Invasive plant ecology and management research

Integrated control of aquatic weeds

Project leader: Tobias Bickel

Flumioxazin and florpyroxyfen-benzyl effectively control a range of established and emerging aquatic weeds. They provide excellent control of cabomba and Amazon frogbit at low application rates and are promising tools to manage sagittaria, salvinia and other floating weeds.

Some of the aquatic weeds we focus on in this project are established Weeds of National Significance that are currently difficult to manage due to a lack of control options; others are emerging weeds. We will continue research carried out recently in collaboration with CSIRO. While CSIRO will focus on aquatic plant biological control, we will investigate herbicide control techniques, integrated with other aquatic weed control options.

Expanding herbicide techniques for controlling woody weeds

Project leader: Dannielle Brazier

In this project we will conduct field trials of herbicides applied to weeds in the dry tropical areas of northern Queensland. We have identified a variety of application techniques and herbicides but will investigate only a prioritised subset. We will tailor the herbicides and application techniques to each target weed based on morphology, depth of current control recommendations and past herbicide research.

The project aim is to minimise the amount and costs of herbicide applications while diversifying options and maximising the efficacy, safety and environmental outcomes of control operations. Trials are likely to include Argyreia nervosa, and possibly Ziziphus mauritiana, Tecoma stans and Parkinsonia aculeata. We will seek suggestions from local stakeholders.

A previous project (encapsulated herbicides) conducted 9 trials on 5 weeds with replicate blocks and capsule, liquid drill and fill, and basal bark treatments. We will continue 2 of these trials in this new project.

Research on weed seed dynamics

Project leader: Simon Brooks

In this project we gather information on the seed ecology of priority weeds across northern Queensland to find out how long weed control sites need treatment, providing there is no further seed input. Testing involves exhuming buried packets of seeds and has been completed on chinee apple, calotrope, Captain Cook tree, neem tree, mesquite, yellow bells, lantana, leucaena, parthenium, sicklepod and gamba grass. Testing continues for sagittaria, prickly acacia, tropical soda apple, harrisia cactus and African tulip tree. More species may be included in the project.

To provide further evidence of their seed longevity, we are studying seedling emergence of chinee apple, leucaena, prickly acacia, mesquite, elephant ear vine, neem tree and parkinsonia. We are also estimating seed longevity using controlled aging tests in the laboratory, and comparing this with seed longevity estimated from field burial.

We are planning additional experiments (such as salinity, water stress, temperature and depth responses) to identify weed seed germination requirements and emergence triggers.

Research supporting the national tropical weed eradication program

Project leader: Simon Brooks

In this project we support the National Four Tropical Weeds Eradication Program by researching weed ecology and control. We focus on:

• determining seed longevity
• investigating plant growth and age at reproductive maturity
• identifying effective herbicides.

Our staff and collaborators continue to gather data on melastome biology to refine survey frequencies and estimate detection probabilities. We also develop and report on indicators of progress towards eradication based on field data from control teams.

Chemical control of glory lily

Project leader: Katrina Hodgson-Kratky

Glory lily (Gloriosa superba) is a perennial climbing vine native to tropical Asia and Africa. While it is valued as an ornamental species, it has become a weed in sandy coastal areas of eastern Australia. It strongly competes with native species and forms dense monocultures that replace diverse coastal vegetation. These monocultures present significant risks to coastal landforms because they provide little resistance against wind and water erosion.

Glory lily does not form fibrous surface roots and dies back in the cooler months, leaving the ground bare for over half of the year. Its large, persistent tubers and fragile underground stems make glory lily difficult to control, and no effective mechanical or chemical control options are available. Our research will focus on identifying and optimising the use of herbicides for controlling glory lily.

Improved control strategies and methods for leucaena

Project leader: Katrina Hodgson-Kratky

Leucaena (Leucaena leucocephala), a small to medium-sized woody weed native to southern Mexico and Central America, was introduced to Australia as a forage crop for livestock production. While valued as forage, it has become a major environmental weed in tropical and subtropical Australia, particularly coastal Queensland, and has naturalised in over 125 countries. It is readily observed growing along road reserves and disturbed areas and can form dense infestations, making areas inaccessible and unusable.

