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Phalaris minor Retz. is the major grass weed of wheat, which has developed resistance to multiple herbicides working through three modes of action. The identification of suitable herbicides with different modes of action will assist in the control of this weed in resistance affected areas. Keeping this in view, the efficacy of flufenacet, an oxyacetanilide herbicide, was investigated in 2013 and 2014 at Ludhiana, India. Three doses of flufenacet (200, 250 and 300 g ha−1) were tested at three application timings on Zadoks wheat stages (Z00, Z13 and Z21) and compared with clodinafop application and weedy check for the control of resistant P. minor biotype. Flufenacet 250 and 300 g ha−1, applied at Z00 and Z13 wheat stages, had more than 85% mortality and more than 90% growth reduction of P. minor compared to the unsprayed check (76–109 plants m−2; 60–69 g m−2) at 45 days after sowing in both years, whereas clodinafop just provided 26–37% reduction in density and 39–40% reduction in biomass of this weed. Flufenacet 250 g ha−1 at Z00 and Z13 produced better wheat grain yield (4.2–4.5 t ha−1) in both years, while weed competition in the unsprayed check reduced wheat grain yield by 54–67% (1.75–1.97 t ha-1). This study suggests that flufenacet could be used to control multiple herbicide resistant P. minor in northern Indian wheat production systems. • Flufenacet 250 – 300 g ha−1 applied at Z00 and Z13, provided >85% mortality and >90% growth reduction of P. minor. • Clodinafop @ 60 g ha−1 provided only 26–37% reduction in density and 39–40% reduction in biomass of P. minor. • Flufenacet efficacy was higher in 2014 over 2013, owing to higher rainfall events in second year. • Flufenacet 250 g ha−1 applied at Z00 and Z13 produced better wheat grain yield (4.2–4.5 t ha−1) in both years. • Flufenacet provided better control of resistant P. minor population as compared to clodinafop. [ABSTRACT FROM AUTHOR]

The amino acid substitutions that confer herbicide resistance may also involve fitness costs leaving mutant plants at a competitive disadvantage compared with wildtypes. This research investigated the effect of two target–site point mutations of ACCase gene: Ile-1781-Leu/Val and Ile-2041-Asn on plant growth and fecundity of Hordeum glaucum biotypes grown in monoculture and/or under interspecific competition in the field with Triticum aestivum L. and Lens culinaris M. The amino acid substitutions at 1781 position of ACCase gene did not impose any negative pleiotropic effects on relative growth rate (RGR), panicle emergence, plant height, total biomass, and seed production in H . glaucum mutant plants. There was some evidence for fitness cost associated with Ile-2041-Asn mutation in terms of reduced RGR and reduced vegetative biomass and seed production when grown in competition with L . culinaris . The absence of measurable negative pleiotropic effects on plant growth and fecundity associated with Ile-1781-Leu/Val ACCase mutations in H. glaucum suggest that the frequency of these alleles will not decline in the absence of herbicide selection pressure. However, the 2041-Asn allele could decrease in frequency in the absence of herbicide selection pressure. [ABSTRACT FROM AUTHOR]

Four field experiments were conducted over a three-year period in Victoria and South Australia to investigate the effectiveness of pre-emergence (PRE) applications of pyroxasulfone, flufenacet and their mixtures with triallate for the control of Bromus diandrus in spring wheat. Herbicide mixtures of pyroxasulfone plus triallate and flufenacet plus triallate applied PRE to wheat provided consistently high levels of B. diandrus control (≥85%). In contrast, applications of pyroxasulfone and flufenacet applied alone along with trifluralin plus metribuzin (a common farmer practice in southern Australia) provided more variable control of B. diandrus (33–90%). Pyroxasulfone plus triallate treatments had a much lower (≤47 panicles m −2 ) panicle density of B. diandrus than trifluralin plus metribuzin (42–318 panicles m −2 ) and the non-treated control (118–655 panicles m −2 ). PRE herbicides which were safe to spring wheat and provided the greatest level of control of B. diandrus resulted in significantly ( P < 0.05) higher grain yields at Culgoa (120%) and Gama (13%) than non-treated wheat (720 and 1740 kg ha −1 ). Although flufenacet was effective against B. diandrus , crop phytotoxicity at the higher dose (900 g ai ha −1 ) reduced spring wheat grain yield. Based on these results, PRE pyroxasulfone plus triallate could play an important role in the management of B. diandrus in spring wheat. However, high cost of these herbicides (AUS$35-$70 ha −1 ) may limit their adoption in low rainfall and low yielding wheat environments in southern Australia where B. diandrus is most prevalent. [ABSTRACT FROM AUTHOR]

