Emerging challenges and opportunities for education and research in weed science
- Chauhan, Bhagirath, Matloob, Amar, Mahajan, Gulshan, Aslam, Farhena, Florentine, Singarayer, Jha, Prashant
- Authors: Chauhan, Bhagirath , Matloob, Amar , Mahajan, Gulshan , Aslam, Farhena , Florentine, Singarayer , Jha, Prashant
- Date: 2017
- Type: Text , Journal article
- Relation: Frontiers in Plant Science Vol. 8, no. (2017), p. 1-13
- Full Text:
- Reviewed:
- Description: In modern agriculture, with more emphasis on high input systems, weed problems are likely to increase and become more complex. With heightened awareness of adverse effects of herbicide residues on human health and environment and the evolution of herbicide-resistant weed biotypes, a significant focus within weed science has now shifted to the development of eco-friendly technologies with reduced reliance on herbicides. Further, with the large-scale adoption of herbicide-resistant crops, and uncertain climatic optima under climate change, the problems for weed science have become multi-faceted. To handle these complex weed problems, a holistic line of action with multi-disciplinary approaches is required, including adjustments to technology, management practices, and legislation. Improved knowledge of weed ecology, biology, genetics, and molecular biology is essential for developing sustainable weed control practices. Additionally, judicious use of advanced technologies, such as site-specific weed management systems and decision support modeling, will play a significant role in reducing costs associated with weed control. Further, effective linkages between farmers and weed researchers will be necessary to facilitate the adoption of technological developments. To meet these challenges, priorities in research need to be determined and the education system for weed science needs to be reoriented. In respect of the latter imperative, closer collaboration between weed scientists and other disciplines can help in defining and solving the complex weed management challenges of the 21st century. This consensus will provide more versatile and diverse approaches to innovative teaching and training practices, which will be needed to prepare future weed science graduates who are capable of handling the anticipated challenges of weed science facing in contemporary agriculture. To build this capacity, mobilizing additional funding for both weed research and weed management education is essential. © 2017 Chauhan, Matloob, Mahajan, Aslam, Florentine and Jha.
- Authors: Chauhan, Bhagirath , Matloob, Amar , Mahajan, Gulshan , Aslam, Farhena , Florentine, Singarayer , Jha, Prashant
- Date: 2017
- Type: Text , Journal article
- Relation: Frontiers in Plant Science Vol. 8, no. (2017), p. 1-13
- Full Text:
- Reviewed:
- Description: In modern agriculture, with more emphasis on high input systems, weed problems are likely to increase and become more complex. With heightened awareness of adverse effects of herbicide residues on human health and environment and the evolution of herbicide-resistant weed biotypes, a significant focus within weed science has now shifted to the development of eco-friendly technologies with reduced reliance on herbicides. Further, with the large-scale adoption of herbicide-resistant crops, and uncertain climatic optima under climate change, the problems for weed science have become multi-faceted. To handle these complex weed problems, a holistic line of action with multi-disciplinary approaches is required, including adjustments to technology, management practices, and legislation. Improved knowledge of weed ecology, biology, genetics, and molecular biology is essential for developing sustainable weed control practices. Additionally, judicious use of advanced technologies, such as site-specific weed management systems and decision support modeling, will play a significant role in reducing costs associated with weed control. Further, effective linkages between farmers and weed researchers will be necessary to facilitate the adoption of technological developments. To meet these challenges, priorities in research need to be determined and the education system for weed science needs to be reoriented. In respect of the latter imperative, closer collaboration between weed scientists and other disciplines can help in defining and solving the complex weed management challenges of the 21st century. This consensus will provide more versatile and diverse approaches to innovative teaching and training practices, which will be needed to prepare future weed science graduates who are capable of handling the anticipated challenges of weed science facing in contemporary agriculture. To build this capacity, mobilizing additional funding for both weed research and weed management education is essential. © 2017 Chauhan, Matloob, Mahajan, Aslam, Florentine and Jha.
