Major Weed Research Articles

An Overview: The Toxicity of Ageratina adenophora on Animals and Its Possible Interventions.

Ageratina adenophora is one of the major invasive weeds that causes instability of the ecosystem. Research has reported that A. adenophora produces allelochemicals that inhibit the growth and development of food crops, and also contain some toxic compounds that cause toxicity to animals that consume it. Over the past decades, studies on the identification of major toxic compounds of A. adenophora and their toxic molecular mechanisms have been reported. In addition, weed control interventions, such as herbicides application, was employed to reduce the spread of A. adenophora. However, the development of therapeutic and prophylactic measures to treat the various A. adenophora—induced toxicities, such as hepatotoxicity, splenotoxicity and other related disorders, have not been established to date. The main toxic pathogenesis of A. adenophora is oxidative stress and inflammation. However, numerous studies have verified that some extracts and secondary metabolites isolated from A. adenophora possess anti-oxidation and anti-inflammation activities, which implies that these extracts can relieve toxicity and aid in the development of drug or feed supplements to treat poisoning-related disorders caused by A. adenophora. Furthermore, beneficial bacteria isolated from rumen microbes and A. adenophora can degrade major toxic compounds in A. adenophora so as to be developed into microbial feed additives to help ameliorate toxicity mediated by A. adenophora. This review presents an overview of the toxic mechanisms of A. adenophora, provides possible therapeutic strategies that are available to mitigate the toxicity of A. adenophora and introduces relevant information on identifying novel prophylactic and therapeutic measures against A. adenophora—induced toxicity.

SOIL WEED SEED BANK STATUS IN THE AGROECOLOGICAL CONDITIONS OF CHITRAL, PAKISTAN

A greenhouse experiment was carried out at the Agricultural Research Station (ARS), Shen Lasht, Chitral during 2016-17. There were five different locations in district Chitral from where the soil samples were collected which included Drosh, Shen Lasht, Garam Chashma, Ayun and BoonyLasht. A total of 300 samples were collected from all locations with 60 samples from each location. The 300 soil samples collected were placed in trays of medium sizes i.e. 27 cm x 21 cm x 4 cm = 2268 cm3. The trays were arranged in three repetitions having 100 samples in each repetition. Each repetition of 100 samples contained samples from 5 locations, in each location 4 sites (east, west, north and south each at 100 m distance from each other) and at each site samples were collected from 5 different depths, making a total of 100 samples in one repetition i.e. 5 x 4 x 5 = 100 and with repetitions making a total of 300 samples in one district. The results indicated that in the soil samples of district Chitral a total of 31 noxious weeds were recorded. Out of the 31 different weeds, 23 were broad leaves, eight were grasses and one was sedge. In another angle, 24 weeds were annuals while the rest were perennials out of the 31 weeds identified. A total of 17 different plant families were represented by the weeds recorded in the soil samples of Chitral region. Among the different locations of Chitral, the highest weed seed bank was recorded in the soil samples of ARS Shen Lasht area. Weed seed banks have always been higher in areas with mild winters, where the Shen lasht area is having milder winters as compared to the other areas in Chitral. The lowest seed bank was recorded in the soil samples of Garam Chashma, which was however statistically at par with the rest of the locations studied in Chitral. As far as the seed banks in the depths are concerned, largest weed seed bank was observed in the depth of 6 to 12 cm. The smallest seed bank was at the depth of 30 cm followed by the depth of 24 and 18 cm. Therefore, it is evident that the major weed seed bank lies in the upper 6-12 cm depth of the soil. In case of the interaction, the largest weed seed bank was recorded at ARS Sheen lasht at the depth of upper 6 cm of the soil profile whereas the weed seed bank was very low below the 12cm depth of soil upto 30 cm in the Garam Chashma area of Chitral. Out of the total 31 weeds recorded in soil samples of Chitral, the top 10 weeds in terms of the relative weed densities, relative weed frequencies and importance value indices were Convolvulus arvensis, Rumex crispus, Poa annua, Galium aparine, Avenafatua, Trianthemaportulacastrum, Silybum marianum, Sorghumhalepense, Euphorbia helioscopia, and Loliumtenulentumspecies. The IVI values for these weeds were 14.01, 13.96, 13.07, 11.83, 11.57, 11.12, 10.35, 10.09, 10.02, and 9.99, respectively. Moreover, these IVIs indicate that out of the topmost 10 problematic weeds eight weeds are broad leaved and two are grassy weeds.

