Extending the frontiers of aerially sown pastures in temperate Australia: a review

Abstract

Over the past 40 years large areas of pastures on hill country in temperate Australia have been improved through aerial distribution of herbicides, pesticides, seed, and fertiliser, which has increased animal production and helped to control weeds. Refinements detailed in this review could extend the use of these techniques to promote sustainable systems by the establishment of perennial pasture species on unploughed land. It is argued that the most urgent requirement is ensuring that aerial spraying is not abolished by government regulation in response to demands by specialist groups, because perennial pasture species will not establish on hill country without prior aerial spraying of herbicides. The major technical refinement needed is the reduction of losses of establishing plants due to weed competition and dry periods during their first spring and summer. This could be accomplished by increasing the spectrum of weeds controlled by the most widely used herbicide, glyphosate; applying new herbicides that give longer weed control in spring than the presently used herbicides; using herbicides that can selectively remove annual grass weeds from establishing perennial grasses; or using strategic grazing with cattle or goats to reduce weed competition. Breeding, selecting or importing pasture species specifically designed for establishment from surface sowing has never been attempted. Attributes that could improve establishment include germination that occurs only under favourable conditions; seeds resistant to weathering on the soil surface; seedlings with fast radicle entry, hairs on the radicle, fast root development, and better seedling vigour; and for subtropical species sown in semi-arid New South Wales, tolerance of low winter temperatures. Improved distribution of herbicides, seeds and fertilisers, particularly in the more rugged hill country, is needed to ensure complete cover of the treated area with minimum drift. Techniques that allow establishment of aerially sown pastures on hill country with very acid soil are needed to facilitate the development of further, large areas of Australia.