Considering the preferences for nitrogen forms by invasive plants: a case study from a hydroponic culture experiment

Although preference for NH₄⁺, NO₃^? or a combination of the two often differs among species, we know little about the responses of invasive plants to different inorganic N forms. Furthermore, many studies have suggested that an increase in N availability may facilitate further invasions. However, most of these studies predicted the positive feedback without considering the preference for N forms of invasive plants. Therefore, we cultivated four common invasive species (Mikania micrantha, Ipomoea cairica, Wedelia trilobata and Bidens pilosa) in South China with hydroponic media containing different forms of N (i.e. NO₃^?, NH₄NO₃ and NH₄⁺) at equimolar concentrations. Our results showed that the N forms significantly affected the growth, biomass allocation and physiological traits of the plants. All four invasive plants supplied with NO₃^? alone had better performance and greater allocation to root biomass than did plants that were supplied with NH₄⁺ alone. Moreover, the photosynthetic rate, pigment content and photosystem II activity of plants supplied with NO₃^? or NH₄NO₃ were significantly higher than those of plants supplied with NH₄⁺alone. The results suggested that all four invasive plants preferred NO₃^? rather than NH₄⁺, and changes in NO₃^? played an important role in furthering the invasions of these plants than did changes in NH₄⁺. Our results implied that decreasing NO₃^? may be a useful tool for controlling and managing invasive plants preferring NO₃^?. In addition, this study highlighted the importance of considering plant N form preference to better understand plant invasions.     

Rising CO2 can alter fodder–weed interactions and suppression of Parthenium hysterophorus

Three C₄ grass (Setaria incrassata, Astrebla squarrosa and Bothriochloa decipiens) and one C₃ legume (Clitoria ternatea) suppressive fodder species, were re‐evaluated against the growth of the C₃ Parthenium hysterophorus under an ambient (390 μmol mol^?1) and an elevated atmospheric CO₂ concentration (550 μmol mol^?1). Under the elevated atmospheric CO₂, shoot dry biomass and suppression index (SI) value of the C₄ S. incrassata were both reduced by 32% and 0.7 respectively, while those for A. squarrosa were reduced by 23% and 0.3. In contrast and under the same elevated atmospheric CO₂ concentration, the shoot dry biomass and SI of the C₄ B. decipiens were increased by 8% and 0.1 respectively, while those for the C₃ C. ternatea were increased by 38% and 0.8. Our results suggest that C₃ fodder plants along with certain C₄ species could be utilised for the effective management of P. hysterophorus under the future elevated atmospheric CO₂ conditions. However, this system needs more fodder species to be investigated. Our results suggest that rising CO₂ per se may alter the efficacy of suppressive fodder management of an invasive C₃ species, P. hysterophorus.     

Susceptibility of tomato borer,Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) populations from Turkey to 7 different insecticides in laboratory bioassay

The tomato borer, Tuta absoluta (Meyrick), was first recorded in Turkey in August 2009 and rapidly became a serious pest in the Mediterranean and Aegean coastal regions in field and greenhouse grown tomatoes. Currently, insecticides are considered one of the major tools for the management of T. absoluta in Turkey. This study, investigated the efficacy of 7 different insecticides, against T. absoluta in laboratory bioassays. To determine the lethal concentration (LC) values and feeding activity of the larvae, tomato leaf parts mined by 1–3 day old L1 larvae were dipped into different insecticide concentrations. Mortality was recorded 5 days after insecticide treatments. Spinosad, chlorantraniliprole + abamectin or indoxacarb treatment resulted in 100% mortality with minimal or no feeding in all populations at their recommended doses of 120, 50.4 and 60 mg a.s. L^?1, respectively. In general, the LC₉₉ values of populations for these insecticides were similar and also lower than that of the recommended field doses. The effect of pyridalyl was low, resulting in low mortality with serious feeding damage at the dose of 125 mg a.s. L^?1. The efficacies of abamectin, metaflumizone and azadirachtin were found to be moderate to low at the recommended doses (4.5, 240 and 50 mg a.s. L^?1, respectively). However, these insecticides may affect pupation and adult emergence rates hence further studies are recommended to investigate these insecticides.     