The management of leucaena is problematic—there are limited cost-effective control options, particularly for large and dense infestations. A major obstacle to effective control is leucaena's long-lived seed bank, which results in heavy regrowth following above-ground control.

This is a collaborative project led by The University of Queensland. We will evaluate a range of control techniques and strategies for different life stages of leucaena in different environments.

Improving pest control activities through timely submission of permits

Project leader: Katrina Hodgson-Kratky

For many weed species and management situations, chemical control options are limited. This is because the cost of registering new use patterns on herbicide labels often outweighs the expected economic return for product registrants. To address this gap, minor use permits issued by the Australian Pesticides and Veterinary Medicines Authority (APVMA) allow for ‘off-label’ use of registered products, enabling chemical control for weeds and situations not covered by product labels. In this project we facilitate the development of chemical registration submissions, and review and evaluate herbicide permits and products used by state and local governments for the control of invasive plants.

There are currently 52 minor or emergency use permits issued to Biosecurity Queensland by the APVMA. For a further 7 permits that were issued to other states, Biosecurity Queensland has sought inclusion to allow use of the products for the control of declared and emerging weeds found in Queensland.

Integrated management of giant rat's tail grass

Project leader: Katrina Hodgson-Kratky

Sporobolus is a genus of about 200 grass species found in tropical and subtropical parts of the world, including Africa, temperate and tropical Asia, Australasia, North America and South America. In Australia, 19 species are endemic, and a further 8 species are naturalised weeds.

Giant rat’s tail grass and the other introduced weedy Sporobolus grasses are unpalatable, perennial, tussock-forming grasses of serious concern to the grazing industry across eastern Australia. This weed reduces the carrying capacity and productivity of more than 450,000 hectares of pastoral land in eastern Queensland, New South Wales and Victoria and is a high-risk fodder contaminant.

Our research will focus on optimising the use of herbicides and endemic and naturalised pathogens for control of giant rat’s tail grass.

Biological control and ecology of chinee apple

Project leader: Olusegun Osunkoya

Ziziphus mauritiana (Rhamnaceae), often called Indian ber or chinee apple, is a major pasture and environmental weed in northern Australia. Its impenetrable thickets hinder stock and affect pasture production. Current management options (mechanical and chemical) are expensive.

Though this weed has been present since 1880, we have only limited data on its distribution, its population biology, economic loss from the weed, and prospects for its biological control. Through this project we will:

• gain a better understanding of the weed's ecology and spread potential
• pursue future biological control to cost-effectively support its management.

Our research involves:

• developing models of likely spread of the weed
• investigating the economic and environmental impact of the weed on infested landscapes
• identifying potential biological control agents in its native range.

Impact and management of Navua sedge

Project leader: Olusegun Osunkoya

We have now quantified the economic cost of managing Navua sedge across northern Queensland on both grazing and sugarcane farms. We have also established research plots at numerous sites infested with the weed. Within these plots, we assess pasture diversity, crop yield, soil seed bank, chemistry and microbial communities at different weed densities. We also assess grazing and herbicide treatments.

Risk assessment for new and emerging invasive weeds

Project leader: Olusegun Osunkoya

There are limited funds available to assess and manage the numerous new and emerging invasive plants in Queensland. Because of this, we need to prioritise these weeds for management. They can be ranked in terms of current and future distribution, impact, and feasibility of management.

The most recent assessment and ranking of new and emerging invasive weeds in Queensland was completed in 2013, so an update is needed. Local government officers are often the best source of information for established and new weeds that have shifting distribution and abundance. Since 2021, local governments and other stakeholders have provided information on local spread and abundance of many emerging weeds. We are extracting other data, especially for impact, from grey literature (for example publications of CABI and GBIF). We are also investigating modelling of range shifts of emerging weeds in response to climate change.

