R.D. van Klinken

Worth the risk? Introduction of legumes can cause more harm than good: an Australian perspective

Weeds are serious threats to Australias primary production and biodiversity conservation. For example, a recent Australia Bureau of Statistics survey found that 47% of farmers across Australia have a significant weed problem. A literature review revealed that legumes represent a significant proportion of the national weed problem and most serious Australian legume weeds are exotic thicket-forming species that were deliberately introduced for their perceived beneficial properties, such as for shade and fodder, or even quite trivial reasons, such as garden ornamentals. The low economic value of the rangelands most of these species infest, compared with control costs, hinders chemical and mechanical control of these weeds, such that biological control, which takes time, is expensive to implement and has no guarantee of success, may represent the only economically viable alternative to abandoning vast tracts of land. We argue that, because the behaviour of an introduced species in a novel environment is so hard to forecast, better predictive techniques should be developed prior to further introductions of plant species into novel environments. We also discuss the potential of legumes currently being promoted in Australia to become weeds and suggest the recent trend of exporting Australian Acacia spp. to semiarid regions of Africa risks history repeating itself and the development of new weed problems that mirror those posed by Australian Acacia spp. in southern Africa.

Learning from Past Attempts: Does Classical Biological Control of Noogoora Burr (Asteraceae: Xanthium occidentale) Have a Promising Future?

Noogoora burr (Asteraceae: Xanthium occidentale) is an annual from the Neotropics that is a serious weed of rangeland and agricultural regions in many parts of the world. It was one of the first weeds to be systematically targeted for biological control and there were two major phases in the Australian program; 1929-1940, and 1953-1975. Past attempts at biological control are reviewed to identify opportunities for renewed efforts, and for its historical value. Only one insect species was released in the first phase, but host-specificity restrictions were loosened during the second phase resulting in the release of two other insect species. None have been effective. A fourth agent, released primarily for parthenium weed, has had limited impact. However, the rust, Puccinia xanthii, was accidentally introduced in 1975. It has resulted in complete control of Noogoora burr in much of eastern Australia, but has had little or no impact in far northern Australia. Past failures, judged through hindsight, can be attributed to a failure to identify the full native range, lack of consideration for pathogens prior to 1975, and poor understanding of plant compensatory mechanisms and other challenges that an agent must overcome to be effective. A renewed effort specifically targeting Noogoora burr in far northern Australia holds considerable promise. It should include surveys for new agents within the native range of the Xanthium complex, and a systematic search for isolates of the P. xanthii rust that are climatically adapted to tropical conditions in Australia.

Periodic rest from grazing provided no control of an invasive perennial forb

This study examined if one grazing strategy (namely seasonal rest) was effective in the control of the invasive forbPhylacanescens(Kunth)Greene(hereafterlippia).Weexaminedifrestfromgrazingcouldincreasethecompetitiveness of native palatable species by allowing time to recover from defoliation, thereby altering competitive interactions between native species and lippia. In a field trial, we manipulated cattle grazing to determine its effects on the biomass of lippia and nativespecies.Wecomparedrestfromgrazingatdifferenttimesoftheyearwithyear-longgrazing(lowintensitycontinuous and high intensity short duration) and no grazing (permanently excluding large grazing animals). Experimental plots were stratified into different hydrological areas (approximately annual flooding and flooded less than once every 5 years) to include flood dynamics in the management scenarios. We detected no negative impacts of seasonal rest on lippia, but some positiveeffectsonnativespecies.Wefoundthatcompleteexclusionfromgrazinginareasthatalreadyhavesubstantiallippia invasion (and no flooding) may actually favour the expansion of lippia (at certain times). This study does not suggest that grazing management cannot be used as a tool for lippia control - simply that seasonal resting had no effect over a 3-year period.Thisislikelyduetothedynamicsofaboom-and-bustlandscapeinwhichiftheabioticconditionsarenotsuitablefor growth, then native species will not grow whether grazed or rested.

How sensitive is weed invasion to seed predation

1 CSIRO Entomology and CRC for Australian Weed Management, 120 Meiers Road, Indooroopilly, Brisbane, QLD 4068, Australia. 2 University of Queensland, School of Integrative Biology, St. Lucia, Brisbane, QLD 4072, Australia. 3 CSIRO Sustainable Ecosystems, 306 Carmody Road, St. Lucia, QLD 4067, Australia. Corresponding author: R.D. van Klinken <rieks.vanklinken@csiro.au.

