Amaranthus Retroflexus Research Articles

Synthesis of Novel α-Trifluoroanisole Derivatives Containing Phenylpyridine Moieties with Herbicidal Activity.

To find novel herbicidal compounds with high activity and broad spectrum, a series of phenylpyridine moiety-containing α-trifluoroanisole derivatives were designed, synthesized, and identified via nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRMS). Greenhouse-based herbicidal activity assays revealed that compound 7a exhibited > 80% inhibitory activity against Abutilon theophrasti, Amaranthus retroflexus, Eclipta prostrate, Digitaria sanguinalis, and Setaria viridis at a dose of 37.5 g a.i./hm2, which was better than fomesafen. Compound 7a further exhibited excellent herbicidal activity against Abutilon theophrasti and Amaranthus retroflexus in this greenhouse setting, with respective median effective dose (ED50) values of 13.32 and 5.48 g a.i./hm2, both of which were slightly superior to fomesafen (ED50 = 36.39, 10.09 g a.i./hm2). The respective half-maximal inhibitory concentration (IC50) for compound 7a and fomesafen when used to inhibit the Nicotiana tabacum protoporphyrinogen oxidase (NtPPO) enzyme, were 9.4 and 110.5 nM. The docking result of compound 7a indicated that the introduction of 3-chloro-5-trifluoromethylpyridine and the trifluoromethoxy group was beneficial to the formation of stable interactions between these compounds and NtPPO. This work demonstrated that compound 7a could be further optimized as a PPO herbicide candidate to control various weeds.

Synthesis, herbicidal activity and soil degradation of novel 5-substituted sulfonylureas as AHAS inhibitors.

Chlorsulfuron, metsulfuron-methyl and ethametsulfuron can damage sensitive crops in rotation pattern as a result of their long persistence in soil. To explore novel sulfonylurea (SU) herbicides with favorable soil degradation rates, four series of SUs were synthesized through a structure-based drug design (SBDD) strategy. The target compounds, especially Ia, Id and Ie, exhibited prospective herbicidal activity against dicotyledon oil seed rape (Brassica campestris), amaranth (Amaranthus retroflexus), monocotyledon barnyard grass (Echinochloa crusgalli) and crab grass (Digitaria sanguinalis) at a concentration of 15 a.i. g ha-1 . Additionally, Ia, Id and Ig displayed excellent inhibitory effects against AtAHAS, with Kapp i values of 59.1, 34.5 and 71.8μm, respectively, which were much lower than that of chlorsulfuron at 149.4μm. The π-π stack and H-bonds between the Ia conformation and AtAHAS in the molecular docking results confirmed the series of compounds to be conventional AHAS inhibitors. In alkaline soil (pH=8.46), compounds Ia-Ig revealed various degrees of acceleration in the degradation rate compared with chlorsulfuron. Besides, compound Ia showed considerable wheat and corn safety under postemergence at the concentration of 30, 60 and even 120 a.i. g ha-1 . Overall, based on the synthetic procedure, herbicidal activity, soil degradation and crop safety, the Ia sulfonylureas series were chosen to be investigated as prospective AHAS inhibitors. The 5-dimethylamino group on SUs accelerated the degradation rate at different levels in alkaline soils which seems to be controllable in conventional cropping systems in their further application. © 2022 Society of Chemical Industry.

Synthesis of Novel α-Trifluorothioanisole Derivatives Containing Phenylpyridine Moieties with Herbicidal Activity.

To discover novel herbicidal compounds with favorable activity, a range of phenylpyridine-moiety-containing α-trifluorothioanisole derivatives were designed, synthesized, and identified via NMR and HRMS. Preliminary screening of greenhouse-based herbicidal activity revealed that compound 5a exhibited >85% inhibitory activity against broadleaf weeds Amaranthus retroflexus, Abutilon theophrasti, and Eclipta prostrate at 37.5 g a.i./hm2, which was slightly superior to that of fomesafen. The current study suggests that compound 5a could be further optimized as an herbicide candidate to control various broadleaf weeds.

