Redroot pigweed (Amaranthus retroflexus L.) and slender amaranth (Amaranthus viridis L.) are considered emerging problematic weeds in summer crops in Australia. An outdoor pot experiment was conducted to examine the effects of planting time on two populations of A. retroflexus and A. viridis at the research farm of the University of Queensland, Australia. Both species were planted every month from October to January (2017 to 2018 and 2018 to 2019), and their growth and seed production were recorded. Although both weeds matured at a similar number of growing degree days (GDD), they required a different number of days to complete their life cycles depending on planting date. The growth period was reduced and flowering occurred sooner as both species experienced cooler temperatures and shorter daylight hours. Both species exhibited increased height, biomass, and seed production for the October-sown plants compared with other planting times, and these parameters were reduced by delaying the planting time. The shoot and root biomass of A. retroflexus and A. viridis (averaged over both populations) was reduced by more than 70% and 65%, respectively, when planted in January, in comparison to planting in October. When planted in October, A. retroflexus and A. viridis produced 11,350 and 5,780 seeds plant−1, but these were reduced to 770 and 365 seeds plant−1 for the January planting date, respectively. Although the growth and fecundity of these species were dependent on planting time, these weeds could emerge throughout the late spring to summer growing season (October to March) in southeast Australia and could produce a significant number of seeds. The results showed that when these species emerged in the late spring (October), they grew vigorously and produced more biomass in comparison with the other planting dates. Therefore, any early weed management practice for these species could be beneficial for minimizing the subsequent cost and energy inputs toward their control.

Applying control measures when carbohydrate levels are low can decrease the likelihood of plant survival, but little is known about the carbohydrate cycles of dewberry (Rubus spp.), a problematic weed group on cranberry (Vaccinium macrocarpon Aiton) farms. Weedy Rubus plants were collected from areas adjacent to production beds on commercial cranberry farms in Massachusetts, two locations per year for 2 yr. For each site and year, four entire plants were collected at five phenological stages: budbreak, full leaf expansion, flowering, fruit maturity, and after onset of dormancy. Root sections were analyzed for total nonstructural carbohydrates (TNC; starch, sucrose, fructose, and glucose). Overall trends for all sites and years showed TNC were lowest at full leaf expansion or flowering; when sampled at dormancy, TNC concentrations were greater than or equal to those measured at budbreak. Starch, a carbohydrate form associated with long-term storage, had low levels at budbreak, leaf expansion, and/or flowering with a significant increase at fruit maturity and the onset of dormancy, ending at levels higher than those found at budbreak. The concentration of soluble sugars, carbohydrate forms readily usable by plants, was highest at budbreak compared with the other four phenological samplings. Overall, our findings supported the hypothesis that TNC levels within the roots of weedy Rubus plants can be predicted based on different phenological growth stages in Massachusetts. However, recommendations for timing management practices cannot be based on TNC cycles alone; other factors such as temporal proximity to dormancy may also impact Rubus plants recovery, and further research is warranted. Late-season damage should allow less time for plants to replenish carbohydrate reserves (before the onset of dormancy), thereby likely enhancing the effectiveness of weed management tactics over time. Future studies should consider tracking the relationship between environmental conditions, phenological stages, and carbohydrate trends.

