Management options for large plants of glyphosate-resistant feather fingergrass (Chloris virgata) in Australian fallow conditions

2022

Plants

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Glyphosate alone or a tank mixture of glyphosate and 2,4-D is commonly used for broad-spectrum weed control under fallow conditions in Australia. Air temperature or mixing glyphosate with 2,4-D, may influence the efficacy of glyphosate on feather fingergrass (Chloris virgata Sw.), a problematic summer-season weed of Australia. Dose–response studies were conducted with four populations of feather fingergrass under temperature-controlled glasshouse conditions (35/25 °C and 25/15 °C at 12 h/12 h) to assess the level of glyphosate resistance in relation to temperature regimes. Four parameter log-logistic models were used to develop dose–response curves. Based on plant mortality percentage, LD50 (lethal dose for 50% mortality) values of glyphosate at 25/15 °C for populations Ch, SGM2, SGW2, and CP2 were 137, 60, 650, and 1067 g ae ha−1, respectively. However, at 35/25 °C, the corresponding LD50 values were 209, 557, 2108, and 2554 g ae ha−1, respectively. A similar response was observed for the parameter GR50 (dose for 50% growth reduction) values of glyphosate. These results indicate that populations SGW2 and CP2 are highly glyphosate-resistant and in the summer season, it may be very difficult to control these populations due to poor glyphosate efficacy. These results further suggest that the efficacy of glyphosate for feather fingergrass control can be improved if applied during cooler temperatures (25/15 °C) or the spring season compared with warmer temperatures (35/25 °C) or the summer season. In another study, 2,4-D antagonized glyphosate remarkably in the CP2 (glyphosate-resistant) population but only marginally in the Ch (glyphosate-susceptible) population. Thus, it is not advisable to mix 2,4-D with glyphosate for the control of glyphosate-resistant feather fingergrass populations. The results further suggest that the use of this mixture is useful if the feather fingergrass is not glyphosate-resistant; however, the use of the mixture is to be avoided if the population is glyphosate-resistant in order to not exacerbate the potential resistance problem.

Section: Resultsmentioning

confidence: 99%

Glyphosate Efficacy in Chloris virgata Sw. in Response to Temperature and Tank Mixing

Mahajan

2022

Plants

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“…Haloxyfop is used to control grass weeds in fallow and broadleaf crops (Chauhan et al 2021). Although there are several cases of winter-emerging rigid ryegrass accessions resistant to haloxyfop, this is the first study showing poor control of summer-emerging accessions.…”

Section: Haloxyfopmentioning

confidence: 87%

“…However, these parameters were not studied in the current study. In Australia, glufosinate usage is expected to increase to manage glyphosate-resistant weed species (Chauhan et al 2021). Summer-emerging accessions were collected from the cotton-growing fields and fence lines, and the poor control of these accessions with glufosinate suggests that the use of XtendFlex ™ (Bayer Cropscience, Hawthorn East, Victoria, Australia) cotton (resistant to glyphosate, glufosinate, and dicamba) in the future (Werth et al 2021) may not provide effective control of these accessions.…”

Section: Glufosinatementioning

confidence: 99%

Differential response of winter- and summer-emerging accessions of rigid ryegrass (Lolium rigidum Gaudin) to postemergence herbicides in Australia

Walsh²

2022

Weed Technol

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Rigid ryegrass is a problematic weed species in winter crops and winter fallow; however, recently, this weed species has been observed in summer crops and fallow. These observations warrant the evaluation of different postemergence herbicides for its control. Outdoor pot studies were conducted during the spring-summer of 2021-22 to determine the performance of POST herbicides on two summer- (S3 and S6) and two winter-emerging (W3 and W8) accessions of rigid ryegrass. Across all accessions, butroxydim, clethodim, paraquat, and paraquat + amitrole at the field rate provided complete control of rigid ryegrass. Both summer-emerging accessions were found to be resistant to the field rates of glufosinate (750 g ai ha-1), glyphosate (454 g ae ha-1), haloxyfop (52 g ai ha-1), and pinoxaden (30 g ai ha-1). The S6 accession had the highest GR50 value (dose required for a 50% reduction in biomass) for these herbicides (glufosinate 1120 g ai ha-1, glyphosate 1210 g ae ha-1, haloxyfop 140 g ai ha-1, and pinoxaden 55 g ai ha-1). This summer-emerging accession (S6) was also resistant to iodosulfuron. All four accessions were found susceptible to imazamox + imazapyr (a commercial mixture) and mesosulfuron. The study provides the first evidence of poor control of summer-emerging accessions of rigid ryegrass to different herbicides. Multiple herbicide-resistant summer-emerging rigid ryegrass accessions would be a challenge to the production of summer crops (e.g., cotton and sorghum) as well as winter crops that rely on weed-free summer fallows for soil moisture retention and therefore, warrant diversified management strategies.

“…The recommended doses of clodinafop and glufosinate did not The present study identified clethodim, cyhalofop, haloxyfop, and imazapic as the most effective herbicide treatments to control U. panicoides at 6-leaf and 18-to 20-leaf stages. Clethodim and haloxyfop have also been found to be very effective in controlling large C. virgata plants in southeastern Australian conditions (Chauhan et al 2021). In E. colona, however, clethodim at 60 and 90 g ai ha −1 and haloxyfop at 52 and 78 g ai ha −1 provided poor control when applied at the 8-leaf stage rather than at the 4-leaf stage (Ndirangu Wangari et al 2022).…”

Section: Experiments 6 Performance Of Postemergence Herbicidesmentioning

confidence: 99%

“…Herbicide efficacy can also be affected by growth stage. In some situations (e.g., under environmental constraints), growers may not be able to spray at a young seedling stage (Chauhan et al 2021). Therefore, there is a need to evaluate the performance of postemergence herbicides at different stages of U. panicoides.…”

Section: Introductionmentioning

confidence: 99%

Germination biology of liverseedgrass (Urochloa panicoides) and its response to postemergence herbicides in Australian conditions

2022

Weed Sci

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Liverseedgrass (Urochloa panicoides P. Beauv.) is one of the most important summer grass weed species in the eastern cropping system of Australia. Experiments were conducted to evaluate the effects of temperature, salt stress, water stress, burial depth, and sorghum crop residue load on germination and emergence of U. panicoides and the performance of postemergence herbicides on this weed species. The optimal germination temperature regimes for U. panicoides were 30/20 C and 35/25 C (alternating day/night temperatures) but seeds also germinated at temperatures occurring in winter, spring, and autumn seasons in Australia (15/5, 20/10, and 25/15 C). A concentration of 48 mM sodium chloride and -0.27 MPa osmotic potential inhibited 50% germination of U. panicoides, indicating that this weed species is not salt and drought tolerant at germination. The maximum germination was obtained for the surface seeds and a burial depth of 1.9 cm inhibited 50% emergence. No seedlings emerged from 12 cm depth but about 3% of seedlings emerged from 8 cm. The addition of sorghum residue amounts up to 8000 kg ha-1 to the soil surface stimulated its emergence compared with the no-residue treatment, suggesting that conservation agriculture will promote the emergence of U. panicoides. Several postemergence herbicides were found to be effective in controlling this weed species, especially when applied at an early stage. Information obtained from this study will help to develop effective and sustainable control measures for U. panicoides and other weed species with similar germination requirements.