Alligator weed control 2011/2012

Report: TR 2012/40

Author: Wendy Mead

Abstract

Prior to 1990 there were two small infestations of alligator weed known in the Waikato region, one on land at Orongo near Thames, and the other a very small infestation in a small wetland area on the outskirts of Te Aroha. By 1990 the Orongo infestation was thought to be eradicated. In 1990 alligator weed was discovered on the lower Waikato River. Although control work began at this time, by 1999 it had spread further upriver and had also been discovered in Hamilton city. In 2003 it was found in Lake Whangape, and in a wetland area and paddocks on two dairy farms at Te Rore. Since 2004, several new infestations have been found throughout the region (see Technical Report 2005/38).

Alligator weed (Alternanthera philoxeroides) has been described as one of the world's worst aquatic and terrestrial weeds. Originally from Brazil, alligator weed is now a major weed problem in parts of the United States, Australia, China, India, Thailand and Indonesia. It was first discovered in New Zealand in the northern Wairoa River, near Dargaville, in 1906. Alligator weed was an accidental introduction to New Zealand and is believed to have arrived with ship ballast water. It is now widespread in Northland where it has become a serious weed of waterways and cropping land. It is common in Auckland waterways and there are one or two sites in the Bay of Plenty, Christchurch and Taumarunui. There are several infestations in a range of habitats in the Waikato.

Alligator weed control 2011/2012 [PDF, 1.3 MB]