Control of competing vegetation in planted coniferous forests in Australia and New Zealand

Summary

Forestry organisations in Australia and New Zealand were canvassed for their use of weedicides in planted coniferous forests. The main expenditure was on the control of grasses on second rotation sites in New Zealand, and acacias and eucalypts on cleared native forest sites in Australia. Aerial application predominated in New Zealand where weed control costs were 1.7 times those in Australia (1983 A$ values).

Non-woody weeds had a mean treatment productivity (ha man⁻¹d⁻¹) some 2.5 times higher than woody weeds, but high variation in treatment costs resulted in no difference between mean treatment costs for woody and non-woody weeds. Twenty chemical formulations in 46 prescriptions and six application methods were used to control only 20 weed groups. Six of the chemicals and mixtures were applied over most (78%) of the surveyed area with 78% of the expenditure. 2,4,5-T alone and in mixtures was applied to 40% of the area, and 79% of organisations were testing alternatives to 2,4,5-T. Other prominently used weedicides were 2,4-D, hexazinone, amitrole and atrazine, and glyphosate.

Ecological successional processes operating in planted forest sites and the energy cost of arresting successions to the benefit of tree crops are seen as foci for designing weed control strategies. A high level of training in weedicide use for all levels of forest operations personnel is necessary for effective and safe use of the large number of weedicide prescriptions available for use in forestry.