Can we manage alligator weed better in Australia? Lessons from herbicide trials.
Alligator Weed [Alternanthera philoxeroides (Mart.) Griesb] is acknowledged as the aquatic invader that poses the largest threat to Australian waterways and moist, terrestrial habitats. Despite control efforts over several decades, alligator weed is now widespread across NSW, and occurs as sporadic infestations in Queensland, ACT and Victoria, as well. It has the potential to cause losses of millions of dollars from agricultural, tourism and extractive industries across major waterways and catchments in Australia. Control methods for alligator weed include mechanical control, classical bio-control and herbicides, and combinations of these. Of these, mechanical control may provide immediate control, but also results in fragmentation and increased risks of further spread, and bio-control agents have not been particularly successful on aquatic or terrestrial infestations. Chemical control has been successful, but only short term, and several repeat applications have been required per season to contain or eradicate local infestations. Recent glasshouse trials evaluated the efficacy of a range of herbicides (glyphosate, metsulfuron, 2, 4-D, triclopyr, a mixture of mecoprop and dicamba, and imazamox) on Alligator Weed, with and without adjuvants. Field trials conducted in Fairfield and Liverpool Local Government Areas in NSW, demonstrated that effective reduction of alligator weed infestations in urban creeks requires multi-year, multiple herbicide treatments. This research provides new insights into alligator weed control using herbicides, and should offer more effective options for managing both aquatic and terrestrial infestations.