Weed Survey Research Articles

Weed Composition in Hungarian Phacelia (Phacelia tanacetifolia Benth.) Seed Production: Could Tine Harrow Take over Chemical Management?

Phacelia tanacetifolia, an excellent cover, green manure and honey crop is now widely cultivated throughout the world. One of its principal European seed production regions is north-western Hungary, where the recent withdrawal of a potent herbicide, linuron, created a new challenge for many growers. The goal of this study is to identify the main factors determining weed species composition in the phacelia fields of the region and to assess the efficiency of tine harrow and clopyralid herbicide in reducing weed abundance and biomass. We carried out a series of weed surveys across the study region following a two-level design: (i) we estimated the cover of all weed species in 205 fields (broad-scale survey, BS); and (ii) in 22 of these fields, we provided more precise biomass measurements (counting the individuals and measuring the dry weights of all weed species) in microplots samples (fine-scale survey; FS). To characterize the fields, 34 background variables were also collected for all of the studied fields. In both investigations, Chenopodium album was by far the most abundant weed. Within the BS, using a minimal adequate model containing 11 terms with significant net effects, 20.93% of the total variation in weed species data could be explained. The variation in species composition was determined by environmental factors (soil pH, clay and K; precipitation and temperature), non-chemical management variables (crop cover, preceding crop, irrigation and tillage system) and herbicides (linuron and clopyralid). Variation partitioning demonstrated the dominance of environmental and cultural components in shaping the weed species composition. Although the effect of mechanical treatments was most likely masked in the BS by the soil properties, our FS suggests that tine harrow could efficiently decrease the total number and biomass of weeds and can be a useful tool in the phacelia management of the future.

Amatrop: an open-access collection of weed survey datasets of tropical cropping systems

Amatrop: an open-access collection of weed survey datasets of tropical cropping systems

Assessments and Identification of Major Weed of Hot Pepper (<i>Capsicum annuum</i> L.) in West Shoa and East Wollega Zones, Ethiopia

Hot pepper is the most important vegetable crop belonging to the family Solanaceae and grown as a spice crop in different parts of the world. Hot pepper is one of the important cash crops to Ethiopian smallholder farmers and an important agricultural commodity which contributes to export earnings. Peppers cultivation in the field are subject to biotic and abiotic factors effects that influence the yield. Weeds emerge fast and grow rapidly competing with the crop for growth resources viz., nutrients, moisture, sunlight and space during entire vegetative and early reproductive stages of hot pepper. there is a dire need of identification major hot pepper weed in the study area for develop management option and this activity was initiated to assess and identify distribution and status of major hot pepper weeds in the study area. The weed survey was conducted in West Shoa and East Wollega Zones of Oromia Reginal state during 2020 main cropping season. The weed Survey was conducted to assess Abundance, Dominance and Frequency of major Hot pepper weeds. Kebeles were randomly selected from each District and based on the representativeness of hot pepper production of the area. Weed survey was performed along two diagonals (“X” pattern) of a five points field of 1m x 1m (1 m²) quadrates. A total of 46 weed fields were surveyed from Hot Pepper farms of Ilu Galan, Bako Tibe, Sibu Sire and Boneya Boshe Districts. From study fields 15 weed family and 39 weed species were recorded and identified. The assessments result also showed that, Broad leaf weeds dominate over grass and sedge weed species. 76.92% broad leaf, 17.95% grass types, and 5.13% sedge types from a total of 39 weed species of hot pepper farm fields. The occurrence of each weed species ranged from 2.78 up to 97.22% while the dominance value ranged from 0.3% up to 28%. The most common and prevailing weed was Ageratum conyzoides L. and Guizotia scarab in hot pepper field. Hence when developing a weed management approach in the future, different weed controlling options must be planed next coming years, toward those major Weed families and species; especially broad leaf weed.

