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The effect of different cultivation and sowing methods on wild radish (Raphanus raphanistrum L.) density in 4 successive wheat crops was measured in an experiment in north-eastern Victoria. The number of seasons taken for populations to decline below an estimated threshold for economic spraying of wild radish (5-10 plants/m2) was examined. Two herbicide applications in each crop in all but one treatment prevented or significantly reduced wild radish seed production during the experiment. Wheat sown after mouldboard ploughing (MBP) in the first season contained wild radish at 42 plants/m2, before spraying. Densities were significantly higher (P<0.05) when wheat was direct drilled (96 plants/m2), or sown after cultivation to 80 mm (116 plants/m2) or to 50 mm (202 plants/m2). MBP in the first season followed by cultivation to 80 mm or direct drilling in subsequent seasons resulted in wild radish populations below the threshold for economic spraying in the second crop. Cultivation to 80 mm before sowing in the first 2 years, followed by direct drilling in subsequent years resulted in a wild radish population of 6.9 plants/m2 in the third crop. This density was within the range estimated as the threshold for economic spraying. Wild radish densities on treatments cultivated to 50 or 80 mm before sowing, or direct drilled each year, had declined to within or below the threshold for economic spraying by the fourth crop.

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