In recent years STEP has become increasingly concerned about the proliferation of Spanish Moss on our local trees and its potential impact on our bushland. So in December 2023 we asked members to send us details of any Spanish Moss they have seen growing on trees. We then undertook a preliminary survey from Cowan to Marrickville to determine what tree species it grew on. What we found horrified us.

Trees most affected by Spanish Moss

Turpentine (Syncarpia glomulifera) is the most severely affected of all the 76+ species of plants we recorded Spanish Moss growing in. Infestations can be so dense and widespread that whole trees are festooned. Spanish Moss flourishes over Turpentine leaves and worryingly it appears it may be able to kill mature trees by preventing photosynthesis. Locally, Turpentines are important trees in the critically endangered Sydney Turpentine-Ironbark Forest and Blue Gum High Forest as well as in sandstone gullies. Their loss would be disastrous. Worse still, Turpentines are common trees in fertile forests from the Queensland border to near Ulladulla and our evidence suggests that Spanish Moss could damage Turpentines all the way along the coast and ranges. We are not sure why it flourishes so well on Turpentines but we are prepared to speculate that leachates from the fungi on the leaves encourages its growth.

More bad news for our rainforests and wet sclerophyll forests is that Lilly Pilly (Acmena smithii), Cheese Tree (Glochidion ferdinandi) and Brush Box (Lophostemon confertus), all major components of our east coast rainforest, can be severely affected while Coachwood (Ceratopetalum apetalum) and Blueberry Ash (Elaeocarpus reticulatus) can certainly carry Spanish Moss. In addition to causing damaged or dead trees, threats to ecosystems include subtle effects such as altered water and nutrient cycles, changed predator/prey interactions, habitat alteration, moderation of the microclimate and transformed fire regimes. Changes such as these are some of the greatest conservation threats to biodiversity in Australia.

The good news is that eucalypts, bloodwoods and Sydney Red Gum (Angophora costata) seem to be resistant to it. We only repeatedly recorded Spanish Moss flourishing on Red Mahogany (Eucalyptus resinifera).

How it spreads

Spanish Moss is obviously well loved by many gardeners, but STEP is not sure that gardeners realise how rapidly it can grow and spread. What today may be a gentle grey ornamental addition to the garden may overwhelm it with dense heavy screens of moss up to 3 m long over a few years. Overseas, festoons over 8 m long have been recorded. The artistic addition to the garden today may be a nightmare tomorrow. You may think that your garden is safely distant from bushland, but we recorded a jump of 70 m from the nearest Spanish Moss when it was used by Noisy Miners in their nest. All gardens must therefore be viewed as sources of bushland infestations.

Spanish Moss can spread in several ways. Asexual spread can occur with the tip of plants blowing in the wind and becoming entangled in other parts of the plant or a different plant. Birds are obvious dispersers as they move Spanish Moss for nest construction.

Physical control will be difficult as it is an air plant and has no contact with the ground. In most cases we found it out of reach, sometimes 15 m up a tree. We haven’t trialled chemical control methods used in the USA, but they are listed in our report.

Recommendations

• Gardeners remove all moss they can reach, put it in their green bin and prevent spread.
• Local authorities such as local councils and NPWS remove it from all public places, including trees on nature strips.
• Add Spanish Moss to the next iteration of the Greater Sydney Regional Strategic Weed Management Plan and all other relevant regional strategic weed management plans.
• Classify Spanish Moss at a level that enables its eradication and containment, prohibition of sale and distribution, e.g. as a regional priority weed.
• Undertake research into why Turpentines are a favoured host and the ecological effects of Spanish Moss on bushland.
• Undertake research into control methods.

Swaying veils of grey in dead or dying trees and simplified bushland is not something to look forward to. Let’s not risk it.

Read our full report or check out our website.

Spanish moss

Control

We found no mention of an obvious biological control. Overseas examples of control include hand removal and spraying with potassium or sodium bicarbonate or copper sulphate.

Hand removal is often recommended as the best way to control Spanish moss but in our survey only approximately 12% was within easy reach. Rakes, ladders, professional tree climbers, industrial vacuum cleaners and specialised equipment such as spider lifts and elevated platforms would be needed in many infestations.