Two sides of one medal: Arable weed vegetation of Europe in phytosociological data compared to agronomical weed surveys

AbstractQuestionsTwo scientific disciplines, vegetation science and weed science, study arable weed vegetation, which has seen a strong diversity decrease in Europe over the last decades. We compared two collections of plot‐based vegetation records originating from these two disciplines. The aim was to check the suitability of the collections for joint analysis and for addressing research questions from the opposing domains. We asked: are these collections complementary? If so, how can they be used for joint analysis?LocationEurope.MethodsWe compared 13 311 phytosociological relevés and 13 328 records from weed science, concerning both data collection properties and the recorded species richness. To deal with bias in the data, we also analysed different subsets (i.e., crops, geographical regions, organic vs conventional fields, center vs edge plots).ResultsRecords from vegetation science have an average species number of 19.0 ± 10.4. Metadata on survey methodology or agronomic practices are rare in this collection. Records from weed science have an average species number of 8.5 ± 6.4. They are accompanied by extensive methodological information. Vegetation science records and the weed science records taken at field edges or from organic fields have similar species numbers. The collections cover different parts of Europe but the results are consistent in six geographical subsets and the overall data set. The difference in species numbers may be caused by differences in methodology between the disciplines, i.e., plot positioning within fields, plot sizes, or survey timing.ConclusionThis comparison of arable weed data that were originally sampled with a different purpose represents a new effort in connecting research between vegetation scientists and weed scientists. Both collections show different aspects of weed vegetation, which means the joint use of the data is valuable as it can contribute to a more complete picture of weed species diversity in European arable landscapes.

Weed control of maize (Zea mays L.) in university farming

Purpose. Regarding the area of maize in Hungary, we can state that it is one of the largest crops grown in the area. Maize was grown on 1,048,070 hectares in Hungary in 2019. The purchase price depends, among other things, on the size of the sown area and the yields, but many other things can also have an impact in either a positive or negative direction. In recent years, the purchase price of maize has been around HUF 50,000/tonne. Maize is one of the heat-demanding plants that needs 500 mm of rainfall during its growing season to develop smoothly. The expected yield is significantly influenced by the type of soil grown. Meadow chernozem and brown forest soil are the most favorable for maize.
 Methods. The maize was sown on April 17, 2020. In the experimental area were selected 5 squares. A square has a floor area of 4 m2. In the research area were conducted three weed surveys. The dates were: May 18, June 22, and July 29, 2020. The following herbicides were released on 15th May: Sulcotrek (sulcotrione and terbuthylazine); Tegoplant (trisiloxane); Trend (adjuvant).
 Results. The area was harvested on 21 September by a combine harvester equipped with a corn tube breaker adapter. From an area of one hectare, 9.4 tons of crops were harvested with a moisture content of 14%.
 Conclusions. In the case of chemical weed control, it is recommended to use an agent or combination which is specifically aimed at reducing unwanted, in this case pine sorghum.

Functional shifts in weed community composition following adoption of conservation agriculture

AbstractTo better understand the changes in weed communities following the adoption of conservation agriculture (CA), we investigated the functional composition of weed communities in fields implementing CA continuously from 1 to 21 years. Weed surveys were conducted in 100 winter wheat fields of 53 farmers in the Bourgogne‐Franche‐Comté region, Eastern France. Ten response traits were selected to highlight changes in the functional composition of weed communities, using weighted mean value for quantitative traits and an approach based on composition analysis for qualitative traits. Out of the 10 traits, four were impacted by the time following the adoption of CA significantly, whereas two only showed trends. Specific leaf area, leaf dry matter content, seed dispersal mode and soil seedbank longevity did not change over time following adoption of CA, whereas changes were observed for plant type, Raunkiær's life forms, Ellenberg's indicator value for light and, germination and flowering periods. Phanerophyte and geophyte life forms, summer‐germinating species and spring‐ and summer‐flowering species increased with time following adoption of CA. Shade‐tolerant species, not present in fields recently converted to CA, established later. Community‐weighted mean of seed mass and the percentage of graminoids tended to increase with time following adoption of CA. Some functional shifts in weed communities occurred quicker than others (i.e., summer‐germinating species increased after at least 10 years of continuous application of CA principles). These results can be used to inform farmers moving towards CA about expected changes.

Unmanned Aerial System-Based Weed Mapping in Sod Production Using a Convolutional Neural Network.

