Selected Weed Species Research Articles

Evaluation of the potentiality of diverse weed species in mobilising soil bioavailable phosphorus

The present study was carried out to assess the inorganic phosphorus (P)- dynamics under the rhizosphere of 10 weed species belonging to 8 different families. A fractionation study revealed that sol-P and Ca2-P were highest in M. denticulata L. and C. rotundus L. with 67.25 mg kg-1 and 48.37 mg kg-1, respectively (p<0.05) which could be attributed to high alkaline phosphatase activity in the rhizosphere. Out of the selected weed species, labile-P: nonlabile- P content was highest in M. denticulata L. (0.42) which is 38% higher than C. arvensis L. In terms of biomass and leaf P (%) C. didymus (L.) Sm. recoreded highest but, interestingly M. denticulata L. though had a higher sol-P but failed to translocate P-to the above and below-ground parts. Hence, M. denticulata L. being legume was an excellent mobilizer of non-labile P and can improve the available P for the subsequent crop.

The finger weeder cultivator for intra‐row mechanical weed control: Effects of uprooting force on selected weed species

AbstractMechanical weed control tools are commonly used in the production of many vegetable and field crops. This study aimed to determine the impact of weed species and growth stage on the finger weeder performances and to reveal the relation between root morphology, uprooting force and control efficacy. A one‐month field experiment with two model species, Triticum aestivum L. (grass) and Sinapis alba L. (broadleaf), showed that finger weeder control efficacy was affected by species and growth stage: Finger‐weeder application during the first two growth stages (cotyledon and second leaf) was more effective for S. alba than for T. aestivum (p < 0.0001), but at fourth‐leaf stage values for control efficacy were not significantly different (p = 0.134). In an experiment conducted in pots it was found that, at all three growth stages, the uprooting force required for S. alba was significantly lower than that for T. aestivum (p < 0.0001), indicating a lower anchoring force of the former. Determination of root‐morphology parameters revealed significantly higher root parameters, like length, in T. aestivum than in S. alba at the early developmental stages. Correlation of the control efficacy and uprooting force revealed a 2.5‐N threshold value for effective weed control. Additionally, net‐house and field experiments showed significant differences in the uprooting forces required for 10 different Mediterranean grasses versus broadleaves weed species at all developmental stages. To translate these findings into applicative recommendations, future research should characterize the relationship between the operational factors of this tool and the required uprooting force.

A Study on the Potentiality of Bioethanol Production from Selected Weed Species of the Asteraceae Family


 
 
 Increasing population growth, industrialization, and the harmful impacts of fossil fuel burning on the environment fascinated the researchers to find a low-cost, environmentally friendly alternative substitute. A potential substitute feedstock for the synthesis of second-generation bioethanol is the lignocellulosic biomass from invasive weedy plants. The aim of this study was to determine the potential of bioethanol production from two weedy plant species using physical, chemical, and physiochemical pretreatment methods, as well as to optimize the pretreatment and culture conditions to obtain a higher reducing sugar amount and ethanol yield. The collected invasive weedy plants, Chromolaena odorata and Tridax procumbens, were cleaned, then pretreated with different acids and bases (4% v/v) at 121oC for 15 min. Then the filtrate was incubated with Saccharomyces cerevisiae (baker‘s yeast) in the peptone yeast extract and nutrient medium (PYN) at room temperature, the pH was maintained at 5.0. T. procumbens plant substrate with the performic acid pretreatment agent produced a significant amount (0.2%) of ethanol, and further studies were conducted with the same substrate and the pretreatment agent. The conditions were optimized successively by changing one factor at a time while keeping the other variables constant. Several important hydrolysis factors were studied for the optimization, including performic acid concentration (0.2–5%), hydrolysis time (10–60 min), fermentation time (24–120 h), inoculum concentration (1.25–7.5 g/100 ml), and rotation speed (50–250 rpm). The maximum ethanol yield of 0.47% was observed at 0.6% performic acid concentration, 30 min of hydrolysis time, 48 h of fermentation time, 5 g/100 ml of inoculum concentration, and 100 rpm rotation speed with T. procumbens using S. cerevisiae.
 Keywords: Bioethanol, Lignocellulosic biomass, Acid hydrolysis, Saccharomyces cerevisiae
 
 

Allelopathic Effects of Selected Weed Species on Seed Germination and Seedling Growth of Mungbean (Vigna radiata L.)