Spanish moss has been underestimated as a threat. We recommend that it be added to the next iteration of the Greater Sydney Regional Strategic Weed Management Plan, not be distributed or sold, and be added as a separate threat to Sydney Turpentine-Ironbark Forest in the Sydney Basin Bioregion.

Widespread education about its potentially disastrous impact on some bushland communities and urban forests is urgently needed through gardeners, horticulturalists, bushland managers and professional organisations.

Also, research is urgently needed into the ecology of Spanish moss, why it flourishes on some trees and not others, the ecological consequences of its presence as well as control methods suitable to Australian ecosystems and conditions.

Spanish moss

Recommendations

Individuals

Remove all reachable festoons in your garden and put them into the green bin.

Control all festoons in garden trees by other means, e.g. spraying when safe effective methods have been established.

Do not give Spanish moss to friends, neighbours, passers-by and the local community.

Join campaigns to alert the local community and authorities to the threat posed by Spanish moss to bushland and gardens.

Authorities

Control authorities, e.g. state government, local councils, local land services and National Parks and Wildlife Service to urgently remove and control Spanish moss.

Educate the community about the threat posed by Spanish moss to bushland.

The Threatened Species Scientific Committee needs to add Spanish moss as a specific threat to the Critically Endangered Sydney Turpentine-Ironbark Forest.

Regulatory

Spanish moss must be added to:

• the next iteration of the Greater Sydney Regional Strategic Weed Management Plan and all other relevant regional strategic weed management plans
• these plans at a classification level that enables its eradication and containment, prohibition of sale and distribution, e.g. as a regional priority weed

Research

Immediate research is needed into:

• why Spanish moss flourishes on Turpentine, Brush Box and other rainforest species but not on most eucalypts
• the ecological consequences of infestation on individual trees and native plant communities
• the rate of growth and variation of growth with weather
• safe effective control options in Australian conditions
• fire ecology

Education

Education about the threat posed by Spanish moss to bushland through:

• TAFE NSW and private vocational providers – Spanish moss must be included on weed lists for horticultural, landscape, conservation and ecosystem management courses
• community groups – conservation groups (many are members of the Nature Conservation Council), gardening clubs (many are members of Gardening Clubs of Australia), Landcare, Greening Australia
• professional organisations – Australian Association of Bush Regenerators, The Society for Ecological Restoration Australasia, Ecological Society of Australia, Australian Institute of Horticulture
• gardening media – TV gardening and home improvement programs such as Gardening Australia, radio programs, magazines such as ABC Gardening Australia Magazine, Landscape Architecture Australia, Australian House & Garden
• social media – Facebook groups such as NSW Introduced Plant Identification and Bush Revegetation and Regeneration

Spanish moss

Findings

Spanish moss can grow almost anywhere, but during our survey it was obvious it flourished on some tree species and not others. Our observations indicate that the leachate from the host, or epiphytic species such as lichens and fungi, may be a determining factor for Spanish moss success. Spanish moss was recorded on trees from 32 plant families and 65% of records were from the Myrtaceae (Myrtle) family where turpentine and brush box dominated recordings. Of all the eucalyptus in the northern suburbs only one, red mahogany, was recorded repeatedly carrying substantial amounts of Spanish moss.

Festoons commonly occurred in the middle layer of the support plants (60%) and almost 90% were out of easy reach. Branches were the most common support (56%) followed by leaves, but only 12 host species (26%) were involved, primarily turpentines. Festoons were mostly 0.5 to 2 m long but some extended over 3 m. Sparse infestations were the norm (48%) but most individual festoons were dense.

Dispersal rate appears to have been slow with people and animals the main dispersal agents over long distances, but many observations indicate that the spread, density and size of festoons is increasing exponentially. It is no longer a sleeper weed.

Tradescantia fluminensis, commonly known as wandering trad is one of the worst weeds in Sydney’s bushland and home gardens. This highly invasive weed rapidly takes over the ground layer in gullies and temporary watercourses, forming a thick blanket of leaves that excludes light and warmth. Trad aggressively smothers low plants and seedlings and cools the soil, preventing native plant germination and regeneration.