Weeds are a persistent problem on sod farms, and herbicides to control different weed species are one of the largest chemical inputs. Recent advances in unmanned aerial systems (UAS) and artificial intelligence provide opportunities for weed mapping on sod farms. This study investigates the weed type composition and area through both ground and UAS-based weed surveys and trains a convolutional neural network (CNN) for identifying and mapping weeds in sod fields using UAS-based imagery and a high-level application programming interface (API) implementation (Fastai) of the PyTorch deep learning library. The performance of the CNN was overall similar to, and in some classes (broadleaf and spurge) better than, human eyes indicated by the metric recall. In general, the CNN detected broadleaf, grass weeds, spurge, sedge, and no weeds at a precision between 0.68 and 0.87, 0.57 and 0.82, 0.68 and 0.83, 0.66 and 0.90, and 0.80 and 0.88, respectively, when using UAS images at 0.57 cm–1.28 cm pixel–1 resolution. Recall ranges for the five classes were 0.78–0.93, 0.65–0.87, 0.82–0.93, 0.52–0.79, and 0.94–0.99. Additionally, this study demonstrates that a CNN can achieve precision and recall above 0.9 at detecting different types of weeds during turf establishment when the weeds are mature. The CNN is limited by the image resolution, and more than one model may be needed in practice to improve the overall performance of weed mapping.

The Biology of Canadian Weeds. 159.Capsella bursa-pastoris(L.) Medik.

Capsella bursa-pastoris (L.) Medik, shepherd’s purse, is a cosmopolitan summer or winter annual weed species distributed throughout temperate and subtropical regions of the world and is considered one of the most common plants on earth. It is an opportunistic annual that colonizes newly disturbed, open or dry environments and is ubiquitous in cultivated lands in Canada. In annual crops in western Canada, C. bursa-pastoris has been among the 20 most abundant weeds since the first weed surveys in 1970. It is most easily distinguished by its small white four-petalled flowers and its heart-shaped seed-pods, but exhibits considerable variation in leaf shape and flowering time. It has been used for food and medicine by numerous cultures. Its golden-brown seeds are produced in large numbers predominantly through self-pollination and can form a substantial seed bank, with reported values ranging to several hundred thousand seeds m−2. While seeds usually disperse near the mother plant, long-distance dispersal by attaching to vehicles, people and other vectors may be facilitated by its mucilaginous coat. Capsella bursa-pastoris does not produce fertile hybrids with other species of economic or ecological significance. It is generally well controlled by soil-applied and foliar (post-emergence) herbicides although its presence in agricultural fields may result in substantial yield loss, as documented in cole crops in North America and grain crops in Europe. The species can host a wide range of insect, nematode, fungal, viral, and bacterial pests that may damage crop species.

A survey evaluating the spatial and temporal distribution of horseweed (Conyza canadensis) late season in Ohio soybean fields from 2013 to 2017

AbstractOn-site surveys of weed populations provide information on the relative occurrence and density of weeds that can be useful to growers in that region. Data generated by weed surveys can aid in the management of weed issues by monitoring the movement of problem weeds and forecasting areas susceptible to infestations. Currently, on-site surveys are often performed on a small scale, within single fields or counties. Questionnaire surveys are helpful for assessing relative abundance but do not always provide detailed information on weed distribution in time or space. A survey was conducted annually in Ohio from 2013 through 2017 in 49 counties with soybean [Glycine max (L.) Merr.] production to assess the late-season occurrence of horseweed [Conyza canadensis (L.) Cronquist]. The objectives of this research were to: (1) determine the frequency, level of infestation, and distribution of C. canadensis in soybean fields in the primary soybean-producing Ohio counties over 5 yr; and (2) identify significant spatial clusters or movement trends over time. Conyza canadensis was encountered in each county from 2013 through 2017. Spatial cores of interest, or counties identified as having significant levels of C. canadensis infestations or a lack thereof relative to surrounding counties, were identified in all years except 2017. The lowest frequency of C. canadensis encountered at all rating levels occurred in 2017, which coincided with second-highest frequency of infestations (highest density level) among years. There was no distinct distribution or pattern of C. canadensis movement within the state from year to year, but there was an increase in counties with infestations over time compared with the early years of the survey when many counties had few to no infestations. These results suggest that C. canadensis persists as a common and troublesome threat to Ohio soybean producers and that growers should continue making C. canadensis management a priority when developing weed control programs.

