Abundant Weed Species Research Articles

Composition of weed communities in seasonally flooded rice environments in East Africa is determined by altitude

Weeds are major biotic constraints to rice production worldwide. Compared to other sub-regions, weed communities of rice are not well described for East Africa and there is limited information on environmental factors affecting the distribution of species. This study aimed to address these knowledge gaps. Seasonally flooded rice production fields of 31 sites in Rwanda, Tanzania, Kenya and Uganda, across three altitude classes (Low: <200 m; Medium 200–1,000 m; High: >1,000 m), were surveyed for weed species using quadrats. Data analyses involved multivariate approaches, non-parametric Kruskal–Wallis tests and logistic regressions, followed by calculation of ranked species abundance and Shannon Wiener Index diversity analyses. A total of 286 weed species, belonging to 59 families, were recorded with 42 species not previously reported as lowland rice weed in the sub-region. Twenty-four species were identified as abundant across altitudes. Weed species diversity was higher at medium altitudes compared to high and low altitudes. Significant patterns of floristic distinction between altitudinal classes were observed, with 80% of dissimilarity. The high altitude was dominated by Echinochloa colona, Leptochloa squarrosa and Sphaeranthus suaveolens, the medium altitude was dominated by Crassula granvikii, Pycreus lanceolatus and Ageratum conyzoides while the low altitude was dominated by E. colona, Cyperus difformis and Cyperus esculentus. The weed species composition of seasonally flooded rice fields in East Africa is diverse. Identification of a limited group of (24) commonly abundant weed species as well as the articulation of altitude-specific weed species groups will facilitate the development of better tailored weed control programmes.

Weed Species Dominance and Abundance in Tea (&amp;lt;i&amp;gt;Camellia sinensis&amp;lt;/i&amp;gt; L.) Plantation of Southwest Ethiopia

Tea (<i>Camellia sinensis</i> L.) is one of the most popular beverage crops. Among tea production constraints, weed is one of the detrimental factors in tea productions in Ethiopia. For the possibility of developing weed management method determining the dominant and abundant weed species is highly important to identify and prioritize the most noxious and prevalent weed that associated with tea production in the country. Weed flora survey was conducted in two different tea estate farms Wushwush and Gumero tea plantations in 2019/20 cropping seasons. The field survey was done according to the quantitative survey method by using 1m² quadrate size. Weeds present in each quadrate were counted and identified to species level. Weed abundance, dominance, frequency and similarity index was determined at two tea producing locations. A total of 63 weed species were identified from assessed tea plantation farms. The result revealed that 61.3% and 71.9% of broad leaf weed was recorded at Wushwush and Gumaro tea plantation, respectively. Only, two (6.5%) parasitic weed species were recorded at Wushwush. The most prevalent and abundant weed species at Wushwush was <i>Ageratum conyzoides</i> followed by <i>Hydrocotyle americana</i>, whereas, <i>H. americana</i> was the most dominant species at Gumero tea plantation. Generally, from survey results, the weed flora composition was similar in both assessed areas, as its similarity index resulted above 70%. Hence, similar weed management methods should be recommended for both locations.

Weeds in Florida Sugarcane as Host Plants for Three Species of Rice Stink Bugs (Hemiptera: Pentatomidae)

Weeds in Florida Sugarcane as Host Plants for Three Species of Rice Stink Bugs (Hemiptera: Pentatomidae)

Future distribution of invasive weed species across the major road network in the state of Montana, USA

