Emergence of four weed species in response to rainfall and temperature

The key to achieving effective weed control is to target them when they are young. Understanding their temperature and moisture requirements for emergence will help growers to develop timely control strategies. This study examined the emergence requirements of four key species: Conyza bonariensis, Sonchus oleraceus, Echinochloa colona and Chloris virgata. Two experiments were conducted in a growth room with temperatures of 25/15 and 30/20°C day/night with a photoperiod of 12 h. The first experiment examined emergence under single rainfall events of 0, 2, 5, 10, 20, 30 and 50 mm. The second experiment examined emergence under accumulated rainfall events of 0 mm, 5 mm × 2 (consecutive) days, 5 mm × 4 days, 5 mm × 6 days, 10 mm × 1 day, 10 mm × 2 days and 10 mm × 3 days. The temperature was not significant on emergence in both experiments. In the first experiment, at least 10 mm of rainfall was required for the emergence of all the species, with significantly higher germination rates at rainfall amounts of >20 mm. In the second experiment, the species had higher emergence rates with accumulated rainfall over consecutive days, rather than single rainfall events of the same amount. The length of time that the soil surface remained above the permanent wilting point, allowing the imbibition of water, was also an important factor. This study has provided information on the drivers for emergence of these species and will assist growers in determining what rainfall events are likely to trigger emergence in the field and make timely weed management decisions.     

The ecophysiological determinants of nitrophily in annual weed species

Plant nitrophily plays a key role in weed community assembly. To date, the determinants of the success of nitrophilic weeds and of the decline of oligotrophic weeds in intensive cropping systems are not fully understood. This study investigated which ecophysiological traits related to carbon and N nutrition explain plant nitrophily in field annual species. Twelve species (consisting of monocotyledonous and dicotyledonous species, as well as crops and weeds) covering the oligotrophic‐nitrophilic continuum were grown in a glasshouse experiment at two contrasted conditions of soil‐nitrogen supply. From measured plant growth variables, ecophysiological traits were calculated to account for plant nutritional strategies. Globally, whatever the soil‐nitrogen supply, increased nitrophily was associated with a decreased allocation of carbon to root vs. shoot. At high soil‐nitrogen only, increased nitrophily was also generally associated with an increased nitrogen uptake activity per unit of root biomass, pointing to a trade‐off between oligotrophic species with a preferential carbon investment in root structure and nitrophilic species with a preferential carbon investment in root activity. Beyond these global trends explaining nitrophily, results also show that different strategies are possible for plant species to be considered as nitrophilic. This study provides evidence on why adjusting N fertilisation in quantity, in space (with nitrogen fertiliser placement on the row) or in time can be useful strategies to manage the most nitrophilic weeds, which are also the most problematic in intensive cropping systems.     

几种常用杀虫剂对异色瓢虫的敏感性测定

在实验室及田间罩笼条件下，进行了异色瓢虫对8种杀虫剂的敏感性测定。结果显示：8种供试药剂对异色瓢虫幼虫的毒性（LC50值）差异很大，矿物油类药剂敢死虫对异色瓢虫最安全，其LC5。值高于其田间常用有效剂量；苦参素植物保护剂、吡虫啉、阿维菌素对异色瓢虫成虫的LC50值也高于各自的田间使用剂量，但对幼虫的LC50值却介于推荐的田间有效剂量与高限剂量之间，对瓢虫幼虫安全有一定威胁。     