Weed Survey in Different Fields of Transplanted Rice (Oryza sativa L.) in North Pulinpur Area under Khowai District of Tripura

The present investigation was carried out during kharif season 2017-18 at North Pulinpur area under Khowai district, Tripura (23°52.836′ N, latitude of 91°35.275′ E, longitude, and 940 m above sea level). North Pulinpur is one of the drought prone areas of Khowai district, Tripura. The area falls under the subtropical hill zone, and the climate is humid. An average annual rainfall ranges from 2050-2550 mm. The soil of the experimental field was sandy loam in texture acidic in reaction with a soil pH of 4.5-5.8 and medium in fertility status with low water holding capacity. Rice field surveyed covering 435 fields of four villages (V-I, II, III and IV) the number of respective field was 102, 141, 75 and 117, respectively. Weeds indicated there were 42 species belonging to 20 families of which 22 species were broad-leaved, 10 grasses, 7 sedges and 3 aquatics. Species diversity ranking of weed community for the villages were Village-II>Village-III>Village-I>Village-IV.  Based on Sorenson’s Index of Similarity of the S value is 87.67-102.77 %. The highest S value of 102.77% was between Village-I and Village-III, while the lowest value of 87.67% between Village-II and Village-IV. The higher S value indicated that species composition between villages was closely similar and the lower S value indicated species compositions in both villages were diverse. Out of 42 weed species, six species namely Oryza sativa (Weedy rice) followed by Echinochloa crus-galli, Leptochloa chinensis, Cynodon dactylon, Ludwigia hyssopifolia, Fimbristylis milacea were most abundant in all villages with a greater proportion of severe infestation (score of 5:41-50 % weed cover).

Weed community diversity in conservation agriculture: Post-adoption changes

Conservation agriculture has been identified as one of the farming systems likely to deliver sustainable agriculture but its effects over time on the diversity and composition of weed communities are poorly documented. Using a network of 100 winter wheat fields selected to encompass a gradient of years in conservation agriculture from 1 to 20 years in the Bourgogne-Franche-Comté region (France), we analyzed the changes that occurred in the diversity of weed communities over several years, both in α- and β-diversity using a taxonomic (species level) and functional (10 response traits) approach. Based on three weed surveys (before the last herbicide use, before harvest, before sowing the following crop), we identified weeds able to maintain and/or to produce propagules. All the observed weed communities were rich (average species richness of 23.9 species), diverse (average Shannon diversity of 2.15) and equitably composed of low-density species. The results showed an increase in species richness, total weed abundance and α-functional diversity but no change in species diversity and species evenness over time. Heterogeneity and average values of β-taxonomic and β-functional diversity between communities were high in the early years following the adoption of conservation agriculture. Heterogeneity and average β-taxonomic and β-functional diversity decreased over time, leading to a homogenization of weed community assemblages. Despite major changes in cultural practices related to conservation agriculture, homogenization of weed community was not immediate and did not concern all the traits studied.

Weed Survey of Nova Scotia Lowbush Blueberry (Vaccinium Angustifolium Ait.) Fields

ABSTRACT Weed surveys provide the basis for weed management research in lowbush blueberry, but have not been conducted in Nova Scotia since 2001. Documented declines in herbicide efficacy, loss and/or acquisition of herbicide active ingredients, confirmation of herbicide-resistant weed biotypes, and documented vectoring of weed seeds by machinery necessitate a new weed survey. A total of 165 bearing year lowbush blueberry fields were surveyed from 2017 to 2019, within which approximately 211 weed species were identified. Most weed species were herbaceous perennial forbs (89 species) and woody perennials (50 species), followed by annual broadleaf (24 species) and perennial grass weeds (20 species). The remaining flora consisted of a range of ferns, biennials, sedges and rushes, and orchids. The most common weed species were red sorrel (Rumex acetosella L.), poverty oatgrass (Danthonia spicata L. Beauv.), haircap moss (Polytrichum commune Hedw.), hair fescue (Festuca filiformis Pourr.), narrow-leaved goldenrod (Euthamia graminifolia (L) Nutt.), tickle grass (Agrostis hyemalis (Walter) BSP.), woolly panicum (Panicum lanugosum Ell.), cow wheat (Melampyrum lineare Desr.), bunchberry (Cornus canadensis L.), and yellow hawkweed (Hieracium caespitosum Dumort). Increased occurrence of these weed species is likely the result of documented or observed reductions in hexazinone and terbacil efficacy, confirmation of triazine-resistant biotypes, and common occurrence of seeds of these weed species on machinery. Low crop prices have also caused reduced pronamide use, contributing to increased occurrence of hair fescue. Results are guiding future research priorities for weed management in lowbush blueberry.