Bioherbicidal Activity and Metabolic Profiling of Potent Allelopathic Plant Fractions Against Major Weeds of Wheat-Way Forward to Lower the Risk of Synthetic Herbicides.

The productivity of major field crops is highly compromised due to weed infestation. Inefficient weed management practices and undue and excessive use of chemical herbicides have drastically contaminated the environment and human health, in addition to resistance development in weed species. Therefore, utilization of allelopathic plants to explore phytochemicals as potent organic alternatives to such chemical herbicides has become indispensable. The current study evaluates the comparative bio-herbicidal potential of methanolic extracts of castor (Ricinus communis), artemisia (Artemisia santolinifolia), wheat (Triticum aestivum), and sorghum (Sorghum bicolor) to suppress growth of major weeds, i.e., wild mustard (Sinapis arvensis), Italian ryegrass (Lolium multiflorum), and carrot grass (Parthenium hysterophorus). The results demonstrated a concentration-dependent effect on weeds’ growth. Overall, in vitro seed germination was reduced from 60 to 100% in response to 5% (w/v) extract concentration. Significant reduction in radicle length, hypocotyl length, and fresh biomass of the weeds was also observed. A strong inhibitory effect was seen in in vivo pot experiments, revealing that application of 10–20% methanolic extracts induced permanent wilting and substantial reduction in the chlorophyll content of weeds along with 20–80% increase in oxidative stress. Artemisia showed the most significant allelopathic effect, on account of highest phenolic and flavonoid contents, followed by castor, wheat, and sorghum, against S. arvensis, L. multiflorum, and P. hysterophorus, respectively. Phytochemical analysis, through high-performance liquid chromatography (HPLC), also exhibited a correlation between extract’s phytotoxicity and their antioxidant potential due to their major constituents (rutin, quercetin, catechin, gallic acid, vanillic acid, syringic acid, ferulic acid, p-hydroxy benzoic acid, p-coumaric acid, and sinapic acid), among the total of 13 identified in methanolic fractions. Comprehensive profiling of allelochemicals with liquid chromatography–mass spectrometry (LC-MS) determined 120, 113, 90, and 50 derivates of phenolic acids, flavonoids, and alkaloids, reported for the first time through this study, demonstrating significant allelopathic potential of the targeted plant fractions, which can be explored further to develop a sustainable bio-herbicidal formulation.

Seedbank persistence and emergence pattern of Argemone mexicana, Rapistrum rugosum and Sonchus oleraceus in the eastern grain region of Australia

A thorough understanding of the emergence pattern and persistence of weed seeds is a prerequisite in framing appropriate weed management options for noxious weeds. In a study conducted at the University of Queensland, Australia, the emergence and seed persistence behavior of three major weeds Sonchus oleraceous, Rapistrum rugosum, and Argemone mexicana were explored with seeds collected from Gatton and St George, Queensland, Australia, with an average annual rainfall of 760 and 470 mm, respectively. Seed persistence was evaluated by placing seeds at the surface layer (0 cm) or buried at 2 and 10 cm depths enclosed in nylon mesh bags and examined their viability for 42 months. In another study, the emergence pattern of four populations, each from these two locations, was evaluated under a rainfed environment in trays. In the mesh-bag study, rapid depletion of seed viability of S. oleraceous from the surface layer (within 18 months) and lack of seed persistence beyond two years from 2 and 10 cm depths were observed. In trays, S. oleraceous germinated 3 months after seeding in response to summer rains and there was progressive germination throughout the winter season reaching cumulative germination ranging from 22 to 29% for all the populations. In the mesh-bag study, it took about 30 months for the viability of seeds of R. rugosum to deplete at the surface layer and a proportion of seeds (5 to 13%) remained viable at 2 and 10 cm depths even at 42 months. Although fresh seeds of R. rugosum exhibit dormancy imposed due to the hard seed coat, a proportion of seeds germinated during the summer months in response to summer rains. Rapid loss of seed viability was observed for A. mexicana from the surface layer; however, more than 30% of the seeds were persistent at 2 and 10 cm depths at 42 months. Notably, poor emergence was observed for A. mexicana in trays and that was mostly confined to the winter season.