Navua sedge [Cyperus aromaticus (Ridl.) Mattf. & Kuek.], is a hard to control C4 perennial weed species in tropical regions of Australia. Knowledge of its seed biology could help to develop integrated weed management programs for this species. This study was conducted under laboratory and screenhouse conditions to evaluate the effect of alternating day/night temperatures, light, pretreatment high temperatures, burial depth, and flooding depth on the germination and emergence of two populations (Ingham and Tablelands) of C. aromaticus. Both populations germinated at temperatures ranging from 20/10 to 35/25 C; however, the Ingham population germination (76%) was greater than the Tablelands population (42%) at the highest temperature regime (35/25 C). None of the populations germinated at 15/5 C. Darkness completely inhibited germination in both populations, suggesting that the seeds are positively photoblastic. Seeds (dry and wet) of both populations germinated after exposure to pretreatment temperatures of up to 100 C for 5 min. After pretreatment at 150 C, only the Ingham population germinated, and germination was greater for dry seeds (62%) than for wet seeds (1%). Neither population germinated after exposure to 200 C. For both populations, maximum germination was observed for seeds at 0 cm; a burial depth of 0.5 cm completely inhibited emergence of the Tablelands population, and a burial depth of 2.0 cm completely inhibited germination of the Ingham population. A flooding depth of 10 cm greatly reduced emergence in both populations compared with 0 cm (62% and 78%) but 12% to 14% of seedlings still emerged, suggesting the need to integrate flooding with other management tools. The results also suggest that the Ingham population may have a greater potential to spread into new areas or become more invasive than the Tablelands population. Knowledge gained from this study can be used to manage C. aromaticus by fire/burning, tillage, and flooding.

The abundance of weedy rice (Oryza sativa L.) in the soil seedbank was estimated in 2011 in Italian rice (Oryza sativa L.) fields with different histories of imidazolinone-resistant Clearfield® rice varieties (CL), non-Clearfield® varieties (NCL), and planting methods. A model was used to predict weedy rice seedbank dynamics over time under different control strategies. Soil samples were taken from 50 rice fields cultivated with CL varieties consecutively for 0, 1, 2, or 3 yr, and weedy rice seedbank data were used in a model considering eight scenarios: (A) rice monoculture with CL and NCL varieties in alternate years; (B) 2 yr of CL, followed by 1 yr with NCL; (C) 3 yr of CL followed by 1 yr of NCL; (D) rice monoculture with only CL; (E) rice monoculture with only NCL; (F) 2 yr of CL followed by 1 yr of rotation with another crop (CR), and then by an additional year with NCL; (G) 1 yr of CR followed by 2 yr of CL, and then by 1 yr of NCL; (H) 2 yr of CR followed by 2 yr of CL. The weedy rice seedbank exceeded 1,000 seeds m−2 in the surveyed fields with no significant differences between rice planting methods. Highest densities were found in fields cultivated for 1 yr with CL varieties. Simulations indicated that where CL varieties were used in rice monoculture, the susceptible weedy rice seedbank was gradually reduced, producing a depletion after 17, 13, 11, and 9 yr in scenarios A, B, C, and D, respectively. The weedy rice seedbank increased in NCL monoculture (E) and declined significantly in crop rotation scenarios (F, G, H). The simulations indicated that the introduction of crop rotation is crucial for obtaining a relatively fast reduction of weedy rice seedbank and delaying the evolution of herbicide-resistant populations.

Barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] is a problematic weed in rice (Oryza sativa L.) fields. Overapplication of herbicides causes environmental pollution and the emergence of resistant weeds, and integrated weed management methods can reduce dependence on herbicides. The growth of E. crus-galli and rice seedlings was shown to be significantly inhibited by high concentrations of fulvic acid (FA, C14H12O8) under flooding conditions (HF, 0.80 g L−1) (P < 0.05). In contrast, seedling growth was promoted by the application of very low concentrations of FA (LF, 0.02 g L−1). The activities of glutathione S-transferase (GST) and antioxidant enzymes, including total superoxide dismutase (T-SOD), peroxidase (POD), and catalase (CAT), in E. crus-galli seedlings were enhanced by the LF treatment; while POD activity decreased and GST, T-SOD, and CAT activity was not significantly altered by the HF treatment. The metabolomic and transcriptomic analyses showed that FA regulated E. crus-galli seedling growth by affecting the synthesis of indole derivatives and flavonoid compounds. Compared with the blank control (CK, 0 g L−1), the levels of four indole derivatives were upregulated under the HF treatment, and the indole derivatives were slightly downregulated under the LF treatment. The flavonoids, including naringenin, naringenin chalcone, eriodictyol, kaempferol, and epigallocatechin, were downregulated under HF treatment, and the growth of E. crus-galli was reduced. In contrast, the metabolism and transcription of flavonoids were not significantly altered by the LF treatment. The addition of 0.80 g L−1 FA obviously inhibited the growth of newly sprouted E. crus-galli, whereas rice growth was significantly promoted 8 d after rice planting (P < 0.05). The application of FA, therefore, might be a potential integrated weed management method to control the damage caused by E. crus-galli in paddy fields.

