Weed Survey Research Articles

Geographical Distribution and Survival of Iris yellow spot virus in Spiny Sowthistle, Sonchus asper, in Georgia.

Iris yellow spot virus (IYSV) has occurred in Georgia since 2003. IYSV is transmitted by onion thrips, Thrips tabaci. During a weed survey in the Vidalia onion-growing zone (VOZ), spiny sowthistle (Sonchus asper) was identified as a host for IYSV. Spiny sowthistle is widespread in Georgia, and this presented an opportunity to study the natural spread of IYSV and assess its potential role in IYSV epidemiology. From 2007 to 2009, during the spring season, 2,011 sowthistle samples were collected from various counties within and outside the VOZ. The samples were tested for IYSV infection by enzyme-linked immunosorbent assay and confirmed by reverse-transcription polymerase chain reaction and sequencing. IYSV sequences from sowthistle were 98 to 99% identical to onion IYSV sequences from onion originated from Georgia. By the third year, IYSV-infected sowthistle plants were found in 79% of the counties in the VOZ and in 61% of the sampled counties in all directions, except to the east of the VOZ. Furthermore, thrips-mediated transmission assays confirmed that T. tabaci can efficiently transmit IYSV from onion to sowthistle. Sowthistle also supported T. tabaci survival and reproduction. These findings demonstrate that sowthistle plants can serve as an IYSV inoculum source and as a thrips reservoir.

Trajectories of weed communities explained by traits associated with species’ response to management practices

Two large-scale weed surveys conducted on winter wheat crops in France in the 1970s and the 2000s were used to determine the influence of management on weed communities. A trait-based approach was used to identify the mechanisms associated with the changing status of arable weeds over a 30 year period.A three-table ordination method (RLQ analysis) of the data set was performed to relate the environmental table to the species trait table using a species composition table to extract the joint structure (synchronic analysis). We then conducted a diachronic analysis to investigate the relationship between traits, alone or in combination, and the changing status of weeds.The synchronic analysis showed that tillage intensity filtered weeds according to height, seed weight, life forms and dispersal. Conversely, herbicides selected for species with delayed germination, which allows them to escape herbicide treatments. The diachronic analysis showed that successful weeds that have expanded were small plants, with rather light seeds, that can germinate over a long time frame during the vegetative period. This trait syndrome was probably favoured by profound changes in crop rotation and by increasing herbicide pressure. Our approach provides an excellent example of how future shifts in weed communities can be predicted and hence how weed management can be adapted so as to avoid promoting selection of problematic weeds.

Effects of Mulching Materials on Soil and Performance of cv. Nero di Troia Grapevines in the Puglia Region, Southeastern Italy

The responses in soil conditions, vine growth, and physiological, yield, and composition components of cv. Nero di Troia to the application of synthetic and organic mulches were studied for two years (2006–2007 and 2007–2008). The effects of the application in the vine rows of two synthetic mulches (geotextile as polypropylene and black polyethylene) and an organic mulch (exhausted olive pomace 3- and 6-cm thick) were compared to a control (weed mowing) in an organic vineyard. Throughout the trial, we conducted soil and leaf analyses, weed surveys, and phytotoxicity tests and measured vegetative activity, leaf gas exchange and water status, yield, and composition components. The exhausted olive pomace showed positive effects on some soil fertility variables and on vine physiology (stomatal conductance, transpiration, and net assimilation). Black polyethylene and geotextile provided good control of the weeds, especially in the first year, but positive results were also obtained with the exhausted olive pomace. Yield and composition components of grape were unaffected by any of the organic and synthetic mulches compared to weed mowing. The exhausted olive pomace provided good control of weeds, improved the fertility of the soil, and could be acceptable in terms of sustainability. The mode of action of the exhausted olive pomace was both physical and phytochemical through the release of phytotoxic compounds.