Increasing cassava root yield on farmers' fields in Nigeria through appropriate weed management

Weed competition is the major biological stress affecting cassava production in smallholder farms in West and Central Africa, where yields are low compared with those in Asia and Latin America. Options for improved weed management are crucial in increasing productivity. Selected pre- and post-emergence herbicides, integrated with appropriate tillage and plant spacing, were tested in 96 sites in four locations in Nigeria, 24 in 2016 and 72 in 2017. Trials were split plots with six pre-emergence herbicides and no post-emergence treatment as main plots. Subplot treatments were four post-emergence herbicides, weeding with a motorized rotary weeder, short- and long-handled hoes, and no post-emergence weed control, i.e., regardless of pre-emergence treatments. Indaziflam-based treatments, irrespective of post-emergence treatment, and flumioxazin + pyroxasulfone applied pre-emergence followed by one weeding with a long-handled hoe provided >80% control of major broadleaf and grass weeds. Compared with herbicide use, farmer control practices (53%) were not efficient in controlling weeds. The highest root yield was produced where (1) s-metolachlor was combined with atrazine, and one weeding with a long-handled hoe or clethodim with lactofen, and (2) indaziflam + isoxaflutole was combined with glyphosate. An increase in root yield from 3.41 to 14.2 t ha-1 and from 3.0 to 11.99 t ha-1 was obtained where herbicides were used compared with farmers’ practice and manual hoe weeding. Our results showed that integrating good agronomic practices with safe and effective use of appropriate herbicides can result in root yield >20 t ha−1. i.e., twice the national average root yield of 8–12 t ha−1, with >50% net profit. The use of appropriate herbicides can reduce the amount of manual labor required and improve livelihoods, specifically for women and children. Smallholder cassava farmers would require continuous training on the safe use and handling of herbicides to improve efficiency and prevent adverse effects on humans and the environment.

Effect of sunnhemp (Crotalaria juncea L.) green manuring on weed dynamics in puddle transplanted rice-based systems

Effects of Crotalaria juncea green manure on weed dynamics in transplanted rice-based systems were investigated in a field study conducted over two cropping seasons, 2016 and 2017, at Ludhiana, India. The major weed species in the field, during the green manuring phase, included Cyperus rotundus, Digitaria ciliaris and Eleusine indica. The use of cover/green manure crops and their residues to suppress weeds has shown potential to manage weeds. In this context, green manuring/cover cropping has great potential and is feasible in a rice-wheat system in northern India as there is a 45 to 60 days’ fallow period between wheat harvest and transplanting of rice. C. juncea with 50 and 100 kg seed ha-1 recorded significantly lower density and biomass of aerobics weeds and weed density as compared to without green manure in both years; GM with 100 kg seed ha-1 had a more suppressing effect on weeds than green manuring with 50 kg seed ha-1. The residual effects of weed control treatments, applied during 2016 to succeeding transplanted rice crops, did not have any specific trend on weed density in 2017. The major weeds in green manuring crop were C. rotundus, D. ciliaris and E. indica. But in transplanted rice, Echinochloa colona, E. crus-galli and Leptochloa chinensis were major weeds

Differences in seed germination response of two populations of Phelipanche ramosa (L.) Pomel to a set of GR24 concentrations and durations of stimulation