Herbicide resistance is an increasing issue in many weed species, including rigid ryegrass (Lolium rigidum Gaudin); a major weed of winter cropping systems in southern Australia. Recently, this weed has also been found in summer crops in the southeastern region of Australia. Effective control of this herbicide-resistant weed across southeastern Australia requires alternative management strategies. These strategies can be informed by analyses on the interaction of germinable seeds with their regional environments and by identifying the differences between populations of varying herbicide-resistance levels. In this study, we explore how various environmental factors differentially affect the seed germination and seedling emergence of three L. rigidum populations, including one glyphosate-resistant population (GR), one glyphosate-susceptible population (GS), and one population of unknown resistance status (CC04). Germination was greater than 90% for all populations at each temperature regime, except 15/5 C. Populations germinated at a lower rate under 15/5 C, ranging from 74% to 87% germination. Salt stress had a similar effect on the germination of all populations, with 0% germination occurring at 250 mM salt stress. Population GS had greater tolerance to osmotic stress, with 65% germination at −0.4 MPa compared with 47% and 43% germination for CC04 and GR, respectively; however, germination was inhibited at −0.8 and −1.6 MPa for all populations. All populations had lower germination when placed in complete darkness as opposed to alternating light/dark. Germination in darkness was lower for CC04 (69%) than GR (83%) and GS (83%). Seedling emergence declined with increasing burial depth with the lowest emergence occuring at 8 cm (37%) when averaged over the populations. These results indicate that L. rigidum can survive under a range of environmental variables and that the extent of survival differs based on population; however, there was no difference based on herbicide-resistance status.

Navua sedge [Cyperus aromaticus (Ridley) Mattf. & Kük.] is an aggressive perennial sedge native to equatorial Africa that has become problematic in many Pacific islands and wet, tropical Queensland, Australia. It has had a significant impact on the livestock-grazing industry, sugarcane (Saccharum officinarum L.) and banana (Musa acuminata Colla) plantations, and various other ecosystems. A laboratory-based research investigation was conducted to understand germination and emergence requirements under various environmental conditions of three geographically varied populations sourced from South Johnstone (SJ), Mackay (M) and Nyleta Creek (NC) in Queensland. Germination was identified to be stimulated by light, with no germination recorded under darkness. Populations SJ and NC had optimal germination at alternating temperatures of 25/15, 30/20, and 35/25 C, whereas population M had optimal germination at 25/15 and 30/20 C. All populations recorded greater than 85% germination at all pH levels tested. Seeds of population SJ were more sensitive to salinity compared with populations M and NC, with SJ showing no germination at 100 mM, whereas populations M and NC had 23% and 9% germination, respectively. An inverse relationship was observed between osmotic potential and germination, with no germination recorded at osmotic potentials below −0.8 MPa in any population, indicating moisture availability is a critical requirement for germination. Exposing seeds to 120 C radiant heat completely inhibited germination in populations M and NC, whereas 3% of population SJ germinated following a 180-s exposure at 120 C. Seedling emergence decreased as planting depth increased. Emergence was greatest for seeds on the soil surface or at 0.5-cm burial depth, consistent with germination being stimulated by light. Knowledge of these biological characteristics of C. aromaticus seed germination will assist in investigation of suitable control actions for this species, particularly in the early stage of its invasion into new areas, and will contribute to significant reduction in the soil seedbank.

