Myrtle Rust in Australia – a National Action Plan

Myrtle Rust, a plant disease caused by the introduced fungal pathogen Austropuccinia psidii, poses a serious and urgent threat to Australia’s native biodiversity. Myrtle Rust affects plant species in the family Myrtaceae (paperbarks, tea-trees, eucalypts, and lillipillies), which are key and often dominant species in many Australian ecosystems. To date it has proved capable of infecting 382 native species and this number is likely to grow. Serious declines towards extinction are underway in some species, and broader ecological consequences are expected. Myrtle Rust is likely to have a significant impact on matters of national environmental significance protected under national environment law, including listed threatened species and ecological communities, wetlands of international importance, world heritage properties, and national heritage places

Can we grow certified eucalypt plantations in subtropical Australia? An insect pest management perspective

In the past few years several Australia forestry companies have set in place procedures for certification in sustainable forest management (Forest Stewardship Council and Australian Forestry Standard). Eucalypt plantation forestry in sub-tropical New South Wales and Queensland is substantially different from that in temperate southern Australia, with currently the majority of plantations grown for long-rotation sawlogs, and a range of tree species different from that planted for pulp in southern Australia. Also, the major insect pests in this region are multivoltine and active for much of the year, due to the warmer climate and the short milder winters, compared to shorter periods of activity of larvae of any one species of mostly univoltine insects in temperate Australia. Insect pest management strategies currently used in Australia include tree improvement, improved site-species matching, and chemical control, mostly using an integrated pest management approach. Monitoring is essential for correct timing of insecticide application but, due to limited resources, forestry companies in Australia struggle to monitor effectively for multiple insect pests over extended periods of insect activity. Because of the relative immaturity of the plantation industry in subtropical Australia, and the sensitivity over the use of chemical insecticides by Government forestry organisations (the major growers), little research has been conducted on establishing integrated pest management strategies. In contrast, such strategies, including regular monitoring and chemical control, have been developed in temperate Australia. There are regional issues for cost-effective management of insect pests in relation to certification, including targeted use of slow-release systemic insecticides and future development of insect-active pheromones, kairomones, and synomones. There are many areas that require further research before forest companies in subtropical Australia will be able to sustain forest certification over the long term

Impact of the invasive rust Puccinia psidii (myrtle rust) on native Myrtaceae in natural ecosystems in Australia

The invasive rust Puccinia psidii (myrtle rust) was detected in Australia in 2010 and is now established along the east coast from southern New South Wales to far north Queensland. Prior to reaching Australia, severe damage from P. psidii was mainly restricted to exotic eucalypt plantations in South America, guava plantations in Brazil, allspice plantations in Jamaica, and exotic Myrtaceous tree species in the USA; the only previous record of widespread damage in native environments is of endangered Eugenia koolauensis in Hawai’i. Using two rainforest tree species as indicators of the impact of P. psidii, we report for the first time severe damage to endemic Myrtaceae in native forests in Australia, after only 4 years’ exposure to P. psidii. A 3-year disease exclusion trial in a natural stand of Rhodamnia rubescens unequivocally showed that repeated, severe infection leads to gradual crown loss and ultimately tree mortality; trees were killed in less than 4 years. Significant (p < 0.001) correlations were found between both incidence (r = 0.36) and severity (r = 0.38) of P. psidii and subsequent crown loss (crown transparency). This provided supporting evidence to conclude a causal association between P. psidii and crown loss and tree mortality in our field assessments of R. rubescens and Rhodomyrtus psidioides across their native range. Assessments revealed high levels of damage by P. psidii to immature leaves, shoots and tree crowns—averaging 76 % (R. rubescens) and 95 % (R. psidioides) crown transparency—as well as tree mortality. For R. psidioides, we saw exceptionally high levels of tree mortality, with over half the trees surveyed dead and 40 % of stands with greater than 50 % tree mortality, including two stands where all trees were dead. Tree mortality was less prevalent for R. rubescens, with only 12 % of trees surveyed dead and two sites with greater than 50 % mortality. Any alternative causal agents for this tree mortality have been discounted. The ecological implications of this are unclear, but our work clearly illustrates the potential for P. psidii to negatively affect Australia’s biodiversity