AbstractPhelipanche ramosa is a major weed holoparasite characterized by a broad host range with a suboptimal development on numerous hosts, suggesting inter- or intra-species specificities. Seeds of P. ramosa germinate after exposure to exogenous chemicals exuded by surrounding host roots such as strigolactones, the concentrations of these germination stimulants varying between hosts. In France, P. ramosa is characterized by genetically differentiated populations presenting varying germination rates and a host specificity. The objective of our study was to investigate the sensitivity of seeds of two P. ramosa populations harvested on tobacco and oilseed rape, to a set of GR24 concentrations, a synthetic strigol analogue. The assessment of the germination rate was based on in vitro experiments. Seeds of P. ramosa were placed in Petri dishes with various concentrations of GR24. The cumulative number of germinated seeds of P. ramosa was counted several times after application of the treatment. Cumulative germination curves were analysed using a three-parameter log-logistic model and a time-to-event approach. The results show that the germination rate of P. ramosa seeds depends on the GR24 concentration and the duration of stimulation, but also that the response to these two factors varies greatly according to the origin of the P. ramosa seeds. The difference in germination speed between P. ramosa populations further shows distinct responses at the intraspecific level, thus suggesting that the specialization of P. ramosa probably occurs at least from the first stage of the holoparasite cycle.

Evaluation of Pre and Post Emergence Herbicides in Greengram (Vigna radiata L.) during Kharif and Rabi Seasons in the Uplands of Krishna Zone of Andhra Pradesh

Background: Greengram crop is grown round the year as a catch crop in different cropping systems of the uplands of the Krishna Zone of Andhra Pradesh. The practice of application of pre emergence herbicide like pendimethalin is very popular with the farmers for the control of weeds in the uplands, both in kharif and rabi seasons. Further spraying of a selective post emergence herbicide is also practiced by farmers. However, some of the weeds of kharif viz., Phyllanthus maderaspatensis and rabi viz., Chrozophora rottleri could not be controlled with these herbicides due to their late emergence or due to development of partial resistance to these herbicides. Certain new pre (PE) and post emergence (PoE) herbicides viz., pendimethalin 30% + imazethapyr 2%, acifluorfen sodium 16.5% + clodinafop propargyl 8%, fomesafen 11.1% + fluazifop -p-butyl 11.1%, are recommended in crops like soybean and groundnut. However, there is need to test these herbicides available in market for their suitability to control the weeds in greengram. Methods: A field experiment was carried out at Regional Agricultural Research Station, Lam, Guntur, Andhra Pradesh, with an objective to evaluate selected PE and PoE herbicide mixtures in greengram managing the major weeds of greengram grown in vertisols of Krishna Zone of Andhra Pradesh during Kharif and rabi seasons of 2018 under upland conditions. Result: Among the two PE herbicides tested on greengram, pendimethalin 30% + imazethapyr 2% @ 0.75 + 0.05 kg/ha was found to be more effective in reducing the weed density and dry matter compared with pendimethalin 30% @ 0.75 kg/ha. The PoE herbicide mixtures tested viz., fomesafen 11.1% + fluazifop -p-butyl 11.1% @111g/ha, propaquizafop 2.5% + imazethapyr 3.75% @ 50+75 g/ha were on par with imazethapyr 10% @ 50g/ha in controlling the weed population without having any adverse affect on the growth and yield of greengram during kharif and rabi.

Effect of planting time and row spacing on growth and seed production of junglerice (Echinochloa colona) and feather fingergrass (Chloris virgata) in sorghum

