Development of a rapid detection assay for acetolactate synthase inhibitors resistance in three Amaranthus weed species through loop-mediated isothermal amplification.

BACKGROUND: The early detection of herbicide resistance in weeds is a key factor to avoid herbicide waste and improve agriculture sustainability. The present study aimed to develop and validate an allele-specific loop-mediated isothermal amplification (AS-LAMP) assay for the quick on-site detection of the resistance-endowing point mutation Trp-574-Leu in the acetolactate synthase (ALS) gene in three widely diffused Amaranthus weed species: Amaranthus retroflexus, Amaranthus hybridus and Amaranthus tuberculatus. RESULTS: The AS-LAMP protocol was developed on wild-type and ALS-mutant plants of the three species and revealed that the amplification approach with only the primer set specific for the mutant allele (574-Leu) was the most promising. The validation and estimation of the AS-LAMP performance evaluated by comparing the results with those of the molecular marker (cleaved amplified polymorphic sequences) indicated that, although the sensitivity and specificity were relatively high in all species (overall 100 and > 65%, respectively), precision was high for A. hybridus L. and A. retroflexus L. (75 and 79%, respectively), but quite low for A. tuberculatus (Moq.) J. D. Sauer (59%). The LAMP assay was also effective on crude genomic DNA extraction, allowing the quick detection of mutant plants in field situation (on site resistance detection). CONCLUSION: The proposed AS-LAMP method has proven to be a promising technique for rapid detection of resistance as a result of Trp-574-Leu on the two monoecious weedy Amaranthus species but resulted less effective in the genetically variable dioecious species A. tuberculatus. © 2024 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Comparative transcriptomic analysis of male and females in the dioecious weeds Amaranthus palmeri and Amaranthus tuberculatus.

BACKGROUND: Waterhemp (Amaranthus tuberculatus (Moq.) Sauer) and Palmer amaranth (Amaranthus palmeri S. Wats.) are two dioecious and important weed species in the world that can rapidly evolve herbicide-resistance traits. Understanding these two species' dioecious and sex-determination mechanisms could open opportunities for new tools to control them. This study aims to identify the differential expression patterns between males and females in A. tuberculatus and A. palmeri. Multiple analyses, including differential expression, co-expression, and promoter analyses, used RNA-seq data from multiple tissue types to identify putative essential genes for sex determination in both dioecious species. RESULTS: Genes were identified as potential key players for sex determination in A. palmeri. Genes PPR247, WEX, and ACD6 were differentially expressed between the sexes and located at scaffold 20 within or near the male-specific Y (MSY) region. Multiple genes involved with flower development were co-expressed with these three genes. For A. tuberculatus, no differentially expressed gene was identified within the MSY region; however, multiple autosomal class B and C genes were identified as differentially expressed and possible candidate genes. CONCLUSIONS: This is the first study comparing the global expression profile between males and females in dioecious weedy Amaranthus species. Results narrow down putative essential genes for sex-determination in A. palmeri and A. tuberculatus and also strengthen the hypothesis of two different evolutionary events for dioecy within the genus.

Resistance to a nonselective 4-hydroxyphenylpyruvate dioxygenase-inhibiting herbicide via novel reduction-dehydration-glutathione conjugation in Amaranthus tuberculatus.

Metabolic resistance to 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicides is a threat in controlling waterhemp (Amaranthus tuberculatus) in the USA. We investigated resistance mechanisms to syncarpic acid-3 (SA3), a nonselective, noncommercial HPPD-inhibiting herbicide metabolically robust to Phase I oxidation, in multiple-herbicide-resistant (MHR) waterhemp populations (SIR and NEB) and HPPD inhibitor-sensitive populations (ACR and SEN). Dose-response experiments with SA3 provided ED50 -based resistant : sensitive ratios of at least 18-fold. Metabolism experiments quantifying parent SA3 remaining in excised leaves during a time course indicated MHR populations displayed faster rates of SA3 metabolism compared to HPPD inhibitor-sensitive populations. SA3 metabolites were identified via LC-MS-based untargeted metabolomics in whole plants. A Phase I metabolite, likely generated by cytochrome P450-mediated alkyl hydroxylation, was detected but was not associated with resistance. A Phase I metabolite consistent with ketone reduction followed by water elimination was detected, creating a putative α,ß-unsaturated carbonyl resembling a Michael acceptor site. A Phase II glutathione-SA3 conjugate was associated with resistance. Our results revealed a novel reduction-dehydration-GSH conjugation detoxification mechanism. SA3 metabolism in MHR waterhemp is thus atypical compared to commercial HPPD-inhibiting herbicides. This previously uncharacterized detoxification mechanism presents a unique opportunity for future biorational design by blocking known sites of herbicide metabolism in weeds.