Weed composition in conventionally and organically grown medical and aromatic plants

This study aimed to compare weed flora in conventionally and organically grown medicinal and aromatic plants (MAPs): basil, pot marigold, dill, and peppermint; in terms of weed composition and weed abundance. A total of 28 weed species (25 and 15 species in conventional and organic crops, respectively) were identified.The presence and abundance of certain weed species were affected by MAP species and farming system. Higher weed diversity and weediness, and lower floristic similarity were found in conventionally grown crops. Also, the analysed MAPs differed in weediness by individual weed species. Correspondence analysis pointed to conventional and organic MAPs with the most frequent and most abundant weed species. Setaria pumila and Portulaca oleracea were the most frequent species in conventional; and Amaranthus retroflexus, Datura stramonium, and Sorghum halepense in organic crops. In both conventional and organic farming systems, therophytes were the most dominant life forms indicating a strong anthropogenic influence. The results should contribute to establishing weed control measures that are adequate for the two farming systems.

Inhibitory Effect of Oregano and Laurel Essential Oils and Their Main Com-ponents on Seed Germination of Some Weed and Crop Species

The essential oils from oregano (Origanum syriacum L.) and laurel (Laurus nobilis L.), and their main components, namely, carvacrol, 1,8-cineole and α-pinene, were tested to determine their inhibitory effects on the seed germinations of three different weeds [redroot amaranth (Amaranthus retroflexus L.), wild licorice (Glycyrrhiza glabra L.), curled dock (Rumex crispus L.) and cutleaf ground-cherry (Physalis angulata L.)] and three crops [(wheat (Triticum aestivum L.), corn (Zea mays L.) and cotton (Gossypium hirsitum L.)]. Gas chromatography/mass spectroscopy (GC-MS) analysis showed that 1,8-cineole and carvacrol were the major components of laurel and oregano essential oils, respectively. An in-vitro bioassay seed germination test showed that oregano essential oil and carvacrol completely inhibited the germination of weeds at all the concentrations ranging from 1 to 5 µl/Petri dish, while seed germination of test weeds significantly decreased with increasing of the concentrations of laurel essential oil and its main components, 1,8-cineol and α-pinene ranging from 5 to 20 µl/Petri dish. Oregano essential oil and carvacrol were totally ineffective on cotton and corn germination (except for the concentration of 5 µl/Petri dish of cavracrol), whereas they had a strong inhibitory activity against wheat seeds. On the other hand, the laurel essential oil and its main component, 1,8-cineole, showed less selective action on test crop species. It could be concluded that volatile oil from O. syriacum and its main component, cavracrol, possessed a strong inhibitory effect on germination of the weeds and was totally selective action on some crops, and could be utilized as bioherbicide for future weed management programmes.

Herbicidal activity and biochemical characteristics of the botanical drupacine against Amaranthus retroflexus L.

Botanical herbicide has been a hot topic in the research and development of novel pesticides. The herbicidal activity and biochemical characteristics of the botanical compound drupacine were studied by evaluating its effects on seed germination, seedling growth, morphological and physiological characteristics of Amaranthus retroflexus. Drupacine inhibited seed germination and seedling growth, and had a median inhibition concentration (IC50) value of 38.99 mg L−1 against A. retroflexus root. The α-amylase activity and soluble sugar content in treated plants were significantly lower than that of the control. The expression of α-amylase gene was dosage-dependently inhibited compared to the untreated control. This suggested that inhibition of α-amylase activity was a mode of action on seed germination. The root hairs were significantly decreased and part of the root cap fell off after treatment with drupacine. The ultrastructure observation showed that cell damage of root tips increased with the treatment time. Drupacine also increased the relative conductivity and malondialdehyde (MDA) content. Peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD) activities were significantly enhanced in the treatment compared to the control. These findings indicated that the physiological and biochemical reaction changes leading to morphological and membrane injuries were the main effects of drupacine on the inhibition of seedling growth. Drupacine can be developed as a botanical herbicide.

Barcoding High Resolution Melting (Bar-HRM) enables the discrimination between toxic plants and edible vegetables prior to consumption and after digestion.

