Aspects of woody weed control in radiata pine plantations in Victoria.  P. C. Fagg and D. W. Flinn.  February 1983.  22 pp. (unpubl.)

SUMMARY

Three field experiments are described that evaluated the herbicides hexazinone and 3,6-dichloropicolinic acid (3,6-DP) for the control of silver wattle (Acacia dealbata Link) and eucalypt (Eucalyptus spp.) regrowth in young plantations of radiata pine (Pinus radiata D. Don). In Experiment 1, which compared the efficacy of the two herbicides applied in the presence and absence of a petroleum oil, it was found that hexazinone (3 kg ha^-1) plus oil killed 87% and 97% of the eucalypt and silver wattle populations respectively, whereas 3,6-DP (1.5 kg ha^-1) plus oil caused a mortality of 20% for eucalypts and 80% for silver wattle. The addition of a petroleum oil substantially improved the efficacy of both herbicides for control of silver wattle. It was concluded that the choice of herbicide should largely be determined by the composition of the woody weed population.

In Experiment 2, 1.8 kg ha^-1 of 3,6-DP in a spray volume of 51.2 L ha^-1 containing 33% v/v petroleum oil was aerially applied (helicopter) to an 8.2 ha section of a radiata pine plantation. Spray coverage was monitored using sensitised cards. Within 11 months of treatment, 45.4% of the silver wattle population (average of 11500 stems ha^-1) was dead and a further 23.7% severely defoliated. This result was considered to be satisfactory  operationally.

Experiment 3 examined the rate and formulation (liquid and granular) of soil-applied hexazinone for control of eucalypt coppice. Triclopyr, dicamba, and karbutilate were also tested in unreplicated trials. The quantity of herbicide applied to the soil was based on the height of coppice clumps, which varied from 30 to 300 cm. All hexazinone treatments tested caused a mortality in excess of 90% after six months, compared with 38% for a combination of stem injection with picloram plus 2,4,5-trichlorophenoxyacetic acid and slashing/grubbing (small clumps only). The unreplicated treatments also gave results inferior to hexazinone. Caution should be exercised in extrapolating results from this experiment to other localities due to variations in edaphic and climatic factors and species composition.

Also published:

Fagg, P.C. and Flinn, D.W. (1983)  Evaluation of hexazinone and 3,6-dichloropicolinic acid for control of Acacia dealbata and Eucalyptus spp. in young Pinus radiata plantations in Victoria.  Aust. For. 46(3): 190-9.