Invasive plant species are a significant global problem, with the potential to alter structure and function of ecosystems and cause economic damage to managed landscapes. An effective course of action to reduce the spread of invasive plant species is to identify potential habitat incorporating changing climate scenarios. In this study, we used a suite of species distribution models (SDMs) to project habitat suitability of the eleven most abundant invasive weed species across road networks of Montana, USA, under current (2005) conditions and future (2040) projected climates. We found high agreement between different model predictions for most species. Among the environmental predictors, February minimum temperature, monthly precipitation, solar radiation, and December vapor pressure deficit accounted for the most variation in projecting habitat suitability for most of the invasive weed species. The model projected that habitat suitability along roadsides would expand for seven species ranging from + 5 to + 647% and decline for four species ranging from − 11 to − 88% under high representative concentration pathway (RCP 8.5) greenhouse gas (GHG) trajectory. When compared with current distribution, the ensemble model projected the highest expansion habitat suitability with six-fold increase for St. John’s Wort (Hypericum perforatum), whereas habitat suitability of leafy spurge (Euphorbia esula) was reduced by − 88%. Our study highlights the roadside areas that are currently most invaded by our eleven target species across 55 counties of Montana, and how this will change with climate. We conclude that the projected range shift of invasive weeds challenges the status quo, and requires greater investment in detection and monitoring to prevent expansion. Though our study focuses across road networks of a specific region, we expect our approach will be globally applicable as the predictions reflect fundamental ecological processes.

Survey and documentation of the Weed Flora in NBU Garden of Medicinal Plants

Weeds are the plants with generally undesirable properties. They spread rapidly and competitively. When it grows in garden it reduces air flow in garden, keeping plants wetter and more prone to pathogens. They are unattractive and can cause health problems such as Hay fever, skin rashes, etc. It also affects quality of product and income of grower. Traditionally, weed control in India has been largely dependent on manual weeding. Understand weed ecology, biology and using information technology should be part of developing and disseminating effective, economical and ecologically advantageous in India. Some weeds release nitrogen from root nodules into soil which automatically add fertilizer into the soil. A survey was conducted in NBU Garden of Medicinal Plants in West Bengal to identify most common and prevalent weeds associated with medicinal plants. A total of 86 different weed species belong to 25 families were identified of which 53 annual and 32 perennial. Among the most abundant weed species are Axonopus compressus, Eleusine indica, Cyperus rotandus, Cyperus haspan, Kylinga brevifolia, Melastoma malabathricum, Osbeckia nepalensis, Nicotiana plumbaginifolia, Persicaria orientalis.

Interactions between crop sequences, weed populations and herbicide use in Western Australian broadacre farms: findings of a six-year survey

Six years of survey data taken from 184 paddocks spanning 14 million ha of land used for crop and pasture production in south-west Western Australia were used to assess weed populations, herbicide resistance, integrated weed management (IWM) actions and herbicide use patterns in a dryland agricultural system. Key findings were that weed density within crops was low, with 72% of cropping paddocks containing fewer than 10 grass weeds/m2 at anthesis. Weed density and herbicide resistance were not correlated, despite the most abundant grass weed species (annual ryegrass, Lolium rigidum Gaudin) testing positive for resistance to at least one herbicide chemistry in 92% of monitored paddocks. A wide range of herbicides were used (369 unique combinations) suggesting that the diversity of herbicide modes of action may be beneficial for reducing further development of herbicide resistance. However, there was a heavy reliance on glyphosate, the most commonly applied active ingredient. Of concern, in respect to the evolution of glyphosate resistant weeds, was that 45% of glyphosate applications to canola were applied as a single active ingredient and area sown to canola in Western Australia expanded from 0.4 to 1.4 million hectares from 2005 to 2015. In order to minimise the weed seed bank within crops, pastures were used infrequently in some regions and in 50% of cases pastures were actively managed to reduce weed seed set, by applying a non-selective herbicide in spring. The use of non-selective herbicides in this manner also kills pasture plants, consequently self-regenerating pastures were sparse and contained few legumes where cropping intensity was high. Overall, the study indicated that land use selection and utilisation of associated weed management actions were being used successfully to control weeds within the survey area. However, to successfully manage herbicide resistant weeds land use has become less diverse, with pastures utilised less and crops with efficacious weed control options utilised more. Further consideration needs to be given to the impacts of these changes in land use on other production factors, such as soil nutrient status and plant pathogens to assess sustainability of these weed management practices in a wider context.