This plant spreads vegetatively, no seed is produced. Garden refuse dumped in bushland is a common form of spread. Stem fragments and roots readily wash down waterways or spread in mud from vehicles. Trying to remove trad is a very time-consuming process. Repeated follow up is required because a tiny stem or leaf left behind can regrow.

But now there is hope of a solution, a leaf-smut fungus called Kordyana brasiliensis. This agent was discovered on wandering trad during surveys in Brazil performed by researchers at the Universidade Federal de Viçosa. This exploratory research was part of the biocontrol program for this weed in New Zealand, led by Landcare Research.

After years of testing in Brazil, in New Zealand and in the CSIRO containment facility in Australia, researchers applied for approval to release the leaf smut fungus. They were granted approval by the Department of Agriculture and Water Resources in December 2018.

Researchers first released the leaf smut fungus at ‘nursery sites’ in the Dandenong Ranges during the cooler months of 2019. Nursery sites are areas where our staff will monitor the progress of the biocontrol agent to ensure it can survive and spread in the local area and is having a damaging effect on the wandering trad.

A new project from July 2020 to June 2023, co-funded by CSIRO and the NSW government through its Environmental Trust, is facilitating stakeholders’ releases of the fungus across the range of wandering trad in NSW. The project will also monitor the impact of the fungus on the weed and flow-on indirect impact on other vegetation at several sites during that period.

Ku-ring-gai Council is participating in the project and has released infected trad plants in several sites. It has been spreading rapidly in some sites such as the Gordon Flying Fox Reserve. The very damp conditions experienced over the past few months may be a factor. In other sites the spread has been fairly slow.

How it works

The leaf smut fungus (K. brasiliensis) spreads through spores, and it needs wandering trad leaves to survive. This pathogen enters wandering trad through the leave’s air holes (stomata), and slowly uses the weed’s energy for its own fungal growth. After two to three weeks, the leaves begin to develop yellow spots, caused by a lack of chlorophyll. Eventually the fungal infection is so severe that the wandering trad leaves die. The sick plant becomes less competitive against neighbouring native plants, giving them an advantage, and the opportunity to grow.

Don't worry, it's not another cane toad. It has been carefully tested by the CSIRO and only infects trad and not its close native relative Commelina which has blue flowers. The fungus needs the leaves of the wandering trad to survive – if there is no wandering trad to infect, the fungus dies.

Benefits of biocontrol agents

Biological control is the practice of managing a weed by deliberately using one or more of its natural enemies (biocontrol agents) to suppress it.

Specialised fungi, like the leaf smut, have specific genes that enable them to successfully infect and cause disease only on single or a narrow range of plant species. Testing involved looking at plants that are related to wandering trad including native plants to make sure the fungus will only infect the weed.

CSIRO field biologist Dr Ben Gooden, who is coordinating the rollout of the biocontrol program across Australia, said highly targeted and tested biocontrol agents like the fungus were a more environmentally sustainable option than other available tools. Scientifically tested biocontrol agents like this fungus provide a longer term, environmentally sustainable way of controlling weeds like wandering trad, without harming Australian plants or animals.

Thanks to the Facebook page of the Pittwater Natural Heritage Association and CSIROscope for some of this information.

With the recent introduction of the Biosecurity Act, there is now more emphasis to think about our action in terms of weed spread and dispersal. The act specifically focuses on the shared liability relating to containment and control of weeds.

There is a significant and unresolved conflict between the retention of trees of species that are invasive and ecologically-damaging but are also recognised for their cultural, historic or aesthetic significance.

Camphor Laurel is one such species. They were planted extensively for amenity or cultural reasons but the species readily invades natural areas, impacting on biodiversity and ecosystem functions. Individual trees can generate copious progeny annually through seed production and dispersal.

Killing such trees will certainly stop seed set but this may result in community angst. There are instances where the removal of such trees is curbed by community or historic values. Protestors may only have their thoughts on a few issues, such as shade or the loss of very old picturesque trees, however we must consider that the seed from some of these invasive species may be transported long distances via birds and deposited in other areas.

Is it possible to preserve these trees whilst preventing them from producing seed?

