Courtney Peirce1, Kenton Porker1 and Michael Moodie2
1 Agronomy SARDI, Gate 1, Building 4c, Waite Road, Urrbrae, South Australia, 5064, firstname.lastname@example.org,
Despite the acknowledged benefit of summer spraying of weeds to conserve soil moisture, the subsequent presence of herbicide residues has led to growers and advisors questioning whether these residues may be affecting biomass and early vigour of the following crop. This is particularly of concern in low rainfall regions with sandy soils where rainfall is sporadic and microbial activity low. Through a combination of field and glasshouse experiments across the Mallee region of South Australia and Victoria, we investigated the impact of summer spraying of glyphosate, 2-4, D amine or a mixture of both on early biomass, vigour and yield of four crop species wheat, barley, lentils, and lupins. The herbicide applied over the summer period established high concentrations of the active ingredient in soil when measured prior to sowing. The herbicide residues did not negatively affect the early biomass, vigour, or yield of cereal crops wheat or barley at any of the three 2018 field sites despite the autumn period being among the driest on record. Only negative biomass and yield responses were measured for 2,4-D herbicide treatments when label plant back recommendations were not adhered to with the lightest textured soil more prone to crop damage. These results suggest that current summer spraying practices of glyphosate and 2,4-D amine as recommended by label rates are unlikely to cause any significant crop damage in wheat, barley, lentils and lupins.