Observed changes in soyabean growth and seed yield from Abutilon theophrasti competition as a function of carbon dioxide concentration

Soyabean (Glycine max) was grown at ambient and projected levels of atmospheric carbon dioxide (+250 μmol mol^?1 above ambient) over two field seasons with and without the presence of a weed, Abutilon theophrasti, to quantify the potential effect of rising atmospheric carbon dioxide concentration on weed–crop interactions and potential yield loss in soyabean. Under weed‐free conditions, elevated CO₂ resulted in stimulations in soyabean seed yield and associated components, including pod number. At an approximate density of 6 plants m^?2, A. theophrasti competition resulted in a significant reduction (?40%) in soyabean seed yield. Although differences in seed yield reduction by A. theophrasti were observed as a function of year, the relative decrease in seed yield with A. theophrasti biomass did not differ in response to CO₂. Although careful weed management will be necessary if CO₂‐induced increases in seed yield for soyabean are to be achieved, these data suggest that soyabean seed yield may be more resilient in competition with A. theophrasti as a function of rising atmospheric levels of carbon dioxide.     

Weed–pathogen interactions and elevated CO2: growth changes in favour of the biological control agent

In this study, we used Parthenium hysterophorus and one of its biological control agents, the winter rust (Puccinia abrupta var. partheniicola) as a model system to investigate how the weed may respond to infection under a climate change scenario involving an elevated atmospheric CO₂ (550 μmol mol^?1) concentration. Under such a scenario, P. hysterophorus plants grew significantly taller (52%) and produced more biomass (55%) than under the ambient atmospheric CO₂ concentration (380 μmol mol^?1). Following winter rust infection, biomass production was reduced by 17% under the ambient and by 30% under the elevated atmospheric CO₂ concentration. The production of branches and leaf area was significantly increased by 62% and 120%, under the elevated as compared with ambient CO₂ concentration, but unaffected by rust infection under either condition. The photosynthesis and water use efficiency (WUE) of P. hysterophorus plants were increased by 94% and 400%, under the elevated as compared with the ambient atmospheric CO₂ concentration. However, in the rust‐infected plants, the photosynthesis and WUE decreased by 18% and 28%, respectively, under the elevated CO₂ and were unaffected by the ambient atmospheric CO₂ concentration. The results suggest that although P. hysterophorus will benefit from a future climate involving an elevation of the atmospheric CO₂ concentration, it is also likely that the winter rust will perform more effectively as a biological control agent under these same conditions.     

Baseline and differential sensitivity of Peronophythora litchii (lychee downy blight) to three carboxylic acid amide fungicides

Downy blight, caused by Peronophythora litchii, is an important disease of lychee (litchi) plants in China. The in vitro sensitivities of various asexual stages of P. litchii to the three carboxylic acid amide (CAA) fungicides dimethomorph, flumorph and pyrimorph were studied with four single‐sporangium isolates. None of the three fungicides affected zoospore discharge from sporangia, but they strongly inhibited mycelial growth (mean EC₅₀ values of 0·075, 0·258 and 0·115 mg L^?1, respectively); sporangial production (mean EC₅₀ values of 0·085, 0·315 and 0·150 mg L^?1, respectively); germination of cystospores (mean EC₅₀ values of 0·140, 0·150 and 0·645 mg L^?1, respectively); and germination of sporangia (mean EC₅₀ values of 0·203, 0·5 and 0·743 mg L^?1, respectively). As mycelial growth was the most sensitive stage to dimethomorph and pyrimorph, it was chosen to test baseline sensitivities to the three fungicides. In 2007, from 131 isolates collected in Fujian, Guangdong and Guangxi provinces, 127, 116 and 113 isolates were used to establish baseline sensitivity for dimethomorph, flumorph and pyrimorph respectively. Isolates from different provinces exhibited similar baseline sensitivity to the same fungicide. Baseline sensitivities to dimethomorph, flumorph and pyrimorph were distributed as unimodal curves, with mean EC₅₀ values of 0·082 (± 0·01), 0·282 (± 0·047), and 0·115 (± 0·032) mg L^?1, respectively. This information will serve as a baseline for tracking future changes in sensitivities of P. litchii populations to these three CAA fungicides.     