Effects of tillage practices on soil microbiome and agricultural parameters

No-tillage (NT) is a common soil-conservation management practice with known agricultural advantages and drawbacks. However, its short- and long-term effects on the soil microbiome have not been well established. Here, we compared conventional (CT), minimal (MT) and NT practices in two agricultural fields in the north of Israel over a period of 3 years. Edaphic properties, plant-associated pests, weed species abundance and soil microbial community structure were assessed to examine the effects of tillage. Tillage significantly altered physical and chemical soil properties, and a significant increase in hydrolytic and redox microbial activities was observed in NT soils from both sites. Consistent with this, the microbial community structure of NT samples diverged significantly over time from those of CT samples. Repetitive tillage and even a single tillage event caused significant changes in the relative abundance of microorganisms at taxonomic levels ranging from phylum to OTU. However, no significant difference between treatments was found in microbial community alpha-diversity or crop yield. Conversely, higher levels of weed diversity and some pests number were found in NT samples. Overall, we demonstrate that tillage plays a major role in shaping microbial community structure, and in influencing additional environmental, ecological and agricultural soil parameters.

Differences in growth, development and innate seed dormancy of susceptible and fenoxaprop-P non-target site resistant black-grass sub-populations

Alopecurus myosuroides Huds. is the most abundant herbicide-resistant weed species in Western Europe. Herbicide resistance management programs may rely, amongst other things, on information about fitness of resistant sub-population i.e. the number of offspring a genotype produces and contributes to next generation. Growth and phenological development of susceptible (S) and fenoxaprop-P resistant (R) A. myosuroides sub-populations from a non-target site resistant (NTSR) Danish population was studied for two years, while the primary seed dormancy of the populations was evaluated for three years. The genetic background of the S and R sub-populations was controlled using a plant cloning technique. No statistically significant differences were observed in the development of vegetative growth stages between the R and S sub-populations. In contrast, the R sub-population required more thermal time (at least c. 40 °C d) compared with the S sub-population to reach the reproductive phenological stages including booting and flowering. There were no vegetative (biomass) and reproductive (seed production) fitness costs in the R sub-population, however, the harvest index of the R sub-population was significantly lower than of the S sub-population. Moreover, the R sub-population had a lower primary dormancy than the S sub-population. The lower primary dormancy of the R sub-population can be considered as agronomical fitness costs of the NTSR to fenoxaprop-P, if pre-sowing seedbed preparation are implemented. The results can be implemented in models simulating phenological development and in models predicting the proportion of resistant individuals in a population.

Phytodiversity of Pyrogenic Formations of the Usman Forest (Voronezh Oblast)

Postfire (2010) formations of Pinus sylvestris and Betula pendula (51°48′30.1′′ N, 39°23′58.4′′ E) have been studied. This article presents the results of these studies for 2015–2016. Descriptions of these formations have been carried out since 2012. Methods for the analysis of the structures of plant communities are of especial importance, both for an understanding of their annual ecological state and the identification of plant resistance to the pyrogenic factor. Information on the beginning of restoration of the phytocenosis structure and flora, on the change of dominants in vegetation layers, an increase of the projective cover, and the formation of forest phytocenosis is given on example of common and pyrogenic associations of these formations. A decrease in weed species abundance and their projective cover was noted. The current list of flora includes 84 species from 75 genera, 33 families, and 2 divisions: Pinophyta and Magnoliophyta. The dominant families are Poaceae with 12 species (14.1%), Asteraceae with eight species (9.4%), and Fabaceae with six species (7%). The small list of dominant families with a small number of species confirms the large disturbance of flora by the pyrogenic factor. The dominance of rhizome plants (42 species, 44.6%) and a small number of cespitose plants (4 species, 4.8%) indicates the advantage of the forest phytocenotic group. The presence of a xerophytic group (15 species, 17.9%) indicates increased insolation and a decreased moisture content in these postfire formations. Eight geoelements and 14 types of habitats have been identified. The European one predominates, with 53 species (63.1%) and 12 types of habitats.

Interactions between rodents and weeds in a lowland rice agro-ecosystem: the need for an integrated approach to management.