The consumption of poisonous plants can lead to serious health problems or even casualties due to various factors, including easy access to poisonous plants due to their common distribution, co-occurrence and resemblance with edible plants, and the lack of regulation in the food product supply chain. Clinical diagnosis of intoxications usually relies on the availability of the plant consumed by the patient and on the morphology of the plant parts found in the patient's stomach. Therefore, given the fragmented nature of ingested plant material, species identification may face serious difficulties, can be inaccurate, and time-consuming. This highlights the need for rapid and reliable tools to identify toxic species. In the present study, we developed an ITS2-high-resolution melting (HRM) assay for: (1) the discrimination of common toxic plants and their edible lookalikes, and (2) the detection of toxic plants in digested samples. More specifically, we designed species-specific ITS2 primers for the authentication of poisonous species in simulated mixtures and verified them with Bar-HRM. Moreover, the developed HRM-based molecular tool was capable of quantifying the toxic species Datura stramonium in simulated mixtures with the edible Amaranthus retroflexus down to at least 0.5% v/v. This study shows that species-specific ITS2 primers can amplify the DNA from fragmented and/or artificially digested samples and that Bar-HRM is capable of detecting poisonous plant species in digested samples even after 4h. The developed Bar-HRM protocol has important implications for application in medicine, forensics, and the agricultural industry, either to accurately detect the cause of plant intoxications or as a tool for quality control in the supply chain. PRACTICAL APPLICATION: In this work, we established a high-resolution melting DNA-based protocol capable of discriminating between phenotypically similar common toxic and edible plant species in mixtures, even at very low quantities. This technology also proved efficient in detecting the toxic species in mixtures digested in artificial gastric acid, as it would be the case after accidental ingestion. This work is expected to have important implications for application in medicine, forensics, and the agricultural industry, either for identifying the cause of plant intoxications or as a tool for quality control in different steps of the supply chain.

Selective Phytotoxic Effects of Sesquiterpenoids from Sonchus arvensis as a Preliminary Approach for the Biocontrol of Two Problematic Weeds of Wheat.

The objective of this study is to find new selective allelochemicals for managing two problematic weeds redroot pigweed (Amaranthus retroflexus) and common lambsquarters (Chenopodium album) with minimal negative effects on wheat, thereby facilitating the development of eco-friendly botanical herbicide. Three new sesquiterpenoids, sonarvenolide A-C (1-3), and nine known sesquiterpenoids (4-12) were isolated from Sonchus arvensis. Compound 1 was a rare peroxide-substituted eudesmane-type sesquiterpenoid, and compound 3 was a rare iphionane-type sesquiterpenoid. Notably, compounds 1, 3, 4, 6-8, and 11 showed selectivity phytotoxic activity. In particular, compounds 1, 3, and 4 exhibited excellent germination inhibitory effect on A. retroflexus (IC50 = 32.0-129.0 μM), higher than that of the positive control triasulfuron (IC50 = 141.7 μM), and compound 4 showed excellent inhibition on C. album (IC50 = 82.0 μM), higher than that of triasulfuron (IC50 = 100.9 μM). In addition, compounds 1, 3, and 4 showed allelopathy to the growth of two weeds, which were more potent than or close to that of triasulfuron. Furthermore, these compounds were not toxic to wheat even at a high concentration (1000 μM). Structure-activity relationships (SARs) revealed that the presence of peroxides or the absence of hydroxyl at C-5 in the eudesmane-type sesquiterpenoids could strengthen the inhibitory activities. The discovery of selective allelochemicals provides not only a new choice to control two problematic weeds of wheat but also new natural lead compounds for herbicides.