Seed germination ecology of Bidens pilosa and its implications for weed management
- Chauhan, Bhagirath, Ali, Hafiz, Florentine, Singarayer
- Authors: Chauhan, Bhagirath , Ali, Hafiz , Florentine, Singarayer
- Date: 2019
- Type: Text , Journal article
- Relation: Scientific Reports Vol. 9, no. 1 (2019), p.
- Full Text:
- Reviewed:
- Description: It is now widely recognized that Bidens pilosa has become a problematic broadleaf weed in many ecosystems across the world and, particularly in the light of recent climate change conditions, closer management strategies are required to curtail its impact on agricultural cropping. In this investigation, experiments were conducted to evaluate the effect of environmental factors on the germination and emergence of B. pilosa, and also on the response of this weed to commonly available post-emergence herbicides in Australia. The environmental factors of particular interest to this current work were the effect of light and temperature, salinity, burial depth and moisture on B. pilosa since these are key management issues in Australian agriculture. In addition, the effects of a number of commonly used herbicides were examined, because of concerns regarding emerging herbicide resistance. In the tested light/dark regimes, germination was found to be higher at fluctuating day/night temperatures of 25/15 °C and 30/20 °C (92–93%) than at 35/25 °C (79%), whilst across the different temperature ranges, germination was higher in the light/dark regime (79–93%) than in complete darkness (22–38%). The standard five-minute temperature pretreatment required for 50% inhibition of maximum germination was found to be 160 °C, and it was further shown that no seeds germinated at temperatures higher than 240 °C. With regard to salinity, some B. pilosa seeds germinated (3%) in 200 mM sodium chloride (NaCl) but all failed to germinate at 250 mM NaCl. Germination declined from 89% to 2% as the external osmotic potential decreased from 0 to −0.6 MPa, and germination ceased at −0.8 MPa. Seeding emergence of B. pilosa was maximum (71%) for seeds placed on the soil surface and it was found that no seedlings emerged from a depth of 8 cm or greater. A depth of 3.75 cm was required to inhibit the seeds to 50% of the maximum emergence. In this study, application of glufosinate, glyphosate and paraquat provided commercially acceptable control levels (generally accepted as >90%) when applied at the four-leaf stage of B. pilosa. However, none of the herbicide treatments involved in this study provided this level of control when applied at the six-leaf stage. In summary, B. pilosa germination has been clearly shown to be stimulated by light and thus its emergence was greatest from the soil surface. This suggests that infestation from this weed will remain as a problem in no-till conservation agriculture systems, the use of which is increasing now throughout the world. It is intended that information generated from this study be used to develop more effective integrated management programs for B. pilosa and similar weeds in commercial agricultural environments which are tending toward conservation approaches. © 2019, The Author(s).
- Authors: Chauhan, Bhagirath , Ali, Hafiz , Florentine, Singarayer
- Date: 2019
- Type: Text , Journal article
- Relation: Scientific Reports Vol. 9, no. 1 (2019), p.
