Lake Nagambie – Spraying for Aquatic Weeds
GMW started spraying in May-June 1996 when lake was dry. 210 litres sprayed. Samples late 1996 <30ug/L.
Nov96/Feb 97: 361L of Nufarm Weedmaster used. Highest level recorded 38ug/L
1999/03 2193.5L Biactive 360 Weedmaster used. Highest level recorded <30ug/L
2007 Glyphosate detected at 120ug/L post spray. No residues detected 19-51 days after spraying.
Goulburn Weir Backwater also has problems with aquatic weeds, including Mexican Water Lily (Nymphaea mexicana) and Cabomba (Cabomba caroliniana). Goulburn Murray Water started a weed control program in May – June 1996 when the lake was sprayed with Roundup biactive in dry conditions. About 210 litres of Glyphosate was used. Water lily clumps were targeted again in late November 1996 – March 1997 with Glyphosate rates of 6L/ha, meaning 577 litres of Glyphosate was used. Samples taken in late1996 showed Glyphosate levels of <0.03mg/L (<30ug/L).
Between November 1997 to March 1998, 361 litres of Nufarm Weedmaster 360 was applied. Glyphosate levels at one point in the lake increased to 38ug/L and then decreased to <30ug/L after two days. From 1999 to 2003 another 2193.5 litres of herbicide (either Roundup Biactive, Roundup 360 and Weedmaster 360) was used in the lake. During 2000/1 monitoring found Glyphosate residues of <30ug/L.
Monitoring of glyphosate post spraying in 2007 saw Glyphosate levels as high as 120ug/L post spray. No residues were detected 19-51 days after spraying.