Weed cover, frequency and diversity in field plots and edges in the soybean central region of Argentina

A comparative survey of the weed species present in field plots and edges was performed in fields at Zavalla (Santa Fe) Argentina in the soybean central region of the country in order to determine changes in cover, frequency and diversity of the weed communities. Five to twelve soybean fields were surveyed in 2006, 2007, and 2009. Weed surveys were carried out in the soybean fallow in winter and after soybean planting in spring. In edges, species richness was higher than in field plots in spring-summer but diversity showed an erratic response. The weed community cover showed a shift in weed vegetation composition relative to the field plot. Our results indicate that the community in crop edges relative to field plots differs in structure and abundance and that many weed species are only present either in crop edges or in field plots.

Relative Composition of Weeds and Integrated Weed Management in Mulberry Garden

Crop-weed competition is a limiting factor in the growth of mulberry plant and weed management practices had marked influence on weed density and weed dry matter production. Based on the weed survey in the farmers field and investigations compared to chemical weeding intercropping with cowpea had an increased weed control effect in mulberry plantations. The lowest density and dry matter of weeds were recorded in cowpea intercropping treatment. Reduced density and dry matter production of weeds resulted in increased production of mulberry growth and yield.

Efficiency and Accuracy of Wildland Weed Mapping Methods

AbstractLand managers must set weed management priorities if limited resources are to be utilized effectively. Weed surveys and inventories assist land managers in this process by providing information regarding the identity, location, and relative abundance of weeds on their land. Although this information is vital, it can be challenging to select a method that provides the necessary data to meet management objectives while remaining accurate and cost effective. This paper critically evaluates four wildland weed mapping methods. These methods were defined as (1) paper-drawn, (2) buffered-point, (3) screen-drawn, and (4) perimeter-walked. Polygons were drawn by hand on topographic maps in the paper-drawn method. The other methods utilized handheld geographic positioning system (GPS) technology to digitally record infestations. Six experienced weed mappers independently recorded the location and size of eight sagebrush patches using each method. Time and accuracy were evaluated for each method based upon mapping time, distance walked, horizontal precision error, estimated size error, and shape error. The paper-drawn method was significantly less accurate than GPS-based methods at recording patch size and location. There was no significant difference in the accuracy of the buffered-point, screen-drawn, and perimeter-walked methods at reporting patch size and location. The need to cover land area quickly and efficiently favors the selection of the buffered-point or screen-drawn method because of time and distance factors. However, if patch shape is an important factor, the perimeter-walked or buffered-point methods may be the best choices of methods tested.

Effective management of viruses in pulse crops in south eastern Australia should include management of weeds

This study addressed the role of weeds in the epidemiology of the six most important pulse viruses in the production areas of south eastern Australia- Alfalfa mosaic virus-Bean yellow mosaic virus-cucumber mosaic virus-pea seedborne mosaic virus-bean leafroll virus-beet western yellows virus-pulse viruses-legume viruses-weeds. We found that the weed host range of these viruses was greater than previously reported and that not only were weeds a potential source of virus during the cropping season, but many persisted over hot, dry summers providing a “green bridge” for the viruses and their aphid vectors between cropping seasons. Weed surveys were conducted for the six pulse viruses in and around pulse crops during the 2000–2001 growing seasons. Virus was detected in 55 of 180 weed samples (selected as representative of 1416 samples), which included 15 species in 12 genera of seven families, including six allegedly new host-virus records. A weed survey was conducted between pulse growing seasons, over the summer of 2002 to determine the survival of weed hosts. It was found that even under severe drought conditions most weed species survived in a range of locations, providing a potential reservoir for viruses and allowing aphid vectors to over-summer on green hosts. Inoculation of 36 weed species common to the area resulted in additional potential weed hosts. As a result, weed control would seem to be an important element in controlling viruses in pulse crops in south eastern Australia.