- Full Text:
- Reviewed:
- Description: It is now widely recognized that Bidens pilosa has become a problematic broadleaf weed in many ecosystems across the world and, particularly in the light of recent climate change conditions, closer management strategies are required to curtail its impact on agricultural cropping. In this investigation, experiments were conducted to evaluate the effect of environmental factors on the germination and emergence of B. pilosa, and also on the response of this weed to commonly available post-emergence herbicides in Australia. The environmental factors of particular interest to this current work were the effect of light and temperature, salinity, burial depth and moisture on B. pilosa since these are key management issues in Australian agriculture. In addition, the effects of a number of commonly used herbicides were examined, because of concerns regarding emerging herbicide resistance. In the tested light/dark regimes, germination was found to be higher at fluctuating day/night temperatures of 25/15 °C and 30/20 °C (92–93%) than at 35/25 °C (79%), whilst across the different temperature ranges, germination was higher in the light/dark regime (79–93%) than in complete darkness (22–38%). The standard five-minute temperature pretreatment required for 50% inhibition of maximum germination was found to be 160 °C, and it was further shown that no seeds germinated at temperatures higher than 240 °C. With regard to salinity, some B. pilosa seeds germinated (3%) in 200 mM sodium chloride (NaCl) but all failed to germinate at 250 mM NaCl. Germination declined from 89% to 2% as the external osmotic potential decreased from 0 to −0.6 MPa, and germination ceased at −0.8 MPa. Seeding emergence of B. pilosa was maximum (71%) for seeds placed on the soil surface and it was found that no seedlings emerged from a depth of 8 cm or greater. A depth of 3.75 cm was required to inhibit the seeds to 50% of the maximum emergence. In this study, application of glufosinate, glyphosate and paraquat provided commercially acceptable control levels (generally accepted as >90%) when applied at the four-leaf stage of B. pilosa. However, none of the herbicide treatments involved in this study provided this level of control when applied at the six-leaf stage. In summary, B. pilosa germination has been clearly shown to be stimulated by light and thus its emergence was greatest from the soil surface. This suggests that infestation from this weed will remain as a problem in no-till conservation agriculture systems, the use of which is increasing now throughout the world. It is intended that information generated from this study be used to develop more effective integrated management programs for B. pilosa and similar weeds in commercial agricultural environments which are tending toward conservation approaches. © 2019, The Author(s).
Herbicide application strategies for wild radish management in Imidazolinone tolerant faba bean
- Authors: Welgama, Amali
- Date: 2020
- Type: Text , Thesis , PhD
- Full Text:
- Description: The extensive and continual use of herbicides in cropping situations has inevitably led to the phenomenon of "herbicide-resistance" in weeds and this has become one of the most challenging issues in modern agriculture. Herbicide-tolerant crops (HTC) were introduced to diversify weed management practices, but the lack of integrated weed management strategies, along with the continuous use of the same herbicide mode of action (MOA) demanded by the HTC has continued to impose selection pressure on weeds to evolve with herbicide resistance. Consequently, this thesis has been focused on the introduction of herbicide MOA combinations into HTC systems in an attempt to reduce the rate of herbicide resistance evolution in weeds. Raphanus raphanistrum is the number one broadleaf weed in Australia, and for this case study, the newly released ALS-inhibiting imidazolinone tolerant faba bean cultivar PBA Bendoc with its conventional cultivar, PBA Samira, were selected as the study species. ALS-inhibiting (imazamox + imazapyr and imazethapyr) and PSII-inhibiting (metribuzin) herbicides were used as the two herbicide MOAs. The herbicide sensitivity of R. raphanistrum was initially evaluated at different growth stages, in glasshouse studies using herbicide-resistant and susceptible biotypes to ALS-inhibiting herbicides. The highest susceptibility was observed at the earliest growth stage regardless of the biotype and Imazamox + imazapyr proved to be more effective in controlling both biotypes compared to imazethapyr. The same two herbicides were tested on faba bean cultivars at different growth stages to assess crop tolerance and identify the herbicide application window. The field trials conducted in 2018 and 2019 showed increased ALS-inhibiting herbicide tolerance in PBA Bendoc compared to PBA Samira even at the most advanced growth stage. Both faba bean cultivars were then evaluated for their tolerance to metribuzin in-crop application at different herbicide rates. Both cultivars responded similarly, showing progressive herbicide damage with increasing application rates. However, the reduced pod number, even at the lowest rate used, flagged the possible yield penalties that may result in using in-crop metribuzin applications. It is thus suggested