy the rest requirement and break bud in the spring. The floricanes then flower, fruit, and senesce while new vegetative primocanes are growing.

The cultivars of red raspberry have been derived predominantly from the European red raspberries and are typically categorized by their fruiting habit: either primocane fruiting (annual fruiting), in which a portion of fruit is produced at the top of primocanes in their first growing year and the other portion is produced on the floricanes in the second year, or floricane fruiting (biennial fruiting), in which the fruit is produced only on canes in their second year.

Primocane-­ fruiting raspberry cultivars are different from floricane-­fruiting cultivars since they have no low-­temperature requirement for flower bud initiation on at least a portion of

Fig. 4. Red raspberry, showing the receptacle on the plant after the fruit has been harvested. (Cour­tesy B. Strik; © APS)

Fig. 5. Black raspberry fruit, showing hollow fruit. (Cour­ tesy B. Strik; © APS)

buds at the top of canes. Primocane-­fruiting raspberries are generally thought to be day-­neutral with regard to flower bud initiation, although photoperiod and temperature can affect flower bud development in some cultivars. The time at which flower bud initiation begins is affected by the physiological age of the cane. The proportion of the primocane tip that fruits in the first growing season is dependent on temperature, day length, cultivar, and cultural practices. The remaining buds on the primocane grow the following year (floricane) after the chilling period has been satisfied. Primocane-­fruiting red raspberry cultivars that fruit on the first-­year canes have long been used for commercial production (e.g., Heritage, Summit, Polka, Caroline), but primocane-­fruiting cultivars have only recently been developed in blackberry (e.g., Prime-­Ark 45) and black raspberry (e.g., Explorer).

Red raspberries are rhizomatous and erect growing, with their primocanes emerging from buds on roots or the base of old canes at the crown. Raspberries have an extensive root system. Roots start growing in the spring after budbreak. If water is adequate, most root growth occurs in midsummer and growth continues in the autumn after top growth has stopped.

Red raspberries can form dense hedges as buds on the root system grow to produce new primocanes.

Black raspberries are crown-­forming, thorny plants that can spread vegetatively by tip rooting. They do not produce buds on their roots like red raspberries. The fruit is small and intensely colored, has a higher seed/flesh ratio, and is used primarily in processing applications as a seedless puree or juice. All commercial black raspberries are floricane fruiting, although primocane-­fruiting black raspberry cultivars exist.

Commercial blackberries are classified into three types based on growth habit: trailing, erect, and semi-­erect. Trailing types: Trailing types are characterized as crown forming, with long canes that trail along the ground if not trained to a trellis.

They tend to have excellent fruit quality but have poorer winter hardiness than the other types. Trailing blackberries were largely derived from the western dewberry (R. ursinus) but also have R. idaeus and R. armeniacus in their ancestry; examples include the cultivars Marion, Boysen, Black Diamond, Obsidian, and Onyx. Although it has a different genetic background, the R. laciniatus-­derived ‘Thornless Evergreen’ is also considered a trailing blackberry because of its growth habit. Erect types: The erect types are characterized by plants that produce stiff, upright canes that are 1–2 m tall in cultivation. These plants sucker to produce a hedgerow; examples include the cultivars Cherokee, Navaho, Natchez, and Ouachita. Semi-­erect types: The semi-­erect type plants are characterized as being thornless, with very vigorous, erect canes that grow 4–6 m long from a crown and arch to the ground; examples include the cultivars Chester Thornless, Triple Crown, and Loch Ness.

The erect and semi-­erect blackberries have a similar genetic background and their fruit is more similar, tending to be rounder, firmer, and less aromatic when compared with the trailing types. The erect and semi-­erect types were derived largely from eastern North American species such as R. allegheniensis and R. argutus. Blackberry and raspberry canes typically have spines, which are colloquially called thorns for blackberry and black raspberry and prickles for red raspberry. Thornless types have been found and incorporated into breeding programs such that there are thornless/spineless blackberry and red raspberry cultivars. While red raspberry spines may be considered a nuisance, the larger thorns of blackberry are more challenging when managing the crop and can become a legal liability if they end up in the final harvested product. The cultivars Merton Thornless, Austin Thornless, and Lincoln Logan have been the primary sources used to develop thornless blackberries. Thornlessness is increasingly common in newly developed cultivars.

In floricane-­fruiting raspberries and blackberries, buds break along the floricane, producing fruiting laterals in the spring.

