1965?: Macalister River Weed Control. Pesticides: Amitrole, Diuron

State Rivers and Water Supply Commission

Increased use of Weedazol – Macalister Irrigation District

Present Position

At the present time, Weedazol is used in relatively small quantities in the Macalister Irrigation District to treat regrowth of water couch in drains, following the application of Karmex (diuron) during winter.

It is not used however in drains flowing into the Macalister or Thompson Rivers. The Macalister River supplies water to Maffra while the Thompson River supplies water to Sale. The Interdepartmental Committee on Pesticides did not favour the use of Weedazol in Gippsland where domestic Water supplies could be contaminated, because Gippsland is regarded as a goitre area.

The limit set by the Committee for water supplies elsewhere was 0.3 ppm of aminotriazole. The State Rivers and Water Supply Commission established a limit of 0.002 ppm to apply to its own operations wherever water was used for irrigation.


The Committee’s approval is sought for a proposal which would result in contamination of the Thompson and Macalister Rivers by aminotriazole between December and April each year. Spraying would be restricted so that the pollution level of aminotriazole does not exceed 0.002 ppm.

The area mainly concerned is Area “A” on the attached plan. Drains in this area flow into the Macalister River which has a controlled summer flow of about 200 cusecs. This would permit the use of some 30 gallons weekly of Weedazol TL i.e. 75 lbs of aminitriazole.

Drains in Area “B” flow into the Thompson River. Only a very limited amount of spraying would be possible in this area because of a small summer flow in the Thompson River.

The consumption of aminotriazole by persons in Maffra and Sale would be very small. Only 0.6 mgm would be consumed each year by a person who drank 2 litres of water daily during the spray period.