Allelopathic Effects of Selected Weed Species on Seed Germination and Seedling Growth of Mungbean (Vigna radiata L.)

Comparative evaluation of four herbicides for effective control of post-emergence weeds in cotton fields

This study aimed to evaluate the effectiveness of four different herbicides, namely Glyphosate, Paraquat, Dicamba, and S-metolachlor, in controlling post-emergence weeds in cotton fields. The experiment was conducted in Layyah, and the selected weed species included Pigweed, Canada thistle, barnyardgrass, Field bindweed, Purslane, Bermuda grass, Green amaranth, and Puncture vine. A randomized complete block design was employed, with four treatments and four replications within each treatment. One-meter quadrates were randomly placed within each replication to collect data on weed abundance. The recommended herbicide doses were applied, including 3 liters per hectare of Glyphosate, 1 liter per hectare of Paraquat, 1 liter per hectare of Dicamba, and 1.5 liters per hectare of S-metolachlor. The effectiveness of the herbicides was observed at regular intervals, noting the time taken for visible weed control and weed mortality. Data were collected for three time points to assess the herbicides' long-term efficacy. Data analysis revealed variations in the effectiveness of the herbicides on different weed species. Treatment T3 (Dicamba) consistently exhibited the highest control, while T4 (S-metolachlor) showed the lowest effectiveness. Mean weed densities across the treatments indicated significant reductions in pigweed, Canada thistle, barnyardgrass, and field bindweed. However, no statistically significant differences were observed among the treatments for purslane, Bermuda grass, green amaranth, and puncture vine. These findings provide valuable insights into the effectiveness of different herbicides in controlling post-emergence weeds in cotton fields. The results can inform farmers and agricultural professionals in selecting appropriate herbicides for effective weed management. Further research is warranted to evaluate the long-term effects and environmental considerations associated with the herbicides. The study highlights the importance of multiple data collection time points to assess the sustained effectiveness of herbicide treatments.

Benzoxazinoids in wheat allelopathy – From discovery to application for sustainable weed management

Allelopathic activity of wheat (Triticum aestivum L.) has previously been associated with the production of phenolic acids and flavonoids (PAF), benzoxazinones (BXZs) and phenoxazinones (PXZs). The biosynthesis of BXZs is closely regulated during cereal growth, with accumulation highest in young tissues with variation associated with genotype and environmental conditions. This review is focused on BXZ metabolites and their impact on germination, seedling growth and physiological, biochemical, transcriptional and proteome traits of surrounding plants and weeds. The major pathways employed by plants for benzoxazinoid detoxification involve hydroxylation and glucosylation and polymerisation of intermediates in these pathways. Allelochemicals from various wheat genotypes have been shown to inhibit the growth of selected weed species, including Bromus japonicus, Chenopodium album, Portulaca oleracea, Avena fatua and Lolium rigidum. Wheat allelopathy is potentially exploited from the standpoint of crop mulches, incorporation of crop residues, tissue disruption, intercropping with allelopathic cultivars and application of aqueous wheat extracts. BXZs have been shown to suppress the growth and development of certain agricultural pests, including insects, fungal pathogens, and weeds. Many native plants, fungi and insect herbivores inherently possess varying tolerance levels towards BXZs. However, other BXZ- susceptible species are adversely impacted by elevated BXZ levels in crop plants. Thus, considerations for the selection and breeding of wheat genotypes possessing enhanced defensive ability via elevated BXZ contents are discussed. Here, these objectives are reconsidered with a focus on co-evolutionary aspects and their potential impacts on biodiversity in the agroecosystems under study. For future breeding efforts to be successful, it is important to take such potential adverse environmental impacts into account, in combination with an increased focus on enhancing beneficial allelopathic effects within agricultural systems.

Evaluation of the phytotoxic and antifungal activity of C17 -sesquiterpenoids as potential biopesticides.

