Avena sterilis ssp. ludoviciana (hereafter, A. ludoviciana) is considered the most difficult-to-control winter weed in the Northern Grains Region (NGR) of Australia. The abundance of this weed has increased after the adoption of the no-tillage conservation agriculture (NTCA) approach, which does not bury seeds deep in the soil profile. In addition, the increasing frequency and intensity of drought stress events during the late winter to early spring period in the NGR may modify this weed’s persistence mechanisms, which may further impact crop production. The present study focused on plant maturity time and seed production, dormancy, and longevity of four NGR A. ludoviciana biotypes in relation to the severity of drought stress over 2 consecutive years. Plants of all four A. ludoviciana biotypes were grown under 100% plant available water capacity (PAWC) until panicle initiation. At panicle initiation, very mild (80% PAWC), mild (60% PAWC), moderate (40% PAWC), and severe (20% PAWC) drought stresses were imposed on plants and continued through to maturity; an additional subset of plants were maintained at 100% PAWC through to maturity (control). Plants exposed to severe drought stress matured 24 days earlier than control plants, and produced 34% fewer filled seeds, with seeds having a 42% lower mass, 70% less dormancy, and shorter predicted longevity of at least 2 years compared to the seeds produced on control plants. All reproductive traits were less affected when the severity of the drought stress was decreased. The increasing frequency of drought stress in combination with the widely adopted practice of NTCA favours seeds of A. ludoviciana to undergo rapid germination in the following autumn/winter NGR planting season. However, effective control of A. ludoviciana remains a challenge in the NGR due to this weed’s genetic variability with respect to its response toward the seasonal variability of the NGR.

For more than two decades, glyphosate has been relied on to control summer annual weeds in fallow systems in Australia's northern grains region. With numerous cases of glyphosate resistance reported in weed species collected from this region, there are concerns about the future viability of this herbicide. A random seed collection survey of summer weeds was conducted between 2016 and 2018 with the aim of determining the frequency and distribution of resistance to glyphosate and other herbicides commonly used for summer weed control. Glyphosate resistance was ubiquitous in fleabane, with all collected populations resistant to this herbicide. Glyphosate resistance was also prevalent in feathertop Rhodes grass, windmill grass, and awnless barnyard grass, with resistance detected in 68%, 58%, and 36% of populations, respectively. Only 14% of sowthistle populations collected between 2013 and 2108 were resistant to glyphosate. Resistance to haloxyfop was detected in feathertop Rhodes grass, albeit at a low frequency (2%). Other herbicides, such as 2,4-D amine, propaquizafop, and clethodim, provided good control of the broadleaf and grass weeds tested. The results from these surveys conducted between 2013 and 2017 provide a first glimpse of the state of herbicide resistance in key crop weeds for Queensland and the northern region of New South Wales. It is clear that farmers and agronomists need to consider incorporating non-chemical weed management tactics to promote the sustainability of current herbicides.

The weed Avena sterilis ssp. ludoviciana has a high economic impact in the winter cereal crop production systems of Australia’s northern grains region (NGR). In the NGR, the frequency of high-temperature periods at the end of winter is increasing. This shift in climate may modify this weed’s maturity time and reproductive biology, and thereby impact on crop production. This study examined the reproductive biology of four A. ludoviciana biotypes in relation to elevated temperature when applied at different times during their seed development. Plants of all four A. ludoviciana biotypes were grown in an ambient temperature glasshouse (23/14 °C day/night). At panicle initiation, a portion of the plants were transferred to an elevated temperature glasshouse (29/23 °C day/night) and remained there until maturity. This process of plant movement was repeated on three further occasions with separate batches of plants, each 10 days apart. The remaining plants were kept under ambient conditions for their whole lifespan. Plants exposed to elevated temperature from panicle initiation to maturity, matured 18 days earlier than plants kept under ambient conditions, had 30% fewer filled seeds, 37% lower seed mass, and 40% less seed dormancy. Depending on the time and duration of plants exposed to elevated temperature, predicted seed longevity was ranged from 1 to 4 years in the soil seedbank. All reproductive traits were less affected when plants were exposed to elevated temperature at a later stage of development. If the frequency of high-temperature periods continues to increase, then it may lead to the development of less dormant populations of this weed that would be ready to germinate and re-infest the next winter crops under no-tillage conservation agriculture (that does not bury seeds deep in the soil profile). However, the seasonal climatic variability of the NGR in addition to the weed’s natural genetic variability may contribute to a seedbank of both dormant and less dormant seeds—making this species an even more difficult-to-control weed.

