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Weeds - Phase 1 - Research Highlights
Hawkweed
Improved detection and eradication of Hawkweed (Hieracium): experiments and second-generation dispersal models
What the report is about
In this report a range of glasshouse and field experiments were undertaken to fill knowledge gaps relating to the seed ecology and biology of Hieracium praealtum (king devil hawkweed) and H. aurantiacum (orange hawkweed).
- For both species rapid germination of seeds is likely because most seed will germinate readily once temperature, moisture and light requirements are met-probably during spring-summer. Late-developing seeds will probably remain dormant during winter and germinate in the following spring.
- Buried seeds, even if they do germinate, are unlikely to emerge through the soil.
Where are the relevant industries located in Australia?
Two areas have been identified as at greatest risk of invasion by the two Hieracium species studied: the Bogong High Plains in the Victorian Alpine National Park, by both H. aurantiacum and H. praealtum, and the Round Mountain region (Jagungal Wilderness) of Kosciuszko National Park in New South Wales, by H. aurantiacum. These two regions have known invasive populations of Hieracium that are believed to have been present for at least 20 years.
Eradication of the populations is the aim of the land management agencies - Parks Victoria and the New South Wales Department of Environment and Climate Change - so this project aimed to help determine which areas should be the priorities for search and control activity in coming seasons.
On the basis of modelling using a plant growth index and climatic stresses to derive a ‘climatic niche', the potential habitat for H. aurantiacum in Australia includes all of Tasmania, the highlands of eastern New South Wales and most of Victoria.
Background
Hieracium aurantiacum and H. praealtum (Asteraceae) are two stoloniferous perennials that have naturalised in a small part of the Victorian Alps.
Both species have now been declared prohibited species at national and state and territory levels in Australia, mainly because of their degradation of large areas of agricultural land and the reduction in amenity value and biodiversity in native tussock grasslands in New Zealand. Revenue lost as a result of invasion by several species of hawkweed in New Zealand was estimated at $45 million dollars in 1993.
Aims/objectives
This report investigates the effects of fire, herbicides and picking on seed production with a view to confirming the ecological responses of the seeds of H. aurantiacum and H. praealtum (Asteraceae).
Methods used
The use of fire as a management tool was explored by conducting a prescribed burn. Fire could be of use to remove seed around adult plants but not as a broad-area management tool or for adult plants.
The potential for production of viable seeds following hand-picking of flowers or herbicide application was also measured.
- Seed dispersal is possible from picked immature flowers, although this depends on the stage of maturity at the time.
- Depending on the flower's stage of maturity, achenes can be produced after herbicide application, although their viability is yet to be determined.
- All flowering stems should be picked, bagged and destroyed before herbicide application.
Results/key findings
A previous model for predicting new occurrences of H. aurantiacum was adapted and applied to newly discovered infestations of that species in New South Wales and a population of H. praealtum in Victoria. Seed dispersal and site disturbance have appeared as the factors promoting increased likelihood of establishment.
Prediction maps were created and distributed to management agencies to guide surveillance and control activity for the 2009-2010 season.
- In Victoria the areas predicted to be at greatest risk of invasion by the H. praealtum population occur under the dispersal plume that stretches from the Rocky Valley dam bank opposite the quarantine area upslope in a southerly direction towards the Bogong High Plains road. This region occurs at the western edge of the known locations.
- In New South Wales the areas most at risk of H. aurantiacum establishment occur under the dispersal plume in the immediate vicinity of known populations. Areas subject to disturbance-for example, roads and Ogilvies Quarry-also appear to be a priority for search and control in coming seasons.
Implications for relevant stakeholders
In the course of the study we identified two primary areas for future research:
- modelling of improved dispersal by wind, changes in detectability over time, the simultaneous optimisation of surveillance for multiple species, and the impact of uncertainty on surveillance decision making
- quantifying detectability under differing conditions using novel field experiments.
Together with our industry partners, we put forward a successful bid for an Australian Research Council linkage grant worth $302 000 over three years. We have thus added considerable value to this current project and have begun to extend our knowledge of the management of Hieracium in Australia.