May 21, 2003

Graingrower adoption of short-term pasture phases has grown in step with their reputation for restoring soil nitrogen levels and helping control weeds, with Cadiz French serradella, for example, being sown to more than 300,000 Western Australia hectares since its 1997/98 introduction.

Almost half Western Australia’s farmers rate weeds their number one problem, making the role of pasture legumes in weed control important, along with their capacity to deliver up to 40 kg/ha of nitrogen to soils.

Pasture phases can drop weed populations through the post-emergent application of herbicides to which the pasture is resistant, but the weeds are not.

However, according to Grains Research and Development Corporation (GRDC) supported research leader, David Ferris of the Department of Agriculture, the resistance profile of many new pasture species and those nearing commercialisation could be falling.

This meant applying post-emergent herbicides to knock out weeds could also diminish the legume content of pastures and therefore curtail nitrogen fixation. To address this, the GRDC has supported a new project in which Mr Ferris and his team will formalise the resistance profile of existing and soon-to-be-released varieties, while developing protocols to screen for herbicide resistance during the breeding of new species.

With co-operation from the Centre for Legumes in Mediterranean Agriculture, the project will record which species go with which herbicides and test glasshouse methodologies to help maintain herbicide resistance in newly bred varieties.

Past GRDC supported trials found great resistance variability between species, with some otherwise promising species only tolerating expensive selective herbicides, costing up to $25/ha.

Techniques being considered for detecting and promoting herbicide resistance in new varieties include solution cultures and a seed-soaking method used in a past GRDC project which investigated herbicide resistance in wild radish.

By providing herbicide management advice for current pasture varieties and establishing programs to breed robust new varieties, this project aims to ensure pasture legumes retain their dual value of soil enrichment and weed control in Western Australia cropping systems.