Many a World Environment Day activity over the years has been spent pulling Boneseed out of the ground, but this April, Boneseed was planted in the heath land of Alcoa’s mining area. Never fear, the plants come armed with the latest biological control agent in the fight to control this wretched weed, the Boneseed Leaf Buckle Mite.
Originating from south-western South Africa, Boneseed was cultivated as a garden plant in Australia last century and most of the existing infestations are believed to be derived from garden escapes. Boneseed is now widespread and densely established in several areas of Victoria, with major infestations in the You Yangs, Mornington Peninsula and Lake Hindmarsh.
Boneseed is a serious weed of native vegetation and reduces the aesthetic and conservation qualities of bushland areas. Dense infestations virtually eliminate native understorey species and reduce the regeneration abilities of native trees and shrubs. Several coastal plant communities and a number of species are threatened with either depletion or extinction by the invasion of boneseed in eastern Australia.
The Boneseed Leaf Buckle Mite is also a native of South Africa and was first released to selected sites in Victoria, South Australia and Tasmania in 2008. The mite induces the formation of specialized galls. These appear as abnormal patches of leaf hairs associated with a distorted area on the leaf (as illustrated on the front cover). The mites divert some of the plants resources, suppressing plant vigour, growth, competitiveness with other vegetation and reproductive output.
The Boneseed Leaf Buckle Mite is very small, even by mite standards, measuring 0.15 mm long and 0.05 mm wide. Therefore for this release, Boneseed plants containing viable mite colonies were planted into an existing population of boneseed. Previous releases involving the transfer of Boneseed Leaf Buckle Mite galls onto wild Boneseed has had little success.
So why does the Boneseed Leaf Buckle Mite now call Alcoa Anglesea home? As it turns out, our secure mining area meets all of the site selection criteria for a release site perfectly.
Release Site Criteria
The release site must be considered low priority for Boneseed control in your area. Our infestations are considered ‘low priority’ from the community’s perspective as they are contained within our mining area boundary and not spreading into the broader Anglesea Heath.
- Unlikely to be targeted for conventional control in the next five years. For the mites to spread from the planted Boneseed into the wild Boneseed population and take a hold, the Boneseed, in the area cannot be removed for 5 years. Pull out the Boneseed, pull out the Boneseed Leaf Buckle Mite.
- Unlikely to be accidentally or inadvertently disturbed. Due to the inaccessibility of our mining area to the general public/community groups without permission, it is unlikely that a weeding activity will accidentally remove Boneseed within the release site.
- No more than ten minutes walk access. Located close to infrastructure, the site is easily accessible for monitoring.
Hearing the words ‘biological control’, most of us immediately think of the very unsuccessful introduction of the Cane Toad. Rest assured, modern weed biological control programs in Australia are regulated by federal legislation that ensures that new biological agents are approved only if it can be demonstrated by the proponent that the risks due to the agent of adverse impacts on the environment, agriculture, and other endeavours is acceptable.
The main tool in this kind of assessment is what’s known as host specificity testing. This involves screening a large number of plant species against the potential new agent to determine its plant host range. The fewer plants the potential agent can utilise, the greater the likelihood that it will be approved for release in Australia.
The risk assessment is prepared by the proponent and distributed nationally to 21 State and Federal government agencies to enable thorough scientific review. The Boneseed Leaf Buckle Mite was assessed under this regime and as it turns out, is a very fussy eater, surviving only on Boneseed, and is even incapable of utilising the very closely related plant Bitou Bush, which is a very serious weed in coastal New South Wales.
While this form of biological control cannot eradicate the weed, it can reduce the spread and density of infestations.
BONESEED (Chrysanthemoides monilifera ssp. monilifera)
| Size: | 1 – 3 metres high |
| Distribution: | native to south-western South Africa, now considered widespread in south-east Australia |
| Habitat: | found in hilly terrain in South Africa but occupies a variety of habitats in Australia |
| Form: | erect multi branched shrub or small tree |
| Foliage: | obovate* to elliptic# leaves, 2 – 8 cm long, margins irregularly toothed, blades thin |
| Flowers: | yellow daisy flowers with 4 – 8 (usually 5 – 6) petals July – December |
| Did you know: | Boneseed is a Weed of National Significance (WONS) a program that coordinates a national effort against 20 of Australia’s worst invasive plants. |
* Elliptical shape with the upper half of leaf broader than
source: Alcoa Environment Report March 2011
Links
- Alcoa Anglesea Environment Reports: www.alcoa.com