Using chemical seed dormancy breakers with herbicides for weed management in soyabean and wheat

Variable dormancies result in periodicity in the germination of weeds and make weed control a repetitive practice. Under some conditions, repeated applications of selective herbicides can lead to the dominance of perennial weeds like Cyperus rotundus . Our hypothesis was that applying a chemical dormancy breaker (DB ) plus herbicide mixture would better control a mixture of weed species. Three experiments were designed to develop a cost‐effective DB treatment and to evaluate its dose with herbicides tank‐mixtures for effective weed management. KNO ₃ and gibberellic acid GA ₃ as dormancy breakers offered comparable effects, but KNO ₃ was more economical than GA ₃. KNO ₃ at a 6% concentration was more effective in promoting weed germination than a 3% concentration in soyabean. A combination of KNO ₃ (6%) and pre‐emergence pendimethalin 0.75 kg a.i. ha^?1 + imazethapyr 0.10 kg a.i. ha^?1 controlled annual weeds by 99% and reduced C. rotundus growth by 83%. This treatment gave significantly higher soyabean yield and net returns. Similarly, a tank‐mixture comprising of clodinafop 0.06 kg a.i. ha^?1 + metsulfuron 0.006 kga.i. ha^?1 was more effective against weeds than pre‐emergence tank‐mix application of pendimethalin 0.75 kg a.i. ha^?1 + carfentrazone‐ethyl 0.02 kg a.i. ha^?1 and isoproturon 0.75 kg a.i. ha^?1. The use of pre‐emergence tank‐mixture of pendimethalin 0.75 kg a.i. ha^?1 + imazethapyr 0.10 kg a.i. ha^?1 should exhaust seed/tuber bank if repeated and reduce the application cost of herbicides by 50% and the dose, residue and cost of pendimethalin by 25%.     

Weeds for weed control: Asteraceae essential oils as natural herbicides

The aim of this study was to test the botanical family of Asteraceae as a source of natural herbicides. Twenty Asteraceae species were collected during flowering time and evaluated in terms of the yield and quality of essential oils (germination inhibition and growth of weeds). Half the species showed a sufficient yield of essential oil (from about 0.1% to 1.43%) when testing these phytochemicals in vitro as germination inhibitors of two typical weeds, Amaranthus retroflexus and Setaria viridis. Despite the higher tolerance of S. viridis, the concentration of 100 μg L^?1 of essential oils of the two Artemisia species and Xanthium strumarium could totally inhibit germination. In addition, at 10 μg L ^?1, the same essential oils showed full inhibition of A. retroflexus seeds. A comparison of their effectiveness at suboptimal doses led to a further selection of the most promising sources of essential oils. After their chemical characterisation, the essential oils were tested as post‐emergence herbicides on seedlings of the above‐cited weeds. After spraying the weeds at different concentrations (10, 100 and 1000 mg L^?1) during two different phenological stages of weed seedlings (cotyledons and the third true leaf), the essential oils of Artemisia annua and X. strumarium showed the best performance. The essential oils of X. strumarium were then tested again on both weeds to monitor the dynamics of plant injury. A reduction in plant fresh weight (about 20%–30% after 10 days) and chlorophyll content (destroyed, after the same amount of time) was found, thus confirming the total and rapid effectiveness of these essential oils. In summary, A. annua and X. strumarium have elicited considerable agronomic interest and appear to be suitable as a source of essential oils to act as natural herbicides.     