Crop diversification affects weed communities and densities in organic spring cereal fields in northern Europe

Within organic crop production, weed interference remains one of the main constraints on productivity, yet diverse weed vegetation supports the ecosystem services of arable fields. The use of crop diversification could alter weed communities and increase diversity, preventing the dominance of single detrimental weed species. This study investigated the type of crop diversification implemented in organic cropping systems in northern Europe and whether this affects the arable weed vegetation. A weed survey was conducted in 207 organic spring-sown cereal fields in five northern European regions (Denmark, Finland, Germany, Latvia and Sweden). Weed density data were combined with management and crop diversification data collected on the farms. The data set was analysed using linear mixed models and multivariate ordinations. The 197 weed species recorded were representative for the type of organic arable farming conducted in the regions. The management and crop diversification variables studied differed considerably among the regions. Management, such as the type of spring-sown cereal and crop mixture during monitoring, the preceding crop and weed harrowing, primarily influenced weed densities, while weed diversity increased with the duration of organic management and use of winter cover crops. The weed species communities were altered by the crop diversification applied. This study reflects the impact of regionally varied crop diversity and reinforces the importance of regionally adapted crop and weed management.

Weed Survey Associated in Tobacco (Nicotiana tabacum L.) in Bilatte Tobacco Farm, Ethiopia

An in-field weed survey method was conducted to estimate the most frequently, density and abundance weed species present in Bilatte tobacco farm, Ethiopia during 2014 totally covered approximately 145 hectares. During study period a total number of 14 weed species belonging to 06 monocot and 08 dicot families were recorded out of 7 families of weed reported form study site. The most predominate was shown by monocot Poaceae having 4 weed species followed by dicot family Composite having 3 weeds. The families Cyperaceous, Solanaceae and Amaranthaceous each having 2 weeds, and the family Papaverceae represented by 1 weed. Based on % of frequency Cyperus esculentus (sedges) family Cyperaceous was 99.30. The data showed that Cynodon dactylon and Digitaria abyssinica belong to family Poaceae and Cyperus esculentus family Cyperaceous were the most abundant weed with a density of 35.9, 14 and 12 of plant m-2 respectively. Relative abundance values quantify the overall weed problem posed by specie Cyperus esculentus that had higher relative abundance was 98.97. The importance value index indicated that Cyperaceous and Poaceae families can be considered the great potential to cause reduce tobacco production. Whereas, Solanium nigrum and Datura stramonium were observed with least population density 0.00 and 1.03 plant m-2, least frequently 2.7 and 13.51 %, least relative weed abundance, 0.07 and 1.03 with importance value index 2.8 and 14.8 occurring weed respectively.

Do ecological specialization and functional traits explain the abundance–frequency relationship? Arable weeds as a case study

AbstractAimThe abundance–frequency relationship (AFR) is among the most‐investigated patterns in biogeography, yet the relative contributions of niche‐based processes related to ecological strategies, and of neutral processes related to spatial colonization–extinction dynamics, remains uncertain. Here, we tested the influences of ecological specialization and functional traits on local abundance and regional frequency, to determine the contribution of niche‐based processes.LocationFrance and the UK.TaxonVascular plants.MethodsWe used two arable weed surveys covering 1,544 fields in Western Europe (France, UK), along with functional traits related to resource acquisition, resource requirements, flowering phenology and dispersal. We quantified specialization both to arable habitat and to individual crop types, and performed phylogenetic path analyses to test competing models accounting for direct and indirect relationships between traits, specialization, abundance and frequency. We performed the analyses for all species in each country, as well as for a subset of the most abundant species.ResultsLocal abundance of weeds increased with their regional frequency, but the relationship became negative or null when considering only the most abundant weeds. Specialization to arable habitat and to individual crop type either had a similar or opposite effect on regional frequency and local abundance explaining these positive and negative relationships, respectively. Regional frequency was not directly explained by any trait but indirectly by resource requirement traits conferring specialization to the arable habitat. Conversely, high local abundance was directly related to low seed mass, high SLA, early and short flowering.Main conclusionsDirect/indirect effects of functional traits on local abundance/regional frequency, respectively, supports a significant role of niche‐based processes in AFR. Neutral spillover dynamics could further explain a direct linkage of abundance and frequency. Similar causal paths and consistent influences of traits on specialization and abundance in the two studied regions suggest genericity of these findings.