Моніторинг забур’яненості посівів сої у короткоротаційній сівозміні

Goal. To monitor the species and quantity composition of weeds in soy sowings of short crop rotation. Methods. Field, laboratory, calculation, and comparison. Results. The research was carried out in 2016–2021 in a stationary 2-factor field experiment on typical chornozem in a short crop rotation (spring barley — sunflower — soy — winter wheat), which includes 3 tillage systems (shelf, shallow disk, and no-till technology), and 3 fertilizer systems (without fertilizers, resource-saving minimized, intensive). The given data indicated that in the agrocenosis of soy, the main type of weediness was mixed, and consisted of small-year monocotyledonous-dicotyledonous, and accompanying rhizomes. It was established that late spring species had the largest share (45–55%). The share of early spring weeds was 18–26%, winter and winter weeds — 7.0–24%, and perennial species — 8–18% of the total amount. The lowest number of weeds in soy crops was fixed for shelf tillage. Conclusions. In the conditions of the zone of unstable moisture of the Left Bank Forest Steppe in short crop rotation with the long-term use of various systems of main tillage on typical shallow low-humus chornozem, for growing soy, it was established that the system of main tillage, which was based on shelf tillage, had significant advantages in terms of reducing weediness of soy sowings over the shelf-less cultivation system with disc tools and no-till technology. It was found that under an intensive fertilizer system, Amaranthus retroflexus L. and Echinochloa crusgalli (L.) Roem. et Schult. develop more intensively. Stellaria media (L.) Vill. and Polygonum scabrum Moench. spread in the background without the use of fertilizers, while under the resource-saving minimized fertilizer system, their number decreases due to the increase in the competitiveness of the culture. The use of shelf cultivation leads to the spread of dicotyledonous weed species in soy agrocenosis. The number of young monocotyledonous and dicotyledonous weed species increases during tillage.

Influence of predecessors on species diversity of weeds in winter wheat crops in the Eastern Forest-Steppe of Ukraine

Goal. Determine the species composition of weeds, their dominant role and establish the type and level of weediness of winter wheat crops by cultivation on black fallow, after peas for grain and winter wheat as forecrops in the Eastern Forest-Steppe of Ukraine.
 Methods. The research was carried out by means of route surveys in field experiments located in a stationary nine-field steam-grain-row crop rotation and in a monoculture of winter wheat.
 Results. In total, according to the results of research in 2011—17, 63 species of weeds were found in crops. In the conditions of crop rotation in the fields of winter wheat after black fallow and peas for grain, 50 species and 45 species were found, respectively, and in monoculture — 41 species. The largest number of spring early and late weeds (41—49%), and the second and third places were occupied by wintering, winter and biennial (33—37%) and perennial (18—22%). The main weeds in the crops were: after black fallow — Setaria glauсa, Chenopodium album, Amaranthus retroflexus, Solanum nigrum, Fumaria officinalis, Polygonum lapathifolium, Cyclachaena xanthifolia, Delphinium consolida, Viola arvensis, Erigeron canadensis, Cirsium arvense; after peas for grain — S. glauсa, Echinochloa crus-galli, C. album, A. retroflexus, S. nigrum, F. officinalis, P. lapathifolium, Stachys annua, Malva neglecta, Polygonum aviculare, D. consolida, Thlaspi arvense, V. arvensis, C. arvense, Convolvulus arvensis; after winter wheat — S. glauсa, E. crus-galli, Ambrosia artemisiifolia, Fallopia convolvulus, Lactuca serriola, Capsella bursa-pastoris, D. consolida, Matricaria inodora, Crepis tectorum. In winter wheat crops, the largest share of dominance and subdominance, respectively, were Solanum nigrum L. (71%) and Setaria glauca (L.) Beauv. (71%) after peas for grain. The type of weediness of winter wheat crops depended on the predecessor. In monoculture, there was a higher level of weediness of winter wheat than in crop rotation.
 Conclusions. Rational selection of predecessors creates the basis for successful weed control in winter wheat crops.

Спектр питания серой куропатки ( Perdix perdix L.) в Центральном Предкавказье

The gray partridge (Perdix perdix L.) is a commercial bird species of the Central Ciscaucasia. In the steppe regions, these birds are found in cultivated gardens, vineyards, green belts along agricultural fields, roads, and railways, etc. The research objective was to study and analyze the diet of the gray partridge in different seasons in the Stavropol Region.
 The study featured the food spectrum consumed by the gray partridge based on the contents of 42 stomachs and 26 crops of birds caught by hunters and hit by vehicles in various Stavropol biotopes in 2008–2021.
 Gray partridges are phytophages, which means they feed mostly on plants and, to a lesser extent, on animals. Their autumn and winter diet includes green mass and wheat grains, seeds of cultivated and wild plants, and insect larvae. The gray partridge prefers weedy herbaceous plants: Polygonum aviculare, Echinochloa crus-galli, Amaranthus retroflexus, Chenopodium album, and Setaria viridis.
 The data obtained can be used to assess food resources of commercial bird species, in gray partridge conservation projects, and winter feeding of birds.

