From: http://www.ipm.ucdavis.edu
Of the 11 species of Rubus in California, four were introduced primarily from Eurasia. Most species of wild blackberry, also called brambles, provide important sources of food and cover for many birds and mammals.
Four species, however, are considered weeds. Two of these are non-natives, cutleaf blackberry (R. laciniatus) and Himalaya blackberry (R. discolor [formerly known as R. procerus]). In addition, two native species also can be weeds under certain conditions. For example, thimbleberry (R. parviflorus) competes with conifers during establishment in reforested areas, and California blackberry (R. ursinus [formerly known as R. vitifolius]) can infest areas adjacent to streams and ditches. Of these weedy species, the most common, vigorous, and troublesome is Himalaya blackberry.
IDENTIFICATION
Of the four weedy wild blackberries, thimbleberry is the only nonvining species. It also lacks prickly stems and has a simple leaf with no leaflets. Both Himalaya and cutleaf blackberry have five-angled stems whereas thimbleberry is rounded in cross section, but Himalaya blackberry is easily distinguishable from the other wild blackberries by its five distinct leaflets, each one toothed and usually oval. By comparison, cutleaf blackberry has five very deeply lobed leaflets, and California blackberry has only three leaflets. Not all wild blackberry leaves are deciduous; many remain evergreen. This is an important feature for chemical control in late fall and winter.
Himalaya blackberry has showy flowers that form in large clusters at the end of shoots. Each flower is about 1 inch across with five white or pink petals. The fruits are black and tasty when ripe. New canes are produced each year from the crown (the base of the plant), replacing those that die naturally. New plants start from crown regrowth, rhizomes (horizontal, underground shoots), and seeds that germinate in fall and spring. Reproduction is similar for the other three species.
IMPACT
The scrambling habit of Himalaya and the other vining wild blackberries smothers existing plant growth. In addition, the tangled mass of thorny stems blocks access of humans, livestock, equipment, and vehicles to pastures and waterways. In addition, it can host Pierce’s disease and serve as a vector to movement of the pathogen to other agricultural and nonagricultural areas, including riparian sites.
In forest areas, timber-logging operations create large open areas that wild blackberries often invade. When grazed, the thorny stems can injure the nasal passages of livestock. Another undesirable aspect of vining blackberry plants is they are a good source of food and shelter for rats.
BIOLOGY
Many animal species feed on wild blackberries; consequently, seeds spread easily from one area to another in animal droppings. Wild blackberry seeds have a hard seed coat and can remain dormant for an extended period. Once seeds germinate and grow and the plants become established, expansion of the thicket is almost entirely a result of vegetative growth from rhizomes. Over time a single plant can cover a very large area.
Wild blackberry plants can live for 25 years or longer. They produce vines that arise from a central crown or from buds that form along rhizomes. First-year canes don’t produce flowers. In the second year, the canes fruit and die. Tips of first-year canes that contact the ground form roots at the nodes, contributing to the lateral expansion of the plant.
