Herbaceous weed control by spot application of herbicides in a young radiata pine plantation on a sandy soil.  P. C. Fagg, D. W. Flinn and G. Hepworth.  December 1985.  16 pp. (unpubl.)

SUMMARY

This report describes a field trial that evaluated hexazinone (at 1, 3, and 6 kg ha^-1), and a mixture of amitrole (1 kg ha^-1) + atrazine (4 kg ha^-1) applied using a spot-spraying technique to control herbaceous weeds competing with recently planted radiata pine (Pinus radiata D. Don) in the Rennick area, Portland Region, South-western Victoria. The trial also examined the effect of timing of herbicide application on pine growth response and weed control on both first-rotation (1R) and second-rotation (2R) sites.

The results showed that on both sites spot-spraying in the September after planting gave much better growth response than if spraying was delayed to December. On the 1R site, all herbicide treatments resulted in significant growth response when sprayed in September, whereas December spraying produced no such response. On the 2R site, hexazinone (1 and 6) significantly improved growth in both spraying months, probably due to differences in site preparation (retention of logging residue) and the weed spectrum (more biennial species). However, the high mortality (23-62%) and cost associated with hexazinone (6) would preclude the use of this treatment on 2R sites at an operational level.

The cheapest, most effective treatments were amitrole (1) + atrazine (4) ($6.10 ha^-1 chemical cost) on the 1R site and hexazinone (1) ($11.60 ha^-1) on the 2R site, both applied in the September after planting.

The results of this trial support those of previous studies, which show that early weed control is important for optimum growth of radiata pine on the sandy soil types of South-western Victoria and South-eastern South Australia.

Also published:

Fagg, P.C., Flinn, D.W. and Hepworth, G. (1988)  Spot-spraying of hexazinone and amitrole/atrazine in the establishment of first and second rotations of Pinus radiata in south-western Victoria.  Plant Prot. Quart. 3 (2): 74-77.