Qualitative and Quantitative Assessment of Common Weed Species in West Gondar Sesame Growing Area, Ethiopia

Weeds compete with crops grown for resource limits such as water, nutrients, and light. Weed infestation is one of the major factors limiting sesame production, as its seedlings grow slowly during the first few weeks making it a weak competitor at earlier crop growth stages. Weed induced sesame yield reductions of up to 65 percent, and a need for a crucial weed-free duration of up to 50 days following planting. Weed surveys are useful for determining the occurrence and relative importance of weed species in crop production systems. Weed survey on a farm basis is needed to establish efficient weed management and decision making mechanisms and to evaluate weed control measures. Therefore this survey was conducted to assess qualitative and quantitative weed species in sesame growing areas of west Gondar, Ethiopia. Weed survey was conducted in 2012 at Metema and 2013 main cropping season at Metema, Tach Armachiho, and Mirab Armachiho district. data on weed species type and count were taken along the diagonal with 50cm x 50cm quadrate at a 15-meter interval at three points. Visual identification, manuals, photographs, leaflets, and books were used for identifying weed species. They conducted interviews with farmers, development agents, and district experts working in the region. Weed species compositions were analyzed by frequency, abundance, dominance, and similarity index. In the districts, 31common weed species or groups of species from 17 families were recorded. Ipomea cordofana Br., Grass spp’, Commelina benghalensis L. Andropogon abyssinicus (Fresen) R.Br., Boerhaavia erecta L., Corchorus olitorius L.kudra, Corchorus trilocularis L., Leucas martinicensis (Jacq) ait.f. and Ipomea triloba are the most prevalent, abundant, and important weeds in sesame fields in north Gondar. As to this on-farm and practical training on identification and demonstration management options should be given on the low land of north Gondar farmers.

Weed Hosts of Field Dodder (Cuscuta campestris Yunck.) in Northwestern Marmara Region of Turkey

Dodder (Cuscuta spp.) is a parasitic weed damaging several crop plants. A weed survey covering vegetable fields, orchards and vineyards was conducted from 2015 to 2018 in Northwestern Turkey. During surveys parasitic weed Cuscuta campestris Yunck was found attached to 23 weed species from 15 families. Higher frequency of parasitism of dodder was determined in Polygonum aviculare L., Amaranthus retroflexus L., Chenopodium album L., Ecballium elaterium (L.) A. Rich., Lactuca serriola L., Portulaca oleracea L. and Cichorium intybus L. weed species. The infection intensity was the highest in Lactuca serriola L., Convolvulus arvensis L., Portulaca oleracea L., Tribulus terrestris L., Ecballium elaterium (L.) A. Rich., Rumex crispus L. and Polygonum aviculare L.

Influence of luminous flux parameters on the formation of re-weeding of hemp crops

Light (energy) growing conditions of hemp plants have a direct effect on both crop plants and their habitat, as well as on new seedling plants of weeds that began their vegetation after soil herbicides weakened their protective function. The appearance of such weeds in crops is called re-weeding. Re-weeding is difficult to control. 
 It is fair to say that the density of hemp crops and, consequently, their optical density is a very effective, cheap and environmentally friendly factor influencing weeding processes. The application of such factors of influence on the indicators of re-weeding of crops is especially effective, when the application of any agronomic or chemical methods on new weed seedlings is very difficult or simply impossible.
 Studies conducted during 2014‒2016 in the field experiment of the Institute of Bast Crops of NAAS to determine the influence of light regimes of hemp sowing on the formation of re-weeding crops provided five options with different stocking densities of hemp sowing, which formed different indicators of optical density of crops. The experiment determined such indicators of the light regime as the incident energy flux of the headlights and the transmission of light by sowing to the ground. Weed surveys were performed according to the requirements of the "Pesticide Test and Application Methods". Crop weeds were determined quantitatively and quantitatively by weight.
 As a result of the conducted researches the regularities of weed formation at different density of stems, as well as between weed parameters and light regimes of sowing hemp crops were established. There is a direct linear relationship between the transmission of light to the soil by sowing hemp and the number and weight of weeds. The critical dates for the release of FAR energy into the soil for re-weeding were the third decade of July and the third decade of September. With a standing plant density of 1.65 million units/ha, conditions developed under which most weed plants in repeated weeding could not reach the virgin stage of organogenesis. That is, it can be argued that it is in crops with a stem density of 1.65 million units/ha conditions are achieved for the least development of re-weeding due to the minimum energy input of the headlights required for full generative productivity of weeds.
 Thus, the development of methods for controlling the processes of re-weeding of hemp crops based on phytocenotic factors deserve widespread introduction into agricultural production, as quite effective and environmentally friendly.