BACKGROUNDNatural products are a promising source for the development of new pesticides with alternative mechanisms of action. In this study, we evaluated the phytotoxic and antifungal activity of a novel family of natural C17‐sesquiterpenoids and performed a study of the effect caused by the elimination of the α‐methylene‐γ‐butyrolactone system and its importance to their biological activity.RESULTSMany tested compounds exhibited a strong phytotoxic activity. Lappalone and pertyolide B were the most potent molecules from the tested group. Lappalone displayed a strong inhibition profile against selected weed species, reaching a half‐maximal inhibitory concentration (IC50) value of 5.0 μm against Echinochloa crus‐galli L. shoot and 5.7 μm against the germination rate of Amaranthus viridis L., as well as a good stimulation of the germination of Phelipanche ramosa L. Pertyolide B demonstrated excellent inhibition against Amaranthus viridis L. (IC50: 56.7, 70.3 and 24.0 μm against the root and shoot growth, and germination rate, respectively) and Allium cepa L. (representative of the Liliaceae family, with IC50 values of 25.3 and 64.4 μm against root and shoot growth). Regarding the antifungal activity, pertyolide B presented significant activity against Colletotrichum fragareae and Fusarium oxysporum with a minimum inhibitory concentration of 6.6 μg μL−1.CONCLUSIONThe bioassays revealed that frequently the presence of the α‐methylene‐γ‐butyrolactone system is not essential for the bioactivities of sesquiterpene lactones, and suggest that C17‐sesquiterpenoids may function through a different mechanism of action not related to the widely assumed Michael addition. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Phytotoxic effects of essential oils from Nepeta glocephalata Rech.f. and N. ispahanica Boiss. on se-lected weed species

In the present study the bioherbicidal activity of essential oils hydrodistilled from Nepeta glocephalata Rech.f and N. ispahanica Boiss were investigated on four weed species (barnyard grass (Echinochloa crus-galli (L.) Beauv), redroot pigweed (Amaranthus retroflexus L.), lambsquarters (Chenopodium album L.) and canary grass (Phalaris canariensis L.)). A total of 37 components were identified from the essential oils of N. glocephalata and N. ispahanica constituting approximately 98.61 % and 96.1 % of the oils, respectively. In laboratory bioassay different concentrations (0, 1, 2, 4 and 8 μl ml-1) of two Nepeta essential oils on germination, root and shoot length were studied. Results showed by increasing the concentration of oils, all studied traits of the weeds were decreased compared with control. In a glass house bioassay post-emergence application of Nepeta essential oils (1.25 %, 2.5 %, 5 % and 10 %, v/v) on 3-week-old weed plants caused visible injury (7-days after spray) ranging from chlorosis to necrosis of plant weeds. In foliar application under glasshouse conditions, both Nepeta essential oils reduced the seedling dry mass and concentrations of chlorophyll a chlorophyll b. The study concludes that Nepeta essential oils have phytotoxic effects and could be used as bioherbicides but the selectivity of these compounds should be considered also.

The Impact of Ensiling at Different Moisture Contents on Germinability and Viability of Selected Weed Species’ Seeds

Weeds are an increasingly significant issue inhibiting agricultural production worldwide. Forage conservation could form part of an integrated weed management program if ensiling killed weed seeds. In Experiment 1, seeds of five grass (Hordeum spp., Bromus diandrus, Bromus hordeaceum, Lolium rigidum and Vulpia spp.) and two broad-leaved temperate weed species (Echium spp. and Raphanus raphanistrum), that were either untreated, ensiled in pasture (Trifolium subterranean/Lolium rigidum mixture) forage for a minimum of three months, underwent 48 h in sacco digestion in steers or ensiled prior to digestion were tested for germinability and viability. In Experiment 2, seeds of eight tropical weed species (Cenchrus ciliaris, Rumex spp., Bidens pilosa, Sorghum halepense, Urochloa panicaoides, Paspalum dilatatum, Brachiara eruciformis and Choris truncata) were ensiled in Sorghum bicolor forage. In Experiment 3, L. rigidum and R. raphanistrum seeds were ensiled in either Medicago sativa forage wilted to 336.9, 506.5 or 610.7 g/kg dry matter; or in chaff to which water or water plus acid was added at rates to achieve 350, 450 or 550 g/kg dry matter content with lactic plus acetic acid added in the ratio of 3:2 at 80, 45 or 10 g/kg DM, respectively. In Experiment 4, L. rigidum and R. raphanistrum seeds were ensiled in cotton wool to which water or water plus acid was added at the same rates as in Experiment 3. Germinability of all seeds following ensiling was substantially reduced or nil. The extent of the reduction varied with species and experiment. In sacco digestion reduced germinability in Experiment 1, but to a lesser extent than ensiling; while ensiling plus digestion reduced germination rates to 0%.