The Effect of Thymus vulgaris L. Hydrolate Solutions on the Seed Germination, Seedling Length, and Oxidative Stress of Some Cultivated and Weed Species.

The aim of this study was to determine the effect of the hydrolates obtained as the by-products of the Thymus vulgaris essential oil steam distillation process. The bioassays, which were undertaken in order to determine the effect on germination and initial growth of seedlings of some cultivated and weed species, were performed under controlled conditions with different concentrations of the hydrolates. Seeds of Glycine max, Helianthus annuus, Zea mays, Triticum aestivum, Daucus carota subsp. sativus, Allium cepa, Medicago sativa, and Trifolium repens, and six weed species—Amaranthus retroflexus, Chenopodium album, Portulaca oleracea, Echinochloa crus-galli, Sorghum halepense, and Solanum nigrum—were treated with 10, 20, 50, and 100% T. vulgaris hydrolate solution. The obtained results showed that the T. vulgaris hydrolate had the least negative effect on the germination of cultivated species, such as soybean, sunflower and maize, whereas clover and alfalfa were the most sensitive. By comparison, all the tested weed species expressed high susceptibility. It can be concluded that the T. vulgaris hydrolate has an herbicidal effect, in addition to its potential as a biopesticide in terms of integrated weed management.

Investment Returns for Preemergence Herbicide Use in No-till Pumpkin

Preemergence (PRE) herbicides are an important part of the overall weed management plan in no-till (NT) pumpkin (Cucurbita pepo) production. A field evaluation was conducted in an NT production system using PRE herbicides labeled for pumpkins to determine the benefits of specific herbicide combinations and the economic returns on investment associated with their use. The PRE herbicide treatments evaluated were 1) s-metolachlor (1360 g⋅ha–1 a.i.), 2) clomazone (350 g⋅ha–1 a.i.) and ethalfluralin premix (1120 g⋅ha–1 a.i.), 3) s-metolachlor + clomazone and ethalfluralin premix, 4) s-metolachlor + halosulfuron (35 g⋅ha–1 a.i.), 5) clomazone and ethalfluralin premix + halosulfuron, and 6) none. The primary weed species present were tall waterhemp (Amaranthus tuberculatus), redroot pigweed (Amaranthus retroflexus), giant foxtail (Setaria faberi), and large crabgrass (Digitaria sanguinalis). The best weed control option for full-season broadleaf and grass weed control was s-metolachlor + clomazone and ethalfluralin. This herbicide combination also provided the greatest economic return on investment, ranging from a 20% to 40% improvement (depending on the year) compared with the next closest PRE herbicide treatment. Those with the lowest returns on investment were s-metolachlor combined with halosulfuron, and clomazone and ethalfluralin combined with halosulfuron. Besides providing the highest returns on investment, the PRE application of s-metolachlor with clomazone and ethalfluralin also produced the largest pumpkin fruit for the weed species present. Although growers often look for ways to reduce input costs in NT pumpkin production systems, the proper selection of PRE herbicides that considers the weed species present is clearly an important investment that improves pumpkin yields and revenues.

Investigation of resistance mechanisms to bentazone in multiple resistant Amaranthus retroflexus populations

Redroot amaranth (Amaranthus retroflexus L.) is a noxious weed that affects soybean production in China. Experiments were conducted to determine the molecular basis of resistance to bentazone. Whole-plant dose-response experiments showed that two populations (R1 and R2) exhibited resistance to bentazone with resistance indices of 9.01 and 6.85, respectively. Sequencing of the psbA gene revealed no amino acid substitution in the two populations. qRT–PCR analysis verified that psbA gene expression in R1 and R2 populations was increased significantly after treatment with bentazone, which was 3-fold and 5-fold higher than that in S1 and S2 populations, respectively. The P450 inhibitor malathion significantly reduced the level of resistance in the R1 and R2 populations when used prior to bentazone treatment. The R1 population exhibited multiple resistance to thifensulfuron-methyl and lactofen, caused by target site mutations (Asp-376-Glu in ALS, Arg-128-Gly in PPO2). In conclusion, increased gene expression of the psbA gene and enhanced herbicide metabolism seem to be the basis of resistance to bentazone in these A. retroflexus populations.