that metribuzin must be used post sowing pre-emergent (PSPE) respecting the label recommendations. The potential herbicide combinations were then tested on herbicide-resistant R. raphanistrum and PBA Bendoc to evaluate their efficacies. Metribuzin was initially used as PSPE in all combinations, and was to be followed by imazamox + imazapyr applications at the same growth stages of the weed and the crop as in previous experiments. However, 100% control of R. raphanistrum was achieved using metribuzin alone, and thus no second herbicide was required. All the assessed herbicide combinations were tolerated by PBA Bendoc, proving the suitability of these herbicide combinations for incorporation into the PBA Bendoc cropping system. These results led to two potential herbicide combination strategies: (i) herbicide rotations, with metribuzin as PSPE in one year along with another potential herbicide MOA in the following year, (ii) herbicide sequential application, with metribuzin applied at PSPE and imazamox + imazapyr applied at the 2-4 leaf stage if R. raphanistrum plants survived the metribuzin treatment. A seed germination study was conducted under different temperature/photoperiods, pH levels, osmotic potentials, salinity and burial depths to identify the optimal germination conditions for R. raphanistrum. The optimum germination conditions for both herbicide-resistant and susceptible biotypes of R. raphanistrum were found to be 25ºC/15ºC temperature range under 24 hours complete dark. However, the significant interaction between photoperiod and temperature indicated that the seed germination under higher temperatures is less favoured by 24 hours dark conditions regardless of the biotype. An increased moisture stress tolerance in herbicide-resistant seeds was observed, whilst both biotypes reacted similarly to different pH levels and burial depths. In summary, this thesis has elucidated the effectiveness of two herbicide MOAs in controlling R. raphanistrum while addressing the crop tolerance to these herbicide MOA combinations. These findings will help in setting up stewardship guidelines to be used with the PBA Bendoc faba bean cultivar to mitigate the misuse of herbicides, thus ensuring their sustainable application. In addition, the demonstration of differential seed germination requirements of resistant and susceptible R. raphanistrum seeds has provided further information to help with its systematic management. Overall, this study can be used as a case study to investigate herbicide options that can be used in different HT crop cultivars to control a range of weed species.
- Description: Doctor of Philosophy
- Authors: Welgama, Amali
- Date: 2020
- Type: Text , Thesis , PhD
- Full Text:
- Description: The extensive and continual use of herbicides in cropping situations has inevitably led to the phenomenon of "herbicide-resistance" in weeds and this has become one of the most challenging issues in modern agriculture. Herbicide-tolerant crops (HTC) were introduced to diversify weed management practices, but the lack of integrated weed management strategies, along with the continuous use of the same herbicide mode of action (MOA) demanded by the HTC has continued to impose selection pressure on weeds to evolve with herbicide resistance. Consequently, this thesis has been focused on the introduction of herbicide MOA combinations into HTC systems in an attempt to reduce the rate of herbicide resistance evolution in weeds. Raphanus raphanistrum is the number one broadleaf weed in Australia, and for this case study, the newly released ALS-inhibiting imidazolinone tolerant faba bean cultivar PBA Bendoc with its conventional cultivar, PBA Samira, were selected as the study species. ALS-inhibiting (imazamox + imazapyr and imazethapyr) and PSII-inhibiting (metribuzin) herbicides were used as the two herbicide MOAs. The herbicide sensitivity of R. raphanistrum was initially evaluated at different growth stages, in glasshouse studies using herbicide-resistant and susceptible biotypes to ALS-inhibiting herbicides. The highest susceptibility was observed at the earliest growth stage regardless of the biotype and Imazamox + imazapyr proved to be more effective in controlling both biotypes compared to imazethapyr. The same two herbicides were tested on faba bean cultivars at different growth stages to assess crop tolerance and identify the herbicide application window. The field trials conducted in 2018 and 2019 showed increased ALS-inhibiting herbicide tolerance in PBA Bendoc compared to PBA Samira even at the most advanced growth stage. Both faba bean cultivars were then evaluated for their tolerance to metribuzin in-crop application at different herbicide rates. Both cultivars responded similarly, showing progressive herbicide damage with increasing application rates. However, the reduced pod number, even at the lowest rate used, flagged the possible yield penalties that may result in using in-crop metribuzin applications. It is thus suggested that metribuzin must be used post sowing pre-emergent (PSPE) respecting the label recommendations. The potential herbicide combinations were then tested on herbicide-resistant R. raphanistrum and PBA Bendoc to evaluate their efficacies. Metribuzin was initially used as PSPE in all combinations, and was to be