Effect of Clay, Soil Organic Matter, and Soil pH on Initial and Residual Weed Control with Flumioxazin

Greenhouse studies were conducted to evaluate the effects of soil organic matter content and soil pH on initial and residual weed control with flumioxazin by planting selected weed species in various lab-made and field soils. Initial control was determined by planting weed seeds into various lab-made and field soils treated with flumioxazin (71 g ha−1). Seeds of Echinochloa crus-galli (barnyard grass), Setaria faberi (giant foxtail), Amaranthus retroflexus (redroot pigweed), and Abutilon theophrasti (velvetleaf) were incorporated into the top 1.3 cm of each soil at a density of 100 seeds per pot, respectively. Emerged plants were counted and removed in both treated and non-treated pots two weeks after planting and each following week for six weeks. Flumioxazin control was evaluated by calculating percent emergence of weeds in treated soils compared to the emergence of weeds in non-treated soils. Clay content was not found to affect initial flumioxazin control of any tested weed species. Control of A. theophrasti, E. crus-galli, and S. faberi was reduced as soil organic matter content increased. The control of A. retroflexus was not affected by organic matter. Soil pH below 6 reduced flumioxazin control of A. theophrasti, and S. faberi but did not affect the control of A. retroflexus and E. crus-galli. Flumioxazin residual control was determined by planting selected weed species in various lab-made and field soils 0, 2, 4, 6, and 8 weeks after treatment. Eight weeks after treatment, flumioxazin gave 0% control of A. theophrasti and S. faberi in all soils tested. Control of A. retroflexus and Chenopodium album (common lambsquarters) was 100% for the duration of the experiment, except when soil organic matter content was greater than 3% or the soil pH 7. Eight weeks after treatment, 0% control was only observed for common A. retroflexus and C. album in organic soil (soil organic matter > 80%) or when soil pH was above 7. Control of A. theophrasti and S. faberi decreased as soil organic matter content and soil pH increased. Similar results were observed when comparing lab-made soils to field soils; however, differences in control were observed between lab-made organic matter soils and field organic matter soils. Results indicate that flumioxazin can provide control ranging from 75–100% for two to six weeks on common weed species.

Identifying Invasive Weed Species in Alpine Vegetation Communities Based on Spectral Profiles

This study examined the use of hyperspectral profiles for identifying three selected weed species in the alpine region of New South Wales, Australia. The targeted weeds included Orange Hawkweed, Mouse-ear Hawkweed and Ox-eye daisy, which have caused a great concern to regional biodiversity and health of the environment in Kosciuszko National Park. Field surveys using a spectroradiometer were undertaken to measure the hyperspectral profiles of leaves and flowers of the selected weeds and companion native plants. Random Forest (RF) classification was then applied to distinguish which spectral bands would differentiate the weeds from the native plants. Our results showed that an accuracy of 95% was achieved if the spectral profiles of the distinct flowers of the weeds were considered, and an accuracy of 80% was achieved if only the profiles of the leaves were considered. Emulation of the spectral profiles of two multispectral sensors (Sentinel-2 and Parrot Sequoia) was then conducted to investigate whether classification accuracy could potentially be achieved using wider spectral bands.