AbstractJunglerice and feather fingergrass are major problematic weeds in the summer sorghum cropping areas of Australia. This study aimed to investigate the growth and seed production of junglerice and feather fingergrass in crop-free (fallow) conditions and under competition with sorghum planted in 50-cm and 100-cm row spacings at three sorghum planting and weed emergence timings. Results revealed that junglerice and feather fingergrass had greater biomass in early planting (November 11) compared to late planting times (January 11). Under fallow conditions, seed production of junglerice ranged from 12,380 to 20,280 seeds plant–1, with the highest seed production for the December 11 and lowest for the January 11 planting. Seed production of feather fingergrass under fallow conditions ranged from 90,030 to 143,180 seeds plant–1. Seed production of feather fingergrass under crop-free (fallow) conditions was similar for November 11 and December 11 planting times, but higher for the January 11 planting. Sorghum crop competition at both row spacings reduced the seed production of junglerice and feather fingergrass >75% compared to non-crop fallow. Narrow row spacing (50 cm) in early and mid-planted sorghum (November 11 and December 11) reduced the biomass of junglerice to a greater extent (88% to 92% over fallow-grown plants) compared to wider row spacing (100 cm). Narrow row spacing was found superior in reducing biomass of feather fingergrass compared to wider row spacing. Our results demonstrate that sorghum crops can substantially reduce biomass and seed production of junglerice and feather fingergrass through crop competition compared with growth in fallow conditions. Narrow row spacing (50 cm) was found superior to wider row spacing (100 cm) in terms of weed suppression. These results suggest that narrow row spacing and late planting time of sorghum crops can strengthen an integrated weed management program against these weeds by reducing weed growth and seed production.

Sorghum cover crop and repeated soil fumigation for purple nutsedge management in tomato production.

Purple nutsedge (Cyperus rotundus L.) is one of the most common and troublesome weeds. Field research trials were conducted in Florida to evaluate the effects of repeated fumigation and a sorghum sudangrass [Sorghum bicolor S. bicolor var. sudanense (Piper) Stapf.] cover crop on purple nutsedge (Cyperus rotundus L.) populations over time in tomato (Solanum lycopersicum L.) production. Among the soil fumigants, DMDS + metam potassium was consistently the most effective treatment in terms of in-crop purple nutsedge control. Plots with a sorghum cover crop during the fallow period exhibited higher purple nutsedge density during the tomato growing season as well as higher purple nutsedge shoot and tuber densities during the fallow period compared to the chemical fallow. DMDS + metam potassium was the most effective fumigant for purple nutsedge control. Unexpectedly, a sorghum cover crop during the fallow period was less effective than chemical fallow for purple nutsedge management, and therefore we do not recommend the use of sorghum cover crops for weed management in fields where purple nutsedge is the major weed species.

Food Security Under The Era Of Climate Change Threat

Food Security Under The Era Of Climate Change Threat

Assessment of the microcyclic rust Puccinia lantanae as a classical biological control agent of the pantropical weed Lantana camara

Lantana camara is a flowering shrub of the family Verbenaceae, native to the Americas which has become a major invasive weed in the Palaeotropics; affecting both natural and agricultural ecosystems. It has been the focus of classical biological control for over a century but has proven to be a problematic target because of its high genetic diversity. Here, we report on an aggressive pathotype of the microcyclic rust Puccinia lantanae collected in the Amazonian rainforest, which – based on greenhouse screening – is damaging to a wide range of biotypes of the L. camara complex. Host-range testing within the Verbenaceae and related plant families, involving leaf clearing and staining, showed the pathotype to be highly specific to L. camara sensu lato but with detectable symptoms in several other verbenaceous species. These results, together with a taxonomic re-appraisal of Puccinia lantanae, are discussed in relation to the potential of the rust as a classical biological control agent of L. camara. We conclude that this pathotype of P. lantanae is a valuable addition to the biological control armoury and posit that it should be especially successful in humid forest situations.

INFLUENCE OF MIXED CROPPING OF CABBAGE AND MUSTARD ON WEED DYNAMICS AND YIELD OF POTATO (SOLANUM TUBEROSUM)