Interspecific and intraspecific transference of metabolism-based mesotrione resistance in dioecious weedy Amaranthus.

Pollen-mediated gene flow (PMGF) might play an important role in dispersing herbicide resistance alleles in dioecious weedy Amaranthus species. Field experiments in a concentric donor-receptor design were conducted to quantify two sets of PMGF studies, an interspecific (Amaranthus tuberculatus × Amaranthus palmeri) and an intraspecific (A. tuberculatus × A. tuberculatus). In both studies, PMGF was evaluated using a resistant A. tuberculatus phenotype with enhanced mesotrione detoxification via P450 enzymes as a source of resistance alleles. For interspecific hybridization, more than 104 000 putative hybrid seedlings were screened with three markers, one phenotypic and two molecular. The two molecular markers used, including 2-bp polymorphisms in the internal transcribed spacer region, distinguished A. palmeri, A. tuberculatus and their hybrids. Results showed that 0.1% hybridization between A. tuberculatus × A. palmeri occurred under field research conditions. For intraspecific hybridization, 22 582 seedlings were screened to assess the frequency of gene flow. The frequency of gene flow (FGF ) varied with distance, direction and year of the study. The farthest distance for 90% reduction of FGF was at 69 m in 2015 however, after averaging across directions it was 13.1 and 26.1 m in 2014 and 2015, respectively. This study highlights the transfer of metabolism-based mesotrione resistance from A. tuberculatus to A. palmeri under field research conditions. The results presented here might aid in the rapid detection of A. palmeri among other Amaranthus species and show that PMFG could be expediting the increase of herbicide resistance in A. palmeri and A. tuberculatus across US crop production areas.

Population genetics and origin of the native North American agricultural weed waterhemp (Amaranthus tuberculatus; Amaranthaceae).

UNLABELLED: • PREMISE OF THE STUDY: The evolution of invasiveness has been extensively studied in natural ecosystems; however, far less is known about the evolution of agricultural invasiveness, despite the major economic impact of weeds on crop productivity. Examining the population structure of recently arisen weeds can provide insights into evolutionary avenues to invasion of agroecosystems. Weeds that originate from wild plants are the most common yet least frequently studied type of agricultural invasive. Here we address several questions about the origin of the native North American agricultural weed waterhemp (Amaranthus tuberculatus), which invaded corn and soy fields in the midwestern United States in the 20th century.• METHODS: We genotyped 38 populations from across the species range with 10 microsatellite markers and used these data to assess genetic diversity and population structure within and outside the geographical region where waterhemp is agriculturally problematic.• KEY RESULTS: We found evidence for two ancestral genetic lineages in our data, supporting the hypothesis that A. tuberculatus was diverging into two evolutionary lineages prior to the 20th century. However, we found no support for the hypothesis that agricultural weed populations arose from admixture of these two lineages after secondary contact. Our data suggest that eastward movement of the western genetic lineage, facilitated by changing agricultural practices, is the source of the agricultural invasion of waterhemp.• CONCLUSIONS: This research demonstrates that agricultural invasion by native, wild plant species can proceed via different evolutionary trajectories from weeds related to domesticated plants, which has implications for evolutionary biology and weed control.

Metabolism of the 4-Hydroxyphenylpyruvate Dioxygenase Inhibitor, Mesotrione, in Multiple-Herbicide-Resistant Palmer amaranth (Amaranthus palmeri).

Metabolic resistance to the maize-selective, HPPD-inhibiting herbicide, mesotrione, occurs via Phase I ring hydroxylation in resistant waterhemp and Palmer amaranth; however, mesotrione detoxification pathways post-Phase I are unknown. This research aims to (1) evaluate Palmer amaranth populations for mesotrione resistance via survivorship, foliar injury, and aboveground biomass, (2) determine mesotrione metabolism rates in Palmer amaranth populations during a time course, and (3) identify mesotrione metabolites including and beyond Phase I oxidation. The Palmer amaranth populations, SYNR1 and SYNR2, exhibited higher survival rates (100%), aboveground biomass (c.a. 50%), and lower injury (25-30%) following mesotrione treatment than other populations studied. These two populations also metabolized mesotrione 2-fold faster than sensitive populations, PPI1 and PPI2, and rapidly formed 4-OH-mesotrione. Additionally, SYNR1 and SYNR2 formed 5-OH-mesotrione, which is not produced in high abundance in waterhemp or naturally tolerant maize. Metabolite features derived from 4/5-OH-mesotrione and potential Phase II mesotrione-conjugates were detected and characterized by liquid chromatography-mass spectrometry (LCMS).

Monitoring the temporal changes in herbicide-resistant Amaranthus tuberculatus: a landscape-scale probability-based estimation in Iowa.