Context Avena sterilis subsp. ludoviciana (wild oats) is one of the major winter weeds of the Northern Grains Region of Australia. The abundance of this weed increased dramatically after the adoption of no-tillage conservation agriculture (NTCA). However, information is lacking on the germination characteristics of the two types of seed (i.e. primary and secondary) that it produces. Aims We aimed to determine the light and temperature requirements for germination and the time to germination of primary and secondary seeds of A. ludoviciana, in order to find ways to manage this weed effectively under NTCA systems. Methods Primary and secondary seeds and caryopses from two southern and two northern biotypes were exposed to a range of temperature and light regimes in the glasshouse, and germination was assessed. Key results All biotypes had ∼25% higher germination from primary than secondary seeds. Removing the hull increased caryopsis germination by ∼70%. The use of a light/dark photoperiod stimulated germination of both types of seed and caryopses compared with continuous darkness. Based on data for caryopses, 7°C and 9°C were found to be optimal germination temperatures for southern and northern biotypes, respectively. At optimum germination temperature, primary caryopses germinated 7–20 days earlier than secondary caryopses. In addition, a light/dark environment resulted in germination 2–6 days earlier than continuous darkness. Conclusions In the Northern Grains Region, seeds retained on or close to the soil surface (i.e. in NTCA systems) can undergo maximum germination during May–June (late autumn–winter), when long-term average temperatures match optimum germination temperatures. This coincides with winter crop plantings. Implications The seasonal timing of germination and the difference in germination timing between primary and secondary seeds, which help to stagger emergence of this weed, are major issues that need to be addressed in NTCA systems.

Context Avena sterilis subsp. ludoviciana (wild oats) is one of the major winter weeds of the Northern Grains Region of Australia. The abundance of this weed increased dramatically after the adoption of no-tillage conservation agriculture (NTCA). However, information is lacking on the germination characteristics of the two types of seed (i.e. primary and secondary) that it produces. Aims We aimed to determine the light and temperature requirements for germination and the time to germination of primary and secondary seeds of A. ludoviciana, in order to find ways to manage this weed effectively under NTCA systems. Methods Primary and secondary seeds and caryopses from two southern and two northern biotypes were exposed to a range of temperature and light regimes in the glasshouse, and germination was assessed. Key results All biotypes had similar to 25% higher germination from primary than secondary seeds. Removing the hull increased caryopsis germination by similar to 70%. The use of a light/dark photoperiod stimulated germination of both types of seed and caryopses compared with continuous darkness. Based on data for caryopses, 7 degrees C and 9 degrees C were found to be optimal germination temperatures for southern and northern biotypes, respectively. At optimum germination temperature, primary caryopses germinated 7-20 days earlier than secondary caryopses. In addition, a light/dark environment resulted in germination 2-6 days earlier than continuous darkness. Conclusions In the Northern Grains Region, seeds retained on or close to the soil surface (i.e. in NTCA systems) can undergo maximum germination during May-June (late autumn-winter), when long-term average temperatures match optimum germination temperatures. This coincides with winter crop plantings. Implications The seasonal timing of germination and the difference in germination timing between primary and secondary seeds, which help to stagger emergence of this weed, are major issues that need to be addressed in NTCA systems.

About 4.17 trillion kWh(e) of electricity were generated at utility-scale electricity generation facilities in the United States in 2018. Of this, 64% was from fossil fuels (coal, natural gas, petroleum, and gas), 19% was from nuclear energy, and about 17% was from solar, wind, hydro, and other "renewable" energy sources. The task before us is to displace this 64% of the electricity from fossil fuels with electricity that does not put more carbon in the atmosphere and that minimizes negative environmental impact, and to make similar displacements elsewhere in the developed and developing world.

Resistance to herbicides and the lack of new herbicide options have led researchers to explore alternate methods to manage weed populations in large-scale cropping systems. Crop competition is an effective weed management approach that can reduce the pressure on herbicides. Faba bean (Vicia faba L.) is an important winter legume crop in Australia. Crop traits such as, height, biomass, growth rate, tillering capacity, leaf area, and root growth have been suggested as indicators of the competitive ability of crops against weeds. Based on pot studies at Narrabri and Toowoomba, we assessed the growth traits (biomass, height, leaf area, relative growth rate, and branch number) of six faba bean cultivars and ranked them for their potential ability to compete with weeds. PBA Marne and PBA Zahra were identified as highly competitive faba bean cultivars based on their higher overall ranking score achieved at both locations. PBA Nasma and PBA Samira were ranked highly and moderately competitive at Narrabri and Toowoomba sites, respectively. At Narrabri, PBA Nanu was ranked poorly competitive based on its lower biomass, height, and leaf area than the other cultivars. The weed suppressive ability of these cultivars needs to be assessed in the presence of weeds under field conditions.