A field experiment was conducted in Horticulture farm of Agriculture and Forestry University, Chitwan, Nepal during September 2018 to January 2019 to evaluate the influence of mixed cropping of cabbage and mustard in weed dynamics and yield of potato. The experiment was carried out in a split-plot design with three replications. The treatment consists of with mustard (M1) and without mustard (M2) as main plot factor and eight treatments namely, sole potato at 0.7m (T1) and 1.4m (T5) inter-row spacing, sole cabbage at 0.35m (T2) and 0.7m (T3) inter-row spacing, potato at 1.4 m row spacing with one (T4), two (T7) and three (T8) row cabbage, and potato at 0.7m row spacing with one-row cabbage (T6), as subplot factor. Effect of broadcasting mustard was found significant in the dry weight of broadleaf weed, the height of cabbage and potato, cabbage canopy, and net production of potato. Net production was calculated by converting the yield of all the three crops in the monetary value of potato. Similarly, the effect of different intercropping of cabbage and potato was found significant on cabbage and potato height, cabbage canopy, dry weight of weed, the yield of cabbage and potato, and net production of potato. The interaction of main plot factors and sub-plot factors was found statistically significant; mustard broadcasting on intercropping of 35cm cabbage within 70cm row to row spacing of potato (M1×T6) was found superior in terms of yield of all the three crops and net production of potato. Similarly, (M1×T6) had a lower dry weight of broadleaf; Solanum nigrum and Chenopodium album were major weeds—both being a broadleaf weed. Thus, it would be better to suggest vegetable growing farmers, to follow mixed cropping of cabbage, mustard and potato for higher return and sustainable ecological weed management.

Seed Germination Ecology of South Eastern Australian Rigid Ryegrass (Lolium rigidum) Populations

Abstract Herbicide resistance is an increasing issue in many weed species, including rigid ryegrass (Lolium rigidum Gaudin); a major weed of winter cropping systems in southern Australia. Recently, this weed has also been found in summer crops in the south eastern region of Australia. Effective control of this herbicide resistant weed across south eastern Australia requires alternative management strategies. These strategies can be informed from analyses on the interaction of germinable seeds with their regional environment and by identifying the differences between populations of varying herbicide resistance levels. In this study, we explore how various environmental factors differentially affect the seed germination and seedling emergence of three L. rigidum populations, including one glyphosate-resistant population (GR), one glyphosate-susceptible population (GS) and one population of unknown resistance status (CC04). Germination was greater than 90% for all populations at each temperature regime except 15/5 C. Populations germinated at a lower rate under 15/5 C, ranging from 74 to 87%. Salt stress had a similar effect on the germination of all populations, with 0% germination occurring at 250 mM salt stress. Population GS had greater tolerance to osmotic stress with 65% germination at −0.4 MPa compared to 47% and 43% germination for CC04 and GR, respectively; however, germination was inhibited at −0.8 and −1.6 MPa for all populations. All populations had lower germination when placed in complete darkness as opposed to alternating light/dark. Germination in darkness was lower for CC04 (69%) than GR (83%) and GS (83%). Seedling emergence declined with increasing burial depth but retained 37% emergence at 8 cm when averaged over the populations. These results indicate that L. rigidum Gaud. can survive under a range of environmental variables and the extent of survival differs based on population, however, there was no difference based on herbicide resistance status.

PARTHENIUM PHYLLODY IN EASTERN UTTAR PRADESH INDIA: EPIDEMIOLOGY AND HOST RANGE OF PHYTOPLASMA WITHIN IMPORTANT CROPS CULTIVATED IN EASTERN UTTAR PRADESH, INDIA

Parthenium hysterophorus L. (family Asteraceae) is one of the 10 worst weeds in the world. This weed became the major invasive weed in both arable and grazing lands due to competitiveness and adaptability to different climates and soils. The natural occurrence of phyllody was noticed ~ 10-15% of Parthenium hysterophorus growing wildly along the roadside in Jaunpur, Azamgarh, Gorakhpur, and Varanasi districts of Uttar Pradesh, India, during summer 2010. To test whether Parthenium plants harbor phytoplasma, which may also infect important agricultural crop weeds and cultivated plants in Eastern U.P. India, phyllody symptoms were collected and assessed by polymerase chain reaction (PCR).