Remarkable changes of weed species in Spanish cereal fields from 1976 to 2007

Management practices, geographical gradients and climatic factors are factors explaining weed species composition and richness in cereal fields from Northern and Central Europe. In the Mediterranean area, the precise factors responsible for weed distribution are less known due to the lack of data and surveys. The existence of weed survey data of year 1976 in the Zaragoza province of the Aragon region, Spain, offered us the opportunity to compare present weed species with weed species growing 30 years ago. No detailed comparison of changes in weed species composition in cereal fields in that period of time has been conducted in the Mediterranean area. Here a survey was conducted in the Aragon region from 2005 to 2007. Weeds were surveyed in 138 winter cereal fields in ten survey areas where winter cereals are the main crops, using the same methodology applied 30 years ago. In the Zaragoza province, 36 fields were chosen in the same municipalities than in the previous survey. Several management, geographic and climatic variables of each field were recorded and related to weed species with multivariate analysis. Diversity index were calculated and related to survey area and altitude. Our results show that out of the 175 species only 26 species were found in more than 10% of the surveyed fields. The main species were Papaver rhoeas, Lolium rigidum, Avena sterilis and Convolvulus arvensis found in more than half of the surveyed fields. L. rigidum was related to dryland, while the other species were found overall. Furthermore, we found that management, geographical and climatic factors were significantly related to weed species distribution. In particular altitude, survey areas, irrigation and herbicide use in post-emergence were the most driving factors explaining weed species distribution. Species richness was higher in survey areas with extensive management practices and increased with altitude excepting a very productive area with intensive management practices at high altitude where richness was as low as in the irrigated lowlands. The main differences found between the 1976 and the 2005–2007 surveys were (1) the striking increase of grass weeds, (2) the high decrease of mean weed species number found in each field declining from 9 to 3 and (3) the frequency decrease of many weed species probably caused by agriculture intensification in that period of time. The growing importance of other weed species is probably related to their adaptation to minimum tillage, which is a widespread technique nowadays.

Sistemas de produção de grãos e incidência de plantas daninhas

O sistema de semeadura direta e os diferentes sistemas de produção nele adotados podem contribuir para a supressão de plantas infestantes. Em razão disso, o objetivo do presente trabalho foi avaliar o controle de plantas daninhas em função de diferentes sistemas de produção de grãos. Os tratamentos utilizados foram: I. Sistema "safra-pousio" - soja/ pousio/milho/pousio/arroz/pousio/soja; II. Sistema "safra-adubo verde" - soja/milheto/ milho/guandu/arroz/crotalária/soja; III. Sistema "safra-safrinha" - soja/aveia-branca/milho/ feijão-da-seca/arroz/mamona/soja; IV. Sistema "safra - forrageira"- soja + braquiária/milho + braquiária/arroz + braquiária/soja. Em novembro de 2009 (após três safras agrícolas), foi realizado o levantamento de plantas daninhas infestantes. Para isso, foi utilizado um quadro (0,3 x 0,3 m), lançado aleatoriamente quatro vezes dentro de cada parcela. As plantas foram identificadas, bem como feita a determinação do número total das espécies invasoras, da massa seca e da porcentagem de controle das espécies de acordo com o sistema de produção. Foi realizada ainda a análise fitossociológica da comunidade de plantas daninhas infestantes. Os sistemas safra-adubo verde, safra-safrinha e safra-forrageira apresentaram bom controle de plantas infestantes quando comparados ao sistema safra-pousio. Portanto, a presença de algum tipo de cobertura é importante para manter as características do solo favorável e um bom controle de plantas invasoras.

Evaluation of changes in weed flora in arable fields of Nordic countries – based on Danish long‐term surveys

Andreasen C & Streibig JC (2011). Evaluation of changes in weed flora in arable fields of Nordic countries – based on Danish long‐term surveys. Weed Research51, 214–226.SummaryDuring the last 50 years, agricultural productivity has increased tremendously, as have changes in the weed flora. In several European countries, weed surveys have been conducted regularly, of which the most frequent and consistent ones are Danish surveys conducted in 1911–1915, 1945, 1960–1970, 1987–1989 and 2001–2004. The surveys were carried out on fields not sprayed with herbicide in the sampling year. On the basis of this frame of reference, we discuss the changes in the weed flora during this period and relate them to findings in other Nordic countries and review the role of different farming practices on the weed flora of the past. Numerous agronomic factors and political initiatives to protect the environment have operated in concert. During the last 30 years, winter‐sown crops have increased by almost 70%, at the expense of spring annual crops and grass leys, and this has favoured winter annual weed species. Maize is now widely grown and new weed species are invading arable land. Also, increased fertilisation levels over time have affected the weed flora. It is, however, obvious that herbicides play a major role in determining the composition, diversity and abundance of weed flora, although other factors such as mechanisation and the Common Agricultural Policy of the EU are also important. For the last 20 years, we have experienced an increase in some of the most frequent weed species without reductions in yield. This is probably due to governmental policies mandating lower herbicide efficacy goals for farmers, but it has been partly counteracted by genetic improvement of crops and better management.