The length of the laterals is cultivar dependent. The range in

flower opening time along the fruiting lateral, coupled with a slightly earlier emergence of laterals at the tip of the cane, leads to a range in fruit ripening time within a cultivar. The ripening season of floricane-­fruiting red raspberries and blackberries is about 30–55 days and about 20–30 days for black raspberries.

Flowers have five sepals and petals, many stamens, and many pistils arranged spirally around a receptacle. Blackberry flowers have white (Fig. 6) or pink/lavender petals, while raspberry flowers have small white petals that are not as showy. Commercial types are self-­fertile in that cross pollination is not required.

However, flowers do require the insect/bee transfer of pollen to the pistils. Insufficient pollination or fruit set within a flower leads to the development of crumbly fruit; however, the flowers are very attractive to bees. If pollination and fertilization are successful, an aggregate fruit (not a true berry) is produced that consists of the central torus (receptacle) surrounded by a number of fleshy drupelets that each contains a seed (pyrene).

Flowers and fruit are borne in a panicle-­like inflorescence, with primary fruit ripening prior to secondary, quaternary, or tertiary fruit. About 30–35 days are required for raspberry fruit to mature after pollination and fruit set. Individual raspberry fruit typically weigh 2.5–6 g, depending on the cultivar. Blackberry fruit mature in 40–60 days after pollination and fruit set. Individual fruit typically weigh 3–12 g, depending on the cultivar.

Fruit firmness decreases in the later stages of fruit maturation and is also cultivar dependent. Many blackberry fruit are not at their optimum flavor until they change from glossy black to dull black. For maximum productivity, flavor, and sweetness, fruit must reach full maturity and size before harvest.

Production Areas Blackberries and raspberries traditionally have been most intensively cultivated where summer conditions are moderate, winter conditions are cool but not too cold, and the growing season is sufficiently long (e.g., northern Europe, Russia, China, Pacific Northwest of the United States, New Zealand, southern Chile). Historically, blackberries were more likely to be grown in warmer climates and raspberries in cooler climates; however, the ability to manipulate plant growth and fruiting and the use of protected culture, i.e., plastic tunnels, has allowed the expansion of both crops into regions where they have not been grown traditionally.

Fig. 6. Flower of ‘Marion’ blackberry. (Cour­tesy B. Strik; © APS)

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The leading regions for production of blackberries for processing are Oregon (United States) and Serbia, with Mexico and China developing new, potentially, significant production areas. The world leader for fresh-­market blackberry production is Mexico, with California and Oregon (United States) and scattered concentrated production in the southeastern United States all contributing significant quantities of fruit to the marketplace.

Primocane-­fruiting raspberries for the wholesale fresh market are now primarily grown in California, with major new production areas in Mexico. Floricane-­fruiting raspberries for the fresh market are commonly produced in many areas but particularly the region composed of Washington and Oregon (United States) and British Columbia (Canada), as well as Spain and Russia.

Pick-­your-­own and roadside markets also are a major point of fresh-­market sales in midwestern and eastern North America.

Most processing raspberries are floricane-­fruiting types and production is concentrated in the Pacific Northwest and Serbia.

Fruit is typically machine harvested for the processing market.

Annual worldwide production of red raspberries is estimated to be more than 357,000 tonnes (approximately 790 million pounds); for black raspberries, more than 1,814 tonnes (approximately 4 million pounds); and for blackberries, more than 154,000 tonnes (approximately 340 million pounds).

Raspberries and blackberries for fresh market are harvested by hand. However, most of the areas where red and black raspberries and blackberries are grown for processing, particularly

Fig. 7. Over-­the-­row mechanical raspberry harvester that is machine harvesting ‘Willamette’ red raspberry. (Cour­tesy B. Strik; © APS)

in North America, is harvested by machine (Figs. 7 and 8).

Aside from decreased labor costs, mechanical harvesting has other advantages, including greater uniformity of fruit maturity and the ability to harvest at night when conditions are cooler.

Machine-­harvested fields often require specific cultivars and production systems, including diligent insect and disease management to reduce harvest contaminants.

Selected References Clark, J. R., Stafne, E. T., Hall, H. K., and Finn, C. E. 2007. Blackberry breeding and genetics. Plant Breed. Rev. 29:19-­144.

Clark, J. R., Strik, B., Thompson, E., and Finn, C. E. 2012. Progress and challenges in primocane-­fruiting blackberry breeding and cultural management. Acta Hortic. 926:387-­392.