Could recent increases in atmospheric CO2 have acted as a selection factor in Avena fatua populations? A case study of cultivated and wild oat competition

Projected increases in atmospheric carbon dioxide concentration [CO₂] may lead to differential selection and competition between weeds and crops. Yet, the current level of atmospheric [CO₂] already reflects a rapid rise (~25%) from mid‐20th century levels. To assess whether this increase could have already resulted in differential selection between weeds and crops, two temporally distinct populations of Avena fatua (wild oat) from the same geographic location, one from the 1960s (WO_old) and one from 2014 (WO_new), were grown with and without a cultivated oat (CO) line, Clintland 64 (Avena sativa) at current and mid‐20th century [CO₂] levels (ca 320 and 402 μmol mol^?1 respectively). Monocultures of each WO population differed in their response to recent increases in atmospheric [CO₂], with WO_new showing a significantly higher response for all vegetative parameters relative to WO_old. Assessment of competitive outcomes indicated that at 315 μmol mol^?1 cultivated oat was at a competitive advantage relative to either A. fatua population for leaf area and total above‐ground biomass. However, at current levels of CO₂, an overall increase in WO_new competitive ability was observed relative to the cultivated oat line. Overall, these differences are consistent with, but not conclusive for, improved evolutionary fitness and increased early competitive ability of A. fatua relative to cultivated oat as a function of the recent increase in atmospheric [CO₂]. While additional empirical studies are needed, these preliminary results indicate that weeds may be adapting rapidly to rising levels of atmospheric carbon dioxide.     

Genetic diversity of giant reed ( A rundo donax) in Australia

The perennial grass, Arundo donax, has shown potential as a promising biomass crop. However, it has become invasive in a number of areas and declared a noxious weed in some jurisdictions, making proposals to grow A. donax for commercial use in Australia controversial. Evidence of asexual reproduction and the presence of a single genetic clone in Australia was investigated, as such characteristics would indicate a limited risk of escape and invasion. Using amplified fragment length polymorphism markers, the genetic diversity of 218 A. donax samples from across Australia was examined. The samples were found to separate into two distinct genetic groups, or clades. There was only a small amount of genetic diversity within a clade (0.9 and 1.5%). However, there was a larger difference between the clades of 19.8%, suggesting the presence of two distinct A. donax genotypes in Australia. The low level of genetic variation in Australian A. donax that was found in this study indicates that spread is essentially by vegetative means and suggests that if grown in areas where it is separated from natural water dispersal events, A. donax poses a low risk of becoming invasive.     

Growth and photosynthetic responses of invasive Bidens frondosa to light and water availability: A comparison with invasive and native congeners

Bidens frondosa is a new invasive species in China. However, the mechanisms underlying its invasiveness are still not understood. This study compared the new invader with its invasive congener, Bidens pilosa, and two native congeners, Bidens biternata and Bidens tripartita, in terms of their morphology, growth, biomass allocation and photosynthetic parameters across variant light and water conditions, aiming to explore the traits that are associated with the invasiveness of the invasive species. All these species are annual herbs. The results showed that the four congeners had a similar tendency of plasticity in their morphological and growth traits to varying light and water, but their response was quantitatively different. Most of the morphological and growing variables, as well as the photosynthetic parameters, were affected more strongly by manipulated light levels. Although B. frondosa had a lower total biomass and relative growth rate than the invasive congener, B. pilosa, the trait values related to growth (e.g. plant height, total biomass, relative growth rate and specific leaf area) and the mean value of the plasticity index were higher for the invasive B. frondosa than for the native B. tripartita. These could contribute to the invasiveness of the invasive species. In addition, the native species, B. biternata, is a vigorous weed with a strong adaptive capacity across various light and water gradients, suggesting that it has the potential to be invasive if introduced into areas with suitable conditions for growth.     