Weed infestations in barley can cause yield reductions and reduce the quality of harvested product. Weed management before, during and after the crop is important to reduce weed populations. Weed management in barley is currently heavily reliant on herbicides for weed control, and this reactive approach has resulted in widespread herbicide resistance across the world. This chapter examines the problem of weeds in barley and explains the application of Integrated Weed Management (IWM) to barley cultivation. The chapter outlines weed control tactics and the practical implementation of IWM, focussing on specific examples of IWM in barley. Finally, the chapter provides detailed further reading on this issue.

Weed risk assessment systems are used to estimate the potential weediness or invasiveness of introduced species in non-agricultural habitats. However, an equivalent system has not been developed for weed species that occur in agronomic cropland. Therefore, the Agricultural Weed Assessment Calculator (AWAC) was developed to quantify the present and potential future adverse impact of a weed species on crop production and profitability (threat analysis), thereby informing or directing research, development, and extension (RDE) investments or activities. AWAC comprises 10 questions related primarily to a weed’s abundance and economic impact. Twenty weed species from across Australia were evaluated by AWAC using existing information and expert opinion, and rated as high, medium, or low for RDE prioritization based on total scores of 70 to 100, 40 to <70, or <40, respectively. Five species were rated as high (e.g., Lolium rigidum Gaud.), eight were rated as medium (e.g., Conyza spp.), and seven were rated as low (e.g., Rapistrum rugosum L.). Scores were consistent with the current state of knowledge of the species’ impact on grain crop production in Australia. AWAC estimated the economic or agronomic threat of 20 major or minor agricultural weeds from across Australia. The next phase of development is the testing of AWAC by weed practitioners (e.g., agronomists, consultants, farmers) to verify its utility and robustness in accurately assessing these and additional weed species.

Australian conservation cropping systems are practiced on very large farms (approximately 3,000 ha) where herbicides are relied on for effective and timely weed control. In many fields, though, there are low weed densities (e.g., <1.0 plant 10 m(-2)) and whole-field herbicide treatments are wasteful. For fallow weed control, commercially available weed detection systems provide the opportunity for site-specific herbicide treatments, removing the need for whole-field treatment of fallow fields with low weed densities. Concern about the sustainability of herbicide-reliant weed management systems remain and there has not been interest in the use of weed detection systems for alternative weed control technologies, such as targeted tillage. In this paper, we discuss the use of a targeted tillage technique for site-specific weed control in large-scale crop production systems. Three small-scale prototypes were used for engineering and weed control efficacy testing across a range of species and growth stages. With confidence established in the design approach and a demonstrated 100% weed-control potential, a 6-m wide pre-commercial prototype, the "Weed Chipper," was built incorporating commercially available weed-detection cameras for practical field-scale evaluation. This testing confirmed very high (90%) weed control efficacies and associated low levels (1.8%) of soil disturbance where the weed density was fewer than 1.0 plant 10 m(-2) in a commercial fallow. These data established the suitability of this mechanical approach to weed control for conservation cropping systems. The development of targeted tillage for fallow weed control represents the introduction of site-specific, nonchemical weed control for conservation cropping systems.

Take home message • Feathertop Rhodes grass (FTR) and awnless barnyard grass (ABG) are both difficult to control summer grass weeds with both species prone to herbicide resistance evolution • Growing a competitive sorghum or mungbean crop can reduce growth and seed production of FTR and ABG • ABG is more susceptible to the impacts of crop competition than FTR • Sorghum competitiveness can be increased by growing the crop at a narrow row spacing (50 cm) and increased density (10 to 15 plants/m2) • Mungbean competitiveness is most effectively increased through the use of narrow row spacing (25 and 50 cm) • Consider growing a competitive summer crop to take pressure off relying solely on in-crop herbicides for summer grass control.

Take home message • Glyphosate resistant weeds are present in the northern region. Glyphosate failed to control all of the fleabane populations tested. Glyphosate resistance was also prevalent in feathertop Rhodes grass, windmill grass and awnless barnyard grass, with resistance detected in 68%, 58% and 36% of populations, respectively. Only 14% of sowthistle populations were resistant to glyphosate • Evolved herbicide resistance to haloxyfop was also detected in feathertop Rhodes grass, albeit at a low frequency • Other herbicides such as 2,4-D amine, propaquizafop and clethodim provided good control of the broadleaf and grass weeds tested • Farmers and agronomists should incorporate non-chemical weed management tactics to ensure sustainability of current herbicides • These survey results provide a first glimpse into the state of herbicide resistance in key crop weeds for Queensland and the Northern region.