Bioefficacy of Imazethapyr Applied Alone and in Combination with other Herbicides in Black Gram and their Residual Effect on Succeeding Pearl-millet and Sorghum Crops

Background: Weeds are one of the major constraints in achieving yield potential of black gram. Due to slow initial growth of black gram, weeds compete effectively and caused reduction in growth as well as yield of black gram. Hand weeding is neither practicable nor economical due to unpredictability of weather and high labour cost, respectively. Therefore, application of herbicides is considered as the best approach for efficient weed control in black gram. Methods: A field experiment was conducted at Research Farm of Department of Agronomy, CCSHAU, Hisar during summer and kharif 2017 to evaluate the effect of different weed control treatments in black gram and their residual effect on succeeding pearl millet and sorghum crops. Total of fourteen weed control treatments were replicated thrice in randomized complete block design (RCBD).Result: Dactyloctenium aegyptium (37%), Trianthema portulacastrum (34%), Cyperus rotundus (21%) and Digera arvensis (8%) were the major weed flora associated with black gram at 30 DAS. Both at 30 and 60 DAS, PE application of imazethapyr + pendimethalin (RM) at 1000 g ha-1 provided 100% control of D. aegyptium and T. portulacastrum. PE application of imazethapyr + pendimethalin (RM) at 1000 g ha-1 was the most significant herbicide treatment (90% control of weeds) at 30 DAS however, 3-4 leaf stage application of imazethapyr + imazamox at 70 g/ha recorded with highest control of weeds (89%) at 60 DAS. Maximum seed yield (912 kg ha-1) and yield attributes of black gram were obtained in weed free treatment which was statistically at par with two hoeing performed at 20 and 40 DAS (895 kg ha-1) and PE application of imazethapyr + pendimethalin (RM) at 1000 g ha-1 (878 kg ha-1). Imazethapyr and its RM combination with imazamox applied at 3-4 leaf stage had phytotoxic effects on black gram at 30 DAS which suppressed the growth and caused yield penalty. Residual effect or phytotoxicity was not observed on succeeding pearl millet and sorghum crops.

Different leaf-mediated deposition, absorbed and metabolism behaviors of 2,4-D isooctyl ester between Triticum aestivum and Aegilops tauschii Coss.

Tausch's goatgrass (Aegilops tauschii Coss.), is a major weed species, infesting wheat (Triticum aestivum) fields in China. 2,4-D isooctyl ester is widely used for broadleaf weed control and selected as a tool to study the differences between, A. tauschii and T. aestivum. In this study, we measured the growth responses of these species to 2,4-D isooctyl ester and found that T. aestivum was more sensitive to the herbicide than A. tauschii. To clarify the reasons for this difference, we measured the leaf-mediated deposition, absorption and metabolism of 2,4-D isooctyl ester and the expression of auxin receptor transport inhibitor response (TIR1) gene in T. aestivum and A. tauschii. The results indicated that the deposition of 2,4-D isooctyl ester droplets may be lower on A. tauschii than on T. aestivum, because of the increased contact angle and greater density of trichomes on the leaves of the former. A distinct increase in 2,4-D isooctyl ester uptake was detected in T. aestivum during the entire experimental period, and the rate was 2.2-fold greater than that in A. tauschii at 6 h after treatment. Compared with A. tauschii, T. aestivum exhibited a greater accumulation of primary metabolite 2,4-D in plants, which may be responsible for the different responses of the two species. Additionally, the absolute expression level of TIR1 was clearly greater in T. aestivum than that in A. tauschii. These data will be helpful to further understand the differences between T. aestivum and A. tauschii, which may provide a unique perspective for the development and identification of new target compounds that are effective against this weed species.

Influences of farming practices on the development and phenological cycles of the major weeds of irrigated rice in Central Côte d’Ivoire