Triggering dieback in an invasive plant: endophyte diversity and pathogenicity

Dieback causes a progressive reduction in plant population health, resulting in the death of plant parts and often plant death. It is prevalent in many invasive woody weeds in Australia and has been suggested as a potential mechanism for biocontrol of these species. Parkinsonia aculeata one such invasive tree in northern Australia. It has naturalised across a wide range of climatic zones and some populations have been heavily reduced by dieback occurrence. The cause(s) of dieback in parkinsonia remain elusive, although fungal endophytes have been previously implicated. In this study, we characterised the culturable fungal endophyte community of healthy and dieback-affected parkinsonia using culture-based techniques, and identified cultured isolates via amplicon sequencing of the internal transcribed spacer (ITS) of the rDNA operon. Eight isolates, identified as pathogens, were selected for a 10-week pathogenicity trial, including water stress treatments, on parkinsonia seedlings. We isolated a taxonomically diverse fungal community from parkinsonia, representing 54 unique species from 25 families. Communities were similar across healthy and dieback-affected plants, but differed by plant tissue. Of the eight putative pathogenic isolates tested in the pathogenicity trial, inoculation with Lasiodiplodia pseudotheobromae, Botryosphaeria dothidea and Pestalotiopsis mangiferae resulted in the largest lesions, but systemic infection or dieback-like symptoms were not observed in any treatment despite plant stress being induced by drought or inundation. We concluded that inoculation of parkinsonia with the tested putative fungal pathogens is unlikely to result in dieback, which has implications for future work in biocontrol of parkinsonia.

Benefits and challenges of maintaining national plant pest lists: an analysis of agricultural pests in Bhutan: An analysis of agricultural pests in Bhutan

Developing and maintaining national plant pest lists helps fulfil international obligations for trading countries, and also provides a foundation for national biosecurity systems. However, if done, lists and analyses are rarely made publically available. We compiled a national plant pest list for Bhutan, a relatively small but agriculturally diverse country for which plant protection is a recent discipline. We treated this pest list as a case study to test the benefits and challenges of maintaining such lists. Six hundred and forty-five pest species were recorded across 64 different crops. Of those, only 17.0% were listed for Bhutan in the widely used CABI Crop Protection Compendium. Most species (86.4%) were first recorded during the initial discovery phase (1985–88) of a long-running European Community funded aid programme. Regular taxonomic changes means keeping pest lists up to date requires both effort and expertise (27.0% of the 407 species identified by 1988 have since undergone name changes). Confidence in taxonomic identifications reduced drastically as access to international expertise decreased, from about 69.1% of species being identified with high confidence prior to 1988 to 8.1% afterwards. Many recent records lacked reference material, and voucher specimens for older material are mostly located internationally, making any revision challenging. Of the best represented taxa, greatest taxonomic uncertainty was for nematodes and viruses. Similar patterns were evident for the 112 damaging pest species, defined as those that at least occasionally and locally cause significant losses or require management actions within Bhutan. Of the damaging pests identified to species, all but one was also recorded in India, Bhutan’s most important trading partner, and only 16 were restricted to Asia. New damaging pests continue to be recorded, but only five species may represent new incursions since 1988. National pest lists are critical, but to be of greatest value they need to capture taxonomic uncertainty, and focus on pests of greatest significance. For most countries, the development, maintenance and use of a national plant pest list will require ongoing regional and global cooperation to overcome taxonomic impediments, and to maximise the benefits of such lists in terms of facilitating trade and guiding domestic biosecurity activities.

First report of oomycetes associated with the invasive tree Parkinsonia aculeata (Family: Fabaceae)

Phytophthora species have caused the decline and dieback of multiple tree species in Australia and around the world. Dieback in invasive trees in Australia has been observed for decades, motivating research into the potential causes of dieback to be used for biological control of these invasive species. Despite wide-ranging and ongoing research into invasive plant dieback, Phytophthora species have been largely ignored as potential causal agents of dieback, with the focus more on latent fungal pathogens living as endophytes. We conducted the first survey of Phytophthora and other oomycetes to determine their association with dieback of the invasive tree, Parkinsonia aculeata L. (Fabaceae). Using zoospore baiting, we recovered 37 oomycete isolates from roots and soil of healthy and dieback-affected P. aculeata in Kununurra, Western Australia and Charters Towers, Queensland. Using molecular taxonomy, we identified ten unique oomycete taxa, predominantly composed of Phytophthora palmivora, Ph. nicotianae and Phytopythium vexans. Parkinsonia dieback occurs across multiple climatic zones including those experiencing severe drought. We recovered fewer oomycete isolates from soil and roots in drought-affected Charters Towers than Kununurra, which had experienced recent rainfall. This may be because oomycetes require soil moisture for the dispersal of zoospores. None of the genotypes identified were consistently isolated from dieback-affected trees suggesting that any association with parkinsonia dieback may be localised. More extensive surveys and pathogenicity screenings of isolated oomycetes are required to evaluate their role in the parkinsonia dieback phenomenon.