Influence of the nitrogen form on in vitro organogenesis in Equisetum arvense

The physiological and biochemical mechanisms of organogenesis in Equisetum arvense have not been clarified yet. However, high concentrations of nitrogen have been shown to exert an inhibitory effect on in vitro tuber formation in E. arvense. The aim of this study was to clarify the influence of the form of nitrogen in a medium on in vitro organogenesis in E. arvense. Single‐node segments of E. arvense rhizomes were cultured in the test medium. The NH₄‐N and NO₃‐N concentrations of the test medium, respectively, were adjusted by adding NH₄H₂PO₄ and KNO₃ to the basal medium. The basal medium was a nitrogen‐free, modified form of White's medium. Vegetative shoots were newly formed in the test tubes for concentrations of NO₃‐N and NH₄‐N that exceeded 56 mg L^?1. However, no rhizome was formed at NH₄‐N concentrations exceeding 28 mg L^?1. The number of newly formed tubers decreased at an NH₄‐N concentration of 28 mg L^?1 and no tuber was formed at NH₄‐N concentrations exceeding 56 mg L^?1. In summary, although the presence of NO₃‐N in the medium did not inhibit in vitro rhizome or tuber formation in E. arvense, the presence of NH₄‐N in the medium exerted a strong inhibitory effect on the in vitro formation of both of these organs.     

Competitive ability of ALS‐inhibitor herbicide‐resistant Fimbristylis miliacea

Fimbristylis miliacea, a weed in rice, has evolved resistance to acetolactate synthase (ALS) inhibitors. This study aimed to investigate the competitive abilities of ALS‐resistant (R) and ALS‐susceptible (S) F. miliacea with rice. A replacement series experiment was conducted in the glasshouse at the Federal University of Pelotas, Brazil. The proportions of rice to F. miliacea were 100:0, 75:25, 50:50, 25:75 and 0:100, with 1060 plants m^?2. The experimental units were arranged in a completely randomised design with four replications. A follow‐up study was conducted at the University of Arkansas, Fayetteville, USA, in a split‐plot design with four replications. The main plot was species mixture (rice × R, rice × S, R × S). The subplot was competition partitioning (below‐ and above‐ground, below‐ground only, above‐ground only and no interspecific competition). Leaf area, plant height and shoot dry mass were recorded. Rice was more competitive than the R or S F. miliacea. In equal proportions of rice and F. miliacea, regardless of ecotype, the relative leaf area, height and dry mass of rice were greater than that of F. miliacea. The ALS‐resistant ecotype was less competitive with rice than the S ecotype. Intraspecific competition among rice plants was stronger than rice competition with F. miliacea. Competition for below‐ground resources was the most critical aspect of interference among rice and F. miliacea. In production fields, high infestation levels of F. miliacea results in significant yield losses; thus, resistance to ALS inhibitors needs to be curtailed.     

Competition between Imperata cylindrica and maize in the forest savannah transition zone of Nigeria

Imperata cylindrica is a noxious weed that infests annual and perennial crops in most tropical regions. High crop densities may offer opportunities to reduce I. cylindrica competition in small‐scale farming systems. The competitive ability of maize relative to I. cylindrica was evaluated in an addition series experiment in the forest savannah transition zone in 2006 and 2007 at Ibadan, Nigeria. Maize and I. cylindrica were planted in eight monoculture densities (4, 8, 12, 16, 20, 32, 48 and 64 plants m^?2) and in a 1:1 mixture at eight total densities (2:2, 4:4, 6:6, 8:8, 10:10, 16:16, 24:24 and 32:32 maize: I. cylindrica plants m^?2) as in monoculture. Non‐linear regression models were used to relate crop and weed shoot biomass to their densities and total grain yield to maize density. In maize, intraspecific competition was more than interspecific competition; in I. cylindrica, interspecific competition was higher than intraspecific. As expected, total grain yield was lower in the mixture than in maize monoculture at all total densities. Average maize grain yield in maize monoculture differed from that in mixtures by 0.77 t ha^?1 in 2006 and 0.57 t ha^?1 in 2007. Niche differentiation indices were <1 in 2006 and >1 in 2007, indicating that both species competed for similar resources in 2006, but not in 2007. The greater competitive ability of maize over I. cylindrica may be associated with rapid growth and canopy development observed in the field.     

Is the temporary grazing exclusion a good management alternative for arid peatlands?

