Factors affecting the control of Cytisus scoparius and restoration of invaded sites

Dean DoughertyA and Sarah Hayden ReichardB, University of Washington, Ecosystem Sciences and the Center for Urban Horticulture, Box 354115, Seattle, WA 98195, USA.

A Current address: San Juan Preservation Trust, 136 Belle Lane, Olga, WA 98279, USA.

B Corresponding author


Cytisus scoparius (Scotch broom) is a leguminous shrub native to Europe and North Africa but it is invading numerous locations in North America, New Zealand, Australia and other countries. Restoration of many sites requires not only the removal of this species but the suppression of its long-lived seeds and an understanding of possible long-term effects following removal. We tested the effectiveness of two methods of manual control (cutting vs. pulling) in conjunction with two post-control mulch treatments (arborist vs. Cytisus chips). The cutting vs. pulling and mulch experiments were conducted in the spring and the cutting vs. pulling portion repeated in the summer. The mulch treatments were effective at suppressing Cytisus seedlings to the following spring and the Cytisus mulch was slightly more effective. For the manual control treatments, season contributed more to success than method, with summer control being more effective than spring. We also performed tests on soil collected beneath the crown of Cytisus plants at four different sites in Washington State (USA) and compared the results with those of soil collected at the same sites where Cytisus was not growing. The Cytisus soil consistently had higher levels of total nitrogen and nitrate and lower pH levels versus the non Cytisus soil. These differences persist for at least several months and may affect restoration efforts.

Keywords: Cytisus scoparius, Scotch broom, invasive species, manual weed control, mulch.


Plant Protection Quarterly (2004) 19 (4) 137-142.