Weihe & Nees

Himalayan blackberry, Himalayaberry

Rubus procerus, R. armeniacus

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CalEPPC List A-1,CDFA nl

Marc C. Hoshovsky

Himalayan blackberry (Rubus
discolor) grows as a dense thicket of long, bending branches (canes),
appearing as tall, ten-foot mounds or banks, particularly along watercourses.
Canes have hooked prickles. Flowers are white, yielding black berries that
usually ripen later than native blackberries.

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Leaves: 5 foliolate, glabrous above when
mature and cano-pubescent to cano-tomentose beneath. Hooked prickles on petioles
and petiolules. Leaflets large and broad; terminal leaflet roundish to
broad-oblong. Leaflets abruptly narrowed at the apex, unequally and coarsely
serrate-dentate. Floricane leaflets 3-5 foliolate and smaller than on
primocanes. Inflorescence: a large terminal cluster with branches in lower
axils. Peduncles and pedicels cano-tomentose and prickly. Flowers: white or
rose, 0.8-1 in (2-2.5 cm) across, with broad petals. Sepals broad,
cano-tomentose, conspicuously pointed and soon reflexed, +/- 0.28-0.32 in (7-8
mm) long. Fruit: roundish, black, and shiny, up to 0.8 in (2 cm) long, with
large succulent drupelets. Fruit ripens late compared with native blackberries
and over a considerable interval (Bailey 1945), from mid-summer to fall (Bailey
1923).

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Himalayan blackberry occurs in California
along the coast in the Coast Ranges, Central Valley, and the Sierra Nevada
(Dudley and Collins 1995). It forms impenetrable thickets in wastelands,
pastures, and forest plantations. It grows along roadsides, creek gullies, river
flats, fence lines (Parsons and Amor 1968), and right-of-way corridors. It is
common in riparian areas, where it establishes and persists despite periodic
inundation by fresh or brackish water. Periodic flooding can produce long-lived
early seral communities conducive to the growth and spread of blackberries.
Himalayan blackberry is one of few woody plants that pioneer certain intertidal
zones of the lower Sacramento River (Katibah, et al. 1984).

Blackberries grow well on a variety of barren, infertile soil
types (Brinkman 1974). These shrubs tolerate a wide range of soil pH and
texture, but do require adequate soil moisture. Himalayan blackberry prefers
disturbed and wet sites even in relatively wet climates. It prefers areas with
an average annual rainfall greater than 76 cm on both acidic and alkaline soils
(Amor 1972). It appears to be tolerant of periodic flooding by brackish or fresh
water (Willoughby and Davilla 1984). It grows at elevations of over 6,000 feet
in Arizona and to 5,000 feet in Utah (Kearney et al. 1960, Welsh et al.
1987).

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Himalayan blackberry is native to western
Europe (Hickman 1993). There is no botanical evidence to show that it is native
to the Himalayan region. It may have found its way there as a cultivar.
Himalayan blackberry probably was introduced to North America in 1885 as a
cultivated crop (Bailey 1945). By 1945 it had become naturalized along the West
Coast. By this time it also occurred in nursery and experimental grounds along
the East Coast and in Ohio (Bailey 1945). It seeds heavily, and seeds are
readily dispersed by mammals and birds. Seeds can be spread considerable
distances by streams and rivers (Parsons 1992). It also spreads vegetatively by
rooting of cane tips.

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Himalayan blackberry colonizes areas
initially disturbed and then neglected by humans and can dominate range and
pasture lands if not controlled. Himalayan blackberry is a strong competitor,
and it rapidly displaces native plant species. Blackberries are highly
competitive plants. Thickets produce such a dense canopy that the lack of light
severely limits the growth of other plants. Because plants are prickly,
livestock, particularly sheep and cattle, avoid grazing near them, effectively
decreasing the usable pasture area. Young sheep and goats that get tangled up in
the canes have been known to die of thirst and hunger. In wet areas blackberries
may hinder medium-sized to large mammals from gaining access to water. The
impenetrable nature of blackberry thickets reduces access for maintenance of
fence lines and for forestry practices, as well as recreational pursuits. Dense
thickets around farm buildings and fence lines are a considerable fire
hazard.

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Reproductive versatility is well represented in the genus Rubus, with sexual reproduction, parthenogenesis (development of the egg without fertilization), pseudogamy (a form of apomixis in which pollination is required), and parthenocarpy (production of fruit without fertilization)occurring widely. These modes of asexual reproduction contribute to the aggressive spread of blackberries.

Flowering begins in May and continues through July. Fruit is
produced from July to September. Most blackberries produce good seed crops
nearly every year. Immature fruit of Himalayan blackberry is red and hard, but
at maturity fruit becomes shiny black, soft, and succulent.

Himalayan blackberry thickets can produce 7,000 to 13,000 seeds
per square meter (Amor 1974). When grown in dense shade, however, most species
of blackberry do not form seeds (Brinkman 1974). Seeds of blackberries are
readily dispersed by gravity and by many species of birds and mammals. The
large, succulent fruits are highly favored and, after they mature, rarely remain
on the plant for long (Brinkman 1974). A hard seed coat protects the embryo even
when seeds are ingested. Passing through animal digestive tracts appears to
scarify seeds and may enhance germination. Prompt invasion of cut-over lands by
Himalayan blackberry suggests that dispersed seeds can remain viable in the soil
for several years (Brinkman 1974). Seeds germinate mainly in spring.

