Abstract

Field trials were made on two unlined irrigation channels to measure the extent of water contamination due to residues of dichlobenil (2,6-dichlorobenzonitrile) which had been applied to the empty channel the previous winter. Ten weeks after application, the herbicide remaining in the soil was about 6% of the initial application. About 4 months after application, water was passed through the channels and wasted into drains. The maximum herbicide concentration in this flushing water was 0.18 ppm and was judged to present no potential hazard to crops. The need for prolonged channel flushing is questioned. An alternative procedure, displacing the static water in the channel following by a period of ponding, is suggested as a means of avoiding high herbicide residues in irrigation water.

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