WILD BLACKBERRIES Integrated Pest Management for Home Gardeners and Landscape Professionals Of the eleven species of Rubus in Cali- fornia, four were introduced primarily from Eurasia. Most species of wild blackberry, also called brambles, pro- vide 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 (Rubus laciniatus) (Fig. 1) and Himalaya blackberry (Ru- bus discolor [=R. procerus]) (Fig. 2). In addition, two native species can also be weeds under certain conditions. For example, thimbleberry (Rubus parvi- florus) (Fig. 3) competes with conifers during establishment in reforested areas, and California blackberry (Rubus Figure 1. Cutleaf blackberry. Figure 2. Himalaya blackberry. ursinus [=R. vitifolius]) (Fig. 4) can in- fest areas adjacent to streams and ditches. Of these weedy species, the most common, vigorous, and trouble- some 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 (no leaflets). Both Himalaya and cutleaf blackberry have five-angled stems, but Himalaya black- berry can easily be distinguished from the other wild blackberries by its five distinct leaflets, each leaflet toothed and generally oval in shape. By com- parison, cutleaf blackberry has five very deeply lobed leaflets and Califor- Figure 3. Thimbleberry. Figure 4. California blackberry. nia blackberry has only three leaflets. Not all wild blackberry leaves are de- ciduous—many remain evergreen. This 1 inch across with five white or pink germinate in fall and spring. Repro- is an important feature for chemical petals. The fruits are black and tasty duction is similar for the other three control in late fall and winter. when ripe. New canes are produced species. each year from the crown (base of the Himalaya blackberry has showy flow- plant), replacing those that die natu- IMPACT ers that form in large clusters at the rally. New plants start from crown The scrambling habit of Himalaya and end of shoots. Each flower is about regrowth, rhizomes, and seeds that the other vining wild blackberries PEST NOTES Publication 7434 University of California Agriculture and Natural Resources Revised April 2002 April 2002 Wild Blackberries smothers existing plant growth. In addition, the tangled mass of thorny stems blocks access of humans, live- stock, equipment, and vehicles to pas- tures and waterways. In forest areas, timber-logging operations create large open areas that are often invaded by wild blackberries. When grazed, the thorny stems can injure nasal passages of livestock. Another undesirable as- pect of vining blackberry plants is that they are a good source of food and shelter for rats. Figure 5. Vegetative growth of a blackberry plant from a central crown. BIOLOGY Many animal species feed on wild Because of the extensive underground Biological Control blackberries; consequently, seeds are root system, digging out the plants in a Because many Rubus species are native easily spread from one area to another home landscape is a difficult undertak- or of economic importance, biocontrol in animal droppings. Wild blackberry ing. Home gardeners generally must is not a practical method of control in seeds have a hard seed coat and can rely on foliage-applied herbicide treat- California. In Australia, however, remain dormant for an extended pe- ments to control an infestation of wild blackberry leaf rust (Phragmidium riod. Once seeds germinate and grow, blackberries. One nonchemical option violaceum) has been released for control and the plants become established, in the home landscape is the use of a of the weed. Thus far this program has expansion of the thicket is almost en- rototiller to till the ground several not been successful because the rust tirely a result of vegetative growth times after the canes have been re- has not caused significant damage to from rhizomes. Over time a single moved. its host. plant may cover a very large area. Mechanical Control Chemical Control Wild blackberry plants can live for 25 Wild blackberries can be easily con- Blackberry plants usually regrow fol- years or more. They produce vines that trolled by repeated tillage. For this rea- lowing herbicide application; thus, arise from a central crown or from son, they are not a problem in repeated treatments may be necessary buds that form along rhizomes (hori- cultivated agricultural systems. A for effective long-term control. zontal, underground shoots) (Fig. 5). single cultivation, however, can frag- First-year canes do not produce flow- ment the rhizomes and spread the Herbicides Applied to the Soil. In ers. In the second year, the canes fruit weed. noncrop areas, tebuthiuron (Spike) is and die. Tips of first-year canes that registered for use by licensed applica- contact the ground form roots at the Bulldozing can also cause resprouting tors for brush control. Tebuthiuron is a nodes, contributing to the lateral ex- and can spread the weed by means of nonselective urea herbicide