Finn, C. E., and Hancock, J. F. 2008. Raspberries. Pages 359-­392 in: Temperate Fruit Crop Breeding: Germplasm to Genomics. J. F. Hancock, ed. Springer, Berlin.

Jennings, D. L. 1988. Raspberries and Blackberries: Their Breeding, Diseases and Growth. Academic Press, San Diego.

(Prepared by M. P. Pritts, C. E. Finn, and J. R. Clark)

Raspberry and Blackberry Production Systems Under cultivation, raspberries and blackberries generally have a life of 10–20 years and black raspberries have a life of 5–10 years. Vegetative and reproductive growth is influenced by environment, photoperiod, temperature, and soil type, but cultural practices such as fertilization, irrigation, and pruning have a major impact on the production and longevity of plantings. Open-­field plantings are usually irrigated with overhead or drip systems, depending on the production region. Drip systems are recommended to minimize the wetting of foliage and to reduce disease incidence. Growers commonly fertilize through the drip system.

Each of the various types of raspberries and blackberries requires different cultural practices to optimize production, especially regarding the management of primocanes and floricanes.

Various terms are used to describe cane management practices.

“Thinning” is the selective removal of canes to reduce their number. “Tipping” is the removal of the primocane meristem to induce branching. “Topping” is the removal of the floricane tip (or dormant primocane) to shorten the cane. “Suppression” is the removal, usually by chemical desiccants, of the first flush of primocane growth in the spring to reduce plant vigor and competition between primocanes and floricanes. “Trellising” is the tying up of canes to posts and wires to support them.

Floricane-­Fruiting Raspberries

Fig. 8. Fruit of ‘Willamette’ red raspberry coming off a mechanical harvester. (Cour­tesy B. Strik; © APS)

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The best soils for production are deep and well drained and have a sandy to loamy texture and a pH between 5.6 and 6.5.

The most common planting stock used is dormant, bareroot, certified disease-­free plants or tissue-­cultured plants.

Floricane-­fruiting red raspberries can be grown either in a hedgerow, in a continuous, narrow row of canes, or in hill systems in which individual plants can be distinguished. Overly dense canopies increase pest and disease problems and can reduce flower bud development because of shading. A trellis is required to support the floricanes and primocanes. Plantings are generally established with 0.60–0.75 m (2.0–2.5 ft) between plants in the row and 3 m (10 ft) between rows on raised beds or flat ground (Fig. 9).

At any given time from budbreak in the spring until the removal of the dead floricanes in the late summer or autumn, primocanes and floricanes are both present in a raspberry planting.

The extent of competition or support between the two types of

canes varies with the type of caneberry grown and provides the grower with challenges unique to Rubus production.

Typically, raspberries produce more primocanes than necessary for optimal yield, fruit size, and quality. These are thinned to a desired number during the dormant season and may be topped to eliminate winter injury, which is always greatest at the distal end of the floricane. Shortening/topping of floricanes results in the loss of apical buds, but this does not necessarily reduce yield. Yield is often compensated for by larger size of remaining fruit, more flowers per lateral from the remaining buds, or later emerging laterals from secondary buds. Increases in fruit size and/or delays in flowering and fruiting through tipping, removal of primary buds, and thinning are used to an advantage in warmer production regions to delay the crop to a time when temperatures are lower at harvest. In general, however, highest yields are achieved when the entire cane is kept over the winter. The overwintering canes may be arched and tied to the trellis (Fig. 10).

Pruning expended floricanes earlier in the year is recommended if bacterial or fungal diseases are present on foliage or canes. However, if the planting is relatively “clean,” then late autumn or early winter pruning is best to maximize the time for nutrients to move from the dying floricanes to the crown.

Reductions in primocane numbers also can be achieved by selective primocane removal or suppression in early spring when the new canes begin to grow. This can have a positive effect on current and following season yield and is often implemented to control excessive vigor.

Growing biennial-­fruiting raspberries in open-­field, tunnel, or greenhouse systems for scheduling production over a long period of time is quite common. In these production systems, primocanes must be grown in a nursery to promote maximum flower bud development. The “long canes” are then dug at the end of the first growing season, cold stored to ensure adequate chilling, and then planted at various times to schedule harvest over an extended season.