The influence of farming practices on the development and the phenological cycles of the main weeds of irrigated rice was studied in Central Côte d'Ivoire. The objective of this study was to assess the influences of weeding operations on the development and phenological states of major weeds in irrigated rice. The tests were carried out in a cultivated environment over two consecutive farming cycles. Four elementary plots of 100 m2 each were delimited for the observations. On each elementary plot, the usual cropping practices in rice cultivation was practised. Two weeks after transplanting, chemical weed control was performed with 3 selective post-emergence herbicides. The different herbicides were applied at 14-day intervals. Manual weeding took place 49 days after transplanting. The weekly observations consisted in noting the different stages of development of the major weeds according to the weeding operations. The results showed that chemical and manual weed control 14 and 49 days after planting out, respectively, reduce weeds harmfulness. In view of these results, the use of herbicides coupled with manual weeding can be recommended to rice growers.
 L’influence des pratiques culturales sur le développement et les cycles phénologiques des adventices majeures du riz irrigué a été étudiée au centre de la Côte d’Ivoire. Cette étude avait pour objectif d’évaluer les influences des opérations de désherbage sur le développement et les états phénologiques des adventices majeures du riz irrigué. Les essais ont été réalisés en milieu cultivé sur deux cycles culturaux consécutifs. Quatre parcelles élémentaires de 100 m2 chacune ont été délimitées pour les observations. Sur chaque parcelle élémentaire, l’itinéraire technique habituel de la culture du riz a été pratiqué. A 14 jours après le repiquage, le désherbage chimique a été effectué avec trois herbicides sélectifs de post-levée. Les différents herbicides ont été appliqués à intervalle de 14 jours chacun. Le désherbage manuel a eu lieu 49 jours après le repiquage. Les observations hebdomadaires ont consisté à noter les différents stades de développement des adventices majeures en fonction des opérations de désherbage. Les résultats ont montré que les désherbages chimiques et manuel effectués respectivement 14 et 49 jours après le repiquage réduisent la nuisibilité des adventices étudiées. Au regard de ces résultats, l’utilisation des herbicides couplée à un désherbage manuel peut être recommandé aux riziculteurs.

Monographs on invasive plants in Europe N° 5: Ambrosia trifida L.

ABSTRACT Ambrosia trifida L. (giant ragweed, Asteraceae) is native to the North American continent and was introduced into Europe and Asia at the end of the 19th century. In its native range, this tall annual species is common in riparian and ruderal habitats and is also a major weed in annual cropping systems. For nearly a century, A. trifida has also been of great concern in the U.S. for its highly allergenic pollen, necessitating targeted control measures to reduce its impact on human populations. Based on the distribution of A. trifida in North America and in its introduced range, riparian systems in the rest of the world may be particularly at risk to invasion, with potential negative consequences for their biodiversity. Currently, A. trifida has invaded Asia more widely than Europe, likely due to the more favourable local conditions in Asia. Throughout its introduced range, A. trifida is host to a limited number of invertebrates and pathogens and only a few biological agents are available for its control. The main impacts of A. trifida at a global level are on crop yield and human health, resulting in significant socio-economic impacts. The success of A. trifida invasion in areas in which it has been introduced is still unclear, but climate change may increase climate suitability, increasing the potential for A. trifida to spread. While effective management in cultivated fields seems potentially possible, the development and control of A. trifida in natural riparian habitats is of great concern due to the difficulty of management in these areas.

Characterizing the environmental drivers of the abundance and distribution of Alopecurus myosuroides on a national scale.

Arable weeds threaten farming and food production, impacting on productivity. Large-scale data on weed populations are typically lacking, and changes are frequently undocumented until they reach problem levels. Managing the future spread of weeds requires that we understand the factors that influence current densities and distributions. In doing so, one of the challenges is to measure populations at a large enough scale to be able to accurately measure changes in densities and distributions. Here we analyse the density and distribution of a major weed (Alopecurus myosuroides) on a large scale. Our objectives were to (i) develop a methodology for rapid measurement of occurrence and abundance, (ii) test hypotheses about the roles of soils and climate variation in determining densities, and (iii) use this information to identify areas in which occurrence could increase in the future. Populations were mapped through England over 4 years in 4631 locations. We also analysed UK atlas data published over the past 50 years. Densities of populations show significant interannual variability, but historical data show that the species has spread. We find significant impacts of soil and rainfall on densities, which increase with the proportion of heavy soils, but decrease with increasing rainfall. Compared with independent atlas data we found that our statistical models provide good predictions of large-scale occupancy and we provide maps of current and potential densities. Models of spread highlight the localised nature of colonisation, and this emphasises the need for management to limit dispersal. Comparisons of current, historical and potential distributions suggest sizeable habitable areas in which increases in abundance are still possible. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.