that is used pansion of the plant. root and stem fragmentation. for total control (i.e., it eliminates other vegetation in the treatment area) of Wild blackberry flowers are pollinated Mowing is not an effective means of shrubs, trees, and other weeds. It can primarily by bumblebees and honey controlling wild blackberries. In many be applied in a pelleted formulation at bees. The flowers can be self-pollinated cases it stimulates the formation of the base of the plant to provide long- but fruit set is increased by cross suckers from lateral roots and induces term control of wild blackberries. pollination. branching. Despite the lack of long- term control, however, mowing or Herbicides Applied to the Plant. Her- MANAGEMENT chopping can provide short-term bicides can be used in rangeland, pas- Wild blackberries are able to regener- canopy reduction that will encourage tures, noncrop areas, along roadsides, ate from the crown or rhizomes follow- the growth of grasses and broadleaf and in right-of-ways to control actively ing mowing, burning, or herbicide plants. growing wild blackberry plants. treatment. This makes them difficult to control, and control measures often Burning, like mowing, is not an effec- To effectively control blackberries dur- require follow-up treatment. Land tive long-term strategy because wild ing the growing season, an herbicide managers often rely on a combination blackberry plants vigorously resprout must be transported within the plant to of mechanical and chemical control from rhizomes. However, like mowing, the rhizomes and new growing points. methods followed by a prescribed burn it also provides short-term canopy For this to occur, the herbicide must to dispose of vegetative material. reduction. move in the phloem with the plant ◆ 2 ◆ April 2002 Wild Blackberries sugars produced through photosynthe- glyphosate (Roundup) and triclopyr species of wild blackberries. Absorp- sis. In early summer during the rapid (Brush-B-Gone, Blackberry and Brush tion of the herbicide into the foliage extension of canes and expansion of Killer) are registered for use by home is not as good with the amine form. foliar tissue, sugars are transported gardeners. Nevertheless, it also provides good within the plant from the underground control when applied at a 1% solu- storage tissues to the shoots. After • Glyphosate formulated into a prod- tion. The best time to apply either midsummer, new growth is reduced uct with 41% active ingredient (a.i.) form of the herbicide is midsummer. in wild blackberry first-year canes can provide good to excellent control When air temperatures are above (nonflowering shoots) because these of wild blackberries when applied in 80°F, it is best to use the amine for- shoots are actively transporting sugars a 0.5 to 1.5% solution (i.e., about 0.6 mulation because the ester form is to the rhizomes. These sugars are to 2 oz of product per gallon of wa- subject to vaporization. The timing stored for the following year’s growth. ter). One product available for use in for control of wild blackberries with In the flowering shoots (second-year the home landscape with this con- triclopyr is somewhat earlier than canes), movement of sugars from the centration of active ingredient is that recommended for glyphosate. shoots to the rhizomes occurs later in Roundup Super Concentrate. Gly- Like glyphosate, apply triclopyr the season than it does for first-year phosate products that have a lower spray-to-wet on the foliage. Some- canes and is most active after comple- concentration of active ingredient, times glyphosate and triclopyr (1% tion of fruiting. such as Roundup Concentrate (18% solution each) are used in combina- a.i.), will require a 1.5 to 3.5% solu- tion to achieve better control. Triclo- Time a foliar herbicide application so tion (i.e., about 2 to 4.5 oz per gallon pyr is available in retail stores for that it coincides with the maximum of water) for effective control. Late use in the home landscape in prod- rate of sugar movement to the root summer or early fall treatments give ucts formulated at a lower concen- system. This will depend upon better control than treatments before tration than those available to whether the plants are primarily first- or during flowering. To obtain good licensed applicators. Carefully read year canes or a combination of both control, however, complete foliage and follow the label of these prod- first- and second-year canes. In a situa- coverage (spray-to-wet) is essential. ucts (Brush-B-Gone Concentrate, tion where only first-year canes are Burning or mowing 40 to 60 days Blackberry and Brush Killer) to ap- present (for example when plants have after spraying with glyphosate in- ply the correct amount to plants. been burned or mowed), the most ef- creases the level of control and also fective time for optimal herbicide contributes to good pasture estab- Basal bark treatment.