followed by imazamox + imazapyr applications at the same growth stages of the weed and the crop as in previous experiments. However, 100% control of R. raphanistrum was achieved using metribuzin alone, and thus no second herbicide was required. All the assessed herbicide combinations were tolerated by PBA Bendoc, proving the suitability of these herbicide combinations for incorporation into the PBA Bendoc cropping system. These results led to two potential herbicide combination strategies: (i) herbicide rotations, with metribuzin as PSPE in one year along with another potential herbicide MOA in the following year, (ii) herbicide sequential application, with metribuzin applied at PSPE and imazamox + imazapyr applied at the 2-4 leaf stage if R. raphanistrum plants survived the metribuzin treatment. A seed germination study was conducted under different temperature/photoperiods, pH levels, osmotic potentials, salinity and burial depths to identify the optimal germination conditions for R. raphanistrum. The optimum germination conditions for both herbicide-resistant and susceptible biotypes of R. raphanistrum were found to be 25ºC/15ºC temperature range under 24 hours complete dark. However, the significant interaction between photoperiod and temperature indicated that the seed germination under higher temperatures is less favoured by 24 hours dark conditions regardless of the biotype. An increased moisture stress tolerance in herbicide-resistant seeds was observed, whilst both biotypes reacted similarly to different pH levels and burial depths. In summary, this thesis has elucidated the effectiveness of two herbicide MOAs in controlling R. raphanistrum while addressing the crop tolerance to these herbicide MOA combinations. These findings will help in setting up stewardship guidelines to be used with the PBA Bendoc faba bean cultivar to mitigate the misuse of herbicides, thus ensuring their sustainable application. In addition, the demonstration of differential seed germination requirements of resistant and susceptible R. raphanistrum seeds has provided further information to help with its systematic management. Overall, this study can be used as a case study to investigate herbicide options that can be used in different HT crop cultivars to control a range of weed species.
- Description: Doctor of Philosophy
Erigeron bonariensis, erigeron canadensis, and erigeron sumatrensis
- Florentine, Singarayer, Humphries, Talia, Chauhan, Bhagirath
- Authors: Florentine, Singarayer , Humphries, Talia , Chauhan, Bhagirath
- Date: 2021
- Type: Text , Book chapter
- Relation: Biology and Management of Problematic Crop Weed Species, 1st Edition Chapter 7 p. 131-149
- Full Text: false
- Reviewed:
- Description: The global human population is expected to reach 8-10 billion by 2050. According to the United Nations, this expansion in population is expected to increase food demands by double the current demand by 2050. Consequently, existing food production systems will come under significant strain. Exacerbating this food production problem is that agronomic weed species across the globe are already causing significant impacts on essential grain yields. Over the past decades, to address weed infestations, farmers have been using range of herbicides. However, overuse of these chemicals has resulted in many weed species mutating to a more resistant form. To implement a successful integrated weed management approach in the future, it will be essential to document the changes in ecology and biology of significant weed species. This chapter focuses on the three most globally significant weeds: Erigeron bonariensis, Erigeron canadensis, and Erigeron sumatrensis, summarizing their current global distribution, seed ecology, impacts, control strategies, as well as current herbicide resistance. These three species are causing significant impacts on important agricultural products including corn, soybean, cotton, wheat, chickpea, sorghum, orchards, and vineyards. Addressing the problem of high levels of herbicide resistance within the Erigeron species has been attempted through various solutions, including novel herbicide mixtures and application timing. Targeting these species in their earlier growth stage with herbicide combinations can greatly improve the success of integrated treatments, broadening the options for suitable approaches such as the use of zero or no-till systems. Given that, these species have innate traits including (1) high seed production, (2) low levels of seed dormancy, (3) high emergence rates, (4) efficient seed dispersal mechanisms, and (5) a highly competitive nature. These advantages, coupled with their ability to withstand a range of climatic conditions and their increasing herbicide-resistant biotypes, make them a serious agricultural weed species across the globe. In this chapter, we have synthesized the characteristic biological features and the effectiveness of various control options. Very limited information is available on the ecology and biology of E. sumatrensis. We have, nevertheless, harvested a significant amount of useful information which may assist farmers to effectively develop integrated agricultural management practices to reduce the impacts of these three species in their productive lands. © 2021 Elsevier Inc. All rights reserved.