Development of the Alaska agricultural weed flora 1981-2004: a case for prevention

Summary Alaska provides a unique laboratory to study the development of agricultural weed floras, since fields were first cleared in 1900–1985. Changes in weed species composition between 1981 and 2004 were studied in 80 agricultural fields near Fairbanks, Nenana, Delta Junction and Palmer, Alaska. Cover and density of all plants were measured in quadrats along a transect in each field. Environmental and management information were collected, including field age, weed control methods, crop, elevation, latitude, longitude, surrounding vegetation type and canopy shading. Detrended correspondence analysis was used to ordinate fields based on weed vegetation. Spearman correlations and graphical overlays were used to examine relationships between environmental and management variables and ordination axes. We found seven weed species that were new to Alaskan agriculture since 1981. Crop, canopy shading, elevation, latitude and longitude were important weed flora determinants. Two distinct weed community ⁄ crop associations were identified: (i) vegetables + potatoes and (ii) perennial grass (hay + grass seed). Non-native weed species colonised fields that were largely weed-free in 1981, when a similar weed survey was made. The failure to use weed prevention programmes since 1981, resulted in 40 000 ha of new agricultural land that must be managed for non-native weeds.

Uneven distribution of weeds along extensive transects in Australia’s Northern Territory points to management solutions

Summary The Top End region of the Northern Territory, Australia, is noted for its relatively unmodified natural state. To gain some insight into the potential for maintaining ecosystem health in this region we undertook a study that assessed the distribution of weeds across very extensive transects. This weed survey was distinct from other studies in that many of the sample sites were distant from tracks or other infrastructure. Twenty‐one weed species were recorded along 2000 km of transects. Weeds were reported from 18.7% of the 718 sample points. The incidence of weeds was found to be significantly associated with land tenure, being highest on pastoral lands and peri‐urban areas, and very low on Aboriginal lands. The incidence of weeds increased significantly with increasing levels of infrastructure and with increasing proximity to watercourses. There are three main conclusions from this study. First, much of the Top End, particularly remote Aboriginal lands, has exceptionally low levels of weed infestation. Secondly, in such areas, given the relatively small extent of vegetation change through weed invasion, maintenance or re‐imposition of traditional fire regimes should be achievable. Thirdly, there is substantial potential for spread of weeds to remote areas, with such spread most likely to occur through increased penetration by infrastructure. Importantly this study indicates that there is still opportunity to prevent widespread weed invasion across the Top End, which is timely given the current Government consideration of the potential for the region to support future agricultural expansion and the fast‐paced development of mining, oil and gas resources.

Using Assembly Theory to Explain Changes in a Weed Flora in Response to Agricultural Intensification

The intensification of crop management in the U.K. over the past 60 years has resulted in the decline of the populations of a number of annual plant species adapted to arable habitats. In contrast, other species continue to be common as arable weeds. A community assembly approach was taken to explain these recent changes in the weed flora using databases of plant functional traits, a pot experiment, and weed surveys of the Broadbalk long-term experiment. The hypothesis was tested that species that have been selected against by increased fertilizer inputs and herbicide use share an adverse combination of traits. An analysis comparing the combination of maximum height, seed weight, and time of first flowering of 29 common and 32 rare or threatened U.K. autumn weeds established that rare or threatened species occupied an area of trait space that was distinct from the common species. A rare weed trait syndrome of short stature, large seed, and late flowering was identified. The theory that species with a trait syndrome that is currently unfavorable are better adapted for less fertile environments was supported by the pot experiment. Species with a combination of short stature and large seed had a relatively greater competitive ability in low compared to high fertility treatments. Analysis of survey data from the Broadbalk long-term experiment confirmed that, as N inputs increased, the abundance of the two functional groups that contained only common species remained stable or increased; whereas, the groups dominated by rare or threatened species declined as fertility increased. An understanding of the response traits of arable plants to management filters, including fertilizer inputs and herbicide, is valuable for designing conservation strategies for rare species or predicting future shifts in the functional diversity of weed communities including the potential for invasive species to establish.

