Residues of hexazinone in streamwater after aerial application to an experimental catchment planted with radiata pine.  C. J. Leitch and D. W. Flinn.  March 1983.  9 pp. (unpubl.)

SUMMARY

Residues of hexazinone in streamwater were studied over a nine-week period after a helicopter application of the herbicide at a rate of 2 kg ha to a 46.4 ha experimental catchment. The aerial application was made in December 1981, following conversion of the steeply sloping catchment from native forest to Pinus radiata D. Don (radiata pine) two years previously. Automatic samplers were used to sample streamwater at intervals of 0.25-2.0 h throughout the nine weeks, with the more intensive sampling occurring during and immediately following spraying and during the only substantial storm event.

A total of 69 representative samples were analysed, and 4 µg L^-1 hexazinone was detected in six of these samples; this compares with the maximum recommended concentration for potable water of 600 µg L^-1. Factors that are likely to have contributed to such low residues are that spraying was carried out under calm conditions, the spray system emitted relatively large droplets, and a vegetation reserve was maintained along the entire length of the stream. Soil type and its moisture status at treatment, together with the amount and intensity of rainfall after treatment, may have a significant effect on the residue levels in streams flowing from treated catchments. The conditions applying in this trial do not allow any general rule to be proposed in respect of these factors.

Also published:

Leitch, C.J. and Flinn, D.W. (1983) Residues of hexazinone in streamwater after aerial application to an experimental catchment planted with radiata pine.  Aust. For. 46 (2): 126-31.