Welcome to the latest Weed Spotter newsletter.

In this issue we look at places that Weed Spotters can look for State prohibited weeds, a huge new water hyacinth infestation, volunteering to look for hawkweed at Falls Creek and we bust some more weed myths. Agriculture Victoria would like to hear what you think of the Weed Spotter newsletter. If you are interested, please complete a short survey here.

If you have any feedback on this edition or suggestions for future articles, please email: weed.spotters@agriculture.vic.gov.au.

✉️ Please remember that if you are moving to a new house or changing your employment, the contact details that Agriculture Victoria have recorded for you, including postal address and email address, may need updating. Please send an email to weed.spotters@agriculture.vic.gov.au to avoid missing the latest newsletter.

📅 The State prohibited weed wall calendar will be sent to all Weed Spotters who ‘opted in’ to receive it in December. If you would like to receive a copy and have not opted in in previous years, then please email weed.spotters@agriculture.vic.gov.au.

Weed Spotters assist the Victorian Government by looking out for and reporting State prohibited weeds, which either do not occur in Victoria, or are present in small numbers and can reasonably be expected to be eradicated. These are a group of high-risk invasive plants that are declared under the Victorian Invasive Plants Classifications under the Catchment and Land Protection Act 1994.

Agriculture Victoria is responsible for the eradication of State prohibited weeds. The Weed Spotters program is for those who work in an industry or who are part of a group where they are likely to spend time in places where State prohibited weeds could be found. To catch up on what you’ve missed, have a look at the Agriculture Victoria website to find past issues of this newsletter.

Now that winter is over and the weather is warning up, it is a good time to get out for a walk. Next time you are out walking, remember to look around at the streetscape or fence-lines as you never know what you might see poking through fences or popping up from gaps in pavements or drains. State prohibited weeds (SPWs) that are spotted along fence lines often result in the discovery of much bigger source infestations on the other side of the fence or somewhere nearby.

Many of the examples in this article were taken overseas in Japan, where the species featured (horsetails and Japanese knotweed) are native, not declared weeds. Others are examples from Victoria.

Spring and summer are the best times of year to get outside and look out for State prohibited weeds. You never know when you might come across one. Happy Weed Spotting!

Water hyacinth is usually found in the yards of unassuming gardeners, within artificial environments such as fish tanks, or plastic-lined or fibreglass ponds. These are usually quick and easy to treat due to their small size, easy access for hand removal and the low likelihood that seed will be able to germinate without a silty base.

For every seven backyard ponds found containing water hyacinth, Agriculture Victoria finds one waterway infestation. Waterways contain sediment at their base, where water hyacinth seed can remain viable for at least 30 years. There are significant consequences of finding new waterway infestations as the size and/or location of the infestation make hand removal infeasible and a large seedbank (protected in the soil base) sustains the infestation. These infestations usually need to be treated by contractors who use watercraft such as kayaks, large machinery, and trucks to successfully remove the plants. Not only is the treatment more difficult and costly compared to backyard ponds, but sites must be monitored for at least 30 years to ensure that any new plants are removed before they flower and deposit more seed into the water body. Waterway infestations can be connected to other water bodies, facilitating spread of the floating plants by water movement, threatening the areas downstream.

In the last five years (2020-2025), Agriculture Victoria found 8 new water hyacinth infestations in waterways. The age and size varied greatly as depicted in the below table.

Table 1. Infestation size and cover in ascending order.

Image above: The 3 largest water hyacinth infestations found by Agricuture Victoria between 2020-2025. Images taken from aerial footage. Water hyacinth coverage depicted is lower then at the time of discovery.

In August 2025, Agriculture Victoria received a report of a new infestation, the largest water hyaincth site to date – totalling close to 5000 square meters. The water body includes two connected dams, both heavily infested with mature water hyacinth plants. The infestation has been present for a handful of years, and has grown rapidly in the last twelve months, covering the majority of the dam. Upon realising how destructive and invasive the weed was, the landowners did some research and discovered what the plant was, and reported it to Agriculture Victoria.

Image below: The largest water hyacinth infestation discovered to date, totalling close to 5000 square meters. Water hyacinth coverage depicted is lower then at the time of discovery.

At the time of detection, water hyacinth covered roughly 70-80% of the dam. The water hyacinth plants were mostly brown and dying off after some frost damage, but there was clear evidence of previous flowering and seeding. The dam contains millions of seeds, just waiting for the next warm spring day to germinate.

Water hyacinth infestations with seedbanks, such as this example, are treated by physically removing all plants, and then by scraping away the top 10 cm of soil to eliminate seed. The removed material is then disposed of by deep burial. Depending on weather conditions and other factors, works are expected to take 8-12 weeks for a site this large.

More updates to come!