Rodents and weeds are important pests to rice crops in Southeast Asia. The interaction between these 2 major pests is poorly documented. In temperate cereal systems, seeds of grass weeds can be an important food source for rodents and weed cover along crop margins provides important refuge for rodents. In 2012 and 2013, a replicated study (n = 4) in Bago, Myanmar compared 4 treatments (rodents and weeds; no rodents and weeds; rodents and no weeds; no rodents and no weeds) each of 0.25 ha in transplanted rice. Weeds were managed with hand weeding in the wet season, and hand weeding and herbicides in the dry season. Plastic fences were installed to exclude rodents. We examined the weed cover and relative abundance of weed species, rodent damage, rodent population dynamics and rice yield loss caused by rodents and weeds. The dominant rodent species was Bandicota bengalensis. In the dry season, Cyperus difformis was dominant at the tillering stage and Echinochloa crus‐galli was the dominant weed species at the booting stage. In the wet season E. crus‐galli was a dominant weed throughout the season. Damage by rodents was higher in the dry season. There were larger economic benefits for best weed management and effective rodent control in the dry season (258 US$/ha) than in the wet season (30 US$/ha). Concurrent control of weeds in and around rice fields combined with coordinated community trapping of rodents during the early tillering stage and ripening stage of rice are recommended management options.

Vertical Distribution of Nutsedge (Cyperus spp. L.) and Bahiagrass (Paspalum notatum L.) Seed Bank in Rice Growth Cycle

Weed management in rice continues to be a major challenge to the success of rice growers in northern Iran. Field experiments were conducted at Sari Agricultural Sciences and Natural Resources University to investigate the spatial distribution of weed seeds in the rice growth cycle in 2010 and 2011. Transplanting was done on June 6 in both years. Samples for seedbank analysis were collected 10 days before transplanting and emerged weed density was determined on three different dates during the growing season. Results indicated that nutsedge (Cyperusspp) and bahiagrass (Paspalum notatum) were the two most abundant weed species. The vertical distribution of weed seeds decreased by depth from 0.1 to 0.3 m, while weed pressure was the highest at the 0–0.1 m soil depth. There was no relationship between soil weed seedbanks (at different depths) and emerged weed populations, suggesting that weed seedbank data are not good predictors of weed seedling densities. Nevertheless, Kriging maps indicated that the spatial distribution of weed seeds was in accordance with seedling germination pattern. Also the regression coefficient for 0–0.1 m soil depth was R2= 0.17 and R2= 0.34 for relation between nutsedge and bahiagrass seedlings and their seedbank in 2010 and also, R2= 0.18 and R2= 0.05 in 2011, respectively. Therefore, results achieved from this depth can be used to predict the relationship between nutsedge and bahiagrass seedlings densities and weed seedbanks. The results of this study provide an option for the farmers growing rice to understand the dynamics of weed populations in a cost effective way.

Secondary hosts of the Asian citrus psyllid, Diaphorina citri Kuwayama: Survivorship and preference

AbstractThe Asian citrus psyllid, Diaphorina citri Kuwayama, is the most economically important and difficult to manage citrus pest in Florida due to its role as vector of huanglongbing or citrus greening disease. Spread of the disease is a function of dispersal patterns and thus influenced by availability of suitable hosts. Young leaves of citrus or related plants are required for reproduction, but in their absence, secondary hosts may provide needed resources to enhance survival. Therefore, survivorship on and preference for three abundant weed species was investigated. The suitability of potential secondary host plants Bidens alba (L.), DC, Ludwigia octovalvis (Jacqu.) P. H. Raven, and Eupatorium capillifolium (Lam.) Small was compared to a reproductive host, Murraya paniculata (L.) Jack, in no‐choice tests by assessing survivorship of D. citri adults confined to these plants in cages. Preference was evaluated by choice tests where D. citri adults were released into cages containing all three secondary hosts alone or with M. paniculata. Both B. alba and E. capillifolium increased D. citri survivorship by twofold compared to starvation conditions with only water available. Choice trials revealed no difference in initial selection between true and secondary hosts; however, the true host was favoured over time. This result suggested that hosts were selected initially by sight, and only later by taste and/or smell. While secondary hosts are unable to support reproduction or long‐term survival, these findings establish the ability of D. citri to use secondary hosts that are ubiquitous in Florida citrus groves as temporary reservoirs for food and moisture when ideal host conditions are scarce or absent.

