16 research outputs found

    Better management of 'Sonchus oleraceus' L. (common sowthistle) based on the weed's ecology

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    'Sonchus oleraceus' L. (common sowthistle) was recently identified in a survey as the most common weed of the sub-tropical grain region of Australia. In addition, the weed was identified as having a moderate risk of developing resistance to glyphosate, while populations already have resistance to Group B herbicides. Hence, 'S. oleraceus' is a weed that not only requires better management but also strategies that reduce the risk of resistance to herbicides. Weed ecology was investigated closely to assist devising management strategies. In particular, seed germination, emergence, persistence, dormancy, and production, as well as plant morphology, competition in crop, and response to tillage were studied. The characteristics that are important for better management of this weed are the weed's prolific seed production, the ability of this seed to germinate all year round and the ability of the weed to grow and produce seed across diverse environments. An integrated and sustainable approach to management of 'S. oleraceus' should include growing competitive crops, strategic tillage, follow up herbicide applications, and rotation of herbicide groups especially for Group B and M herbicides

    Flaxleaf fleabane (Conyza bonariensis) populations have developed glyphosate resistance in north-east Australian cropping fields

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    In recent years flaxleaf fleabane has become a widespread and difficult-to-control weed in no-tilled fallowed fields, where weeds are controlled by applications of glyphosate, in annual cropping systems of north-east Australia. Fifty-two populations, collected in a national survey from agricultural and non-agricultural areas, were tested in two glyphosate dose-response pot experiments. In two subsequent pot experiments, a sub-set of these populations was tested with a field rate of glyphosate when weeds of two ages were grown at different soil moistures. In the first and second experiments, most populations collected from chemical fallowed or cropped fields in north-east Australia had GR (estimated dose for 50% biomass reduction) values three to six times greater than the susceptible populations, indicating low levels of glyphosate resistance. Several populations from roadsides adjacent to chemical fallowed or cropped fields also had higher GR values, indicating movement of seeds from resistant plants. In the third experiment, weed biomass of all populations from chemical fallowed or cropped fields was 70-98% of unsprayed compared to 2-3% for the susceptible populations, irrespective of weed age or soil moisture. In the fourth experiment which treated older weeds, the response of several resistant populations to glyphosate was unaffected by differences in weed age and soil moisture, whereas the biomass of the other resistant populations was greater following spraying of older and/or moisture stressed plants compared with smaller non-stressed plants. Thus, exclusive reliance on glyphosate for fallow weed control in this region has resulted in the evolution of resistance in flaxleaf fleabane populations in a cropping system with annual non-transgenic crops. Prolific production of windborne seeds, combined with poor control associated with spraying large moisture-stressed weeds, is likely to have contributed also to flaxleaf fleabane becoming such a problem weed

    Gene movement in herbicide resistant sowthistle (Sonchus oleraceus L.)

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    Robin S. St. John-Sweeting, Christopher Preston, Jeanine Baker, Steve Walker and Michael Widderickhttp://www.weedinfo.com.au/bk_16awc.htm

    Barnyard grass responses to glyphosate - the importance of morphological traits

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    The genus 'Echinochloa' includes the species 'E. colona' (L.) Link and 'E. crus-galli' (L.) Beauv. Both are common summer weeds in farming systems of the northern grain region of Australia. Commonly referred to as barnyard grasses, these species are widespread problems within the region. Glyphosate is commonly relied upon for fallow control of these species. However, farmers are achieving variable control of barnyard grass with glyphosate. In addition, management of barnyard grass in Australia has become an important issue due to the development of populations resistant to glyphosate. Barnyard grass populations are variable in morphology and this may be a cause for differences in glyphosate efficacy. Field surveys found that within populations, individual plants had differences in characteristics such as growth form, culm thickness, and the presence/absence of banding on the leaves. Plants were categorised into one of five growth forms: erect, semi-erect, or prostrate and two intermediary forms, semi-erect/erect or semi-erect/prostrate. The aim of this study was to assess the relationship between plant morphology and their response to glyphosate

    Germination, emergence, and persistence of 'Sonchus oleraceus', a major crop weed in subtropical Australia

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    'Sonchus oleraceus' (common sowthistle) is a dominant weed and has increased in prevalence in conservation cropping systems of the subtropical grain region of Australia. Four experiments were undertaken to define the environmental factors that favor its germination, emergence, and seed persistence. Seeds were germinated at constant temperatures between 5 and 35°C and water potentials between 0 and -1.4 MPa. The maximum germination rate of 86-100% occurred at 0 and -0.2 MPa, irrespective of the temperature when exposed to light (12 h photoperiod light/dark), but the germination rate was reduced by 72% without light. At water potentials of -0.6 to -0.8 MPa, the germination rate was reduced substantially by higher temperatures; no seed germinated at a water potential >-1.0 MPa. Emergence and seed persistence were measured over 30 months following seed burial at 0 (surface), 1, 2, 5, and 10 cm depths in large pots that were buried in a south-eastern Queensland field. Seedlings emerged readily from the surface and 1 cm depth, with no emergence from below the 2 cm depth. The seedlings emerged during any season following rain but, predominantly, within 6 months of planting. Seed persistence was short-term on the soil surface, with 2% of seeds remaining after 6 months, but it increased with the burial depth, with 12% remaining after 30 months at 10 cm. Thus, a minimal seed burial depth with reduced tillage and increased surface soil water with stubble retention has favored the proliferation of this weed in any season in a subtropical environment. However, diligent management without seed replenishment will greatly reduce this weed problem within a short period

    Morphology and molecular characterisation of 'Echinochloa' species in the northern grain region

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    The genus 'Echinochloa' includes two species listed in the top five worst weeds of agricultural crops. 'E. crus-galli' (L.) Beauv. and 'E. colona' (L.) Link, are major summer grass weeds in farming systems of the northern grain region of Australia including dryland cotton, sorghum and fallows. A 2001 survey indicated varied levels of control of these species, with no farmers reporting good control in sorghum and only 38% reporting good control in cotton. Given the variability in control reported by farmers, a detailed knowledge of variability within, as well as among, populations and species of 'Echinochloa' would be useful in directing appropriate management strategies. Currently little is known about the genetic structure of this genus in Australia and the existence of morphologically intergrading types complicates species identification and diversity studies. The development of genetic markers for the measurement of genotypic variation has assisted in resolving taxonomic uncertainties and providing information on population diversity of many plant species. This study reports on the use of molecular techniques, including microsatellites (SSRs), together with classic morphological taxonomy to investigate the genetic diversity of 'Echinochloa' species from a field to a regional level
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