Zastupljenost ekonomski značajnih korovskih vrsta u vegetaciji duž riparijalnih staništa i puteva na području Srbije

Transportation corridors such as waterways and road networks serve as an entranceway for invasive and economically important weed species. The unstable environment of riparian areas and nutrient enrichment of road verges promotes the establishment and spread of these species, which may have a negative effect on nearby arable land, leading to severe yield reductions. We aimed to register the presence and frequency of five selected weed species (Chenopodium album, Cirsium arvense, Convolvulus arvensis, Cynodon dactylon, and Lactuca serriola) within these linear corridors. Sites along waterways were visited during 2013-2016, and road networks during 2018-2019. At each site, studied weed species were registered along 100 m transects, resulting in 250 localities along waterways and 180 near road networks. The most frequent species is C. arvensis, followed by L. serriola and C. album, while less prevalent species are C. arvense and C. dactylon. The main characteristic of studied species is their preference for roadside habitats, except for Chenopodium album, which is more common in riparian areas.

Influence of chaff and chaff lines on weed seed survival and seedling emergence in Australian cropping systems

AbstractChaff lining and chaff tramlining are harvest weed seed control (HWSC) systems that involve the concentration of chaff material containing weed seed into narrow (20 to 30 cm) rows between or on the harvester wheel tracks during harvest. These lines of chaff are left intact in the fields through subsequent cropping seasons in the assumption that the chaff environment is unfavorable for weed seed survival. The chaff row environment effect on weed seed survival was examined in field studies, and chaff response studies determined the influence of increasing amounts of chaff on weed seedling emergence. The objectives of these studies were to determine the influences of (1) chaff lines on the summer–autumn seed survival of selected weed species and (2) chaff type and amount on rigid ryegrass seedling emergence. There was frequently no difference (P > 0.05) in seed survival of four weed species (rigid ryegrass, wild oat, annual sowthistle, and turnip weed) when seeds were placed beneath or beside chaff lines. In one instance, wild oat seed survival was increased (P < 0.05) when seed were placed beneath compared to beside a chaff line. The pot studies determined that increasing amounts of chaff consistently resulted in decreasing numbers of rigid ryegrass seedlings emerging through chaff material. The suppression of emergence broadly followed a linear relationship in which there was approximately a 2.0% reduction in emergence with every 1,000 kg ha–1 increase in chaff material. This relationship was consistent across wheat, barley, canola, and lupin chaff types, indicating that the physical presence of the chaff was more important than chaff type. These studies suggested that chaff lines may not affect the survival over summer–autumn of the contained weed seeds but that the subsequent emergence of weed seedlings will be restricted by high amounts of chaff (>40,000 kg ha–1).

Biocontrol of economically important weed species through endophytic fungi isolated from Parthenium hysterophorus (Family: Asteraceae)

BackgroundFungal endophytes produce a variety of secondary metabolites which can be explored for herbicidal activities. Parthenium is a very aggressive and fast-spreading weed in Pakistan. The endophytes of Parthenium made it superior over other weeds. Those endophytes can be isolated, identified, and incorporated in sustainable agriculture to biologically control other severe weeds.Main bodyThe present study was conducted to isolate and identify the endophytic fungi from the roots of Parthenium hysterophorus (Family: Asteraceae) and evaluate their cultural filtrate against the growth of three selected weed species, i.e., Chenopodium album, Avena fatua, and Convolvulus arvensis. Moreover, pot experiments were conducted to evaluate the effects of cultural filtrates of these endophytic fungi against the germination, growth, and other physiological parameters (cellular contents, respiration, and cellular leakage) of the abovementioned three weed species. Three endophytic fungi, i.e., Alternaria, Aspergillus, and Drechslera spp., were isolated from the roots of P. hysterophorus. Among these endophytic fungi, cultural (hyphal) filtrate of Alternaria spp. exhibited the strongest phytotoxic effect, followed by Drechslera spp. and Aspergillus spp. against the selected weeds. Moreover, all the three endophytic fungi showed significant reduction in the germination as well as other physiological parameters of the weed species.ConclusionIt is concluded that the utilization of endophytic fungi could be a non-chemical, effective, ecofriendly, and low-cost biological control method that can be used for the biomanagement of fast-spreading and aggressive weeds.