Mycosphaerella and Teratosphaeria diseases of Eucalyptus ; easily confused and with serious consequences

The Mycosphaerella complex accommodated thousands of taxa. Many of these species are economically important plant pathogens, notably on native and commercially propagated Eucalyptus species where they cause a wide range of disease symptoms including leaf spot, leaf blotch, shoot blight and stem cankers. Some of these diseases represent major impediments to sustainable Eucalyptus forestry in several countries where infection by Mycosphaerella and Teratosphaeria species can result in reduction of wood volume and in severe cases tree death. Extensive research has been conducted on these disease complexes over the past 40 years. The incorporation of DNA-based molecular techniques has made it possible to define and to better understand the differences between the Mycosphaerella and Teratosphaeria species occurring on Eucalyptus. These studies have also enabled refinement of anamorph and teleomprph generis concepts for the genera and thus facilitated the more accurate identification of species. They have also promoted a more lucid understanding of the biology, life cycles, population biology and epidemiology of the most important pathogens in the group.http://www.springerlink.com/content/1560-2745/nf201

Using dense Sentinel-2 time series to explore combined fire and drought impacts in eucalypt forests

Following one of the driest years on record, millions of hectares of forests in southeast Australia were burned in the 2019-20200 "Black Summer" wildfires. In addition to the areas burned, drought related canopy collapse, dieback and tree mortality was widely observed. In this paper, we present a method to map canopy damage due to drought and fire across a large area. Sentinel-2 satellite imagery was used in a monthly time series to highlight areas of forest where the Normalized Burn Ratio index was significantly below a pre-disturbance "stable" period. The stable period was defined as the 3 years prior to 2019 and the disturbance thresholds are based on bioregion specific standard deviations below pre-disturbance means. The novel methods enabled drought impacted forests to be identified, including those which were subsequently burned by wildfire. Across the 20 Mha of forests studied, 9.9 Mha (49%) fell below the disturbance threshold. Of that, 5.8 Mha was disturbed by fire and a further 4.1 Mha by drought outside of the fire extent. Within the fire extent, almost 0.9 Mha was identified as being significantly drought affected prior to being burned. An analysis of spectral recovery following substantial rainfall from February 2020 onward indicates that most of the areas impacted by both drought and fire have similar rates of recovery to those impacted only by fire. There are some areas, however, where the combined effects of the "double disturbance "appears to be hindering recovery. The methods presented here are easily transferrable and demonstrate an approach for monitoring forest disturbance at higher temporal and spatial scales than those typically used

Cryptic species, native populations and biological invasions by a eucalypt forest pathogen

Human-associated introduction of pathogens and consequent invasions is very evident in areas where no related organisms existed before. In areas where related but distinct populations or closely related cryptic species already exist, the invasion process is much harder to unravel. In this study, the population structure of the Eucalyptus leaf pathogen Teratosphaeria nubilosa was studied within its native range in Australia, including both commercial plantations and native forests. A collection of 521 isolates from across its distribution was characterized using eight microsatellite loci, resulting in 112 multilocus haplotypes (MLHs). Multivariate and Bayesian analyses of the population conducted in STRUCTURE revealed three genetically isolated groups (A, B and C), with no evidence for recombination or hybridization among groups, even when they co-occur in the same plantation. DNA sequence data of the ITS (n = 32), b-tubulin (n = 32) and 27 anonymous loci (n = 16) were consistent with microsatellite data in suggesting that T. nubilosa should be considered as a species complex. Patterns of genetic diversity provided evidence of biological invasions by the pathogen within Australia in the states of Western Australia and New South Wales and helped unravel the pattern of invasion beyond Australia into New Zealand, Brazil and Uruguay. No significant genetic differences in pathogen populations collected in native forests and commercial plantations were observed. This emphasizes the importance of sanitation in the acquisition of nursery stock for the establishment of commercial plantations.The National Research Foundation (NRF), members of the Tree Protection Co-operative Programme (TPCP), the THRIP initiative of the Department of Trade and Industry, the Department of Science and Technology (DST) ⁄ NRF Centre of Excellence in Tree Health Biotechnology (CTHB), South Africa, and the CRC for Forestry in Australia.http://www.wiley.com/bw/journal.asp?ref=0962-108

