Parthenium hysterophorus L. (Asteraceae)

Parthenium is a serious problem in several tropical and sub-tropical areas around the world and particularly an emerging problem in southern Africa. It is a Weed of National Significance in Australia. The chapter summarises current knowledge about the taxonomy, biology, distribution, ecology, impacts and biological control of the weed worldwide. Queensland has led attempts to achieve biological control of parthenium since it first began foreign exploration in 1977. Since then nine insects and two rusts have been released in Queensland. Some of these have since been, or will be, used by other countries. The program has brought significant benefits to Queensland through an increase in grass biomass in some areas. Instances of non-target attack by one agent, particularly in India, are discussed with the conclusion that the effects were ultimately negligible and possibly due to parthenium pollen lodging on the leaves of non-target plants. The insects introduced for parthenium have also given a measure of control for the very closely related weeds, ragweed and Noogoora burr. The paper draws a conclusion that local climatic conditions are very important when considering whether a successful agent in one country will be useful in a second country.

Approaches to selecting native plant replacements for fleshy-fruited invasive species

Invasive plants are a serious threat to biodiversity. Yet, in some cases, they may play an important ecological role in heavily modified landscapes, such as where fleshy-fruited invasive plants support populations of native frugivores. How can such conservation conflicts be managed? We advocate an approach in which native fleshy-fruited plants are ranked on their ability to provide the fruit food resources for native frugivores currently being provided by invasive plants. If these native taxa are preferentially used, where ecologically appropriate, in plantings for restoration and in park and garden settings, they could help support native frugivore populations in the event of extensive invasive plant control. We develop and critically examine six approaches to selecting candidate native plant taxa: a multivariate approach based on the frugivore assemblage, a scoring model, and several multivariate approaches (including trait combinations having the greatest correlation with the diet of the native frugivore assemblage) based on the functional traits of fruit morphology, phenology, conspicuousness, and accessibility. To illustrate these approaches, we use a case study with Bitou bush (Chrysanthemoides monilifera subsp. rotundata) (Asteraceae), an Australian Weed of National Significance. The model using a dissimilarity value generated from all available traits identified a set of species used by the frugivores of C. monilifera more than null models. A replacement approach using species ranked by either all traits available or the frugivore community appears best suited to guide selection of plants in restoration practice.

Chromolaena odorata (L.) King and Robinson (Asteraceae)

Chromolaena, or Siam weed, is a serious problem in several tropical and sub-tropical areas around the world. In our own region, it is a serious weed in New Guinea, East Timor and Indonesia and is also under an eradication regime in North Queensland. The chapter summarises current knowledge about the taxonomy, biology, distribution, ecology, impacts and control of the weed. Biological control has been a major multinational initiative against this weed in recent years and these efforts are described in some detail. Interestingly agents have not been universally effective because of weed biotype differences and climate. Considerable success has been achieved in New Guinea, principally with the tephritid fly Cecidocares connex and by the efforts of Michael Day, Rachel McFadyen and Graham Donnelly from Alan Fletcher Research Station.

Interactions between butterfly pea (Clitoria ternatea) and rubber vine (Cryptostegia grandiflora)

The arutors studied the impact of a forage legume, butterfly pea, on rubber vine at the early establishment phase under seven planting combinations at three nitrogen fertiliser levels. In pure stands, both species increased their shoot and root dry weight yield in response to nitrogen but rubber vine exhibited the greater response. In mixed stands, rubber vine and butterfly pea did not compete with each other at any nitrogen level. An over-yielding response resulted in all mixture combinations in terms of shoot and root yields. Total shoot and root mass of mixed stands significantly out-yielded their highest yielding pure stands by 8% and 27% respectively, suggesting that butterfly pea not only failed to reduce shoot and root growth of rubber vine, but actually improved its growth performance. Consequently, the introduction of butterfly pea to suppress rubber vine is not warranted.

Progress towards the eradication of mikania vine (Mikania micrantha) and limnocharis (Limnocharis flava) in northern Australia.

To eradicate a weed invasion, its extent must be delimited and each infestation must be extirpated. Measures for both of these criteria are utilized to assess the progress of current eradication programs targeting mikania vine and limnocharis in northern Australia. The known infested area for each species is less than 5 ha and has remained largely static for the last 3 or more years against a backdrop of refined and enhanced detection methods. This suggests that delimitation has been approached, if not achieved. Different methods of detection have their places, relative to the stage of the program and the spatial distribution of infestations. Although all known infestations of both species are effectively monitored and controlled, ongoing emergence from persistent seed banks limits progress towards the extirpation of infestations to a slow, but measurable, rate. Nomenclature: Glyphosate. N-phosphonomethyl)glycine; fluroxypyr, [(4-amino-3,5-dichloro-6-fluoro-2-pyridinyl)oxy]acetic acid; limnocharis, Limnocharis flava (L.) Buchenau LIFL5; mikania vine (mile-a-minute), Mikania micrantha Kunth MIKMI.