Relating initial paraquat injury to final efficacy in selected weed species influenced by environmental conditions

AbstractWeed control of paraquat can be erratic and may be attributable to differing species sensitivity and/or environmental factors for which minor guidance is available on commercial labels. Therefore, the objectives of this research were to quantify selectivity of paraquat across select weed species and the influence of environmental factors. Experiments were performed under controlled conditions in the greenhouse and growth chamber. Compared with purple deadnettle (dose necessary to reduce shoot biomass by 50% = 39 g ai ha−1), waterhemp, Palmer amaranth, giant ragweed, and horseweed were 4.9, 3.3, 1.9, and 1.3 times more sensitive to paraquat, respectively. The injury progression rate over 3 d after treatment (DAT) was a more accurate predictor of final efficacy at 14 DAT than the lag phase until symptoms first appeared. For example, at the 17.5 g ha−1 dose, the injury rate of waterhemp and Palmer amaranth was, on average, 3.6 times greater than that of horseweed and purple deadnettle. The influence of various environmental factors on paraquat efficacy was weed specific. Applications made at sunrise improved control of purple deadnettle over applications at solar noon or sunset. Lower light intensities (200 or 600 μmol m−2 s−1) surrounding the time of application improved control of waterhemp and horseweed more than 1,000 μmol m−2 s−1. Day/night temperatures of 27/16 C improved horseweed and purple deadnettle control compared with day/night temperatures of 18/13 C. Though control was positively associated with injury rates in the application time of day and temperature experiments, a negative relationship was observed for waterhemp in the light-intensity experiment. Thus, although there are conditions that enhance paraquat efficacy, the specific target species must also be considered. These results advocate paraquat dose recommendations, currently based on weed height, be expanded to address sensitivity differences among weeds. Moreover, these findings contrast with paraquat labels stating temperatures of 13 C or lower do not reduce paraquat efficacy.

Long‐term trends in the distribution, abundance and impact of native “injurious” weeds

AbstractQuestionsHow can we quantify changes in the distribution and abundance of injurious weed species (Senecio jacobaea,Cirsium vulgare,Cirsium arvense,Rumex obtusifolius,Rumex crispus and Urtica dioica), over long time periods at wide geographical scales? What impact do these species have on plant communities? To what extent are changes driven by anthropogenically induced drivers such as disturbance, eutrophication and management?LocationGreat Britain.MethodsData from national surveys were used to assess changes in the frequency and abundance of selected weed species between 1978 and 2007. This involved novel method development to create indices of change, and to relate changes in distribution and abundance of these species to plant community diversity and inferred changes in resource availability, disturbance and management.ResultsThree of the six weed species became more widespread in GB over this period and all of them increased in abundance (in grasslands, arable habitats, roadsides and streamsides). Patterns were complex and varied by landscape context and habitat type. For most of the species, there were negative relationships between abundance, total plant species richness, grassland, wetland and woodland indicators. Each individual species responds to a different combination of anthropogenic drivers but disturbance, fertility and livestock management significantly influenced most species.ConclusionsThe increase in frequency and abundance of weeds over decades has implications for landscape‐scale plant diversity, fodder yield and livestock health. This includes reductions in plant species richness, loss of valuable habitat specialists and homogenisation of vegetation communities. Increasing land‐use intensity, excessive nutrient input, overgrazing, sward damage, poaching and bare ground in fields and undermanagement or too frequent cutting on linear features may have led to increases in weeds. These weeds do have conservation value so we are not advocating eradication, rather co‐existence, without dominance. Land management policy needs to adapt to benefit biodiversity and agricultural productivity.

Allelopathic effect of buckwheat extract for seedlings of selected weed species

The influence of 1% aqueous extract obtained from a 14-day plants of common buckwheat (Fagopyrum esculentum Moench) on weed species was evaluated. Seedling roots of wild oat (Avena fatua L.), yellow foxtail (Setaria glauca L.), barnyardgrass (Echinochloa crus galli (L.) P. Beauv.), common windgrass (Apera spica-venti (L.) P. Beauv.), catchweed bedstraw (Galium aparine L.), scentless mayweed (Matricaria inodora L), gallant soldier (Galinsoga parviflora Cav.) and tiny vetch (Vicia hirsuta L.) were exposed to buckwheat extract and compared with control plants grown in water. The obtained results show that the buckwheat extract had lower influence on the growth of shoot than on roots of the evaluated weed species. The use of buckwheat extract in the medium caused the inhibition of root growth in all species except from tiny vetch. In the case of shoot of weeds, inhibition of growth by buckwheat extract occurred only in wild oat. Whereas in yellow foxtail, scentless mayweed and tiny vetch, the stimulation of shoot growth was demonstrated. These results may indicate that the buckwheat extracts act on directly exposed tissues. A different metabolic reaction of wild oat to buckwheat extract after 5 days of exposure than after 2 days may indicate a quick adaptation of wild oat seedlings to stressful conditions.