Highland peatlands are one of the most fragile ecosystems in the world. These ecosystems have vital nutritional importance for livestock, however previous research has indicated that intensive grazing could negatively affect these communities, requiring the application of temporary grazing exclusion to restore the health of the peatland. The objective of our study was to evaluate the effect of grazing exclusion on plant allocation strategy and carrying capacity of Oxychloe andina Phil. The plant traits of O. andina were quantified through measurements of specific leaf area (SLA) and leaf dry matter content (LDMC). We estimated the carrying capacity through livestock censuses and vegetational transects. SLA was found to be greater in grazed conditions than in ungrazed conditions (p?=?0.0194) at five months after the application of treatments. Additionally, greater productivity associated with greater LDMC in March was observed under conditions of grazing exclusion (p?=?0.0306). Production estimates of O. andina reached 4816?kg of dry matter (DM) distributed over an area of 9.84?ha, which was equivalent to 489?kg DM of O. andina DM ha^?1. Using DM production as a proxy of the peatland and considering the average vegetation cover of 70%, the peatland produces an estimated of 1370?kg DM year^?1. The temporary grazing exclusion enhanced the productivity of O. andina. However, depending on DM production in relation to grazing demand, there is a possibility of exceeding the animal load for this plant species.     

Growth, reproduction and resource allocation of Tithonia diversifolia and Tithonia rotundifolia

Growth, reproduction and resource allocation of the polycarpic Tithonia diversifolia and the monocarpic Tithonia rotundifolia were studied in mixed and monoculture populations. The aim was to identify the characteristics contributing to the invasive habits of these species. Tithonia rotundifolia attained reproductive maturity at 2 months and T. diversifolia 4 months after planting. Tithonia rotundifolia completed its life cycle after 4 months, just as T. diversifolia was starting to flower. Both plant species produced a high number of seeds per capitulum (136–144 seeds in T. diversifolia; 113–120 in T. rotundifolia). Tithonia diversifolia reproduced asexually and sexually and produced many small light seeds. Tithonia rotundifolia produced large seeds, had early rapid growth, short life cycle and high reproductive effort. Growth in mixture did not significantly affect plant height, numbers of branches and leaves, or leaf size, but affected biomass allocation to reproductive and vegetative activities in the species. The attributes contributing to the invasiveness of these species are large seeds, early rapid growth, short life cycle and high reproductive effort in T. rotundifolia, with many small light seeds and asexual and sexual reproduction in T. diversifolia. For both species, control of recruitment would be a means of limiting their invasiveness.     

Impact of Conyza bonariensis density and establishment period on soyabean grain yield,yield components and economic threshold

Conyza spp. have become a major weed around the world, mainly because of weed resistance issues. The objective of this work was to test the hypothesis that the soyabean crop yield is dependent on the density of Conyza bonariensis and on the timing of weed establishment in relation to the crop sowing date. It was also theorised that these variables affect soyabean crop yield components and the economic threshold of C. bonariensis on soyabean. Field experiments were conducted during 2010 and 2011 using a randomised complete block design. In each experiment, several densities (0, 3, 6, 12, 24, 48, 96 and 192 plants m^?2) of C. bonariensis were established in soyabean fields. Conyza bonariensis establishment dates varied considerably between the experiments [81, 38 and 0 days before soyabean sowing (DBSS)]. Conyza bonariensis plants were first cultivated in a glasshouse and then transplanted to the field at the three‐leaf growth stage. At the lower densities, each C. bonariensis plant decreased soyabean yield by 36%, 12% and 1.0%, when established at 81, 38 and 0 DBSS respectively. The economic thresholds based on sensitivity analysis were below 0.5 plant m^?2 when C. bonariensis was introduced at 81 and 38 DBSS; in contrast, they were between 2 and 4 plants m^?2 when the weed was established at the crop sowing time. The results emphasise the importance of proper C. bonariensis management prior to soyabean sowing and highlight the need for residual herbicides to avoid grain yield losses.     

