Field surveys were conducted on 319 sites of the Western Australian grain belt in 2006 to determine the occurrence and distribution of summer fallow weed species. Sites were located across five growing season regions (north, north central, central, south central, and south) and three annual rainfall zones (high, medium, and low). A total of 51 species (or species groups) from 18 families were identified, with the large majority of species (35%) belonging to the Poaceae family. The most prevalent species found, being present at more than 10% of all sites, were wheat, “melons” (weedy watermelon and paddymelon), rigid ryegrass, capeweed, clover, mintweed, wild radish, fleabane, windmill grass, and rolypoly. Correspondence analysis revealed that the north, central, and southern regions of the grain belt could be predominately segregated according to dominant weed species occurrence; however, no segregation by rainfall zone was apparent. This study has given an overview of summer fallow weed occurrence in the Western Australian grain belt and highlights those weed species that are common and yet lack sufficient research into their ecology and management.

Nomenclature: Wheat, Triticum aestivum L.; weedy watermelon, Citrullus lanatus (Thunb.) Matsumura & Nakai; paddymelon, Cucumis myriocarpus E. Mey. ex Naud.; rigid ryegrass, Lolium rigidum Gaudin; capeweed, Arctotheca calendula (L.) Levyns; clover, Trifolium spp.; mintweed, Dysphania pumilio R. Br.; wild radish, Raphanus raphanistrum L.; fleabane, Conyza spp.; windmill grass, Chloris truncata R. Br.; rolypoly, Salsola australis R. Br.