Wild oat (Avena sterilis ssp. ludoviciana (Durieu) Nyman) is considered the most difficult-to-control winter weed in the northern grain region (NGR) of Australia particularly following the adoption of no-till conservation agriculture and the enhanced reliance on herbicides for weed control. A diversity of survival mechanisms is responsible for its persistence in no-till conservation cropping. Among them long-term, variable seed dormancy is the most important. A number of environmental stresses (for example drought) are known to affect the seed dormancy status. We hypothesized that the increasing frequency of hot and dry period in late winter/early spring season in the NGR might help to mature and shed less dormant wild oat seeds before the wheat crop is harvested. This early shedding of highly germinable seed better aids persistence in no-till conservation cropping systems. Our research showed that soil water stress applied at seed development stage resulted in lower number (16–22% less) of early maturing (5–20 days earlier) less dormant (28% less) seeds compared with control plants. This observation was made for a number of biotypes either coming from within one location or between locations within the NGR. Thus, the frequent hot and dry period at the time of seed development in the NGR is responsible for production of less dormant Avena sterilis ssp. ludoviciana seeds where no-till conservation cropping is helping to retain these seeds on the top soil. Under favourable germination conditions in the following season these less dormant seeds will immediately be available to re-infest the autumn/winter-sown wheat crop.

The grasses Echinochloa colona (L.) Link, Chloris virgata Sw. and C. truncata R. Br. are major problems in summer fallows of the sub-tropical grain region of Australia. Traditionally, these weeds were treated with glyphosate alone, but E. colona and C. truncata populations have evolved glyphosate resistance, and the weed flora is also being dominated by the glyphosate-tolerant species C. virgata. For improved control of these populations, sequential application of glyphosate, or recently haloxyfop, followed by paraquat is being used. The optimal interval between sequential applications of these herbicides needs to be defined for these summer-growing grasses. Pot experiments were conducted using glyphosate or haloxyfop followed by paraquat at intervals from 1 to 21 days. In addition, populations of E. colona and C. truncata with resistance to glyphosate were compared. The optimal interval between sequential applications differed for the three grasses and the herbicide used for the first application. For the glyphosate-paraquat sequential treatments, the optimal intervals were 1–14 days for GS and GR E. colona, 7 days for C. virgata, and 7–14 days and 14 days for GS and GR C. truncata populations. For the haloxyfop-paraquat treatments, the optimal intervals were 1–21 days for E. colona, 1–4 days for C. virgata and 1–7 days for C. truncata. This treatment achieved 100% control irrespective of resistance status. Thus, sequential application, particularly haloxyfop followed by paraquat is a highly effective tactic for control of these three weeds.

Take Home Messages Use chaff lining or chaff tramlining concentrates weed seeds into a narrow area. A heavy layer of chaff will lead to better suppression of weed emergence. Small seeded broadleaf weeds (e.g. common sowthistle) are more easily suppressed than grass weeds with larger seeds (e.g. annual ryegrass). Thick tramlines and chaff lines reduce but do not prevent weed emergence, so other measures may be needed to control weeds in tramlines/chaff lines (e.g. spraying the tramlines with a shielded sprayer). Background Herbicide resistance is a major concern for northern region crop production due to the increasing frequency of resistance in key weeds. Of particular concern is the increasing incidence of glyphosate resistance, with 9 weed species now confirmed as glyphosate resistant in the northern region (Heap, 2018). Regardless of the ever-increasing frequency of herbicide-resistance, herbicides will likely remain the most effective form of weed control in cropping systems. However, for herbicides to remain effective, non-herbicide weed management alternatives are needed to delay the spread and onset of further herbicide resistance (Walsh et al., 2013). One such alternative is harvest weed seed control (HWSC). In this paper we report on research evaluating the effectiveness of chaff tramlining and chaff lining as harvest weed seed control tactics for northern region weeds. Chaff lining and chaff tramlining are forms of harvest weed seed control (HWSC) that have potential for widespread adoption in northern Australia owing to their relative low cost and ease-of-implementation. Chaff tramlining is the practice of concentrating the weed seed bearing chaff material on dedicated tramlines in controlled traffic farming (CTF) systems. Chaff lining is a similar concept, where the chaff material is concentrated in a narrow row between stubble rows directly behind the harvester. The chaff environment is likely to be suboptimal for seed persistence and seedling establishment, therefore, this practice has the potential to be as effective as other forms of harvest weed seed control in depleting weed seed banks.

The rapid spread of herbicide-resistant weeds coupled with the decline in the number of new herbicide modes-of-action under development poses a serious threat to the future productivity of canola (Brassica napus L.). Crop competition is now an essential component of integrated weed management to reduce weed impacts and retard the spread of resistance. Canola plays an important role in any cereal-dominated crop rotation by providing diversification to broaden options for weed management, as well as other agronomic benefits for disease, pest and nutrition management. This review examines the opportunities to manipulate canola agronomy and increase the competitive ability by choice of cultivar, seeding rate, row spacing and orientation, and fertilizer use. The integration of such options for weed management prolongs the effectiveness and availability of herbicides.