Effects of Azolla species on weed emergence in a rice paddy ecosystem

The effects of Azolla pinnata R. Br. on weed emergence were evaluated in terms of plot area coverage by an A. pinnata mat, its biomass production and the amount of weed emergence, using fresh and dry weights, in a rice paddy field experiment. The experiment was conducted following a randomized block design with five combinations of fertilizer and A. pinnata treatments (control, A. pinnata  + superphosphate, A. pinnata  + urea, A. pinnata  + compound fertilizer, A. pinnata  + cow manure). The results revealed that after 18 days of inoculation, all superphosphate (T1) and cow manure (T4)-treated plots were fully covered by the A. pinnata mat. However, coverage of the urea (T2) and compound fertilizer (T3)-treated plots were only 80% and 70%, respectively. The full plot area coverage by the A. pinnata mat and the highest biomass production with superphosphate and cow manure-treated plots were able to completely inhibit two weed species ( Scirpus juncoides Roxb. var. hotarui Ohwi and Monochoria vaginalis Burm. f. Presl var. plantaginea (Roxb.) Solms-Laub) and significantly suppressed four other weeds ( Cyperus serotinus Rottb, Echinochla oryzicola Vasing, and Eclipta prostrata L.). In all the treatments, the fresh weight of weeds significantly reduced to 13, 29, 34, and 9%, respectively, for treatments T1, T2, T3, and T4. The dry weights also were significantly reduced to 10.00, 16.00, 22.00, and 7.26%, respectively, for treatments T1, T2, T3, and T4 over the control. The results revealed that there was a significant correlation among plot area coverage by the A. pinnata mat, its biomass production and weed emergence in a rice paddy field over the control. Azolla pinnata did not have any detrimental effect on the growth of rice plants.     

Development of lowland weed management and weed succession in Japan

Since the introduction of rice production in Japan, lowland areas have been managed for rice production with the purpose of better rice growth, as well as lesser weed infestation. Rice is cropped every year in lowland fields by repeated cultivation of a single crop, with high yields and without soil sickness usually being observed in upland fields. This is probably because the irrigation water supplies various nutrients for healthy rice growth and the drainage washes out and removes harmful factors. However, until recently, the wet or flooded conditions of lowland fields in the Asian monsoon region never have allowed humans to cultivate useful summer crops, except rice or some aquatic plants. Therefore, the management of lowland areas in the Asian monsoon region has been significantly different from European field management, where crop rotation has been the traditional standard practice. Paddy weeds are aquatic plants or hygrophytes that have adapted to lowland fields. Traditionally, tillage and puddling were practiced seasonally in lowland fields on a regular schedule every year. Rice cultivation technology was developed and supported by regional irrigation systems that created stable environments for typical paddy weeds to complete their life cycle. After the introduction of chemical weed control, rice fields became very severe habitats for these paddy weeds, where they could not grow and reproduce without strategies for survival under herbicide exposure. Even so, many of the traditional paddy weeds survived because of their accumulated or uneradicated seed banks, although several aquatic plants were listed as endangered or threatened species. The important weed species changed, sometimes rapidly and sometimes slowly, depending both on their reproductive system and their biological response towards field management and weed control systems. Very recently, the level of perennial weeds, herbicide‐resistant weeds, and weedy rice has increased in paddy fields that are highly dependent on herbicide use. In addition, several hygrophyte species have invaded paddy fields. In order to address these issues, the improvement and application of integrated weed management methods are expected to be critical.     

Modelling interactions between herbicide dose and multiple weed species interference in crop–weed competition

The effects of a range of herbicide doses on crop–multiple weed competition were investigated. Competitivity of Galium aparine was approximately six times greater than that of Matricaria perforata with no herbicide treatment. Competitivities of both weeds decreased with increasing herbicide dose, being well described by the standard dose–response curve with the competitivity of M. perforata being more sensitive than that of G. aparine to a herbicide mixture, metsulfuron‐methyl and fluroxypyr. A combined model was then developed by incorporating the standard dose–response curve into the multivariate rectangular hyperbola competition model to describe the effects of multiple infestation of G. aparine and M. perforata and the herbicide mixture on crop yield. The model developed in this study was used to predict crop yield and to estimate the herbicide dose required to restrict crop yield loss caused by weeds to an acceptable level. At the acceptable yield loss of 5% and the weed combination of 120 M. perforata plants m^?2 and 20 G. aparine plants m^?2, the model recommends a mixture of 1.2 g a.i. ha^?1 of metsulfuron‐methyl and 120 g a.i. ha^?1 of fluroxypyr.     

Competitive ability of five common weed species in competition with soybean

The competitive ability of five prominent weeds species that have the potential to interact in soybean cropping systems of Argentina (Amaranthus quitensis, Chenopodium album, Digitaria sanguinalis, Setaria verticillata and Tagetes minuta) was evaluated in two greenhouse experiments (Exp. 1 and Exp. 2). Crop and weeds were grown in all pairwise mixtures using an additive competition design. Competitive ability was evaluated through competitive indices based on species total biomass. Both experiments showed asymmetric competitive interactions between species, resulting in a competitive network predominantly transitive involving up to four from six species in Exp. 1: Glycine. max > C. album > D. sanguinalis > (A. quitensis, S. verticillata and T. minuta) and up to three from six species in two pathways in Exp. 2: G. max > D. sanguinalis > (C. album, S. verticillata and T. minuta); and G. max > A. quitensis > (C. album, S. verticillata and T. minuta). The hierarchical relationship between species found in this study has implications on weed population dynamics in the context of community assembly framework. We discuss engineered management practices that consider the use of the crop and weed competitive ability to modulate the community structure and the rationalization in the use of herbicides directed to avoid environmental damage.     

