Control of thiocarbamate-resistant rigid ryegrass (Lolium rigidum) in wheat in southern Australia

Abstract

Two field experiments were conducted during 2018 at Paskeville and Arthurton, South Australia, to identify effective herbicide options for the control of thiocarbamate-resistant rigid ryegrass in wheat. Dose–response experiments confirmed resistance in both field populations (T1 and A18) of rigid ryegrass to triallate, prosulfocarb, trifluralin, and pyroxasulfone. T1 and A18 were 17.9- and 20-fold more resistant to triallate than susceptible SLR4. The level of resistance detected in T1 to prosulfocarb (5.9-fold) and pyroxasulfone (4-fold) was lower compared to A18, which displayed 12.1- and 7.8-fold resistance to both herbicides, respectively. Despite resistance, the mixture of two different preplant-incorporated (PPI) site-of-action herbicides improved rigid ryegrass control and wheat yield compared to a single PPI herbicide only. Prosulfocarb + triallate and prosulfocarb + S-metolachlor + triallate did not reduce rigid ryegrass seed set when compared to prosulfocarb applied alone at the higher rate (2,400 g ai ha–1). Pyroxasulfone + triallate PPI followed by glyphosate (1,880 g ai ha-1) as a weed seed set control treatment reduced rigid ryegrass seed production by 93% and 95% at both sites, respectively. These herbicides also significantly improved grain yield of wheat at Paskeville (22%) and Arthurton (38%) compared to the untreated.

Are herbicide mixtures unaffected by resistance? A case study with Lolium rigidum

“…A very recent survey study, with samples collected across the whole Australian cropping system, has re‐confirmed a much lower (up to 10‐fold lower) frequency of resistance to herbicide mixtures in L. rigidum populations highly resistant to trifluralin (Busi R and Beckie HJ, unpublished). Recent field studies and historical field surveys have consistently indicated that herbicide mixtures and combinations of herbicide MOA are deliberately chosen by farmers to effectively diversify the inherent selection pressure of herbicidal weed control operations (Brunton et al ., 2020a; Harries et al ., 2020). The current use of PRE herbicides to control L. rigidum include at least five MOA, with a few more of recent introduction (e.g.…”

“…As the use of herbicide mixtures (pre-formulated and/or 'tank' mixtures) has become an increasingly common practice (i.e. the (Brunton et al, 2020a;Harries et al, 2020). The cation (Yuan et al, 2007;Busi et al, 2014;Yu and Powles, 2014;Brunton et al, 2020b).…”

The Remarkable Journey of a Weed: Biology and Management of Annual Ryegrass (Lolium rigidum) in Conservation Cropping Systems of Australia

“…Applying a non-selective herbicide near to the time of crop maturity, commonly known as crop-topping, is also practiced in Australia. If used correctly, crop-topping can control weed survivors and significantly reduce seed viability and seedset in annual ryegrass [ 51 , 88 , 94 ]. Currently, paraquat, diquat and glyphosate are used as crop-topping agents to control the annual ryegrass seedset close to harvest in many pulse crops.…”

“…Overall, in Australian grain cropping systems, herbicides of distinct groups are often used in tandem and applied sequentially to target annual ryegrass from pre-sowing to seedset [ 51 , 95 ]. Also, there has been a trend of using herbicide mixtures and rotating herbicides from different modes of action within or between seasons to control annual ryegrass and to delay the evolution of herbicide resistance [ 94 , 96 , 97 ].…”

Resistance to bixlozone and clomazone in cross-resistant rigid ryegrass (Lolium rigidum) populations from southern Australia

“…Research into the possibility of L. rigidum evolving resistance to more diverse SOA herbicides has provided some understanding of the likelihood of resistance evolution to herbicides not yet discovered (Busi et al 2012). The current practice of managing L. rigidum in Australia in wheat (Triticum aestivum L.) relies heavily on the use of PRE herbicides, including trifluralin (3 (K1) : inhibitors of microtubule assembly), prosulfocarb, and pyroxasulfone (Boutsalis et al 2014;Brunton et al 2020a). A greater reliance has been placed on PRE herbicides due to significant and widespread resistance to the herbicides diclofop-methyl (1 (A) : inhibitors of acetyl CoA carboxylase) and chlorsulfuron (2 (B) : inhibitors of acetolactate synthase) (Broster and Pratley 2006).…”