It's week seven of Council's Weed of the Week series for the 2024/25 spring and summer season. This series of articles provides our community with information and advice on new, emerging and established invasive plant species threatening our region.
Whether you're living on the land, living in town, or just passing through – we all have a part to play in protecting our natural environment and agricultural land from invasive plants and weeds.
This week we look at alligator weed (Alternanthera philoxeroides), a potentially devastating weed that grows in water and on land, affecting both waterways and floodplain areas. Native to South America, alligator weed is a perennial plant that grows on land in damp soil, or on water as dense floating mats. Alligator weed affects water flow, water quality, native plants and native animals, and has major economic and social impacts. Overseas experience indicates that alligator weed's potential impacts in Australia could be devastating.
Alligator weed leaves are shiny, dark green with a distinct midrib and are on opposite sides of the stem. The flower heads are small, white and papery to touch. The flowers occur at the end of a stem up to 9cm long and arise from the leaf-stem junction. One of the most distinguishing features of alligator weed is its hollow stem.
Dispersal occurs through the transportation of plant fragments on recreational equipment like boats and kayaks, or excavated material like sand and soil. Interestingly, the plants produce no viable seed in Australia. Spread occurs entirely through the movement of plant fragments.
Alligator weed is high on Council's alert list due to its known presence within the Australia Capital Territory, Sydney, Newcastle and isolated sites around Batemans Bay, Nowra and the Illawarra.
What do you have to do if you suspect the presence of alligator weed?
If you suspect the presence of alligator weed, you are required by law to immediately contact Council's biosecurity team on 1300 345 345. As alligator weed is not currently known to occur within the Snowy Monaro region, responding immediately gives us the best opportunity to eliminate any incursion and limit the impact on our community.
Do not try to control alligator weed yourself prior to contacting Council. It is very difficult to control and poorly performed control efforts can help spread the weed and exacerbate the problem.
Alligator weed is subject to a Biosecurity Zone in NSW. Outside of Greater Sydney and parts of the Hunter, land managers must eradicate the weed or destroy as much of the weed as practicable and suppress the spread of remaining plant material.
Council's biosecurity team will provide prompt and thorough weed identification and will assist in control efforts to ensure the best chance of elimination.
As with all weeds, prevention is the best control option. Take precautions when introducing sand and soil to your property and clean down boats and other recreational equipment carefully before transporting them.