Winter wild oat [Avena sterilis ssp. ludoviciana (Durieu) Gillet & Magne; referred to as A. sterilis here] is one of the major weed species of the Avena genus, given its high competitive ability to infest cereal crops worldwide, with special concern in Spain. A nine-location field experiment was established across Spain where a total of 400 A. sterilis seeds per location were sowed in four replicates in autumn 2016 to monitor the emergence during two growing seasons in dryland conditions. The data were used to test the prediction ability of previously published thermal (TT) and hydrothermal time (HTT) models and to develop new models, if required. Overall, the average percentage of emergence was 30% during the first season and 21% during the second season. In both seasons, the main emergence flush occurred between November and February. According to the phenological stage, A. sterilis achieved the tillering earlier in southern sites, between November 25 and the end of December, compared with northern sites, where this stage was reached at the end of January. The newly developed model described the emergence with precision, using three cardinal temperatures to estimate the TT. The three cardinal points were established at −1.0, 5.8, and 18.0 C for base (Tb), optimum (To), and ceiling temperature (Tc), while the base water potential (Ψb) was established at −0.2 MPa for the HTT estimation. This study contributes to improving prediction of the emergence of A. sterilis and provides knowledge for decision support systems (DSS) for the control of this weed.

Sweet acacia [Vachellia farnesiana (L.) Willd.] is a problematic thorny weed species in several parts of Australia. Knowledge of its seed biology could help to formulate weed management decisions for this and similar species. Experiments were conducted to determine the effect of hot water (scarification), alternating temperatures, light, salt stress, and water stress on seed germination of two populations of V. farnesiana and to evaluate the response of its young seedlings (the most sensitive developmental stage) to commonly available postemergence herbicides in Australia. Both populations responded similarly to all the environmental factors and herbicides; therefore, data were pooled over the populations. Seeds immersed in hot water at 90 C for 10 min provided the highest germination (88%), demonstrating physical dormancy in this species. Seeds germinated at a wide range of alternating day/night temperatures from 20/10 C (35%) to 35/25 C (90%), but no seeds germinated at 15/5 C. Germination was not affected by light, suggesting that seeds are nonphotoblastic and can germinate under a plant canopy or when buried in soil. Germination was not affected by sodium chloride (NaCl) concentrations up to 20 mM, and about 50% of seeds could germinate at 160 mM NaCl, suggesting high salt tolerance ability. Germination was only 13% at −0.2 MPa osmotic potential, and no seeds germinated at −0.4 MPa, suggesting that V. farnesiana seeds may remain ungerminated until moisture conditions have become conducive for germination. A number of postemergence herbicides, including 2,4-D + picloram, glufosinate, paraquat, and saflufenacil, provided >85% control of biomass of young seedlings compared with the non-treated control treatment. Knowledge gained from this study will help to predict the potential spread of V. farnesiana in other areas and help to integrate herbicide use with other management strategies.

In central Europe, barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.], has commonly been found in humid lowland areas. As a result of the introduction of new crops and farming practices, in the northwest Carpathians, E. crus-galli has spread from lowland (<200 m altitude) to highland (>400 m altitude) areas. We collected seed samples from local populations lying at a distance of approximately 5 km from each other and lined up along transects following the flows of two rivers. The rivers first flow through the valleys separated by mountain ridges and eventually flow into a common lowland. After ripening, the seeds of all populations were germinated at 25 C under long-day conditions. Only the seeds of some lowland populations germinated up to 75%. The frequency of germinated seeds decreased as the altitude where the population was collected increased, and above 200 m above sea level, germination was mostly zero. We then studied the phenological and morphological differentiation of plants from the original (lowland) and recently occupied (highland) areas. Seeds of the lowest and the highest localities lying on the transect of each river were sown in a common garden experiment. In plants from the highland localities, heading and seed dispersal were earlier, while tiller height and tiller mass were lower than in plants from the lowland localities. Seed mass produced per tiller in the lowland and highland plants was similar, and as a result, highland plants allocated a larger proportion of body mass to seed production than did lowland plants. Echinochloa crus-galli populations from highland localities thus produce their progeny earlier and at a lower energy cost than populations from lowland localities. The plasticity of phenological characters likely facilitated adaptation during E. crus-galli spread from lowlands to highlands. Similar adaptations in plant phenology may contribute to the spread of E. crus-galli in other geographic areas.