Plantings of black raspberries (also called blackcaps) are established in the spring using plants produced by tip rooting or tissue culture. Plants are usually 0.75–0.90 m (2.5–3.0 ft) apart in rows with 3 m (10 ft) between rows. Although black raspberries can be grown without a trellis, an inexpensive support structure of some kind, such as metal posts with twine running on each side of the row, is commonly used. Black raspberry primocanes are summer tipped, by hand, to a height of about 1 m (3 ft) to encourage branching (Fig. 11). In the winter, branches are typically pruned by machine to shorten them. The fruit ripen in early summer, generally with a 4-­week fruiting season. Growers remove dead floricanes when pruning in the winter in some production regions.

Primocane-­Fruiting Raspberries Primocane-­ f ruiting raspberries are typically grown in hedgerows that are maintained to a width of about 0.3 m (1 ft).

This type of raspberry can be managed to produce one or two crops per year—an early crop on the base of the floricane and a later crop on the tip of the primocane. The portion of the primocane that fruited in late summer/autumn dies in the winter. This cane can be pruned to remove the dead portion, leaving the base (floricane) to fruit in early summer the following year. These floricanes die after harvest and are removed during dormant pruning. Primocane-­fruiting raspberries can easily be grown to produce just a primocane crop by mowing all canes to ground level in late winter. New primocanes emerge in the spring, flower in the summer, and fruit in late summer, producing one crop per year.

Primocane-­fruiting raspberries can be grown free standing but are often supported on a simple trellis to keep the canes from bowing out into the alleys. Plantings are irrigated and otherwise maintained similar to those of summer-­bearing raspberry.

Off-­Season Production

Fig. 9. ‘Meeker’ red raspberry field, showing spacing between rows.

(Cour­tesy B. Strik; © APS)

Fig. 10. Red raspberry grown in a hill system and arch-­c ane trained. (Cour­tesy B. Strik; © APS)

Off-­season production, often in tunnels, is common in red raspberry (Fig. 12) and increasing in blackberry. It is possible in many areas to produce raspberries and blackberries nearly year-­round using open fields, high tunnels, shade cloth, and

Fig. 11. ‘Munger’ black raspberry field in early summer after topping primocanes. (Cour­tesy B. Strik; © APS)

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greenhouses with various combinations of cultivars. Covered polyethylene tunnels are used in many production regions to protect fruit from wet weather, but they also retain heat and accelerate flowering. The fruiting season of primocane-­fruiting types can be advanced in tunnels or extended under tunnels by tipping primocanes to delay flowering and fruiting. “Long cane” raspberries can be transplanted into either tunnels or greenhouses for targeting winter production. Shade cloth is also used to protect fruit, since fruit exposed to high ultraviolet light levels can be less firm and may develop white drupelets (see Solar Injury), but shade cloth also can be used to delay the fruiting season somewhat, depending on when it is applied.

Blackberries Blackberry plantings generally have a life of 15–20 years, with some commercial plantings more than 50 years old. Plantings are established in the spring using plants propagated by tissue culture or root cuttings, depending on the type of blackberry grown. Blackberries are tolerant of a wide range of soil pH (4.5 to 7.5) and soil types, although growth is improved under conditions of good soil drainage.

Semi-­erect blackberries are typically grown at an in-­row spacing of 1.2–1.8 m (4–6 ft) with 3.0–3.6 m (10–12 ft) between rows. In many regions, primocanes are tipped during the growing season to encourage branching. In the winter, the dead floricanes are removed and the branches of the new canes are sometimes shortened. Canes are either trained on a multiple-­ wire trellis or to a divided canopy. In most regions, plantings are irrigated using drip, overhead, or micro-­jet systems. Fruit are hand harvested for the fresh market, but machine harvest for processing occurs in some regions.

In the more traditional field production system for erect blackberry, plants are established 0.90–1.2 m (3–4 ft) apart in rows 3 m (10 ft) apart. During the growing season, primocanes are tipped to encourage branching. After fruit harvest or in the winter, dead floricanes are removed by pruning. In the winter, the primocane branches are usually shortened to about 0.45 m (1.5 ft). Erect blackberries are grown without a trellis in some regions. However, since the canes are prone to breaking off at soil level with wind, a two-­to four-­wire trellis is often used to support canes and minimize cane loss. Fruit for the fresh market are harvested by hand every 3–5 days.