АНАЛІЗ СТРУКТУРИ СИНАНТРОПНОЇ ФРАКЦІЇ ФЛОРИ МІСТА ДУНАЇВЦІ (ХМЕЛЬНИЦЬКА ОБЛАСТЬ)

The article presents the results of the analysis of the systematic, biomorphological, geographical and ecological structures of the apophytic and anthropophytic components of the synanthropic fraction of the flora of the town of Dunaivtsi, Khmelnytsky region. Identification of species of the study area was carried out by stationary, semi-stationary, detailed route methods throughout 2016–2019. The research was carried out on natural and anthropogenically altered areas of roadside and forest plantations, abandoned fields, agricultural lands, parks, roadsides, dumps. The summary of the synanthropic fraction of flora in Dunaivtsi includes species of natural flora, as well as those that are mostly cultivated, but for some reason at the time of the study were recorded outside their cultivation: in landfills, roadsides, as weeds in agricultural landscapes or in plantations of different economic purposes. 
 The Floristic list includes 206 species of 147 genera and 45 families, of which 112 species are represented by anthropophytes (54.4 %) and 94 – apophytes (45.6%). Among apophytes at the top there are hemiapophytes (37 species; 39.0 %), followed by evapophytes (33 species; 3 %), then eventapophytes (24 species; 26.0 %). Among anthropophytes, epecophytes predominate in terms of the degree of naturalization – 96 species (86m0 %); significantly fewer agriophytes – 13 species (12.0 %) and ephemerophytes – 3 species (3.0 %). 
 The ratio between the fractions is 1,2:1 in favor of adventitious plants, which indicates the superiority of adventization processes over apophytization processes in the town of Dunaivtsi, Khmelnytsky region.
 The proportion of the studied flora is 1: 3,3: 4,6, the average number of species in the family is 4.6, the generic coefficient being 1.4. The ten leading families include 138 species (67.0 %) and 97 genera (66.0 %) of the region’s flora. 
 In the biomorphological structure of the synanthropic fraction of flora of Dunaivtsi, according to the classification of I. G. Serebryakov, the vast majority of species (174 species, 85 %) are herbaceous plants, among them the duration of the life cycle is slightly dominated by herbaceous polycarpics (88 species, 43 %) over monocarpics (86 species, 42 %). According to the classification of biological types of K. Raunkier, more than half of the synanthropic fraction of flora are hemicryptophytes (107 species, 52 %); significant in number of species are therophytes – 82 species (40 %), and phanerophytes, hamephytes, cryptophytes and geophytes are represented by 17 species (8.2 %). 
 Geographical analysis of the studied synanthropic fraction of flora showed that the widest represented areological groups are Holarctic – 51 species, group of cosmopolitans – 48, Palearctic – 10, Eurasian – 23, Euro-Mediterranean – 44, Euro-Siberian – 10, North American – 12 species. The ecological structure of the flora in the composition of heliomorphs is dominated by heliophytes (112 species, 54.4 %); in the composition of hygromorphs – xeromesophytes (98 species, 47.6 %). 
 It was found that among the invasive species of the town, the most aggressive growth is characterized by Acer negundo, Galinsoga parviflora, Amaranthus retroflexus, Solidago canadensis.

Improving Weed Management Based on the Timing of Emergence Peaks: A Case Study of Problematic Weeds in Northeast USA