African mustard (Brassica tournefortii Gouan) is a problematic winter annual weed in Australia. Germination ecology of B. tournefortii may change in response to the maternal environments or habitats in which the plants grow. A study was conducted to evaluate the effect of environmental factors on germination and emergence of four populations of B. tournefortii that were collected from different fields. Averaged over populations, germination was stimulated by dark and was higher at 25/15 C (92%) compared with 15/5 C (76%) and 35/25 C (45%). Averaged over light/dark regimes, at the lowest temperature regime (15/5 C), population A had higher germination than population D; however, at the highest temperature regime (35/25 C), population D had higher germination than population A. Populations B and C had higher germination in the temperature range of 25/15 C and 30/20 C compared with 15/5 C, 20/10 C, and 35/25 C. Seeds germinated at a wide range of alternating day/night temperatures (15/5 to 35/25 C), suggesting that seeds can germinate throughout the year if other optimum conditions are available. Population A was more tolerant to water and salt stress than population D. The sodium chloride concentration and osmotic potential required to inhibit 50% germination of population A were 68 mM and −0.60 MPa, respectively. Averaged over populations, seeds placed at 1-cm soil depth had the highest emergence (54%), and burial depth of 8 cm resulted in 28% seedling emergence. Averaged over populations, wheat residue retention at 6,000 kg ha−1 resulted in greater seedling emergence than the residue amount of 1,000 kg ha−1. The results suggest that B. tournefortii will be favored in no-till systems and that the seedbank of B. tournefortii could be managed by tillage regimes that bury its seeds below 8-cm depths and restrict seedling emergence and growth of new plants.

Slender amaranth (Amaranthus viridis L.) and redroot pigweed (Amaranthus retroflexus L.) are increasingly problematic weeds of summer crops in Australia. Water is considered the most limiting factor in an agroecosystem, and water stress adversely impacts the growth and reproduction of plant species. The primary objective of this study was to determine the growth and fecundity of two Australian biotypes (Goondiwindi and Gatton) of A. viridis and A. retroflexus under water-stress conditions. Four water-stress treatments (100%, 75%, 50%, and 25% field capacity [FC]) at a 4-d irrigation interval were chosen. No difference was observed for growth and seed production between the two biotypes of both species when grown under varying soil moisture regimes. At 100% FC, A. viridis produced 44 g plant−1 aboveground biomass and 1,740 seeds plant−1. The maximum growth (46 g plant−1) and seed production (3,070 seeds plant−1) of A. retroflexus were observed at 100% FC. The growth and seed production of both species were reduced with increased water-stress levels. Both weeds responded to water stress by decreasing the shoot:root biomass ratio. However, A. viridis (290 seeds plant−1) and A. retroflexus (370 seeds plant−1) were able to produce a significant number of seeds per plant even at 25% FC. Results suggest that both weeds will produce seeds under water-limiting conditions. Therefore, management strategies are required to minimize the growth and survival of weeds in water-deficit conditions.

Clearfield™ (CL) rice (Oryza sativa L.) is a weedy rice (Oryza spp.; synonym = red rice) control tool that has been used in Brazil since 2003. This system includes the use of an imidazolinone (IMI)-tolerant cultivar and the application of IMI herbicides. In this review article, Brazilian weed scientists evaluate the challenges and lessons learned over 18 yr of CL use. CL system benefits include selective weedy rice control, better crop establishment during the most advantageous period of the year, and more efficient fertilizer use. In Rio Grande do Sul state, the CL system, in conjunction with other improvements, has contributed to rice grain yield gains from 5,500 kg ha−1 before 2002 to around 8,400 kg ha−1 currently. In contrast, the main problem that has arisen over this period is the rapid evolution of IMI-resistant weedy rice, caused by gene flow from CL rice cultivars. The off-label use (rate and continuous use) of IMI herbicides has contributed to the evolution of resistance in Echinochloa spp. and other weeds. IMI herbicide carryover has also affected susceptible crops grown after CL rice. Crop rotation with soybean [Glycine max (L.) Merr.] is increasing, ensuring system sustainability. The importance of minimum tillage has also become apparent. Such cultivation includes applying nonselective herbicides before sowing or just before crop emergence (at the spiking stage to eliminate as much weedy rice as possible and other weeds at an early growth stage). It also includes the use of certified seeds free of weedy rice, following label instructions for IMI herbicides, applying the herbicide PRE followed by POST, and complementary weedy rice management practices, such as roguing of surviving weedy rice plants.

