Tackling Tutsan

Tutsan (Hypericum androsaemum) is invasive to New Zealand and Australia. Native to many countries throughout Europe and western parts of Asia, it is thought to have been introduced as a garden ornamental by acclimatisation societies in the 1800s due to its attractive yellow flower. Today, tutsan is a severe weed in several regions of New Zealand, most significantly affecting the Ruapehu District and Bay of Plenty region in the North Island. Over the last 20 years, tutsan has become an increasing problem in these regions; spreading throughout low fertility pastures and along roadsides. There is concern that tutsan has the potential to pose a significant conservation threat if it continues to spread at its current rate through scrub and native forest fringes.

Flowering tutsan plants growing in New Zealand (photo: Lizzie Rendell, 2011)

Flowering tutsan plants growing in New Zealand (photo: Lizzie Rendell, 2011)

Recent estimates indicate that around 150,000 ha of land in the Ruapehu district is affected by tutsan. Within the district, the annual cost of controlling the weed, and loss of farming profit amount to around $NZ1.2 million (£600,000), and loss of current land values is estimated at $NZ27 million (£13 million). Tutsan is a persistent weed for which there are no registered chemicals. Off-label herbicides are currently used in an attempt to limit its spread, but these are proving ineffective with stands typically reappearing several years later. The weed is unpalatable to stock and the topography of the region’s worst affected areas further limits the control methods possible.

Tutsan growing on sheep pasture in the Ruapheu District of the North Island, NZ; the copper colour arises from a reddening of the leaves as the plant matures (photo: Lizzie Rendell, 2011)

Tutsan growing on sheep pasture in the Ruapheu District of the North Island, NZ; the copper colour arises from a reddening of the leaves as the plant matures (photo: Lizzie Rendell, 2011)

In 2007 the Tutsan Action Group (TAG) was initiated, formed of local farmers, farm consultants, regional council Pest Plant Officers and representatives from the governmental Department of Conservation to tackle the growing problem. As well as carrying out their own work to raise awareness of tutsan throughout the region, TAG approached Landcare Research to ask for help and in 2009 a biological control programme was established through support from the Ministry for Primary Industries Sustainable Farming Fund.

To date the programme has consisted of an international effort between Landcare Research New Zealand, CABI Switzerland and more recently, CABI UK. Surveys have been carried out in both the invasive and native ranges of the plant to assess the extent of current populations and to identify potential biological control agents. In recent European surveys, a leaf beetle (Chrysolina abchasica) and a tortricid moth (Lathronympha strigana) were identified as having the potential to become biocontrol agents for tutsan and are currently being reared for host range testing by Landcare Research, under quarantine conditions in Lincoln, New Zealand.

The tutsan rust fungus, Melampsora hypericorum was also evident in surveys, both in the native range and in New Zealand. This pathogen has been known to provide control for tutsan populations in Victoria, Australia. In the early 1990s a biological control programme was initiated in Victoria since tutsan was affecting 67,000 ha in the Otaway Ranges. This programme was soon abandoned as surveys revealed that the rust fungus had self-introduced and was already controlling tutsan populations in this region; by 1993, surveys discovered only one live tutsan seedling. In recent times, tutsan is considered to be an increasing problem in Victoria, with the level of control provided by the rust fungus is currently unknown. Melampsora hypericorum is thought to be acting as an effective biological control agent in some parts of New Zealand, for example on some populations of the South Island, but remains ineffective in the regions worst affected. Molecular studies were conducted to establish where tutsan was originally introduced into New Zealand from, and revealed that several introductions are likely to have occurred. Plants in New Zealand’s North Island are likely to have been introduced from Wales or Ireland, and plants in the South Island from the UK, France or Spain. Genetic analysis of both plant and fungal material has also revealed that different genotypes of both tutsan and the rust occur in different regions across New Zealand. The range of genetic variation gives rise to a complex plant-fungal relationship which is playing a major role in the susceptibility of tutsan populations to M. hypericorum.

Current work at CABI, is focusing on assessing the virulence of 14 different strains of M. hypericorum collected from Europe and Georgia towards tutsan plants from New Zealand. Studies aim to find a strain that is more virulent towards the most problematic plant populations of tutsan that are not currently controlled by the rust. To date, the virulence of two strains of M. hypericorum have been assessed. A strain from Georgia failed to infect tutsan populations that are considered most problematic from the North Island. A strain collected from Pembrokeshire, Wales has produced a reliable infection on tutsan plants collected from four different New Zealand populations, including two populations which were ranked as having a high severity in 2011 surveys. Assessment of the remaining 12 rust isolates is currently ongoing.

Since little is currently known about M. hypericorum, trials are also being carried out to assess the infection parameters of the rust fungus. Free water availability and temperature are being investigated to determine the range and peak of these parameters for the species.

Tutsan in inoculation trials at CABI, Egham infected with the tutsan rust fungus, Melampsora hypericorum (photo: Lizzie Rendell, 2014)

Tutsan in inoculation trials at CABI, Egham infected with the tutsan rust fungus, Melampsora hypericorum (photo: Lizzie Rendell, 2014)

Lizzie Rendell

 Scientific Support

Invasive myrtle rust impacts discussed at international forestry congress

CABI has recently published a comprehensive review and update of its ISC datasheet on the globally important pathogen Puccinia psidii, commonly known as myrtle rust or guava rust. This problematic fungus is of worldwide importance and is capable of infecting a wide range of hosts. To date it has over 440 host species; affecting many plants in the Myrtaceae family, including threatened and endangered species (see IUCN Red List of Threatened Species). Severe impacts have been recorded in amenity plantings, commercial plantations and the native environment.