We reviewed the timing of the peak rate of emergence for 15 problematic weed species as well as ways to use this knowledge to improve control. Much of the previous literature modeled emergence based on growing-degree-days. For these models, we input average temperature data from several zones of Northeast USA. Within species, model-predicted peak emergence in the warmest and coolest zones differed by an average of 39 days. Also within species, there was some variation between models, likely reflecting different conditions in study locations and population-level differences that will need to be addressed in future modelling efforts. Summarizing both observed and modelled results, emergence typically peaked early-season for barnyardgrass, Canada thistle, common lambsquarters, common ragweed, giant foxtail, large crabgrass, perennial sowthistle, and smooth crabgrass. Emergence typically peaked mid-season for hairy galinsoga, mouseear chickweed, and red sorrel. Emergence typically peaked late-season for annual bluegrass. Several species emerged in a protracted manner, including common chickweed, quackgrass, and redroot pigweed. With this improved knowledge, farmers may target key problematic species of a particular field in several ways. Weed seedling control efforts can be timed at the highest densities or most vulnerable phenological stage. Residual herbicides and suppressive mulches can be timed to maximize effectiveness prior to their breakdown. And if management flexibility allows, crop selection and associated planting dates may be adjusted to improve crop competition or facilitate seedbank depletion through timely bare fallow periods. Such improvements to weed management based on timing of emergence will likely become even more impactful as predictive model reliability continues to improve.

Evaluation of Alternaria alternata as a biological control agent of redroot pigweed (Amaranthus retroflexus L.)

Biological control agents, especially some plant pathogenic fungi have the potential of weed control. To evaluate the efficacy of Alternaria alternata on the biological control of red root pigweed, an experiment was conducted based on Randomized Complete Block Design with three replications and different concentrations of the isolates A. alternata (104,107 spore ml-1 with distilled water and 104,107 spore ml-1 with surfactant and tween 40) at three temperature regimes (20/10, 25/15, 30/20 % c) during different growth stages (2, 4, 6 and 8 leaf). The results showed that the disease severity was increased by surfactant and enhanced temperatures. The inoculation of pathogen caused a significant reduction in dry weight at 2, 4 and 8 leaf growth stages and decreased plant height at 2,4 and 6 leaf stages and also reduced leaf area at 2 leaf stages. The results of this reaserch showed that this fungus has potential effectiveness and mycoherbicidal ability for red root pigweed control.

Effective dose of atrazine required to complement tolpyralate for annual weed control in corn

AbstractTolpyralate is an herbicide that is usually mixed with atrazine for broad-spectrum weed control in corn. Previous research has provided information on the effective dose (ED) of tolpyralate applied alone and in a 1:33.3 mixture with atrazine; however, tolpyralate is commercially applied at a dose of 30 to 40 g ai ha−1 with a minimum of 560 g ai ha−1 of atrazine. Therefore, five field trials were conducted over 3 yr (2019 to 2021) to determine the ED of atrazine to complement 30 g ai ha−1 of tolpyralate to achieve 80%, 90%, and 95% control of seven weed species 2, 4, and 8 wk after application (WAA). Tolpyralate was applied alone and in a mixture with atrazine doses ranging from 50 to 2,000 g ai ha−1. At 8 WAA, the ED of atrazine for 95% control of velvetleaf, common ragweed, common lambsquarters, and wild mustard was below the minimum label dose of atrazine on the commercial tolpyralate label, ranging from 430 to 520 g ai ha−1, which supports the use of the minimum label dose of atrazine. In contrast, redroot pigweed required 1,231 g ai ha−1 of atrazine to complement tolpyralate for 95% control 8 WAA. At 8 WAA, barnyardgrass and a mixture of green foxtail and giant foxtail (Setaria spp.) were not controlled by 80%, 90%, or 95% with tolpyralate applied alone or co-applied with any dose of atrazine evaluated in this study. The results of this study conclude that tolpyralate + atrazine is highly efficacious on several weed species at atrazine doses of 40 to 130 g ai ha−1 below the label dose of 560 g ai ha−1, but the use of the higher dose of tolpyralate or another herbicide may be required to improve control of redroot pigweed and grass weed species.

Interaction between tolpyralate and atrazine for the control of annual weed species in corn

