Navneet Aggarwal1, Blake Gontar1, Amanda Pearce1, Brian Dzoma1, Arsego Fabio1, Penny Roberts1, Helena Oakey2, Peter Boutsalis2 and Larn McMurray3
1South Australian Research and Development Institute, 155 Main North Road, Clare SA 5453, email: Navneet.Aggarwal@sa.gov.au,
2The University of Adelaide, Waite Campus, Urrbrae SA 5064, 3Global Grain Genetics, Clare, SA 5453
Controlling Group A and B herbicide resistant annual ryegrass and Group B resistant common sowthistle is becoming increasingly challenging in high break crop intensity (HBCI) systems in South Australia. Ryegrass resistance to recently released pre-emergence herbicides such as Boxer Gold® and Sakura® has been confirmed in HBCI systems. New herbicide Ultro® (active ingredient carbetamide, Group E), currently under development and expected for registration in 2020, provided significant control of dim-resistant ryegrass in lentils. Ultro® will offer an additional tool to support herbicides with alternative modes of action to control ryegrass in break crops. Imidazolinone resistant common sowthistle was detected in paddocks with and without Imidazolinone herbicides use in the past 5 years. Cross-resistance to sulfonylurea herbicides was also confirmed in common sowthistle. Increased crop competition offered by higher plant density of PBA Bendoc was found to have potential to reduce seed set of broadleaf weeds. The adoption of effective and diverse weed management strategies will aid in reducing the risk of resistance developing in HBCI rotations.