Control of Amsinckia spp. by the pastures of north-western Victoria

Abstract

Amsinckia is a serious weed in the wheat growing areas of north-western Victoria. It is successful in the inter-crop pastures, based upon barrel medic, because it grows faster than barrel medic in the cooler months of May to August. In addition, the rapid growth in height associated with the change from rosette to elongating phases ensures a height advantage over the pasture species when the flush of pasture growth does commence. Seed production by each Amsinckia plant is very high, and for this reason any competitive restriction obtained in one year is not necessarily reflected in the establishment phase of the next. Subterranean clover c.v. Clare is more competitive than barrel medic and was able to eliminate Amsinckia from the sward in two years. However it has only limited application in the pastures of north-western Victoria. A mowing treatment was carried out at the commencement of Amsinckia flowering, for this coincides with the beginning of rapid pasture growth. Regrowth produced a reversal of height relationships within the pasture and enabled barrel medic to shade Amsinckia BJ this treatment growth and seed production of Amsinckia were reduced by 99 per cent within the one season.