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Three field trials and a glasshouse experiment were carried out in northern New South Wales to determine the effects of reduced mechanical incorporation and the presence of crop residues on the efficacy of liquid and granular formulations of triallate [S-(2,3,3-trichioroallyl) diisopropylthiocarbamate] for control of wild oats (Avena fatua and A. sterilis ssp. ludoviciana) in wheat. In field experiments, fallow management practices with surface crop residues ranging from nil to complete retention from the previous wheat crop, did not affect the performance of tri-allate (incorporated by sowing) in terms of control of wild oats and wheat grain yield response. Application of a granular formulation resulted in lower than expected wheat grain yields in 2 of the field experiments and phytotoxicity to the crop was suspected as the reason. Although soil incorporation improved the performance of tri-allate at the recommended rate of 0.8 kg/ha, satisfactory control of wild oats and profitable increases in wheat grain yield were obtained with tri-allate at 1.2 kg/ha when incorporated by sowing into seedbeds containing up to 2 t/ha of crop residue. We conclude that tri-allate as the liquid formulation at 1.2 kg/ha gives economic control of wild oats in no-tillage and stubble-mulched seedbeds when incorporated by sowing provided that the weed-free wheat grain yield potential is not less than 1.5 t/ha. Results from the glasshouse experiment, farmer experience and published literature support the practice of incorporating tri-allate into dry soil with subsequent activation by sowing rain. The potential use of the granular formulation is limited by the greater risk of crop damage compared with the liquid formulation. |
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