Weed flora survey in field crops of Northwestern Ethiopia

A survey was conducted in different field crops of six districts (Chilga, Gondarzuria, Metema, Takussa, Dabat and Dembia) in Northwestern Ethiopia within 2016 and 2017 cropping seasons. The objective of the study was to identify the most important weed species and to determine their frequency, density and uniformity at different altitudes. A quantitative and qualitative method was employed for the enumeration and identification of weed species. Quadrats were laid along transects and individual weed species in each quadrat was identified and counted. Frequency, uniformity, similarity index and relative abundance were used to determine the weed community structure. A total of 76 weed species belonging to 65 genera within 27 families were identified across different field crops. The most dominant families, based on the family dominance index (FDI), were Asteraceae, Poaceae, and Fabaceae with 78.97, 63.76, and 20.72 FDI, respectively. The most frequent, abundant and dominant weed species were Digitaria abyssinica (Hochst. Ex A. Rich), Cyperus rotundus L. and Cynodon dactylon L. The average values for frequency and dominance of weed species in arable fields ranged between 49.34 to 59.87% and 3 to 3.69%, respectively. Results obtained from this study would be useful in creating a weed management programme and making inform decision on choice of herbicides and directing research toward new or improved weed control measures. Key words: Altitude, density, district, dominance, family, frequency, species.

Weed Population Assessment in Wheat at Central Highlands of Ethiopia

Study was conducted on Weed Population Assessment in Wheat at Adea, Gimbichu, Minjar shenkora, Akaki, Boro and Lume Districts in Central Highlands of Ethiopia during, 2014/15 main cropping season to determine the distribution of weed species in wheat growing areas of central highlands of Ethiopia and to record the weed infestation level on wheat crop production. Depending on the area coverage of Wheat in each Districts seven to three kebeles, again in each kebele six to four from Wheat fields samples were taken using 0.5 x 0.5m quderate and GPS instrument. The frequency, abundance and dominance regarding different aspects of weeds were calculated. The result revealed that 45 weed species belonging to 33 families as weeds of wheat for each species was calculated. The 5 major families based on number of taxa were: Poaceae (14), Asteraceae (7), three species each under Polygonaceae and Solanaceae, and Papilionaceae (2), totally they contain 66% of the total weed flora. The most frequent, abundant and dominant weed species were found to be setaria pumila, Plantago lanceolata, Bromus pecpectinatus, Cyperus rotudus, Xanthium strumarium L. and Snowdenia polystachya. Greater than 60% similarity index of weed communities was registered across all locations sampled.

Survey and Identification of Major Weeds of Seeds Spice in Ethiopia

In Ethiopia coriander (Coriandrum sativum L.), fenugreek (Trigonella foenum-graecum) and black cumin (Nigella sativa L.) are economically important seeds spices in the family of Apiaceae, Fabaceae and Apiaceae (Umbelliferae), respectively. They are highly suffering due to weed infestation especially competing for water and nutrient. However, before estimating yield losses due to weeds and devising weed control strategies, identification and quantification of weeds are very important. The weed survey was conducted in East showa, Arsi, Bale, North wollo and North Gondar zones during 2016 and 2018 in main cropping seasons to identify most common and prevalent weeds associated with seeds spice (coriander, fenugreek and black cumin). Weed species characteristics, density, frequency, relative density, relative frequency, summed dominant ratio over locations and seasons were calculated. The result shows that a total of 22, 37 and 21 weed species were identified in coriander, fenugreek and black cumin fields, respectively. The most important families according to the number of represented species were Amaranthaceae, Caryophyllaceae, Primulaceae and Fabaceae in coriander, Amaranthaceae, Fabaceae and Polygonaceae in fenugreek and Chlorideae and Scrophulariaceae in black cumin fields. The frequency of individual weed species in coriander, fenugreek and black cumin field ranged from 0.14% up to 1%, 0.13% up to 1% and 0.25% up to 5% while the dominance value ranged from 0.14 up to 49.1%, 0.25 up to 26.5% and 0.25 up to 4.5%, respectively. The most frequent and dominant weed was Chenopodium album in coriander field whereas, the most frequent weed was Chenopodium album and the most dominant weed was Drymaria cordata in fenugreek field. In black cumin field Cynadon dactylon and Solanum nigrum are most dominat and the most frequent weeds respectively. This survey has ranked the most abundant and troublesome weed species in coriander, fenugreek and black cumin growing areas of Ethiopia. Therefore this information is vital for setting research and developmental work priorities concerning coriander, fenugreek and black cumin weeds of the study area

