Comparison of grain crops and their associated residues for weed suppression in the Southern Australian mixed farming zone

We evaluated ten grain crops and theirresidues for their ability to suppress both winter andsummer annual weeds in the mixed cropping regionof southern Australia due to their competitive abilitiesand the presence of residues remaining until thesubsequent cropping season. Research was conductedin Wagga Wagga NSW, in 2012 and 2013 using replicatedRCB designs. Trends in weed suppressionamong years were similar. Weed pressures and yieldswere moderate in 2012'13 and lower in 2013'2014,due to rainfall received. Yields averaged 2.3'4 tonsha-1 for all crops in both seasons. Winter weeds werewell suppressed in crop in 2013 but annual ryegrass(Lolium rigidum Gaud.) was less well suppressed in2012.Annual weeds established following harvest andincluded witchgrass (Panicum capillare L.) and fleabane(Conyza spp.). Witchgrass was most suppressedin grazing wheat and canola stubbles, followed byhybrid canola stubbles in both years. Grazing canolaresidues suppressed nearly all witchgrass and mostfleabane growth for up to 4 monthsfollowing harvest.Soil analysesfor weed suppressive allelochemicals potentiallyproduced by canola residues were performed.