Teratosphaeria pseudonubilosa sp nov., a serious Eucalyptus leaf pathogen in the Teratosphaeria nubilosa species complex

Teratosphaeria nubilosa is one of the most important pathogens of Eucalyptus in commercial plantations. A recent study has shown that the fungus, hitherto treated under this name, represents a complex of two species. Teratosphaeria pseudonubilosa sp. nov. is, therefore, described as a closely related and morphologically similar, sister species to T. nubilosa. T. pseudonubilosa infects leaves of commercially propagated and native E. globulus trees in forests of Victoria and Tasmania (Australia), where it is native. It has also been introduced into Western Australia and New Zealand where it causes serious defoliation of susceptible trees. A revised geographical distribution of T. nubilosa sensu stricto and T. pseudonubilosa is provided to assist in the future management of the diseases that they cause.National Research Foundation (NRF), members of the Tree Protection Co-operative Programme (TPCP), the THRIP initiative of the Department of Trade and Industry and the Department of Science and Technology (DST)/NRF Centre of Excellence in Tree Health Biotechnology (CTHB), South Africa.http://link.springer.com/journal/13313hb201

A study of the species of Mycosphaerella on eucalypts in Australia and the impact of Mycosphaerella leaf diseases on Eucalyptus globulus Labill

© Dr. Angus J. CarnegieIn this study, the taxonomy of the species of Mycosphaerella that cause leaf diseases of eucalypts was reviewed, the effect of these diseases on E. globulus in plantations was quantified, and the use of silvicultural methods, tree selection and resistance breeding to reduce the impact of Mycosphaerella leaf diseases in commercial plantations was investigated. Over 30 species of Mycosphaerella cause leaf spots and defoliation on a wide range of eucalypt species (Eucalyptus and Corymbia), but the taxonomy of some of these is incomplete, and there is confusion in species identity between morphologically similar species. Therefore, herbarium specimens, fresh collections and previous records of Mycosphaerella species from eucalypts in Australia and elsewhere were examined. Widespread surveys of Mycosphaerella species of eucalypts in plantations and native forests were conducted in Western Australia, South Australia, Victoria, Tasmania and New South Wales. A new species of Mycosphaerella (M. vespa) was described from plantations, a previously described species (M. gregaria) was revised following further observations and investigations, further host and location records were reported, and the first record of M. suberosa outside Brazil (its place of description) was made. A detailed list of the species of Mycosphaerella in Australia was compiled, with descriptions, photographs, and illustrations of each species. A table of important taxonomic characteristics of Mycosphaerella species on eucalypts was compiled, and a taxonomic key developed to aid in identification of the species in Australia. (Part of the summary only

Post-Border Forest Biosecurity in Australia: Response to Recent Exotic Detections, Current Surveillance and Ongoing Needs

Assessing exotic pest response and eradication programs can identify factors that will lead to increased pest detection and provide information for prioritizing and enhancing future eradication attempts. We review the forest-related insect and pathogen detections and responses in Australia between 1996 and 2017. Thirty-four detections of new exotic forest species were made in this timeframe; seventeen each of insects and pathogens. Twenty-nine of the species are now established in mainland Australia and another in the Torres Strait. Four of the established species cause high impact, and three of these were subject to failed eradication programs. Two of the four established high-impact species were not previously recognised as threats; indeed, 85% of all new detections were not considered high-priority risks. Only one forest pest has been successfully eradicated, suggesting a lower success rate of Australian forest eradication programs than the world average. Most of these exotic pests and pathogens were not detected early enough to attempt eradication, or they were not deemed a significant enough pest to warrant an eradication attempt. Early detection is key to successful eradication. We discuss current surveillance programs in Australia and the methods (general, specific), locations (urban, regional, amenity, plantation, nursery, native forest), and surveillance type (public, industry, ad-hoc researcher, forest health surveillance, high-risk site surveillance, pest-specific trapping) that detections were made under. While there has been an increase in detections using specific surveillance since 2010, there remains a need for a structured national approach to forest biosecurity surveillance, preparedness, and responses