finalreportp Project code: Weed.120 Prepared by: Raelene Kwong Victorian Department of Primary Industries Date published: May 2006 ISBN: 9781741914542 PUBLISHED BY Meat & Livestock Australia Locked Bag 991 NORTH SYDNEY NSW 2059 Feasibility of biological control of solanaceous weeds of temperate Australia Silverleaf nightshade, Solanum elaeagnifolium Cav. and prairie ground cherry, Physalis viscosa L. This publication is published by Meat & Livestock Australia Limited ABN 39 081 678 364 (MLA). Care is taken to ensure the accuracy of information in the publication. Reproduction in whole or in part of this publication is prohibited without the prior written consent of MLA. Contents Section Page Abstract………………………………………………………………………………………….1 1 Introduction ....................................................................................................... 7 1.1 Background....................................................................................................... 7 1.2 Objectives ......................................................................................................... 8 1.3 Methods ............................................................................................................ 8 2 Silverleaf Nightshade, Solanum elaeagnifolium Cav. ....................................... 9 2.1 Taxonomy ......................................................................................................... 9 2.2 Global Distribution........................................................................................... 10 2.3 Australian Distribution ..................................................................................... 10 2.4 Biology ............................................................................................................ 11 2.5 Economic Importance ..................................................................................... 13 2.6 Current Control Methods................................................................................. 15 2.7 Silverleaf Nightshade National Workshop....................................................... 17 2.8 Victorian Farmer Experiences with Silverleaf Nightshade Management ........ 18 3 Feasibility of Biological Control of Silverleaf Nightshade ................................ 20 3.1 History of surveys for natural enemies of silverleaf nightshade...................... 20 3.2 Analysis of potential agents for biological control of SLN ............................... 20 3.3 Benefit-Cost Analysis of a biological control program for SLN........................ 25 3.4 Discussion....................................................................................................... 34 3.5 Recommendations .......................................................................................... 35 4 Prairie Ground Cherry, Physalis viscosa L...................................................... 36 4.1 Taxonomy ....................................................................................................... 36 4.2 Global Distribution........................................................................................... 37 4.3 Australian Distribution ..................................................................................... 38 4.4 Biology ............................................................................................................ 38 4.5 Economic Importance ..................................................................................... 39 4.6 Current Control Methods................................................................................. 40 4.7 Victorian Farmer Experiences with PGC Management................................... 42 5 Feasibility of Biological Control of Prairie Ground Cherry............................... 42 5.1 Arthropods ...................................................................................................... 42 5.2 Fungi ............................................................................................................... 43 5.3 Benefit-Cost Analysis of a biological control program for PGC....................... 43 5.4 Discussion....................................................................................................... 45 5.5 Recommendations .......................................................................................... 45 6 References..................................................................................................... 47 7 Appendixes ..................................................................................................... 52 7.1 Appendix 1...................................................................................................... 52 7.2 Appendix 2...................................................................................................... 81 7.3 Appendix 3...................................................................................................... 84 7.4 Appendix 4...................................................................................................... 88 7.5 Appendix 5.................................................................................................... 125 Feasibility of biocontrol of solanaceous weeds of temperate Australia 7.6 Appendix 6.................................................................................................... 136 7.7 Appendix 7.................................................................................................... 138 Feasibility of biocontrol of solanaceous weeds of temperate Australia Abstract The solanaceous weeds, prairie ground cherry and silverleaf nightshade, are significant weeds in the cropping/pasture and perennial pasture zones of temperate Australia. The extensive and deep perennial root systems makes them extremely competitive, and the limited control techniques currently available are uneconomical for the treatment of large, dense infestations. Biological control is therefore considered a highly desirable option to reduce the impact of existing infestations and slow their rates of spread. This study aimed to determine the feasibility of commencing biological control programs for silverleaf nightshade and prairie ground cherry based on a review of natural enemies associated with these plant species in their native ranges and an assessment of the organisms’ potential for biological control. A total of 30 species were assessed for silverleaf nightshade but few of these showed much potential for biocontrol because of their apparent lack of specificity. In addition, many of the previous surveys on natural enemies associated with silverleaf nightshade were conducted in regions of the Americas, which have vastly different climates to the regions in Australia where silverleaf nightshade is problematic. No surveys had been conducted in the central regions of Argentina and Chile, where climate analysis indicated more comparable climates with Australia. For prairie ground cherry, no surveys have previously been conducted and therefore little is known about the natural enemies associated with this plant in its native range of South America. Due to this lack of information, combined with uncertainties regarding the origins of Australian populations of these weeds, it is difficult to predict the likelihood of undertaking successful biological control programs for these weeds. However, the reported success of biological control of silverleaf nightshade in South Africa attributed to just one defoliating beetle, provides some promise that the biological control of SLN is possible. The study concluded that investment in biological control of SLN and PGC is warranted and potentially economically viable, however preliminary research is needed to fill key knowledge gaps so that a re-evaluation of the prospects for biological control can be conducted more thoroughly. Executive Summary The weeds prairie ground cherry, Physalis viscosa L. and silverleaf nightshade, Solanum elaeagnifolium Cav. have been identified as Priority Weeds of cropping/pasture zones of temperate rangelands in “Weeds of Significance to the Grazing Industries of Australia” (Grice 2002). The deep and extensive perennial root system of these weeds makes them particularly difficult to control using herbicides and cultivation. As such, biological control is seen as a High Priority Research and Development need for these weeds. This study investigates the rationale for and feasibility of biological control of prairie ground cherry (PGC) and silverleaf nightshade (SLN) by: (1) reviewing the impact of these weeds, (2) current methods and deficiencies in control techniques, (3) reviewing the literature to identify natural enemies associated with these weed in their native ranges, and (4) discussing their potential as biological control agents. Based on the gaps in knowledge identified through this study, a biological control research project incorporating likely costs and time-lines is proposed for each weed. This information, combined with economic data on the current and projected costs of SLN and PGC to agriculture is used to provide an ex ante assessment of the potential economic benefits of an investment in biological control programs for PGC and SLN. 1 Feasibility of biocontrol of solanaceous weeds of temperate Australia A summary of the major findings is provided for each weed. SILVERLEAF NIGHTSHADE Weed impacts. Silverleaf nightshade in Australia is estimated to infest approximately 140,000 ha and is particularly problematic in South Australia,