Volunteers have been a valuable part of the hawkweed eradication program around Falls Creek, contributing to yearly surveillance over large areas of the Bogong High Plains. Due to operational and budget constraints, the volunteer component of the surveillance program has been reduced in recent seasons however interest from Parks Victoria volunteers to return to week-long hawkweed surveillance volunteer events has remained high.

In response to requests, a new volunteer model has been developed for the Falls Creek Hawkweed Eradication Program, in consultation with past volunteers. The proposed model will give volunteers the opportunity to coordinate hawkweed surveillance volunteer events, with guidance from Parks Victoria. This will allow Parks Victoria staff to focus on other key priorities for the Hawkweed Eradication Program, while providing for the volunteer component to continue.

Under the new model, a small number of volunteer coordinators will be inducted and trained by Parks Victoria on the use of safe and best-practice methods of surveying and reporting hawkweed. Volunteer coordinators will be responsible for organising and delivering these volunteer events and are currently working with Falls Creek Alpine Resort Management to secure accommodation for the volunteers during the 2025-2026 summer months.

Parks Victoria will provide volunteers with maps of areas for survey, allocated through Agriculture Victoria’s surveillance planning. Allocated survey grids will largely be in open, grassy areas located in easily accessible terrain. Volunteers will be trained to record hawkweed sightings with a GPS tracker. These recordings will be submitted to Parks Victoria who will manage the site in the future. It will be fantastic to again have volunteers on board to contribute to the survey and eradication of hawkweed on the Bogong High Plains.

Weed Spotters can look for volunteering opportunities through Parkconnect or send enquiries to hawkweed@parks.vic.gov.au.

Image below: Volunteers walking a survey line at Falls Creek looking for hawkweed.

Plants that have a weedy nature often share common characteristics. They grow vigorously, can survive under harsh climatic conditions and have one or more means of spreading. One method that weedy plants utilise to spread is by producing numerous seeds that are hardy, germinate easily and move easily through either wind, water, animal movement or human movement. Another method that some weeds utilise to spread is to grow from plant parts, such as stems, leaves or roots and is known as vegetative reproduction. It can include:

Vegetative reproduction is a very effective method that some weeds, including some State prohibited weeds, utilise to spread and establish in an area. This is one of the reasons why it is so important to eradicate these species from Victoria.

Lagarosiphon (Lagarosiphon major) is a State prohibited weed that has been found in the past in New South Wales and Victoria, mainly as an ornamental plant in aquaria and ponds.

The species originated in southern Africa and has become a major weed in New Zealand and parts of Europe. It prefers the cooler waters of the temperate zone, such as Victoria. Lagarosiphon is an aggressive freshwater aquatic plant that chokes still and slow-moving water such as lakes and dams. It depletes oxygen levels in water, resulting in fish kills and prevents recreational activities like swimming, boating and fishing. It is easily spread between water bodies by stem and root fragments on boats and trailers. Once established it is difficult and costly to eradicate.

Lagarosiphon is an aquatic plant that grows submerged, either rooted to the floor of the water body or free floating.

Stems can grow up to 5m long. It tolerates a range of water conditions but grows best in sheltered, still or slow-moving water bodies.

Leaves are stiff, bright green to dark green 5mm to 20mm in length, arranged in alternate spirals along the length of the stem (not in grouped whorls around the stem like its look-alikes).

Flowers are very small (less than 3mm across), white to pink or purplish in colour and visible on the surface of the water from December to April.

All known infestations of lagarosiphon in Australia have been eradicated. This doesn’t mean that there couldn’t be a plants growing somewhere in an unknown location, therefore it is important for Weed Spotters to learn what lagarosiphon looks like just in case.

Did you know that Weed Spotter training is available to Weed Spotters at any time?

Recent trainees have said:

“The Weed Spotter training was really useful and well set out, I enjoyed completing it.”

“I thought the online training was really good. It didn’t take too long to complete, and the content was meaningful and provided a good introduction to the main issues for Weed Spotters to be aware of.” 

“Loved the course!”

“It was a pleasure and very enlightening.” 

“Thank you for providing access to the Weed Spotter training – I thought the course was terrific. It was clear, informative, and easy to follow.”

“I look forward to spruiking the online training to our local volunteer groups, it is very well set up.”

How to access the training:

• To access the training please go to eLearning section of the Agriculture Victoria website and create a log in for the site by clicking ‘sign up’.
• When creating a new account, make sure you select ‘I am a Weed Spotter’ in the ‘Why are you here?’ drop down menu.
• Once you have created an account, you can select Weed Spotter training.
• Make sure that you navigate right to the end of the training so that it triggers the completion notification.
• You will then be posted a set of State prohibited weed cards.
• Weed Spotters can also download an attendance certificate at the end of the training if they wish.

Image below: The online Weed Spotter training module.