What is the weed problem?
Native to the Americas, parkinsonia (Parkinsonia aculeata) was introduced into Australia as an ornamental tree/shrub and for its potential value for hedging and as fodder. Inhabiting semi-arid and tropical rangelands across northern Australia, its current distribution extends over an area of some 8000 km2, with potential for further range expansion into bioclimatically suitable areas across Australia.
Left: Current distribution of parkinsonia; the shading indicates relative abundance: dark, mid and pale green corresponds with Abundant, Intermediate and Occasional populations, respectively. National management goals are indicated by red letters; A, B and C are Containment, Active Control and Eradication Zones, respectively (Source: Deveze, 2004 & Queensland Government). Right: Projection of suitable climates for parkinsonia. Shading corresponds to an Ecoclimatic Index predicted using CLIMEX (Source: van Klinken et al. 2009)
Parkisonia thicket, with researcher (~180cm tall) in view for scale
Parkinsonia has the ability to form dense thickets in floodplains and grasslands, and along watercourses and bore drains thereby impacting the pastoral industry negatively (e.g. limiting pasture growth, restricting stock access to water and impeding mustering) and the environment (e.g. providing refuges for feral animals like pigs, increasing evapotranspiration, contributing to soil erosion, suppressing the herb layer and reducing wildlife habitat). Parkinsonia is now a declared weed in all states and territories of Australia, and is considered a Weed of National Significance. Parkinsonia has been a target for biological control in Australia since 1983.
How is the weed currently managed?
Current management of parkinsonia uses a combination of mechanical, chemical and biological control tactics. Landscape context, time of year, and soil moisture determines the relative value of each management tool in the toolbox. Often the best management results are achieved by judiciously integrating the different management tactics (see Parkinsonia management guide).
What can biocontrol offer to the weed’s management?
Mechanical and chemical control tactics for parkinsonia already exist and are already being effectively used by land managers wherever possible. But these management tactics require repeat application and are not always possible in all parkinsonia infestations (e.g. in difficult terrain or in sensitive riparian environments). Having a landscape‐scale self‐perpetuating form of control like biological control in these systems may therefore aid in the integrated management of parkinsonia. Biological control is intended to be a chronic stressor on parkinsonia populations that are particularly hard to cost‐effectively control by other means; their impacts will be best judged by their ability to slow plant vigour and reduce seed production, and through that their impacts on the spread of parkinsonia populations.