Seed production and maturation of Limnocharis flava (L.) Buchenau in the field and glasshouse.

The aquatic herb Limnocharis flava, native to tropical America, is the target of an eradication program in Queensland but little is known about its reproductive biology. Their field and glasshouse studies showed that seedlings exhibited relatively high survival (64%) and that fruits containing over 1000 seeds could be produced on young plants within 46 days, at any time of the year. Mature fruits, follicles and seeds were also buoyant. The authors findings were incorporated into the eradication program and influenced the frequency of infestation monitoring.

Biocontrol of Chromolaena odorata in Papua New Guinea

The status of biocontrol of Chromolaena odorata, a weed of significant agricultural importance in Papua New Guinea, is assessed. Chromolaena is confirmed present in 391 sites in 12 of the 20 provinces of PNG. A collaborative project on the biocontrol of chromolaena involving the PNG National Agricultural Research Institute and the Queensland Department of Primary Industries and Fisheries began in1998, with funding from ACIAR. Three agents, the moth Pareuchaetes pseudoinsulata, which has established only in Morobe Province, the stem-galling fly Cecidochares connexa, which has established in all 12 provinces and the leaf mining fly Calycomyza eupatorivora, which is currently being monitored for establishment, have been introduced. Cecidochares connexa has been the most effective of the agents so far and it has spread more than 100 km in five years from some release sites. Preliminary field data have shown that the numbers of galls per plant have increased, coupled with a decrease in plant height and percent plant cover. In parts of New Ireland and Sandaun provinces, C. connexa has controlled chromolaena, resulting in the regeneration of natural vegetation. In addition, some food gardens have been re-established where chromolaena had once taken over. Consequently, food production has increased and income generated from selling agricultural produce has increased two fold. There is also less time spent in clearing chromolaena from food gardens and plantations. The effectiveness of C. connexa has brought relief to many communities, which are helping in the distribution of the gall fly to other areas affected by chromolaena.

Foods of pigeons and doves in fragmented landscapes of subtropical eastern Australia

We report dietary items of pigeons and doves from northern New South Wales and southern Queensland, obtained from opportunistic sampling of the gut contents of dead birds and observing foraging birds. Most records were from fragmented rainforest habitats, which now support abundant invasive fleshy-fruited plants. The fruits and seeds of invasive plants, particularly Camphor Laurel Cinnamomum camphora, formed the dominant food of several of the species sampled, although in some cases these birds appear to destroy most of the ingested seeds in the gizzard, thereby not contributing to weed dispersal. We also describe the first records of White-headed Pigeons Columba leucomela eating flowers and Brown Cuckoo-Doves Macropygia amboinensis eating flower buds. Camphor Laurel, via flowers, green and ripe fruits, and seeds, provided food for White-headed Pigeons in the Goolmangar district of New South Wales throughout the entire year. Seventy percent of the plant species whose fruits and seeds were recovered from the gut had not previously been recorded as food items for those bird species, illustrating how little is known about the diets of pigeons and doves in fragmented Australian landscapes.

Predicting invasiveness in exotic species: do subtropical native and invasive exotic aquatic plants differ in their growth responses to macronutrients?

We investigated whether plasticity in growth responses to nutrients could predict invasive potential in aquatic plants by measuring the effects of nutrients on growth of eight non-invasive native and six invasive exotic aquatic plant species. Nutrients were applied at two levels, approximating those found in urbanized and relatively undisturbed catchments, respectively. To identify systematic differences between invasive and non-invasive species, we compared the growth responses (total biomass, root:shoot allocation, and photosynthetic surface area) of native species with those of related invasive species after 13 weeks growth. The results were used to seek evidence of invasive potential among four recently naturalized species. There was evidence that invasive species tend to accumulate more biomass than native species (P = 0.0788). Root:shoot allocation did not differ between native and invasive plant species, nor was allocation affected by nutrient addition. However, the photosynthetic surface area of invasive species tended to increase with nutrients, whereas it did not among native species (P = 0.0658). Of the four recently naturalized species, Hydrocleys nymphoides showed the same nutrient-related plasticity in photosynthetic area displayed by known invasive species. Cyperus papyrus showed a strong reduction in photosynthetic area with increased nutrients. H. nymphoides and C. papyrus also accumulated more biomass than their native relatives. H. nymphoides possesses both of the traits we found to be associated with invasiveness, and should thus be regarded as likely to be invasive.

Ocean dispersal modelling for propagules of pond apple (Annona glabra L.)