In Mexico, specialized production systems have been developed to extend the season for erect blackberry cultivars such as ‘Tupy’. About 5–7 months after primocane emergence, a chemical defoliant (a combination of urea or ammonium sulfate, copper sulfate, and mineral oil) is applied two or three times. The plants are then pruned by topping canes and shortening laterals. Gibberellic acid and thidiazuron (TDZ) are used

Fig. 12. Red raspberry grown in tunnels near Watsonville, California, United States. (Cour­tesy B. Strik; © APS)

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about 3 weeks after defoliation to improve flowering and promote budbreak. Fruit harvest begins about 90–100 days after defoliation. After the first crop is finished, many growers prune again, removing the portion of the cane that fruited, and repeat the defoliation process to obtain multiple crops. Growers then mow the canes to ground level to repeat the cycle. Plants are often grown in tunnels to protect fruit from adverse weather conditions. Using these methods, the Mexican fruiting season extends from mid-­October to June for the export market and May through June for local markets.

Primocane-­fruiting (annual) erect blackberries can be grown for a double crop (floricane in early summer plus primocane in the autumn) or a single crop (primocane only). Primocanes are tipped to a height of 0.5–1.0 m (1.5–3.0 ft) to induce branching and thus increase yield. In some regions, the branches are also tipped to increase yield. Primocane-­fruiting blackberries show great promise for extended season production through growth of different cultivars, advancing production through use of tunnels or row covers, and delaying production by mowing primocanes during the growing season (Fig. 13).

Trailing blackberries are typically grown at an in-­row spacing of 1–2 m (3–6 ft) with 3 m (10 ft) between rows. Most are grown on a trellis with the canes wrapped around two wires. Trailing blackberries can be grown in every-­year (EY) or alternate-­ year (AY) production systems. In EY production, new primocanes are trained along the ground, under the canopy, while the floricanes are on the wire producing the current-­season crop. After fruit harvest, the dead floricanes are removed and the primocanes are trained onto the trellis wires in August or February. Most growers train primocanes in February, leaving canes more protected from cold through most of the winter.

In AY production systems, plants fruit every other year. In the “on-­year,” floricanes produce a crop and primocanes are not managed (Fig. 14). In October, the dead floricanes and the primocanes are pruned off at the crown. The following “off-­year,” primocanes are trained to the trellis as they grow. The yield of an AY field is about 85% of an EY field over a 2-­year period, depending on the cultivar. Primocanes following an off-­year in an AY system are cold hardier than primocanes that grew in the presence of floricanes in an EY system. There is also less cane disease in AY production systems than in EY systems.

Most of the trailing blackberry production is processed and machine harvested. In addition to the possible insect contaminants mentioned for red and black raspberries, thorns can be a serious contaminant in thorny cultivars that are machine harvested. Research has helped growers minimize this risk by

Fig. 13. Primocane-­fruiting blackberry in early October. Canes were tipped in the summer. (Cour­tesy B. Strik; © APS)

tivars a high priority and have recently released several thornless cultivars for processing.

Blackberry and raspberry consumption and production have been steadily increasing around the world, particularly for the fresh market. To meet this demand, not only are acreage and production per acre increasing but the number of new production areas in nontraditional climates and parts of the world is increasing.

Selected References

Fig. 14. Alternate-­year ‘Marion’ blackberry field in late May, during the fruiting year after the primocane suppression. (Cour­tesy B. Strik; © APS)

using machine harvesters equipped with brushes in the winter to remove potential contaminants. Plant breeders consider the development of high-­quality, thornless trailing blackberry cul-

Clark, J. R., Strik, B., Thompson, E., and Finn, C. E. 2012. Progress and challenges in primocane-­fruiting blackberry breeding and cultural management. Acta Hortic. 926:387-­392.

Dale, A. 1989. Productivity in red raspberries. Hortic. Rev. 2:185-­228.

Galletta, G. J., and Himelrick, D. G. 1990. Small Fruit Crop Management. Prentice-­Hall, Englewood Cliffs, New Jersey.

Heidenreich, C., Pritts, M., Demchak, K., Hanson, E., Weber, C., and Kelly, M. J. 2012 update. High tunnel raspberries and blackberries.

Cornell Univ. Dep. Hortic. Publ. No. 47. Online at Cornell Fruit, Production -­Raspberries and Blackberries. (www.fruit.cornell.edu/ berry.html).

Strik, B. C. 2012. Flowering and fruiting on command in berry crops.

Acta Hortic. 926:197-­214.

(Prepared by M. P. Pritts and B. C. Strik)

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