Real-time drone-based weed identification for improved pasture management

Project leader: Olusegun Osunkoya

In this project we test the use of drones to collect weed imagery, which can then be autonomously identified using artificial intelligence. In a controlled environment, we have demonstrated this for the identification of parthenium. This result needs to be recorded in the field and tested for other weeds (such as chinee apple and Navua sedge). A CSIRO grant supports a doctorate student from Central Queensland University for aspects of the work.

We aim for live-stream real-time weed identification from drone imagery. We will address this technically challenging problem in sequential steps:

1. Identify the object and map the weed in the field using high-resolution drone images and improved deep-learning algorithms.
2. Live stream the high-resolution drone video to a ground base, where the weed would be recognised (and potentially controlled) using a field computer in real time.

Thatch grass ecology for better management options

Project leader: Olusegun Osunkoya

Thatch grass is an emerging weed species listed as a new priority invasive plant in many local government areas in Queensland. It has a broad distribution along Queensland’s east coast, extending from the southern border to the Torres Strait. Its potential distribution is extensive and highly stable, even in response to climate change.

Though currently thatch grass is mostly associated with roadsides, it poses a threat to environmental and production values, particularly of the tropical savanna. However, we have little information on its invasiveness, its biology, and how it responds to environmental triggers and management. Given the broad geographical distribution of thatch grass, we need to develop research partnerships with local governments and other stakeholders to complement desktop and laboratory studies.

Gamba grass ecology and management

Project leader: Melissa Setter

Gamba grass (Andropogon gayanus) is a serious weed of many parts of northern Queensland from Cape York to Mackay. It infests pastures, crops, utility corridors and creek banks, reducing biodiversity, cultural values, social amenity and agricultural productivity. It also increases fire risks, wildfire severity and inherent risks to human life.

The Biosecurity Act 2014 lists gamba grass as category 3 restricted biosecurity matter, and it is a declared weed in the Northern Territory and Western Australia. It is a Weed of National Significance and is in the Australian Government’s draft Threat Abatement Plan.

Although there has been some work on gamba grass ecology, knowledge gaps remain (for example about seedling emergence patterns, survival rates and reinfestation rates after control activities). Previous research suggests several pre-emergent herbicides warrant further investigation or field testing, including their use in combination with a proven knockdown.

We aim to improve management by investigating seed and seedling ecology as well as pre-emergent herbicide efficacy and restoration (such as reseeding).

Sicklepod ecology and control

Project leader: Melissa Setter

Sicklepod (Senna obtusifolia) is a serious weed of many parts of northern Queensland from Cape York to Mackay, and is found in many situations, such as pastures, crops, road and power corridors and creek banks. It degrades riparian zones and pasture systems, reducing biodiversity and agricultural production.

In this project we aim to improve management tools for sicklepod by investigating seed production and longevity as well as pre-emergent herbicide efficacy.

Giant rat's tail grass management manual

Project leader: Wayne Vogler

We are finalising an updated management manual for giant rat's tail grass.

Management of sticky florestina

Project leader: Wayne Vogler

Sticky florestina (Florestina tripteris) is an annual plant from semi-arid North America that was (anecdotally) introduced in central western Queensland in the 1960s and reported as a pest in the late 1980s. Local governments are reporting a current profusion of the weed along roadsides. There is considerable scope for further spread of the weed, as seeds are readily spread by livestock, wildlife and machinery, and along waterways.

In this project we are conducting research to improve control of and management outcomes for this invasive weed.

Strategic invasive grass control to reduce the risk of further invasion in northern Queensland

Project leader: Wayne Vogler

Gamba grass, grader grass and giant rat’s tail grass are serious invasive weeds in northern Australia, causing large-scale environmental damage and economic loss. In this project we will engage with a wide range of land managers (including local governments, Aboriginal communities, Torres Strait Islander communities, and conservation and agricultural land managers) to identify and control or eradicate strategic outlier infestations of these grass species on both private and publicly owned land. These outlier infestations are early invasion populations of these invasive grasses that, if not controlled, will become established and provide a continuing source of seed for further invasion.