AbstractMany studies have documented the interaction between 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting and photosystem II (PSII)-inhibiting herbicides. Most have focused on the interaction between mesotrione and atrazine, with only a few studies characterizing the nature of the interaction between tolpyralate and atrazine. Therefore, five field experiments were conducted in Ontario, Canada, over a 3-yr period (2019 to 2021) to characterize the interaction between three rates of tolpyralate (15, 30, and 45 g ai ha−1) and three rates of atrazine (140, 280, and 560 g ai ha−1) for the control of seven annual weed species in corn (Zea mays L.). Tolpyralate at 30 or 45 g ha−1 applied with atrazine at 280 or 560 g ha−1 controlled velvetleaf (Abutilon theophrasti Medik.), redroot pigweed (Amaranthus retroflexus L.), common ragweed (Ambrosia artemisiifolia L.), common lambsquarters (Chenopodium album L.), and wild mustard (Sinapis arvensis L.) >90% at 8 wk after application (WAA). Tolpyralate and atrazine were synergistic at each rate combination for the control of A. theophrasti at 8 WAA. In contrast, A. retroflexus and S. arvensis control at 8 WAA was additive with each rate combination. At 8 WAA, C. album control was generally additive, but one rate combination was synergistic. Ambrosia artemisiifolia control at 8 WAA was synergistic with five rate combinations and additive with the other four. Barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] control at 8 WAA was additive with seven of the rate combinations and synergistic with two. Setaria spp. control at 8 WAA was synergistic with one more rate combination compared with E. crus-galli, but the two weed species shared the same synergistic rate combinations. This study concludes that extrapolation or broad classifications of the interaction between tolpyralate and atrazine would be inappropriate, as the interaction can vary due to herbicide rate, weed species, and the response parameter analyzed.

Identification of acetolactate synthase resistant Amaranthus retroflexus in Ukraine

The problem of weed resistance to herbicides has become very important in the last decade and threatens to dramatically reduce the productivity and profitability of modern crop production. Herbicides – ALS inhibitors dominate among current herbicides and are used annually on large areas of sunflower, wheat, corn, soybean, and rapeseed. Also, in recent years, Clearfield seeds of sunflower, corn, canola, soybean and wheat have been sown in large areas. In recent years, there has been a sharp decrease in Amaranthus retroflexus L. control levels by imidazolinone class herbicides. Thus, the effects of herbicides with different modes of action on the development of A. retroflexus on sunflower after imidazolinone application were investigated in field research. In the conditions of the Cherkasy region of Ukraine, the biotype A. retroflexus was identified, which is resistant to the post-emergence application of herbicides - acetolactate synthase (ALS) inhibitors of the imidazolinone class – imazapyr and imazamox. Weed plants treated with imidazolinone derivatives in the maximum doses registered in Ukraine did not differ from untreated control plants. Also, in the conditions of field experiments, cross resistance of the weed biotype to herbicides – ALS inhibitors of the sulfonylurea class – foramsulfuron and iodosulfuron-methyl-sodium, thifensulfuron-methyl, tribenuron-methyl, nicosulfuron was established; and also, to the triazolinone derivative – thiencarbazone-methyl; to triazolpyrimidine derivatives – florasulam and flumetsulam. Multiple resistance of the A. retroflexus biotype to herbicides of the classes of glycine derivatives – glyphosate, phenoxycarboxylates – 2,4-D, benzoic acid – dicamba has not been established; compositions of dicamba with triketone – topramesone; diphenyl ethers – aclonifen; pyridine carboxylates – clopyralid, picloram and aminopyralid. It was shown for the first time that herbicide compositions with selected nutrients (ammonium pool) can increase the level of effectiveness of controlling resistant weed biotypes. Thus, the addition of ammonium sulfate increases the effectiveness of controlling ALS-resistant A. retroflexus with herbicides – a derivative of benzoic acid (dianate) and a derivative of benzoic acid with a 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor (stellar – dicamba + topramesone). Thus, the A. retroflexus biotype resistant to ALS-herbicides of the imidazolinone class was identified for the first time in Ukraine, which is cross-resistant to other ALS-inhibitors of the sulfonylureas, triazolinones, and triazolpyrimidine classes. Multiple resistance of A. retroflexus to herbicides of the classes of glycine derivatives – glyphosate; phenoxycarboxylates – 2,4-D; benzoic acid – dicamba, triketones – topramesone; diphenyl ethers – aclonifen; pyridine carboxylates – clopyralid, picloram and aminopyralid has not been established. The identification of a highly harmful weed species resistant to widely used herbicides – ALS inhibitors in the central part of the "grain belt" of Ukraine requires a significant revision of the principles of crop rotation formation and ways of controlling weeds in the country in order to maintain high levels of profitability and productivity of agrophytocenoses.