Harvest weed seed control (HWSC) is a weed management technique that intercepts and destroys weed seeds before they replenish the soil weed seedbank and can be used to control herbicide-resistant weeds in global cropping systems. Wild radish (Raphanus raphanistrum L.) is a problematic, globally distributed weed species that is considered highly susceptible to HWSC, as it retains much of its seed on the plant during grain harvest. However, previous studies have demonstrated that R. raphanistrum is capable of adapting its life cycle, in particular its flowering time, to allow individuals more time to mature and potentially shed seeds before harvest, thereby evading HWSC interception. This study compared the vegetative growth plus physiological and ecological fitness of an early-flowering R. raphanistrum biotype with an unselected genetically related biotype to determine whether physiological costs of early flowering exist when in competition with wheat (Triticum aestivum L.). Early flowering time adaptation in R. raphanistrum did not change the relative growth rate or competitive ability of R. raphanistrum. However, the height of first flower was reduced in the early flowering time–selected population, indicating that this population would retain more pods below the typical harvest cutting height (15 cm) used in HWSC. The presence of wheat competition (160 to 200 plants m−2) increased flowering height in the early flowering time–selected population, which would likely increase the susceptibility of early-flowering R. raphanistrum plants to HWSC. Overall, early-flowering adaption in R. raphanistrum is a possible strategy to escape being captured by the HWSC; however, increasing crop competition is likely to be an effective strategy to maintain the effectiveness of HWSC.

The addition of dicamba as a weed control option in soybean [Glycine max (L.) Merr.] is a valuable tool. However, this technology must be utilized with other herbicide sites of action (SOAs) to reduce selection pressure on weed communities and ensure its prolonged usefulness. A long-term trial was conducted for 7 yr in Indiana to evaluate weed community densities and species richness with four levels of dicamba selection pressure in a corn (Zea mays L.)–soybean rotation. Monocot densities and richness increased over time in the dicamba-reliant treatment. Dicot densities in the dicamba-reliant treatment declined over time, but dicot richness increased. The soil weed seedbank was affected by the varying herbicide strategies. The dicamba-reliant strategy had greater than 43% higher total weed density than all other treatments, primarily due to having a monocot density that was at least 71% higher than the other treatments. The fully diversified strategy with eight SOAs and residual herbicides used every year had the lowest total weed species richness in the soil seedbank, which supported the in-field observations.

African lovegrass [Eragrostis curvula (Schrad.) Nees] is a highly invasive C4 perennial grass that threatens global biodiversity. Appropriate management of this species has been hampered by a lack of knowledge concerning its seed ecology, resulting in significant economic and environmental impacts within various environments. Consequently, this study explored the effects of a selection of environmental factors (photoperiod, alternating temperature, pH, and salinity) by analyzing several measures of germination on four geographically distinct populations of E. curvula to assist in its extirpation from infested sites. Seeds were collected in Australia from Maffra and Shepparton, VIC; Tenterfield, NSW; and Midvale, WA. Key results showed that seeds from Maffra (54% vs. 79%), Tenterfield (38% vs. 61%), and Shepparton (34% vs. 71%) had significantly reduced germination in complete darkness compared with an alternating 12-h light and 12-h dark photoperiod, whereas Midvale had consistent germination (91% vs. 99%). Temperatures between 17/7 C reduced germination for Maffra (42% vs. 73%), Tenterfield (34% vs. 55%), and Shepparton (33% vs. 59%) compared with the mean of all other temperature combinations, whereas Midvale had consistent germination. Furthermore, germination for all populations was consistent between pH 4 and 9. For salinity, germination was significantly reduced at ≥100 mM for Maffra (29% vs. 67%), ≥150 mM for Tenterfield (29% vs. 94%) and Shepparton (39.5% vs. 81.5%), and 250 mM for Midvale (39% vs. 82%) compared with the mean of all other concentrations. Although each trial was conducted independently, the data can be used to generate species-targeted management. Such strategies include maintaining high levels of quarantine and hygiene programs to avoid future spread; where practical, applying light-limiting strategies (mulching, tilling, or scraping) for the Maffra, Tenterfield, and Shepparton populations; and maintaining management efforts year-round, as the species can germinate under a wide range of conditions.