Evaluation of the impact of crotonic acid addition to the mixture of bromoxynil with terbuthylazine and nicosulfuron in lowered doses on selected weed species control

Evaluation of the impact of crotonic acid addition to the mixture of bromoxynil with terbuthylazine and nicosulfuron in lowered doses on selected weed species control

Glyphosate sensitivity of selected weed species commonly found in maize fields

AbstractGlyphosate resistance has evolved worldwide. Glyphosate is also the most used herbicide in Spain, and current changes in herbicide usage patterns can increase the risk of glyphosate resistance development. The objective of this study was to assess the glyphosate sensitivity of different selected weed species important in Spanish maize (Zea mays L.) fields. To this end, dose–response experiments were conducted under controlled conditions in a growth chamber to examine variation in glyphosate sensitivity among populations of five grass weed species and eight broadleaf weed species that are commonly found in the maize fields in Castilla y León, the biggest maize-growing region in Spain. The glyphosate doses that caused growth reduction by 50% (GR50) were calculated for each weed population. No populations were resistant to glyphosate. In addition, baseline values of glyphosate sensitivity were determined for each weed species. The GR50 baseline values ranged from 10.25 to 53.23 g ai ha−1 for the dicotyledonous weed species and from 16.05 to 66.34 g ai ha−1 for the monocotyledonous weed species. The ratio between the GR50 values of the least and most sensitive populations was used to determine the SI50 (sensitivity index at 50% growth reduction) for each weed species. The SI50 values showed a 1.4- to 3.3-fold difference in sensitivity for dicotyledonous weed species and 1.4- to 2.4-fold difference for monocotyledonous weed species. The sensitivity index was also calculated as the ratio between the GR50 values of the least sensitive population and the baseline GR50 value estimated for a range of susceptible populations (SI50b). SI50b values showed a 1.2- to 1.6-fold difference in sensitivity for dicotyledonous weed species and 1.1- to 1.2-fold difference for monocotyledonous weed species. The sensitivity data generated in this study provide a reference for determining time-dependent changes in glyphosate sensitivity in the commonly found weeds in the maize fields of Castilla y Léon.

Reaction of weeds, found in vegetable production areas, to root-knot nematodes Meloidogyne incognita and M. enterolobii

ABSTRACT Root-knot nematodes cause great damage to vegetable crops in Brazil, besides having a large range of host plants, such as weeds. Weeds can maintain the inoculums or even favor the multiplication of these nematodes. In this study we evaluated the reaction of selected weed species, present in a vegetable production area, to root-knot nematodes Meloidogyne incognita and M. enterolobii. The trials were conducted in a greenhouse at Embrapa Hortaliças, Brasília-DF, in a completely randomized design with six replicates. Fifteen weed species were evaluated for M. incognita race 1, and 16 weed species were evaluated for M. enterolobii. Two tomato cultivars were evaluated as resistance and susceptibility standards. Gall index (IG), egg mass index (IMO), number of eggs per gram of roots (eggs/g roots) and reproduction factor (FR) were evaluated. M. enterolobii survives and multiplies more easily in weeds collected in vegetable production areas than M. incognita race 1 and, the great majority of weed species evaluated in this study are hosts of both nematode species. Only the species Urena lobata, Sonchus oleraceus, Euphorbia heterophylla, Melampodium perfoliatum and Tagetes sp. were immune to M. incognita race 1. All evaluated species are either hosts or favor the multiplication of M. enterolobii. The species which are the most susceptible to M. incognita race 1, and therefore require greater control of crops infected by this nematode are Ipomoea nil, I. triloba and Eleusine indica, and for M. enterolobii are I. nil, Solanum americanum, Hyptis suaveolens, Portulaca oleracea, I. triloba and Euphorbia heterophylla.