皖北高粱田杂草种类及群落特征分析

为明确皖北高粱Sorghum bicolor田杂草发生现状, 于2020年-2021年采用倒置“W”九点取样法对皖北6市52个乡镇田间杂草进行了调查?结果表明, 皖北高粱田共有杂草36种, 属17科, 其中禾本科?菊科?苋科种类最多?优势杂草为稗Echinochloa crus-galli?马唐Digitaria sanguinalis?牛筋草Eleusine indica?狗尾草Setaria viridis等4种, 区域性优势杂草4种, 常见杂草13种, 一般杂草15种?阜阳市杂草的优势度指数最高, Berger-Parker指数为4.89, Simpson指数?Shannon-Wiener指数?Pielou指数均高于其他5市, 优势杂草以稗?马唐?牛筋草?狗尾草?反枝苋Amaranthus retroflexus和苋Amaranthus tricolor为主; 亳州市杂草的优势度仅次于阜阳市, 以稗?马唐?牛筋草?狗尾草和铁苋菜Acalypha australis为主?淮北市杂草的丰富度指数最高, Margalef指数为3.16, 以稗?牛筋草?狗尾草?鸭跖草Commelina communis为主?此外, 青葙Celosia argentea?金色狗尾草Setaria pumila?马齿苋Portulaca oleracea?反枝苋Amaranthus retroflexus及碎米莎草Cyperus iria等5种杂草在部分区域内优势度较高?经聚类分析, 皖北杂草群落分为两组, 阜阳?亳州及宿州3市的杂草聚为第1组, 淮南?淮北市及蚌埠3市的杂草聚为第2组?造成各地市杂草群落差异较大的原因与当地农田管理水平?用药习惯和种植制度等因素关系密切?     

Effects of human-mediated processes on weed species composition in internationally traded grain commodities

International trade is a major route by which non‐indigenous organisms are introduced into new habitats. Various kinds of weed seeds have been introduced through grain trade. The objectives of this study were to understand the factors that affect the initial assemblage of plant species introduced by the international grain trade and to extract their general attributes. We surveyed weed seed contamination of spring wheat imported from Canada to Japan and analysed the effects of the field abundance of each weed and of harvesting and cleaning on the quantity of weed seed included in the imported wheat. The field abundance was positively correlated with the weed seed quantity. Seeds of short weeds and seeds with a pappus were eliminated from the wheat by the harvesting or cleaning process. Many other crop plants contaminated the wheat. Because various transportation vehicles, temporary storage sites and port elevators are used commonly with all exported crops and it is difficult to remove all residues from them, other crops might be carried over into the wheat commodity. These relationships also apply to other grains.     

Effect of ensiling and in sacco digestion on the viability of seeds of selected weed species

The germinability and viability of mature seeds of five grass (Hordeum spp., Bromus diandrus, Vulpia spp., Avena fatua and Lolium rigidum) and seven broad‐leaved weed species (Echium spp., Physalis hederifolia, Solanum elaeagnifolium, Raphanus raphanistrum, Marrubium vulgare and Malva parviflora) that were either untreated, ensiled for a minimum of three months, underwent 48 h in sacco digestion in steers or ensiled prior to digestion were tested for germinability and viability. Ensiling and digestion both reduced seed viability, although the extent varied with species. The effect of ensiling was generally greater compared with digestion and differed between years for some species. Ensiling or ensiling plus digestion rendered all seeds of Hordeum spp., B. diandrus, Vulpia spp., A. fatua, Echium spp., P. hederifolia (in one year only), S. elaeagnifolium, R. raphanistrum and M. vulgare non‐viable; ensiling and ensiling plus digestion reduced viability of L. rigidum by 74.4% and 92.7% respectively. Viability of M. parviflora displayed the greatest tolerance to damage, with seed viability reduced on average by 31.4%, 27.6% and 27.4% for ensiling, digestion and ensiling plus digestion treatments respectively. These results indicate that ensiling can provide an effective non‐chemical weed management option, as a component of an integrated weed management package, for certain weed species responsible for significant crop and pasture production losses in Australian and world temperate and Mediterranean agricultural systems.     

