July 31, 2002

Herbicide resistance in Western Australia (WA) is forcing graingrowers to investigate non-chemical weed management for wild radish and ryegrass.

The good news is that recent studies have revealed headers with attached chaff carts could remove 75 per cent of ryegrass and 95 per cent of wild radish seeds from the paddock during harvest.

Research, supported by growers and the Federal Government through the Grains Research and Development Corporation, examined how much seed from each weed species could be collected during harvest and the proportion collected in the different harvest residue fractions, the chaff cart and the grain sample.

The study, conducted by the WA Herbicide Resistance Initiative’s Dr Michael Walsh and University of WA student, Wayne Parker, involved collecting ryegrass seed from four headers with attached chaff carts and one without a cart, in ryegrass infested wheat crops.

The amount of seed entering the headers before harvest was determined by surveying the ryegrass seed heads at header cutting height. Soil surface seed was collected by vacuuming before and after harvest, with the amount removed representing the difference between pre and post harvest samples.

Meanwhile, a patch of mature wild radish was established in a wheat crop to calculate how many seeds from this weed species would be collected during the harvest operation.

About 75 per cent of ryegrass seed and 95 per cent of wild radish seed that entered the header during harvest was collected in the chaff fraction and grain sample.

When the chaff cart was not used, about 36 per cent of ryegrass seed was collected. One could therefore deduce that about 40 per cent was collected in the chaff fraction. A far greater proportion of wild radish (75 per cent) was removed in the grain fraction.

The efficiency of ryegrass seed removal was diminished when harvesting was delayed as less seed was retained in upright ryegrass seed heads. This practice demonstrated that growers could use chaff carts as an effective management tool for controlling ryegrass and wild radish infestations.

Overall, this work represents some very practical information arising from the WA Herbicide Resistance Initiative.

The Initiative has operated with considerable energy due to students such as Wayne Parker and a number of WA growers who very actively commit valuable time and resources to support work that is central to the program.