Weed Communities in Strip-Tillage Corn/No-Tillage Soybean Rotation and Chisel-Plow Corn Systems after 10 Years of Variable Management

AbstractPrevious research has shown that strip-tillage (ST) systems conserve soil, reduce production costs, and save time for growers compared with intensive-tillage systems. In contrast to these well-documented benefits, we have limited information on weed community dynamics and management risks in ST corn (Zea maysL.) production systems in the northern Corn Belt. Therefore, we conducted research in 2015 and 2016 to characterize weed community composition, emergence patterns, and aboveground productivity in an ST corn/no-tillage (NT) soybean [Glycine max(L.) Merr.] rotation that was established in 2007 compared with a long-term intensive-tillage chisel-plow (CP) continuous-corn system. Fifteen or more weed species were identified in nontreated quadrats in each cropping system in each year. Common lambsquarters (Chenopodium albumL.) was the most abundant weed species across systems and years.Chenopodium albumdensities were similar between CP and ST corn phases and were approximately 2-fold greater compared with the NT soybean phase. Other abundant weed species occurred at much lower densities thanC. album. In each year, cumulative emergence of nontreated weed communities was described best by a logistic function in each cropping system. Maximum weed community emergence was greater in CP corn than ST corn phases in 2015, but did not differ in 2016. In the ST corn phase, most (about 75%) weed community emergence occurred in the in-row (tilled) zone compared with the between-row (nondisturbed) zone. Total late-season weed shoot biomass did not differ between nontreated CP and ST corn phases in either year, withC. albumaccounting for &gt;85% of total weed biomass in these phases. These results suggest that weed community composition, total emergence, and productivity were similar between CP and ST corn phases after 10 yr. Our findings, coupled with previous research that showed favorable agronomic performance and greater soil conservation associated with the long-term ST corn/NT soybean system, suggest that production risks are no greater than a CP corn system, while processes that underpin ecosystem services are enhanced. These results provide strong evidence to support grower adoption of ST practices as an alternative to intensive tillage.

Weed-Species Abundance and Diversity Indices in Relation to Tillage Systems and Fertilization

Weeds pose a major threat to world agriculture by reducing detrimentally crop yield and quality. However, at the same time, weeds are major interacting components of the agroecosystems. Abundance and diversity of weeds vary significantly among the several communities. In order to evaluate each community’s structure and the interactions among them, several population indices are used as key tools. In parallel, various cultivation and land management strategies, such as tillage and fertilization, are commonly used in terms of integrated weed management. Estimating the response of weed species on those practices is crucial for both biodiversity maintenance and alternative weed control methods. Many experiments have confirmed the fundamental role of tillage intensity and nutrition supply in weed species’ abundance and diversity. For instance, in some studies, the abundance of perennial weeds was doubled under reduced tillage intensity. In addition, higher values of Shannon-Weiner and Pielou indices were reported in the PK fertilization treatment compared to the control and NK fertilization treatments. The objective of this paper is to provide a brief overview of the key results of these experiments and summarize the part of the literature related to the effect of tillage systems and fertilization on weed species abundance and diversity. Such knowledge could contribute to the sound design and implementation of integrated weed management programs which in turn may lead to a decrease in the density of serious and noxious weeds and an increase in the overall balance of agroecosystems.

Abundancia y cobertura de arvenses bajo manejo convencional y orgánico de café y banano

Certain weeds can be used as cover species in bananas and coffee plantations. The objective of this study was to compare ground cover and abundance of weed species, between the organic and conventional production systems of banana and coffee. Selected farms under organic or conventional management located at Limón and Alajuela were surveyed for weeds, during 2015 and 2016. The minimum area methodology was used to determine sampling site size. At each sampling site, all weed species were identified and grouped into their respective taxonomic families. Percent soil cover by each species was also estimated by means of a visual scale. In both crops, weed diversity was higher when the herbicide glyphosate was used for weed control, although the ground cover for these species was kept at a minimum. These results are thought to arise from the fact that under the organic production system, a hierarchy of dominant species is established, which in turn inhibit many of the somewhat less adapted species, whereas under the conventional production system, the use of a non-residual herbicide renders the ground with plenty of space for species regeneration from the soil propagule bank. Organic weed management in both crops showed higher soil cover by weeds, but from a lower number of species. In contrast, chemical weed management with glyphosate showed a higher number at species, but a significant reduction in ground cover by those weeds.