Pond apple invades riparian and coastal environments with water acting as the main vector for dispersal. As seeds float and can reach the ocean, a seed tracking model driven by near surface ocean currents was used to develop maps of potential seed dispersal. Seeds were ‘released’ in the model from sites near the mouths of major North Queensland rivers. Most seeds reach land within three months of release, settling predominately on windward-facing locations. During calm and monsoonal conditions, seeds were generally swept in a southerly direction, however movement turns northward during south easterly trade winds. Seeds released in February from the Johnstone River were capable of being moved anywhere from 100 km north to 150 km south depending on prevailing conditions. Although wind driven currents are the primary mechanism influencing seed dispersal, tidal currents, the East Australian Current, and other factors such as coastline orientation, release location and time also play an important role in determining dispersal patterns. In extreme events such as tropical cyclone Justin in 1997, north east coast rivers could potentially transport seed over 1300 km to the Torres Strait, Papua New Guinea and beyond.

Worldwide phylogeography of the globally invasive plant: Jatropha gossypiifolia

Dhileepan, Raghu and colleagues recently published their paper 'Worldwide phylogeography of the globally invasive plant: Jatropha gossypiifolia' in Proceedings of the 16th Australian Weeds Conference. They used chloroplast microsatellites to establish patterns of phylogeographic structure in the native and introduced range of Jatropha gossypiifolia, and to determine the origin(s) of introductions and the level of genetic diversity present in native and introduced populations. J. gossypiifolia exhibited limited phylogeographic structure in its native range which was best explained by contemporary movement associated with the ornamental plant trade. Multiple introductions from diverse source locations and no reduction in genetic diversity was found in the introduced range which includes Australia, Africa and Asia. These results have implications for our current biocontrol project.

Buoyancy and germination of pond apple (Annona glabra L.) propagules in fresh and salt water

Stephen Setter, Melissa Setter, Michael Graham and Joe Vitelli recently published their paper 'Buoyancy and germination of pond apple (Annona glabra L.) propagules in fresh and salt water' in Proceedings of the 16th Australian Weeds Conference. Stephen also presented this paper at the conference. Pond apple is an aggressive woody weed which has invaded many wetlands, drainage lines and riparian systems across the Wet Tropics bioregion of Far North Queensland. Most fruit and seed produced by pond apple during the summer wet season fall directly into creeks, river banks, flood plains and swamps from where they are dispersed. They reported that pond apple seeds can float for up to 12 months in either fresh or salt water, with approximately 38% of these seeds germinating in a soil medium once removed from the experimental water tanks at South Johnstone. Their study suggested that the removal of reproductive trees from areas adjacent to creeks and rivers will have an immediate impact on potential spread of pond apple by limiting seed input into flowing water bodies.

Proceedings of the 16th Australian Weeds Conference

Invitation to attend: On behalf of the organising committee of the 16th Australian Weeds Conference, we cordially invite you to attend this biannual conference to be held in Cairns, Australia, 19-22 May 2008. The conference will be hosted by the Weed Society of Queensland and has the theme of ‘Weed Management 2008 – hot topics in the tropics’. The conference will showcase recent advances in weed science, extension and policy across Australian and international communities and landscapes. The program for the conference includes plenary, oral, and poster sessions and trade exhibitors. The conference will appeal to anyone involved in weed R & D, management and extension and will be a great opportunity to build new networks and explore existing ones. Michael Widderick (conference chair)

Predicting weediness - what has the CRC achieved?

Dane Panetta and colleagues recently published their paper 'Predicting weediness - what has the CRC achieved?' in Proceedings of the 16th Australian Weeds Conference. They reviewed the research outcomes from the CRC for Australian Weeds Management for predicting weediness of plant species and concluded that advances have been made in identifying traits that distinguish high impact species for a range of environments. However these were not consistent between studies. They considered that Australia's border Weed Risk Assessment System has performed well under considerable local and international scientific scrutiny though minor improvements could still be made.

Grader grass (Themeda quadrivalvis): changing savannah ecosystems.

Wayne Vogler and Nikki Owen recently published their paper 'Grader grass (Themeda quadrivalvis): changing savannah ecosystems' in Proceedings of the 16th Australian Weeds Conference. Grader grass is an invasive exotic 'high biomass' grass from India that is increasing its distribution in northern Australia. It is unpalatable and can dominate ecosystems, thereby decreasing grazing animal production, degrading conservation areas and increasing fire intensity and hazard. They studied aspects of its biology at a field site in north Queensland where the initial biomass of the grass layer was found to be 70% grader grass. Grader grass also produced 80% of the seed input into this ecosystem during the first growing season. These factors, in combination with a large viable seed bank and rapid germination at the start of the wet season, demonstrate the potential of grader grass to dominate and degrade the savannah ecosystems of northern Australia.