Development of chemical weed control and integrated weed management in China

More than 200 species of weeds are infesting main crop fields in China, among which approximately 30 species are major weeds causing great crop yield losses. About 35.8 million hectares of crop fields are heavily infested by weeds and the annual reduction of crop yields is 12.3–16.5% (weighted average). Along with rural economic development, approximately 50% of the main crop fields undergo herbicide application. Chemical weed control has changed cultural practices to save weeding labor in rice, wheat, maize, soybeans and cotton. At the same time, continuous use of the same herbicides has caused weed shift problems and weed resistance to herbicides. Consequently, integrated weed management in main crops is being developed.     

Combining a weed traits database with a population dynamics model predicts shifts in weed communities

A functional approach to predicting shifts in weed floras in response to management or environmental change requires the combination of data on weed traits with analytical frameworks that capture the filtering effect of selection pressures on traits. A weed traits database (WTDB) was designed, populated and analysed, initially using data for 19 common European weeds, to begin to consolidate trait data in a single repository. The initial choice of traits was driven by the requirements of empirical models of weed population dynamics to identify correlations between traits and model parameters. These relationships were used to build a generic model, operating at the level of functional traits, to simulate the impact of increasing herbicide and fertiliser use on virtual weeds along gradients of seed weight and maximum height. The model generated ‘fitness contours’ (defined as population growth rates) within this trait space in different scenarios, onto which two sets of weed species, defined as common or declining in the UK, were mapped. The effect of increasing inputs on the weed flora was successfully simulated; 77% of common species were predicted to have stable or increasing populations under high fertiliser and herbicide use, in contrast with only 29% of the species that have declined. Future development of the WTDB will aim to increase the number of species covered, incorporate a wider range of traits and analyse intraspecific variability under contrasting management and environments.     

Distribution of parthenium weed (Parthenium hysterophorus L.), an alien invasive weed species threatening the biodiversity of Islamabad

Biological invasion by alien invasive species is now recognized as one of the major threats to native species and ecosystems. Parthenium weed ( Parthenium hysterophorus L.), an alien invasive weed species, is spreading throughout Pakistan. Worldwide, it has been designated as one of the most troublesome weed species. The adverse effects of this weed on human beings, livestock, crop production, and biodiversity are well-documented. As a result of a lack of information on its spread in Pakistan since its invasion, a phytosociological survey, with special reference to parthenium weed, was carried out in Islamabad from August–October 2002. Six main sectors of Islamabad were selected for sampling. The phytosociological survey of these sectors of Islamabad revealed a total of 30 weed species to be associated with P. hysterophorus . The survey also showed a high relative frequency, relative density, and importance value of P. hysterophorus in general; however, the percentage relative frequency of the weed in these sectors ranged from 10.6–30.3%. This survey revealed that P. hysterophorus had an appreciable degree of sociability with Senna occidentalis (L.) Link, Malvastrum coromandelianum (L.) Garcke and Lantana camara (L.). The data on the association of L. camara with P. hysterophorus suggests that a transition phase of competition or succession is in progress between these two alien species. The population of many common medicinal plants growing in the wastelands of Islamabad might be rapidly declining because of the aggressive colonization by P. hysterophorus . The ever-increasing infestation of this weed in urban areas also poses a serious threat to the health of the inhabitants of Islamabad.     