Weed emergence time and the longevity of weed seeds within the soil play an important role in implementing a timely and effective weed control program. In this study, the seed longevity and emergence pattern of wild oat (Avena fatua L.) and sterile oat [Avena sterilis ssp. ludoviciana (Durieu) Gillet & Magne] were monitored in field conditions. Fresh seeds of A. fatua and A. ludoviciana were placed into nylon bags (50 seeds per bag in three replications for three locations in eastern Australia: Gatton, Narrabri, and St George) and buried at depths of 0, 2, and 10 cm in November 2017. Bags were exhumed at 6-mo intervals over 30 mo to evaluate seed germination, viability, and decay components. The seed decay component of A. fatua and A. ludoviciana followed an exponential pattern. On both the surface and at the 10-cm burial depth, 50% of the seeds of A. fatua and A. ludoviciana had decayed by 6 mo. The seeds of A. fatua persisted longer at 2-cm depth than at other depths, particularly at St George, where 90% of the seeds decayed after the 30-mo study. However, at Gatton and Narrabri, 90% of the seeds of A. fatua at this depth had decayed after 18 mo of burial in the soil. In the emergence pattern experiment (2017 to 2019), the emergence of A. fatua and A. ludoviciana from different burial depths was also studied. The emergence of A. fatua and A. ludoviciana was greater from 2-cm (29% to 36%) and 5-cm (18% to 43%) soil depths compared with the surface (5% to 10%) and 10-cm (3-9%) soil depth. Avena ludoviciana emerged earlier (2,253 growing degree days [GDD]; March 14, 2018) than A. fatua (3,364 GDD; May 23, 2018). Both species exhibited high emergence between May to June 2018, and the last cohort of each species was observed in October 2018. The highest seedling emergence occurred at the start of the winter season (May), which emphasizes the need for early PRE weed control such as tillage, herbicide application, and cover crops to ensure crops are planted in a clean seedbed. The continued emergence of these weeds into the spring season (October) emphasizes the need for extended periods of A. fatua and A. ludoviciana management. The results also suggest that management strategies that can control all emerged seedlings over 2 yr and restrict seed rain in the field could lead to complete control of Avena spp. in the field.

Weedy rice (Oryza sativa f. spontanea or O. sativa complex) has become a severe threat to Malaysian rice (Oryza sativa L.) granaries after the direct-seeding method of rice cultivation was introduced in the late 1980s. Since then, researchers have studied the biology and ecology of weedy rice and espoused the evolutionary theory of the origin of Malaysian weedy rice. This review paper aimed to synthesize the body of knowledge about weedy rice and the evolution of herbicide-resistant (HR) weedy rice in Malaysia. The imidazolinone (IMI) herbicide component of the Clearfield® Production System (CPS) rice package is among the most effective tools for weedy rice control. However, dependence solely on this technology and farmers’ ignorance about the appropriate use of IMI herbicides with the CPS rice package have resulted in the evolution of IMI-resistant (IMI-R) weedy rice. This has reduced the efficacy of IMI herbicides on weedy rice, ultimately nullifying the benefit of CPS rice in affected fields. At present, it is assumed that IMI-R weedy rice populations are widely distributed across the rice granaries in Malaysia. Therefore, it is important that integrated management measures be adopted comprehensively by Malaysian rice growers to curb the spread of IMI-R weedy rice problem in Malaysia, especially in fields planted with CPS rice. This review focuses on the biology of Malaysian weedy rice, the history of the establishment of weedy rice in Malaysian rice fields, the impact of HR rice technology on the evolution of IMI-R weedy rice in Malaysia, the distribution of resistant weedy rice populations across Peninsular Malaysia rice granaries, the weedy rice resistance mechanisms, and weedy rice management. The synthesis of all this information is helpful to researchers, policy makers, the private agricultural industry, advisers to farmers, and proactive farmers themselves with the goal of working toward sustainable rice production.

