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Top- terrestrial shoot, middle- aquatic growth, bottom- herbicide control allows grasses to regrow

Alligator Weed

A national Alligator Weed control manual is available

Alligator Weed identification and control

Alligator Weed is a summer growing perennial herb (non woody plant). It has small white flowers that appear mainly between November and March. The plant has hollow stems with shiny, spear-shaped, opposite paired leaves. Of the total Alligator Weed recorded in Australia about three quarters (3500 Ha) is located in Port Stephens.

A plant of many disguises, Alligator Weed takes on different appearances in water, on land and at different times of the year. The downloadable file at the bottom of this page contains images of several plants which are commonly confused with Alligator Weed.

How it spreads

Alligator Weed does not produce seeds in Australia and spreads only from plant fragments. These fragments can be very small and are able to survive extreme conditions. Alligator Weed spreads naturally when fragments float downstream; this is exacerbated during flooding when mat sections are deposited on the floodplains.

Spread assisted by human activity is responsible for moving Alligator Weed between catchments and into new areas. Examples of human assisted spread include movement on contaminated machinery and in soil supplies, resulting in new outbreaks throughout Port Stephens and as far afield as Griffith. The Protocols for Working in Alligator Weed Affected Areas provide guideance on how to prevent the spread of fragments during excavation and other activities.

Impact of Alligator Weed

Alligator Weed disrupts the aquatic environment by blanketing the surface and reducing light penetration. It competes with native flora, contaminates grazing pastures, threatens our drinking water supplies and renders valuable land unfit for cropping. The weed mat impedes stream flow promoting sedimentation and flooding problems as well as providing a habitat for mosquitoes.

It is illegal to sell turf from land affected by Alligator Weed.

Control Methods

The control requirement for Alligator weed throughout Port Stephens is" The plant must be fully and continuosly suppressed and destroyed". The regional Weed Management Plan is available below and contains an overview of the strategies used to manage infestations.

The four broad methods of controlling weeds are chemical, biological, cultural and physical.

Chemical

Control using herbicides has been generally patchy due to the need to repeat the applications frequently. New outbreaks can be eradicated with herbicides if they are treated before the plant has developed a deep root system. Old, well established infestations are very difficult to eradicate. Contact the weed officers for advice before commencing a chemical treatment.

Biological

The Flea Beetle (Agasicles hygrophila) was introduced as a biological control in 1976 and provides good control for aquatic infestations, although it has little impact on the terrestrial Alligator Weed.

The Flea Beetle is widespread and has been found at all known aquatic infestations. New insects are being evaluated for release in Australia, and work is also underway researching the potential to use native fungi to control Alligator Weed. Flea Beetles are suited to areas that cannot or will not be otherwise treated, and should be integrated with other methods. When using herbicides to control aquatic infestations, consider leaving a small patch untreated as a refuge for the Flea Beetles to breed in and spread out to eat the regrowth. Try to time herbicides so that the peak of Flea Beetle activity (usually just after christmas) coincides with the regrowth phase of Alligator Weed.

Physical

A permit is required before moving Alligator Weed plant material, even if it is included in excavated soil. Any machinery and equipment used to dig Alligator Weed must be cleaned of all soil and plant material before leaving the site. Anyone intending to conduct excavations in Alligator Weed affected areas should contact the council for advice before commencing.

The value of excavation is usually limited to small and isolated infestations. The deep roots must be carefully removed and follow up digging maintained until no new shoots emerge. Disposal of fragments and excavated soil must be done carefully to avoid spreading the weed. Follow up work involving spraying and hand picking fragments is also required.

Cultural

Cultural control involves manipulating the site to favour plants other than Alligator weed, for example a dense cover of Kikuyu has been demonstrated to inhibit Alligator Weed in pastures. At no stage should ploughing or cultivation be used in Alligator Weed affected areas.

What can you do

It is vital to combat the spread of alligator weed by reporting sightings to Council's Weeds Officer to assist in mapping, recording and managing this problem. All property owners/occupiers should conduct regular monitoring to control infestations.

Suspect plants can be identified by council weed officers, who can also show you the confusing species and explain how to identify Alligator Weed. It is best to leave plants where they are found and simply mark the spot with a semi permanent marker such as a timber stake rather than collect some to bring in.

If Alligator Weed is confirmed, a thorough search of the site is required to determine the source and extent of the infestation. The key to controlling Alligator weed is to stop the spread of it through human activity and to keep infestations suppressed at all times.

For further information on Alligator Weed visit Department of Primary Industries or the Weed Management Guide of the Australian Weed Management Cooperative Research Centre

Contact details
Senior Weeds/Pest Management Officer
02 4980 0392 (ph)
graham.prichard@portstephens.nsw.gov.au

© 2008 Port Stephens Council
This page: http://portstephens.local-e.nsw.gov.au/environment/1276/1337.html