1962 June – 1962 September: Tongala drains (Vic). Pesticide: Monuron

State Rivers and Water Supply Commission

29th March 1963

Pollution of Water Supplies by CMU

Control of water couch in drains can be obtained by application of Telvar (CMU) at a rate of 50 lbs per acre, provided the drains are relatively dry and there is little foliage present.

The experiment described below was conducted in order to determine the extent of pollution of water supplies resulting from the use of CMU is this way and the time at which it occurs. The information obtained enabled an assessment to be made of the risk of injury to crops being irrigated directly from drains treated with CMU and from streams into which the treated drains flow.

Experimental Procedure.

From the 11th to 22nd June, 1962, 560 lbs of Telvar was applied to the batters of a drain in the Tongala district with the standard Furphy spray unit, the application rate being approximately 50 lbs per acre. Before spraying, batters had been cleaned with the Briscoe sloper in the usual way.

During application, and until the 26th September, 88 water samples were taken at the point furthest downstream of treatment…

Results and Discussion

Analysis of the water samples for CMU content produced two important facts. Firstly the contamination of drain water during the three months after application was fairly constant – 1.3% per month of the quantity applied. Secondly, contamination during the first days high flow after the commencement of irrigation was 9% of the quantity applied.

The considerable loss of CMU during the first high flow in drains is most significant. Unless CMU was used on a small scale only, a loss to drain water of the order of 9% of the applied material in such a short period as one day, could cause a dangerously high pollution level in irrigation supplies…

As the quantity of CMU that can be safely used is so small, it is suggested for practical purposes, that it’s use be confined to one district. Tongala is preferred as it has the worst weed problems…

CMU content ranged from 0.18ppm to 6.6ppm in June 1962.

To between 0.3 to 1.31 ppm in July 1962

To between 0.03ppm – 0.5 ppm in September 1962