New insights into the biological and chemical control of English broom(Cytisus scoparius) in the Victorian Alps

摘要

Parks Victoria has led a program to control English broom Cytisus scoparius (L.) Link in the Alpine National Park for 25 years. Two elements of this program have been the introduction of biological control agents and the establishment of an adaptive experimental management program (AEMP) to assess different herbicide treatments.Four biocontrol agents (3 insects; 1 mite) were released from 1995-2011 and a rust self-established by 2005. Assessments of agent establishment, abundance, dispersal and impacts have enabled an evaluation of their potential to contribute to the suppression of broom infestations. The broom seed-feeding beetle, broom gall mite and broom rust were all found to be well established and beginning to reduce plant vigour and/or seed production.The AEMP compared broom control effectiveness, and outcomes for grasses and sedges (graminoids), for three herbicides applied in two seasons. After seven years the mean broom cover was reduced to <5% in the majority of plots. The trajectories for reduction, however, varied. Broom cover returned to initial levels in plots which missed treatment for two successive years. The results indicate that, once cover is reduced to a sufficiently low level, non-treatment for one year may not affect effectiveness, but non-treatment for two successive years will. Graminoid cover varied with herbicide treatment.