Once established in a new country myrtle rust can spread quickly and this has been the case in many countries including Jamaica, Hawaii, Australia and New Caledonia. Its successful global and local dispersal through urediniospores and human-aided movement of diseased plants, combined with its massive host range make myrtle rust an effective and devastating invasive. It was first identified as an invasive pathogen in the 1930s when it caused extensive damage to allspice (Pimenta dioica) plantations in Jamaica.

Puccinia psidii on Melaleuca quinquenervia in Australia

Effects of the invasive myrtle rust (Puccinia psidii) on the paperbark tree (Melaleuca quinquenervia) in Australia (July, 2011)

Discussions of myrtle rust impacts and a variety of other forestry related issues are currently underway at the 24th IUFRO World Congress, which is being held from the 5th-11th October 2014 in Salt Lake City, USA.

IUFRO is the International Union of Forest Research Organizations – the world’s forest network. The organisation promotes global cooperation on forest-related research and is composed of over 15,000 scientists from 650 member organizations in more than 100 countries.

The Congress is the largest forest research conference worldwide and is held every 5 years. It brings together delegates from varying forestry backgrounds and this year over 3500 scientists, researchers, graduates, decision makers, policy makers and land managers are expected to attend the event, which is focused on “Sustaining Forests, Sustaining People: the Role of Research”. Over the course of the week a number of plenary, sub-plenary, technical and poster sessions will cover themes, such as:

Under the theme of Forest Health in a Changing World, a session dedicated to emerging invasive forest pathogens will see notable speakers discuss the impacts of myrtle rust in the southern hemisphere, including its effects on diversity in both Australia and Hawaii (see p103-104 of the Scientific Program). This session will also focus on ash dieback and the invasive pathogen Hymenoscyphus pseudoalbidus, which causes the disease in ash trees. This pathogen has recently been causing severe impacts across Europe.

For full details of the distributions, impacts, descriptions (and much more!) of both ash dieback and myrtle rust you can access the fully updated and peer reviewed datasheets on CABI’s open access Invasive Species Compendium.

To keep up to date with all the latest news from the 24th IUFRO World Congress, visit the blog here.

Getting swamped: Australian swamp stonecrop (Crassula helmsii) in the UK

In January this year, large parts of southern Australia were ablaze with fierce bush fires, while most of the UK was covered in snow. Half a world away from each other, and at one point nearly 40ºC apart, there aren’t too many similarities to be drawn between the two locations. And yet, there is a water weed, Crassula helmsii, that survives happily in both extremes – and in the UK, where it has been introduced, this adaptability is proving extremely problematic.

 Crassula helmsii, also known as Australian swamp stonecrop or New Zealand pygmyweed, is a small semi-aquatic plant in the Crassulaceae family. As its common name implies, this low-growing succulent originates from the antipodes, but was introduced to Britain from Tasmania almost 100 years ago. Initially sold by garden and aquatic centres as an oxygenating plant, by the 1950s it had established in the wild, and from there it has spread to numerous ponds, lakes and waterways throughout the UK.

A mat of Crassula helmsii in flower

A mat of Crassula helmsii in flower

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Rhododendron ponticum – much more than just an invasive weed!

Rhododendron ponticum, native to southern Europe and south west Asia was introduced into the UK in the 18th Century. Since then, this plant has grown uncontrollably and is now a common sight throughout western parts of the British Isles in areas such as Cornwall, Wales and parts of Scotland and Ireland. Despite producing an attractive flower in the spring, Rhododendron can have damaging effects on the local environment. By growing rapidly this plant outcompetes native flora, decreases biodiversity and furthermore constitutes a sporulating host for the two devastating pathogens Phytophthora ramorum and Phytophthora kernoviae, meaning these pathogens not only infect but also reproduce on R. ponticum.

Rhododenron ponticum

A stand of invasive Rhododendron ponticum in Windsor Great Park (Picture copyright CABI).

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Biological control of Mikania micrantha: Have we found the silver bullet?

Mikania micrantha (mile-a-minute weed or South American Climber) is a major invasive alien weed in many of the tropical moist forest regions of Asia.  This neotropical vine is able to smother plants in agricultural ecosystems, agroforestry and native habitats.  Conventional control methods of manual removal (slashing) or herbicide application, are expensive, ineffective, not sustainable, and can be environmentally damaging.  Classical biological control was considered the best option to manage this weed, and CABI was funded by DIFID (UK- Department for International Development) to implement this strategy in India.  The research culminated in the release of a coevolved, host specific, rust pathogen (Puccinia spegazzinii), from the South America native range of the weed, into Kerala and Assam.  This rust pathogen infects all aerial parts of the plant (leaf, petiole and stem), leading to cankering and whole plant death (see image below).

Puccinia spegazzinii Nov 10

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Our rivers – corridors for colonisation

Our river systems are undoubtedly one of the most diverse habitats found within the British Isles.  They provide us with numerous benefits including areas for relaxation and recreation, they harbour high levels of biological diversity, act as natural flood management, provide water for consumption and irrigation, and act as corridors for the movement of nutrients and species in an otherwise fragmented landscape.  However, our river systems are highly vulnerable habitats.  Seasonal variations in hydrological processes render riparian habitats prone to high levels of disturbance which aid the invasion and colonisation of invasive plant species.

RT.13.5.06.Devon.site.5 (5) Himalayan balsam monoculture on the banks of the River Torridge, North Devon, UK (CABI)

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Are we fuelling future invasions?

The world is fast running out of fossil fuels and with an energy crisis looming, intensive research is being carried out across the globe to find renewable alternatives. Top of the list are biofuels; fuels derived from biomass. Will the plants grown to provide this biomass behave themselves when introduced to sites outside their native range, or escape cultivation and invade the regions to which they are introduced?

Arundo donaxGiant reed, Arundo donax (credited to Steve Loya and sourced from the Lompoc Record)

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