Chemicals can be used to Modify Growth

We are all too familiar with herbicides and their primary role to kill weeds. However, there are many herbicides that have been used to modify the growth of plants without the aim of death. Other active ingredients (non-herbicides) have also been identified to alter plants growth for a desired outcome.

New Project

A federally funded project commenced in July 2017, courtesy of the Department of Agriculture and Water Resources and the lead agency MidCoast Council and other collaborating agencies. The primary aim was to undertake some research in the following two years to scope a handful of chemicals to de-flower or prevent fruit from developing on African Olives and Camphor Laurels. There is potential to use this technique, if successful, on other species. However, as there is limited project time it was decided to stay focused on these species.

African Olive

African Olive is a garden escape plant and has become a serious weed in bushland. It can further spread to and heavily impact upon agricultural land. More than 4,000 hectares of dense African Olive infestation has been identified across the western Sydney region alone. African Olive was listed as a key threatening process to biodiversity by the NSW Scientific Committee in 2010.

It is estimated that African Olive is having a negative impact on at least 25 endangered ecological communities as well as 13 threatened flora and 4 threatened fauna species in NSW. African Olive has further been listed in the Global Invasive Species Database. African Olive out-competes established native vegetation, casting dense shade which prevents the regeneration of native plants. Infestations can alter the floristic structure and habitat value of remnant bushland areas.

Camphor Laurel

Camphor Laurel is considered a threatening weed under similar listings to African Olive. They have the ability to adapt to the disturbed environment, have prolific seed production and a rapid growth rate as well as a lack of serious predators or diseases, they also possess many specific attributes which enhance its weed status.

Camphor Laurels are ecosystem changers. They have a tendency to form single species communities and exclude most other tree species, including desirable native vegetation. They have a very dense, shallow root system which, when accompanied by the shading provided by the canopy, suppresses the regeneration of native seedlings. They have the ability to replace and suppress native vegetation and have an allelopathic effect on other species.

Interim Results from Year 1

The list of potential chemical candidates for testing was rather lengthy and after an extensive literature review the list was trimmed down to three chemicals for Camphor Laurels and two for African Olives. Growth habit of the weed plays a large role into determining the type of treatment selected and how it is applied. A species like African Olive is often multi-stemmed and would be impractical for stem injecting whereas the single stemmed Camphor Laurel trees are ideal for a range of chemical deliver systems.

A long dry period of weather from winter to spring played havoc on the flowering times and synchronicity of Camphor Laurels and African Olives. Fortunately significant rains fell in early October to rejuvenate the weeds, however flowering was still not ideal. Timing of treatments was closely linked to flowering, namely near early-mid flower bud opening stage.

Assessment of treatment impacts on flowering or fruiting capacity of the weeds was undertaken in March and May 2018, but careful consideration was made to foliage changes. An ideal treatment is one that suffers no foliar damage while completely aborting reproductive issue.

The interim results from the African Olive experiments suggest this species is rather difficult to selectively control flowering/fruiting without severely affecting foliage.

The best compromise appeared to be treatment A with two times concentration that reduced fruit setting by 90% with a foliage damage score of 3 out of 10 which equates to some very noticeable symptoms from which the plant will take some time to recover. Four times concentration reduced fruit setting by 98% but with much more severe foliage damage. There is scope to apply various rates around this two times rate in the second year of the project, to better fine tune treatment outcomes.

It appears treatment A (same treatment for African Olives) was the most suitable for temporarily sterilising Camphor Laurels. It subtly made the foliage paler whilst significantly reducing reproductive capacity. Treatment B achieved very little. Treatment C will be tested in year 2 at much lower rates due to excessive foliage damage in year 1.

Concluding Comments

The second and last year of testing will be focused on getting consistency and robustness of the likely treatments that may be considered for registration or permits. The key to success is developing a treatment that can be easily and evenly applied that doesn’t leave obvious scarring of bark while achieving near perfect seed set control and barely noticeable effects on foliage. Timing of treatments could be investigated in subsequent projects, however there is only enough time to investigate rate responses of treatment A.

Fingers crossed for a better season than 2017-18.

This is a shortened version of an article in the Autumn 2018 edition of A Good Weed, the newsletter from the NSW Weed Society. Here’s hoping this idea can be extended to many more weed species, in particular privet.