Control of Acacia verticillata and other woody weeds in a young Pinus radiata plantation by an aerial application of hexazinone.  P. W. Geary and D. W. Flinn.  June 1985.  10 pp. (unpubl.)

SUMMARY

The effects of an aerial application of hexazinone (at 2.5 kg ha^-1), plus petroleum oil, on competing Acacia verticillata (L’Hérit.) Willd. (prickly moses), A. mearnsii De Wild. (black wattle) and Eucalyptus spp. (various eucalypts) were assessed in a young Pinus radiata D. Don (radiata pine) plantation near Heywood, in the Portland Region in South-Western Victoria. The herbicide was applied by helicopter in December 1982, during a drought period.

Sixteen months later, 50% of A. verticillata and 53% of A. mearnsii plants assessed on plots located in the 50 ha treated area were dead, and growth of surviving plants was retarded. This level of control was satisfactory for operational purposes. Control of Eucalyptus spp. was not satisfactory, as only 17% mortality was recorded. Pinus radiata suffered some herbicide damage (needle scorch and isolated dieback of leading shoots), but quickly recovered. No mortality of P. radiata attributable to hexazinone was observed. Measurements 16 months after spraying showed no height response by P. radiata to the reduction in competition.

Although the results of the operation were satisfactory, it may have been more effective if:

1. spraying had taken place under more favourable soil moisture conditions,
2. the target plants were smaller when treated,
3. a higher rate of hexazinone, e.g. 3-3.5 kg ha^-1, was applied, or
4. Eucalyptus of coppice origin was spot-treated following the aerial spraying, with either hexazinone (soil application), triclopyr (basal bark spraying), or an appropriate herbicide (stem injection).