African lovegrass [Eragrostis curvula (Schrad.) Nees] is an invasive weed that is threatening biodiversity around the world and will continue to do so unless its efficient management is achieved. Consequently, laboratory and field-based experiments were performed to analyze several measures of germination to determine the effect of drought stress, radiant heat stress, and burial depth and duration (longevity) on E. curvula seeds. This study investigated seeds from four spatially varied populations across Australia: Maffra and Shepparton, VIC; Tenterfield, NSW; and Midvale, WA. Results showed that increasing drought stress reduced and slowed germination for all populations. Maffra (24% vs. 83%) and Shepparton (41% vs. 74%) were reduced at the osmotic potential of ≤−0.4 MPa, while Tenterfield (35% vs. 98.6%) and Midvale (32% vs. 91%) were reduced at ≤−0.6 MPa, compared with the mean of all other osmotic potentials. Radiant heat at 100 C significantly reduced and slowed germination compared with 40 C for Tenterfield (62% vs. 100%), Shepparton (15% vs. 89%), and Midvale (41% vs. 100%), while Maffra (75% vs. 86%) had consistent germination. For the effect of burial depth and duration (longevity), there was no significant difference across the 14-mo period; however, the 0-cm burial depth had a significantly lower final germination percentage compared with depths of 3, 5, and 10 cm (24% vs. 55%). Although each trial was conducted independently, the results can be used to help identify efficient control measures to reduce infesting populations. Recommended measures include using soil moisture monitoring to detect which conditions will promote germination, as germination is encouraged when the osmotic potential is >−0.6 MPa; exposing seeds to radiant heat (>100 C) using methods such as prescribed burning; and limiting soil disturbance over time to reduce seed establishment.

Sumatran fleabane [Conyza sumatrensis (Retz.) Walker] is an emerging weed in the Australian cropping region. Populations resistant to glyphosate have evolved in Australia, creating the demand for information regarding the seed germination ecology of glyphosate-resistant (R) and glyphosate-susceptible (S) populations of C. sumatrensis. A study was conducted to examine the effects of temperature, light intensity, salt stress, osmotic stress, and burial depth on the germination and emergence of two populations (R and S) of C. sumatrensis. Both populations were able to germinate over a wide range of alternating day/night temperatures (15/5 to 35/25 C). In light/dark conditions, the R population had higher germination than the S population at 20/10 and 35/25 C. In the dark, the R population had higher germination than the S population at 25/15 C. In the dark, germination was inhibited at 30/20 C and above. Averaged over populations, seed germination of C. sumatrensis was reduced by 97% at zero light intensity (completely dark conditions) compared with full light intensity. Seed germination of C. sumatrensis was reduced by 17% and 85% at osmotic potentials of −0.4, and −0.8 MPa, respectively, compared with the control treatment. The R population had lower germination (57%) than the S population (72%) at a sodium chloride concentration of 80 mM. Seed germination was highest on the soil surface and emergence was reduced by 87% and 90% at burial depths of 0.5 and 1.0 cm, respectively. Knowledge gained from this study suggests that a shallow-tillage operation to bury weed seeds in conventional tillage systems and retention of high residue cover on the soil surface in zero-till systems may inhibit the germination of C. sumatrensis. This study also warrants that the R population may have a greater risk of invasion over a greater part of a year due to germination over a broader temperature range.