Weediness and Nutrient Uptake by Weeds in Relation to the Soil Tillage

The study was carried out in 2006 in Keszthely, on the soil tillage portion of a long‐term experiment. In this experiment, a combination of three cultivation methods [no‐till drill, disk tillage, conventional tillage (plowed)] and five nitrogen (N) rates (N0: 0, N1: 120, N2:180, N3: 240, and N4: 300 kg N ha−1) were assessed. The trial was arranged in a split‐plot design with four replications, and it was carried out during the first occurrence of maize in winter wheat–winter wheat–maize–maize rotation. Maize was sown on 10 May 2006; the weed survey was carried out using Balázs‐Ujvárosi coenological method on 5 June 2006, after which weed control was implemented. Maize biomass of plants at the three to four leaf stage was determined at the same time. Sixteen weed species were identified in the no‐till treatment, and 14 each in the in the conventional and the disk tillage treatments. Cultivation systems had a profound effect on the weediness of maize, with the lowest weediness occurring in the conventional tillage treatment. There was a strong interaction between N application and weed biomass that favored increased yield of maize over all cultivation treatments at higher N rates. The N content of weeds decreased as follows: conventional tillage < disc tillage < no‐till.

Weed hosts of Verticillium dahliae in cotton fields in Turkey and characterization of V. dahliae isolates from weeds

A weed survey conducted in 2004 and 2005 in Aydin province of Turkey showed that Solanum nigrum, Xanthium strumarium, Amaranthus retroflexus, Portulaca oleracea, Sonchus oleraceus and Datura stramonium were the most prevalent weeds in the cotton fields exhibiting Verticillium wilt. Verticillium dahliae Kleb. was recovered from A. retroflexus and X. strumarium in those cotton fields. This is the first report of V. dahliae occurring naturally in A. retroflexus in Turkey. Pathogenicity tests on cotton and weeds showed that the virulence of V. dahliae isolates from weeds was higher on cotton plants than on weeds, with the disease severity ranging from 31.7% to 98.0%. Disease severity of V. dahliae isolates was 54.7–93.9% on eggplant, 23.7–51.6% on cucumber and 11.0–16.4% on tomato, whereas it did not cause any disease symptoms, or only low levels, on pepper and bell pepper. Two vegetative compatibility groups (VCGs) were identified among seven tested weed isolates: VCG2A (two isolates) and VCG2B (three isolates) using international reference strains.

Weed occurrence in Finnish coastal regions: a survey of organically cropped spring cereals

Weed communities of organically cropped spring cereal stands in the southern and the northwestern coastal regions of Finland (= south and northwest, respectively) were compared with respect to number of species, frequency of occurrence, density and dry weight. Regional specialization of agricultural production along with differences in climate and soil properties were expected to generate differences in weed communities between south and northwest. Total and average numbers of species were higher in the south than in the northwest (33 vs. 26 and 15.6 vs. 10.0, respectively). Some rare species (e.g. Papaver dubium) were found in the south. Fumaria officinalis and Lamium spp. were found only in the south. The densities and dry weights of Lapsana communis, Myosotis arvensis, Polygonum aviculare, Tripleurospermum inodorum and Vicia spp. were higher in the south, while the densities and dry weights of Elymus repens, Persicaria spp. and Spergula arvensis were higher in the northwest. Total density of weeds did not differ between south and northwest (average = 565 vs. 570 shoots m-2, respectively). Total dry weight of weeds was higher in the northwest compared with the south (average = 1594 vs. 697 kg ha-1, respectively), mainly due to the high dry weight of E. repens. The only variable that was dependent on the duration of organic farming was weed density in the south. The abundance of nitrophilous in relation to non-nitrophilous weed species was higher while the abundance of perennial ruderal and grassland weed species was lower compared with previous weed surveys. This can be regarded as the result of increasing cropping intensity on organic farms in Finland. Different weed communities call for the application of specific target-oriented weed management in the respective coastal regions.;