Weed composition study on wheat and boro rice in research and farmers’ fields

A weed survey was conducted in Agronomy Field Laboratory, BAUFarm and farmers’ fields of Sutiakhali Natunchar village in Mymensingh district during the period from December 2015 to March 2016 to study the weed vegetation in wheat and boro rice. Ten fields were selected for each crop from each location. A quadrat of 0.25 m2 was placed randomly at four places in each plot and the weeds within the quadrat were identified and counted species-wise. The results revealed that the composition of weed species in two different crops was different and the composition of weed flora in each crop under different locations was also different. In wheat, a total number of 29 weed species belonging to 16 families were found from all three locations. The infesting weed species were 18 in Agronomy Field Laboratory, 16 species in BAU Farm and 19 species in farmers’ fields. From the five most dominant species, Polygonum hydropiper had the highest relative abundance value in both Agronomy Field Laboratory and BAU Farm and on the other hand, in farmers’ field, a new weed species, Eleusine indica was in the top most of the dominant list. The other weed species which were present in the dominant list of three locations were Cynodon dactylon, Cyperus rotundus, Paspalum distichum, Chenopodium album, Marsilea quadrifolia and Leucas aspera. In boro rice fields, among the three locations, 25 weed species were observed in total belonging to 13 families. Of which, 20 weed species were found in both Agronomy Field Laboratory and BAU Farm whereas in farmers’ fields, 21 weed species were identified. In both Agronomy Field Laboratory and BAU Farm, Eleocharis atropurpurea had the highest abundance value but in farmers’ field, Cyperus difformis occupied the highest value. The other dominant weed species were Leersia hexandra, Monochoria vaginalis, Echinochloa crusgalli, Paspalum distichum and Alternanthera philoxeroides found in three locations. Many common weeds were present in three locations in a crop but their frequency, uniformity, density and relative abundance value were different. The similarity index of weed species between wheat and boro rice indicated that the infesting weed species between the two crops was less associated. Thus the weed divergence in boro rice with wheat was high. From this study it was clear that the weed infestation was changed by crop and locations. In this study a little bit divergence and ranking of five most abundant weed species and low similarity index value of weed species in different crops under a specific area or among the area indicated that weed control measure should be adopted on crop basis in a specific area considering the dominant weed species.J. Bangladesh Agril. Univ. 15(2): 148-157, December 2017

Weed species composition of small‐scale farmlands bears a strong crop‐related and environmental signature

SummaryWeed species loss due to intensive agricultural land use has raised the need to understand how traditional cropland management has sustained a diverse weed flora. We evaluated to what extent cultivation practices and environmental conditions affect the weed species composition of a small‐scale farmland mosaic in Central Transylvania (Romania). We recorded the abundance of weed species and 28 environmental, management and site context variables in 299 fields of maize, cereal and stubble. Using redundancy analysis, we revealed 22 variables with significant net effects, which explained 19.2% of the total variation in species composition. Cropland type had the most pronounced effect on weed composition with a clear distinction between cereal crops, cereal stubble and maize crops. Beyond these differences, the environmental context of croplands was a major driver of weed composition, with significant effects of geographic position, altitude, soil parameters (soil pH, texture, salt and humus content, CaCO3, P2O5, K2O, Na and Mg), as well as plot location (edge vs. core position) and surrounding habitat types (arable field, road margin, meadow, fallow, ditch). Performing a variation partitioning for the cropland types one by one, the environmental variables explained most of the variance compared with crop management. In contrast, when all sites were combined across different cropland types, the crop‐specific factors were more important in explaining variance in weed community composition.