- Roberts, Jason, Florentine, Singarayer
- Authors: Roberts, Jason , Florentine, Singarayer
- Date: 2022
- Type: Text , Journal article , Review
- Relation: Weed Research Vol. 62, no. 2 (2022), p. 113-122
- Full Text: false
- Reviewed:
- Description: Amaranthus palmeri S. Watson (Palmer amaranth) is an invasive agricultural weed that has quickly risen from a state of relative obscurity to now being globally regarded as one of the most economically destructive and difficult to manage weed species. It is now found in more than 45 countries where it poses a serious threat to agricultural production systems. Amaranthus palmeri is known to aggressively compete against crop plants for resources such as light, space, nutrients and soil moisture, all of which can result in significant crop yield reduction or even lead to crop failure. It has also been reported that A. palmeri is highly prone to evolve herbicide resistance; this makes management exceedingly challenging. Whilst there have been several control approaches introduced to manage the spread and impact of A. palmeri, many of them require more specific and focused research for their successful local and widespread application. In this regard, this global review explores the species’ biology and global distribution patterns, together with previous and current management strategies. It also explores and identifies promising areas of research that still require further investigation to more confidently assist in the control and containment of this globally concerning weed. © 2021 European Weed Research Society.
- Jabran, Khawar, Florentine, Singarayer, Chauhan, Bhagirath
- Authors: Jabran, Khawar , Florentine, Singarayer , Chauhan, Bhagirath
- Date: 2020
- Type: Text , Book chapter
- Relation: Crop protection under changing climate Chapter 2 p. 17-56
- Full Text: false
- Reviewed:
- Description: The prevention and management of weeds have been difficult throughout the history of food production. We are now entering into a new era where new challenges are arising more rapidly due in part to the rapid population growth, which places an unprecedented demand upon both natural and agricultural ecosystems to fulfil food, fibre, and feed for at least another two billion people by 2050. Climatic change is associated with a higher frequency of extreme weather events, and it is generally agreed that this will have a drastic impact on ecosystem productivity and biodiversity. The present world atmospheric temperature has increased by 1.0 °C since 1900 with half of this rise coming in the past 30 years. Crop production is directly affected by the direct effects of climate change (temperature and water stress) and indirect effects of increased competition from weeds and other pest species. In a field situation, crop plants are inevitably surrounded by an assemblage of C3 and C4 plants, and a considerable variation in the growth response of weeds to climate change have been reported. In this chapter, we present an overview of the impact of temperature rise, carbon dioxide increase, and changed rainfall patterns on weed composition, distribution, abundance, and our current approaches to weed management. There is a high risk that some weed species will shift their range with the change in temperature and precipitation patterns. The efficacy of chemical weed control depends on the environmental conditions before, during and after the herbicide application. The changes in physiology, morphology, and anatomy of plants will result in altered weed growth, crop-weed competition, and herbicide efficacy under elevated temperature and/or carbon dioxide. Global warming may increase the risk of evolution of nontarget site resistance mechanisms against herbicides in the weed plants and thus decrease herbicide efficacy. The anticipated actions in these areas are also discussed in the end which may enhance our understanding of the impact of climate change on the practice and future of weed management and crop production.
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