Arable weeds as indicators of agricultural intensity – A case study from Finland

The study aimed at developing an agro-biodiversity indicator based on trophic interactions between 25 common arable weeds and individual groups of farmland birds, pollinators (wild bees), phytophagous insects and insect pests. Each weed species was weighted based on the number of reported linkages with each animal group. Four biodiversity indices based on these weights were constructed and applied to exploring the ecological consequences of long-term changes in weed populations in Finland. Data were used from weed surveys of Finnish spring cereal fields conducted in the 1960s, 1980s and 1990s. The relative importance of weed species varied according to animal groups. Annual weed species able to produce numerous seeds were important for the farmland birds and some perennial weed species were important for the pollinators. The highest number of linkages was established between weed species and phytophagous insects. The number of harmful pest species associated with broad-leaved weeds was low for all species. The general pattern of changes in values of indices over recent decades was similar: there was a marked decline in the values between the 1960s and the 1980s, and a slight increase between the 1980s and the 1990s. These changes were regarded as being a consequence of changes in the intensity of agricultural practices. The slowest recovery of the values was for pollinators. The results suggest that the ecological consequences of changes in the intensity of agriculture can be explored with the aid of a biodiversity indicator based on species interactions. Owing to the differences in the importance of weed species for different animal groups, maintaining weed species richness is necessary to ensure ecosystem services are provided for the higher trophic levels in farmland.

Introducing an abundance index for assessing weed flora in survey studies

This study was carried out to propose a simple abundance index (AI) of weed species, to describe the ranking of weeds in weed communities, and to evaluate weed flora. Based on a 4 year weed survey program conducted in Tehran province, the Thomas methodology for determining the relative abundance (RA) in weed communities was applied and a new, improved method (called the AI method) was introduced. Sixty‐one irrigated wheat fields were selected using a stratified sampling procedure. The boundaries of each county in the province formed the strata. For the Thomas method, the data were summarized for each county using five quantitative measures for determining the RA of each species. For the AI method, three quantitative measures were used, including frequency, uniformity, and mean field density. In the Thomas method, the mean field density had a significant role in determining the RA of a species, while the frequency and uniformity had a less significant role. However, for determining the AI, the frequency and uniformity had a higher value than the mean field density. Higher values for these two parameters for a particular species indicates that this species was more compatible with the soil and climate conditions in which it was growing, while higher values for the mean field density for a particular species indicates that the species had a higher competitive or reproductive ability than other species. In the Thomas method, the weed species with a low mean density were less abundant and not a serious weed for agroecosysytems but, in the AI method, an invasive weed could be detected before the colonization stage.

Ivor Ernest Doney

The responses in soil conditions, vine growth, and physiological, yield, and composition components of cv. Nero di Troia to the application of synthetic and organic mulches were studied for two...

Weed diversity in crop edges and inner fields of organic and conventional dryland winter cereal crops in NE Spain

A comparative survey of weed vegetation in organic and conventional dryland winter cereal fields was performed in central Catalonia (NE Spain) in order to assess the effects of agricultural intensification on the diversity, structure and composition of weed communities. A total of 36 cereal fields were surveyed in nine agricultural sites, where a pair of one long-established organic and one conventional farms were selected. Weed surveys were carried out before harvest in 2003 and 2004, taking into account the spatial pattern. Organic practices produced an increase in weed cover, species richness and Hill's first order diversity (but not in equitability), as well as a shift in weed vegetation composition, which favoured potentially rare arable, broad-leaved, insect-pollinated and legume weeds. Weed diversity was concentrated in the crop edges, especially in the weed communities of conventional cereal fields, which were found to be more spatially heterogeneous than the organic ones.