Invasive Blackberry Species in Oregon, USA: Their Identity and Susceptibility to Rust Disease, and Implications for Biological Control

Authors: Bruckart, William; Thomas, Jami; SOCHOR, MICHAL - Crop Research Institute - Czech Republic; TRAVNICEK, BOHUMIL - Crop Research Institute - Czech Republic

Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2017
Publication Date: 6/6/2017
Citation: Bruckart, W.L., Michael, J.L., Sochor, M., Travnicek, B. 2017. Invasive Blackberry Species in Oregon, USA: Their Identity and Susceptibility to Rust Disease, and Implications for Biological Control. Invasive Plant Science and Management. 10:143-154.

Interpretive Summary: Blackberries from Europe are invasive along the Pacific Coast and need to be controlled. One possible approach is biological control that uses a rust disease. In 2005, a rust disease was discovered in Oregon similar to a disease that had been used in Australia to control blackberries. In Oregon, however, some of the blackberries were not diseased. The objective of this research was to evaluate effectiveness of the rust disease on blackberry in Oregon. As a result, it was determined that there are two species of invasive blackberry, identified as Rubus armeniacus and R. praecox. The rust disease only occurred only on R. praecox in the field, and that was confirmed in greenhouse inoculation tests. Also, greenhouse tests showed that R. armeniacus does not get the rust disease. It is clear that the rust disease will not be useful for biological control of R. armeniacus and that management of this species will require the use of chemical herbicides or physical removal of plants (pulling).

Technical Abstract: Two of five species of European blackberry (Rubus fruticosus L. Aggregate) along the West Coast of the United States are invasive, and they are also similar in appearance. Biological control by Phragmidium violaceum, causal agent of a rust disease, was under consideration when rust-diseased blackberry was discovered in Oregon in 2005. An investigation was initiated to determine whether this disease would be an important factor affecting population density of these blackberries. Surveys were made over a 5-year period at >30 field sites in the Willamette Valley and along the Pacific Coast of Oregon. Diseased and non-diseased blackberry specimens were collected for artificial greenhouse inoculations and for identification. The two blackberry species, i.e., Rubus armeniacus and R. praecox were identified as the most invasive. They can be distinguished morphologically, particularly on the basis of inflorescence and flower characteristics, and to a certain extent on the basis of primocane leaf and leaflet shape. Artificial greenhouse inoculation studies revealed that only R. praecox is susceptible to the rust disease; R. armeniacus is not, and these results were confirmed in the field. It is clear that biological control of R. armeniacus by the rust disease is not an option and that other approaches to management of this species, in particular, are needed.