Fusarium crown rot under continuous cropping of susceptible and partially resistant wheat in microcosms at elevated CO2

This study examines the CO₂‐mediated influence of plant resistance on crown rot dynamics under continuous cropping of partially resistant wheat line 249 and the susceptible cultivar Tamaroi. Disease incidence, severity, deoxynivalenol and Fusarium biomass were assessed after each cycle in microcosms established at ambient and 700 mg kg^?1 CO₂ using soil and stubble of these wheat lines from a field experiment with free to air CO₂ enrichment. Monoconidial isolates from wheat stubble were collected initially, and after five cropping cycles, to compare the frequency and aggressiveness of Fusarium species in the two populations. Aggressiveness was measured using a high‐throughput seedling bioassay. At elevated CO₂, the higher initial incidence in Tamaroi increased with cropping cycles, but incidence in 249 remained unchanged. Incidence at ambient CO₂ did not change for either line. Elevated CO₂ induced partial resistance in Tamaroi, but not in 249. Increased Fusarium biomass in wheat tissue at elevated CO₂ matched raised deoxynivalenol of the stem base in both lines. After five cycles of continuous wheat cropping, aggressiveness increased in pathogenic F. culmorum and F. pseudograminearum by 110%, but decreased in weakly pathogenic F. equiseti and F. oxysporum by 50%. CO₂ and host resistance interactively influenced species frequency, and the highly aggressive F. pseudograminearum became dominant on Tamaroi irrespective of CO₂ concentration, while its frequency declined on 249. This study shows that induced resistance at elevated CO₂ will not reduce crown rot severity, or impede the selection and enrichment of Fusarium populations with increased aggressiveness.     

Response of Sorghum halepense demographic processes to plant density and rimsulfuron dose in maize

In spatially heterogeneous weed infestations, variable dose technologies could be used to minimise herbicide use; high doses could be applied to reduce high‐density patches and low doses to maintain weed populations in low‐density portions of a field. To assess the potential short‐ and long‐term effects of variable herbicide dose and site‐specific management, the major weed demographic processes were described and parameterised in this study. Various doses of rimsulfuron (from 0 to 12.5 g a.i. ha^?1) were applied to different densities of Sorghum halepense (0–100 plants m^?2). Contrary to similar studies with other weed species, higher herbicide efficacy was not observed at low densities, suggesting that the same rimsulfuron dose should be applied regardless of the S. halepense density. The highest percentage of control was obtained with the full rimsulfuron dose. However, it did not guarantee a decrease of the infestation in the following season in the field areas where the initial S. halepense density was lower than 60 plants m^?2. Reduced doses of rimsulfuron to control S. halepense cannot be recommended based on our results.     

Germination ecology of five arable Ranunculaceae species

Germination and emergence are critical life stages for annual plants and so their full understanding is essential for managing arable plant populations. This study investigated the most important species‐specific environmental cues that regulate seed germination and emergence (temperature and light) of the arable Ranunculaceae species Consolida orientalis, Consolida pubescens, Delphinium gracile, Delphinium halteratum ssp. verdunense and Nigella gallica, to propose management strategies for their preservation in agro‐ecosystems. Growth chamber and outdoor pot experiments were conducted for two consecutive seasons to analyse light (complete darkness or 12 h light) and temperature (5/10, 5/15 and 10/20°C) requirements and emergence patterns. The relative light germination requirement (ΔG_light), which extends from ?100 (complete darkness) to 100 (light), was estimated. Weibull functions were fitted to observed emergence (%) in pots. For all species, germination was higher in complete darkness than with a light regime (?60 < ΔG_light < ?95). This dark requirement indicates better germination for buried seeds. A tillage operation just after seed shed is therefore recommended. Consolida spp. germinate and emerge almost exclusively in autumn–winter, while Delphinium spp. and N. gallica can also germinate in spring. These arable plants would be able to adapt to delayed sowings, an important strategy for avoiding early‐emerging competitive weeds. Facultative winter‐germinating species could face early herbicide treatments if sufficient emergence occurs in winter–spring. These results bring new information to help develop conservation strategies for these species in agro‐ecosystems.