Growth response of six weed species and spring barley (Hordeum vulgare) to increasing levels of nitrogen and phosphorus

A glasshouse experiment was carried out to investigate the influence of increasing levels of nitrogen and phosphorus on the growth of six common weed species growing alone or in competition with spring barley (Hordeum vulgare). Capsella bursa‐pastoris, Chenopodium album, Papaver rhoeas, Sinapis arvensis, Spergula arvensis, Viola arvensis and spring barley were grown in pots with different levels of nitrogen (0, 30, 60, 90, 120 and 150 kg N ha^?1) or phosphorus (0, 10, 20, 30, 40 and 60 kg P ha^?1). The aboveground parts of the plants were harvested after 7 weeks and the dry weight of shoots, percentage N and P content of the shoot and uptake of N and P were determined. A linear or a polynomial model was used to describe the data. Growing alone, Spergula arvensis was the only weed species that increased its dry weight at the same rate as barley. Weed species with low dry weight increase had larger increases in percentage N or P content than barley, indicating a luxury accumulation of nutrients. The uptake of N and P per pot did not differ much between weeds and barley. V. arvensis and P. rhoeas accumulated least nutrients (per cent of dry matter) and Spergula arvensis accumulated most. Weeds grew poorly in competition with barley. The percentage N and P content in barley did not change when they grew in competition with weeds.     

沿江圩区长期稻麦连作田土壤杂草种子库的研究

通过对沿江圩区长期稻麦连作田土壤杂草种子库研究,结果表明,土壤杂草种子库中小麦田有8科14种、水稻田有9科17种。2种类型田块的种子库主要分布在0～10cm的土层中。小麦田该层出草量达77.74%,水稻田为72.05%。麦田土壤总出草量为11930株/m2,主要是日本看麦娘、草和稻槎菜,出草量占总量的59.96%;稻田土壤总出草量达9855株/m2,主要是稗草、节节菜、千金子和异型莎草,出草量占总量的51.03%。上述7种杂草是该区农田的主要杂草,均为当前防除的重点,其中日本看麦娘和稗草分别是小麦、水稻田的优势种。通过研究提出了减少土壤杂草种子库种源的对策。     

Effects of duck activities on a weed community under a transplanted rice–duck farming system in southern China

Rice–duck farming is one of the traditional, but current and gradually popularized, ecological farming techniques for paddy rice production in China. In comparison to rice monoculture farming, we investigated a weed community and weed infestation in a transplanted rice–duck farming system and examined the effects of duck activities on the weeds. Three treatments were imposed in the experiment: a rice–duck coculture with duck grazing and disturbance effects, a rice–duck coculture with duck disturbance effects only, and a control (rice monoculture, no duck effects). Rice seedlings were nursed and transplanted in this experiment. The total number of weed species was significantly lower in the treatment with both duck grazing and disturbance and in the treatment with duck disturbance only than in the monoculture rice treatment (control). The Shannon‐Wiener Biodiversity Index of the weed species decreased but the Pielou Evenness Index increased in both treatments with ducks compared to the monoculture control. Sorensen's coefficient of similarity of the weed communities was low between the treatments with ducks and the monoculture control, implying that the weed communities diverged. The total density and biomass of the weed community in both the treatments with ducks were significantly lower compared to the monoculture control. However, compared to the rice monoculture control, the weed biomass was reduced by 98% in the treatment with duck grazing and disturbance and by 84% in the treatment with duck disturbance only, implying that only 14% of the weeds were controlled by duck grazing and that 84% of the weed biomass was inhibited by duck activities in the rice field with ducks. The rice grain yield increased in the treatments with ducks compared to the control. The results suggested that duck activities, like grazing weeds and disturbance of the soil and water, had a significant effect on the weed community structure and that weeds could be well controlled without herbicide application under a rice–duck farming system.     

Response of weed flora to combinations of reduced tillage, biocide application and fertilization practices in a 3-year crop rotation

Weed flora in a crop rotation of soybean, sugar beet, and spring wheat were studied under combinations of conventional and reduced tillage, biocide application, and chemical fertilization to investigate whether any combination of conservational practices offers the potential to increase weed community diversity while maintaining weed biomass at an acceptable level. Weed density increased under reduced biocide application. Weed density and size increased under manure compost application (with reduced chemical fertilization) because of weed seed introduction. Weed emergence from seeds dispersed in the previous year was greater under reduced tillage. Two-year individuals increased under a combination of reduced tillage, reduced biocide application and manure compost application. These increases in weed population density and size under conservational practices were yet not consistent; rather, they showed an annually fluctuating trend. In terms of weed diversity, species richness and Shannon's diversity index were higher under manure application because of the introduction of new species and probably as a result of suppression of weed growth and reproduction, which can reduce the chance of dominance by certain species. When combined with manure application, reduced tillage may offer the potential for increasing diversity by reducing the competitiveness of dominant species and facilitating establishment of new or minor species.