Two field experiments were conducted during 2013 and 2014 at Roseworthy, South Australia, to identify effective herbicide options for the control of clethodim-resistant Lolium rigidum in triazine-tolerant canola. Dose response experiments in pots confirmed resistance in both field populations (F4-2013 and S2-2014) of L. rigidum to clethodim and butroxydim. At the recommended field rate of clethodim (120 g ha −1 ), F4 and S2 populations had 45% and 67% survival, respectively. Therefore, the field populations F4 and S2 were approximately 16- and 26-fold more resistant to clethodim than the susceptible population, SLR4. Also, the S2 population had greater resistance to butroxydim (7-fold) than the F4 population (4.5-fold). Sequencing of the target site of acetyl co-enzyme A carboxylase gene identified two known mutations (aspartate-2078-glycine and cysteine-2088-arginine) in the F4 population and three known mutations (isoleucine-2041-asparagine, aspartate-2078-glycine and cysteine-2088-arginine) in the S2 population. Even though L. rigidum was confirmed resistant to clethodim and butroxydim, use of these (POST) herbicides in combination with preplant incorporated (PPI) herbicides improved weed control and canola yield relative to PPI herbicides only. Atrazine PPI followed by (fb) clethodim + butroxydim POST and atrazine PPI fb atrazine + clethodim POST reduced L. rigidum plant density (∼52%) and seed production relative to the standard grower practice of atrazine PPI fb clethodim POST. These two herbicide combinations produced the highest seed yield of canola (1839–2196 kg ha −1 ). Propyzamide alone (PPI) or as a split application (PPI fb POST) and in a mixture with clethodim improved L. rigidum control (32–63%) as compared to the standard grower practice but had limited impact on L. rigidum seed production. PPI herbicides alone were unable to effectively control clethodim-resistant L. rigidum in triazine-tolerant canola. [ABSTRACT FROM AUTHOR]

Abstract: Five field experiments were undertaken over a three-year period in South Australia to investigate the efficacy of imidazolinone herbicides for the control of rigid brome in imidazolinone-tolerant wheat (Clearfield™, CLF). Imidazolinone herbicides, imazapyr, imazapyr plus imazapic and imazapyr plus imazamox applied post-emergence to imi-wheat (cvs. CLF-Janz and CLF-Stiletto) at the four-leaf stage, provided consistent and high levels of rigid brome control (≥87%). In contrast, applications of the alternative herbicide mesosulfuron-methyl (post-emergence) provided limited and variable control of rigid brome (11–67%). Furthermore, imidazolinone treatments caused a large reduction (P <0.05) in rigid brome seed production (≤6 seedsm−2) as compared to mesosulfuron-methyl (461–3983 seedsm−2) and the non-treated control (2257–11 865 seedsm−2). Imazapyr plus imazapic provided consistent control of rigid brome and resulted in higher grain yields (28–45%) than wheat treated with mesosulfuron-methyl. Based on these results post-emergence applications of imazapyr, imazapyr plus imazapic and imazapyr plus imazamox to imi-wheat could play an important role in the management of rigid brome in southern Australia. However, the effect of these herbicides on existing and new cultivars of imi-wheat (multiple-gene resistance) and issues concerning persistence in low rainfall environments and crop damage on sandy soils require attention. [Copyright &y& Elsevier]