Blackberry seeds have a hard, impermeable coat and a dormant
embryo (Brinkman 1974). Consequently, germination is often slow. Most
blackberries require, at a minimum, warm stratification at 68 to 86 degrees F
(20 to 30 degrees C) for ninety days, followed by cold stratification at 36 to
41 degrees F (2 to 5 degrees C) for an additional ninety days (Brinkman 1974).
These conditions are frequently encountered naturally as seeds mature in summer
and remain in the soil throughout the cold winter months.

In Australia Himalayan blackberry seedlings receiving less than
44 percent of full sunlight did not survive (Amor 1974). The slow growth of
seedlings and their intolerance of shading suggest that few seedlings would be
expected to survive in dense pastures or forest plantations. Blackberry thickets
are also poor sites for seedling development. Amor (1972) counted less than 0.4
seedlings per square meter near thickets. Establishment of Himalayan blackberry
seedlings depends on the availability of open habitats such as land neglected
after cultivation, degraded pastures, and eroded soils along streams (Amor
1974). Although seedlings show the potential for rapid growth under laboratory
conditions, they grow much more slowly in the field and are easily surpassed by
the more rapid growth of daughter plants.

Himalayan blackberry can form roots at cane apices. Amor (1974a)
observed canes growing to a height of 40 cm before they arched over and trailed
on the ground. Daughter plants developed where these canes rooted, forming only
on first-year canes. All canes produced berries in the second year and then
died, senescence commencing near the middle and at the apices of canes without
daughter plants. Reentry of canes into the center of the thicket resulted in an
impenetrable mass of prickly canes within two and a half years. Individual canes
may live only two to three years yet reach a density of 525 canes per square
meter. A large quantity of litter and standing dead canes develops in old
thickets.

Canes of Himalayan blackberry can grow to twenty-three feet (7
m) long in a single season. At one site observed by Amor (1974a), the mean
horizontal projection of fifty first-year canes was eleven feet (3.3 m).
Ninety-six percent of these canes had daughter plants at their apices. Lateral
branches on some canes had also formed daughter plants.

The root crown on Himalayan blackberry, from which many lateral roots grow at various angles, can be up to eight inches (20 cm) in diameter. One root had a maximum depth of almost 3 feet (90 cm) and was more than thirty-three feet (10 m) long (Northcroft 1927). Adventitious shoots (suckers) are occasionally formed on the roots and may emerge from a depth of 45 cm. Blackberries also readily propagate from root pieces and cane cuttings (Amor 1974a). In less than two years a cane cutting can produce a thicket sixteen feet (5 m) in diameter (Amor 1973).

(click on photos to view larger image)

Mechanical removal or burning may be the
most effective ways of removing mature plants. Subsequent treatment with
herbicides should be conducted cautiously for two reasons. Himalayan blackberry
often grows in riparian areas, where the herbicide may be distributed to
unforeseen locations by running water, and some herbicides promote vegetative
growth from lateral roots.

Reestablishment of Himalayan blackberry may be prevented by
planting fast-growing shrubs or trees, since the species is usually intolerant
of shade. Regrowth has also been controlled by grazing sheep and goats in areas
where mature plants have been removed.

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Mechanical methods: Most mechanical control techniques, such as
cutting or using a weed wrench, are suitable for Himalayan blackberry. Care
should be taken to prevent vegetative reproduction from cuttings. Burning slash
piles is an effective method of disposal.

An advantage of cane removal over use of foliar herbicides is
that cane removal does not stimulate sucker formation on lateral roots. Amor
(1974b) provides evidence that herbicides such as picloram are not much more
effective than cane removal. However, removal of canes alone is insufficient to
control Himalayan blackberry, as root crowns will resprout and produce more
canes.

Manual methods: Removing rootstocks by hand digging is a
slow but effective way of destroying Himalayan blackberry, which resprouts from
roots. The work must be thorough to be effective because every piece of root
that breaks off and remains in the soil may produce a new plant. This technique
is suitable only for small infestations and around trees and shrubs where other
methods are not practical.

Himalayan blackberry plants may be trimmed back by
tractor-mounted mowers on even ground or by scythes on rough or stony ground.
Perennial weeds such as Himalayan blackberry usually require several cuttings
before underground plant parts exhaust their reserve food supply. If only a
single cutting can be made, the best time is when plants begin to flower. At
this stage the reserve food supply in the roots has been nearly exhausted, and
new seeds have not yet been produced. After cutting or chopping with mechanical
equipment, Himalayan blackberry may resprout from root crowns in greater density
if not treated with herbicides.

Prescribed burning: Burning is suitable for removing large
thickets, but requires follow-up to control resprouts.

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Insects and fungi: The USDA will not
support introduction of herbivorous insects to control Himalayan blackberry
because of the risk posed to commercially important Rubus species.

Grazing: Sheep, cattle, and horses can be effective in reducing
the spread of Himalayan blackberry (Amor 1974). In New Zealand infestations have
been controlled by the grazing of large numbers of goats. This method has been
effective in preventing canes from covering large areas (Featherstone 1957).
Crouchley (1980) mentions that blackberry is readily eaten by goats throughout
the year, even when there is an abundant supply of other plants. In many areas
of California the use of angora and Spanish goats is showing promise in
controlling Himalayan blackberry (Daar 1983).

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Picloram suppresses cane regrowth of Himalayan blackberry but
stimulates the development of adventitious shoots. Picloram is currently not
registered for use in California wildlands. Foliage spraying is more effective
in summer than in winter.

Many other herbicides have been used in efforts to control
Himalayan blackberry with varying degrees of effectiveness. Fosamine can be
effective (Shaw and Bruzzese 1979), and blackberry control has also been
accomplished with amitrole-thiocyanate (Amor 1972), and triclopyr ester (as
Garlonå¨) (McCavish 1980). Not all of these are currently registered for use in
California.

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