Welcome to the latest Weed Spotter newsletter.

In this issue we spot the alligator weed amongst the look-alikes, learn about some surprising online detections, a reminder to look out for parthenium weed and an update on one of Victoria’s largest ever water hyacinth infestations.

We hope you enjoy reading this issue of the Weed Spotter newsletter.

If you have any feedback on this edition or suggestions for future articles, please email us.

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.

In March 2026, a new alligator weed infestation was found at the Perry Road Wetland in Dandenong South. The plants were spotted by contractors working on controlling the species on behalf of Agriculture Victoria in the adjacent Dandenong Creek.

The colouring and habit of the plant growth looked suspiciously like alligator weed from a distance, so the contractors took a closer look.

The find isn’t too surprising, considering alligator weed is present in the creek; however, it does raise questions as to how it got there. Agriculture Victoria believe the creek has not flooded over the levy bank, which could cause spread, so maybe animals or humans are to blame?!

Image above: An aerial image of the new alligator weed site at Perry Road wetland. The alligator weed was mainly found in the large central pond along the edges

The infestation is estimated at 330sqm of plant cover over an area of 1,150sqm, mostly around the edges of the wetland in the large middle pond. Water enters from the nearby industrial area and exits into the Mordialloc Creek through the western pond.

These upstream and downstream areas were checked and fortunately no further plants were found.

This site provides a great opportunity to improve Weed Spotter’s alligator weed identification skills, as there are lookalikes present. The alligator weed in the photo below is amongst the lookalikes persicaria and lesser joyweed (a native).

The flowers help to distinguish between species, with the pink of the persicaria and the flowers in the nodes of lesser joyweed, while alligator weed has white flowers on stalks. The alligator weed in this photo isn’t flowering; can you spot the alligator weed?

Image above: Spot the difference - can you spot the alligator weed in this photo?

It’s also a great site to observe the different growth habits of alligator weed.

The photos below show how the species can creep along the ground on green/pink stems or grow upright with larger leaves.

You can find the solution to the spot the difference at the bottom of this newsletter. 

In February, Agriculture Victoria’s Leading Biosecurity Officer - Detection Bec Schwinghammer was undertaking daily surveillance of online trade platforms and spotted an unusual plant in a post on Facebook Marketplace.

The post was titled ‘Various water plants’, which is the kind of general term that Bec regularly detects with the trade of aquatic State prohibited weeds salvinia and water hyacinth. This time the search detected the State prohibited weed horsetail (Equisetum sp.) which was advertised for sale as ‘rough horsetail’ amongst other legal water plants.

Horsetails are present in Victoria in low numbers, with Agriculture Victoria currently managing just 11 sites, including the site found in February.

When a State prohibited weed is detected for sale online, Biosecurity Officers swing into action. In this case, an eagle-eyed Weed Spotter also noticed the post and made a report by completing the online reporting form on the Agriculture Victoria website.

Biosecurity Officers visited the location and found approximately 50 horsetails stems present across a tub, a pot and a wheelbarrow, which had been removed from the backyard pond in preparation for sale.

The landowner was very cooperative and let Biosecurity Officers know of another infestation located at a second property, which the Officers subsequently removed. Unfortunately, the source of the plants remains a mystery as the owner could not remember where they came from.

This highlights the need for everyone to keep an eye out for horsetails, as there could be more out there.

Image above: The post selling horsetails spotted on Facebook Marketplace by Agriculture Victoria

The seller had included a clear description of the horsetails in their post, including that the species is a ‘low-maintenance plant that spreads easily’, but was unaware of its status as a State prohibited weed or that it is illegal to sell in Victoria.

If the seller had acted on their suspicion of the weedy nature of horsetails, researched the plant before advertising it for sale, and self-reported to Agriculture Victoria, the risk of spreading the weed would have been reduced.

The number of farmers across Victoria utilising donated fodder from interstate has increased in recent months, due to drought and bushfires. Seeds in fodder is a known pathway for weeds to spread, and Weed Spotters are reminded to watch for the State prohibited weed parthenium weed (Parthenium hysterophorus) in areas where imported fodder is used.

Parthenium weed is one of the world’s most aggressive weeds and a continuing threat to Victoria. It isn’t currently found in Victoria, but is present in New South Wales and Queensland, so the potential for it to invade Victoria is real.

Online trade detections of water hyacinth plants have continued during 2026 with 8 discovered in Victoria from January to May. All detections were picked up on Facebook Marketplace under the terms:

• yellow water lilies
• water lettuce
• water plants for ponds
• home grown water plants
• pond plants, and
• water hyacinth.

In a couple of cases the water hyacinth plants were spotted in the background of the photos posted by the seller. Water hyacinth has a very distinctive bright green colouring to the leaves and stems which can stand out against the green colouring of other water plants. 

It's worthwhile for Weed Spotters to keep a close eye on plant sale posts and look for this distinctive bright green colouring particularly if the seller looks to have several different plant species.

Water hyacinth (Eichhornia crassipes) is a highly invasive floating aquatic plant that spreads rapidly and can completely smother water bodies if left unmanaged.

While sometimes unknowingly introduced into garden ponds due to its attractive flowers, the plant poses a serious environmental and agricultural risk when it escapes into natural areas.

Gippsland infestation
Keen Weed Spotters may recall an article in Issue 44 of the Weed Spotter Newsletter which highlighted 9 water hyacinth waterway infestations detected by Agriculture Victoria between 2020 and 2025.

One of these infestations, detected in Gippsland in August 2025, was the largest recorded to date.

This new infestation spans three connected dams with a combined surface area of approximately 5,000 square metres and at the time of detection, the plants covered around 75% of the water surface.

During an initial assessment many plants were observed to be brown and dying back following frost damage but had clear evidence of previous flowering and seed production.

Further discussion with the landholder revealed that the infestation had been present for several years and had expanded rapidly in the previous year.

Greater risks
This new infestation presents a threat to the broader environment due to its proximity to waterways. If plants or seed escape the dams into the adjacent waterway, the weed could spread throughout the greater catchment.

This places high value aquatic environments, including the Gippsland Lakes system, at risk of water hyacinth invasion.

The speed at which the infestation expanded at the site highlights this concern. Since our spring update, the infestation continued to spread until it completely covered the water surface of all three dams.

To treat the infestation, all water hyacinth material was removed and safely disposed of, to prevent further spread and re-establishment.

Treatment and ongoing monitoring
Following detailed planning and coordination with landowners and relevant authorities, treatment works commenced at the site in April 2026, and included:

• water hyacinth plant material removed from the dams and buried on-site.
• the main dam provides a decorative feature at the property, so efforts were made to maintain this by positioning excavators so that they did not trample plantings.
• delimitation surveys completed across the property and in the adjacent waterways to determine whether the infestation had spread. Luckily no additional water hyacinth was found.

Preventing future spread and how you can help
Agriculture Victoria will be undertaking a range of engagement initiatives over the coming months to raise awareness of water hyacinth in the local area.

These initiatives will include media releases, the distribution of posters and brochures, and collaboration with local agencies and groups to promote our message.

While Agriculture Victoria is actively working to increase awareness of water hyacinth in the area, early detection and vigilance by the community remain vital to preventing further spread.

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

Image above: Spot the difference solution - the circle at the top contains the alligator weed, the bottom left contains the persicaria, and the bottom right contains the lesser joyweed.