Differences in efficacy, resistance mechanism and target protein interaction between two PPO inhibitors in Palmer amaranth (Amaranthus palmeri)

AbstractA weed survey was conducted on 134 Palmer amaranth (Amaranthus palmeri S. Watson) populations from Mississippi and Arkansas in 2017 to investigate the spread of resistance to protoporphyrinogen oxidase (PPO) inhibitors using fomesafen as a proxy. Fomesafen resistance was found in 42% of the A. palmeri populations. To investigate the resistance basis of different PPO inhibitors, we further characterized 10 representative populations by in planta bioassay in a controlled environment and molecular characterizations (DNA sequencing and TaqMan® gene expression assay). A total of 160 plants were sprayed with a labeled field rate (1X) of fomesafen or salfufenacil and screened for the presence of three known resistance-endowing mutations in the mitochondrial PPX2 gene (ΔGly-210, Arg-128-Gly, Gly-399-Ala). To compare the potencies of fomesafen and saflufenacil, dose–response studies were conducted on two highly resistant and one sensitive populations. The interaction of the two herbicides with the target protein harboring known PPX2 mutations was also analyzed. Our results showed that: (1) 90% of the fomesafen- or saflufenacil-resistant plants have at least one of the three known PPX2 mutations, with ΔGly-210 being the most prevalent; (2) saflufenacil is more potent than fomesafen, with five to nine times lower resistance/susceptible (R/S) ratios; (3) fomesafen selects for more diverse mutations, and computational inhibitor/target modeling of fomesafen suggest a weaker binding affinity in addition to a smaller interaction volume and volume overlap with the substrate protoporphyrinogen IX than saflufenacil. As a result, saflufenacil shows reduced sensitivity to PPX2 target-site mutations. Results from current study can help pave the way for designing weed management strategies to delay resistance development and maintain the efficacy of PPO inhibitors.

Which Traits Make Weeds More Successful in Maize Crops? Insights from a Three-Decade Monitoring in France.

A major aim in invasion biology is identifying traits distinguishing alien invasive and alien non-invasive plants. Surprisingly, this approach has been, so far, poorly used to understand why some arable weeds are abundant and widespread while others are rare and narrowly distributed. In the present study, we focused on the characteristics of successful weeds occurring in maize fields, one of the most important crops worldwide. Two national weed surveys conducted in France were used to identify increasing and decreasing species based on 175 and 484 surveyed fields in the 1970s and the 2000s, respectively. Weed trait values related to regional frequency, local abundance, and specialization to maize were identified with phylogenetic generalized least-squares (PGLS). We found a positive relationship between regional frequency and local abundance, i.e., the most widespread weeds were also locally more abundant. We highlighted that weeds with the C4 photosynthetic pathway and summer emergence were more abundant, more frequent, and more specialized to maize crops. More generally, we highlighted two successful strategies: On the one hand, traits related to a general weediness syndrome with rapid resource acquisition (high SLA and Ellenberg-N) and high colonization capacity (seed longevity, fecundity, and wind dispersal); on the other hand, traits related to specific adaptation to spring cultivation (thermophilous species with summer emergence, late flowering, and C4 photosynthetic pathway). Deviations from the abundancy–frequency relationships also indicated that species of the Panicoideae sub-family, species with Triazine-resistant populations, and neophyte species were more abundant than expected by their regional frequency. To some extent, it is therefore possible to predict which species can be troublesome in maize crops and use this information in weed risk assessment tools to prevent new introductions or favor early detection and eradication. This study showed how tools developed in functional and macro-ecology can be used to improve our understanding of weed ecology and to develop more preventive management strategies.