BACKGROUND: A landscape-scale probability-based sampling of Iowa soybean [Glycine max (L.) Merr.] fields was conducted in 2013 and 2019; Amaranthus tuberculatus [Moq.] J.D. Sauer seed was collected from 97 random geospatial selected fields. The objectives were to evaluate the prevalence and distribution of herbicide-resistant A. tuberculatus (waterhemp) in soybean fields and evaluate temporal changes over 6 years. Amaranthus tuberculatus seedlings were evaluated for resistance to imazethapyr, atrazine, glyphosate, lactofen and mesotrione at 1× and 4× label rates. RESULTS: Resistance to imazethapyr, glyphosate, lactofen and mesotrione at the 1× rate increased significantly from 2013 to 2019 and was found in 99%, 97%, 16% and 15% of Iowa A. tuberculatus populations in 2019, respectively. Resistance to atrazine at the 4× rate increased over time; atrazine resistance was found in 68% of populations in 2019. Three-way multiple herbicide-resistant A. tuberculatus was the most frequent and increased significantly to 4× rates from 16% in 2013 to 43% of populations in 2019. All A. tuberculatus populations resistant to HPPD-inhibitor herbicides also were resistant to atrazine. CONCLUSION: To the best of our knowledge, this is the first probability-based study that presented evolution of A. tuberculatus herbicide resistance over time. The results demonstrated that imazethapyr, atrazine and glyphosate resistance in Iowa A. tuberculatus populations was frequent whereas resistance to lactofen and mesotrione was less frequent. Most Iowa A. tuberculatus populations evolved resistance to multiple sites of action over time. The results of our study are widely applicable given the similarities in weed management practices throughout the Midwest United States. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Do Traits Travel? Multiple-Herbicide-Resistant A. tuberculatus, an Alien Weed Species in Israel.

Amaranthus tuberculatus is the most common weed in soybean and corn in the USA and Canada. In Israel, it has been a minor riverbank weed. However, in recent years, growing densities of this plant have been observed in field crops, orchards, and roadsides. Between 2017 and 2022, we surveyed the distribution of A. tuberculatus and collected seeds for further study. We identified three main distribution zones in Israel: the Jezreel Valley, Hula Valley, and Coastal Plain. Most of the populations were found near water sources, fishponds, barns, dairies, or bird-feeding sites, suggesting the involvement of imported grain in introducing A. tuberculatus to Israel. Populations were screened for their responses to various post-emergence herbicides (i.e., ALS, EPSPS, PPO, HPPD, and PSII inhibitors). Several populations from the Jezreel Valley were found to be putatively resistant to ALS, EPSPS, and PPO inhibitors. The responses of those populations to trifloxysulfuron, glyphosate, and carfentrazone-ethyl were also studied. A single ALS-, EPSPS- and PPO-resistant plant was vegetatively propagated to create a clonal population, which was treated with foramsulfuron, glyphosate, and carfentrazone-ethyl. No resistance to PSII or HPPD inhibitors was observed, but resistance to herbicides that inhibit ALS, EPSPS, and PPO was observed. A clonal propagation assay revealed the existence of a population that was resistant to ALS, EPSPS, and PPO inhibitors. Since the local A. tuberculatus populations have not been exposed to herbicide selection pressure, these traits probably reached Israel through seed-mediated gene flow via imported grain.

Population structure and evolution of resistance to acetolactate synthase (ALS)-inhibitors in Amaranthus tuberculatus in Italy.

BACKGROUND: Before 2010, Amaranthus tuberculatus (Moq.) J. D. Sauer was barely known to farmers and stakeholders in Italy. Since then, several populations resistant to acetolactate synthase (ALS)-inhibiting herbicides have been collected. In most populations, a known target site resistance-endowing mutation was found, a Trp to Leu substitution at position 574 of the ALS gene, but it was unclear whether they had evolved resistance independently or not. The aims of the work were (i) to elucidate the population structure of Italian ALS-resistant A. tuberculatus populations, and (ii) to analyze the ALS haplotypes of the various populations to determine whether resistance arose multiple times independently. RESULTS: In order to determine the population structure of eight A. tuberculatus populations, eight previously described microsatellite loci were used. Two ancestors were found: three populations derived from one, and five from the other. In the 4-kb ALS region of the genome, including the 2-kb coding region, 389 single nucleotide polymorphisms were found. In silico haplotype estimation was used to reconstruct the sequence of three distinct haplotypes carrying the Trp574Leu mutation. In addition, no mutation was found in 83% of plants of a single population. CONCLUSIONS: (i) Resistance must have arisen independently at least three times; (ii) at least one population was already resistant to ALS inhibitors when introduced in Italy; (iii) a single haplotype with a Trp574Leu mutation was shared among six populations, probably because of broad seed dispersal; and (iv) one population likely evolved nontarget site ALS inhibitors resistance. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Genetic architecture underlying HPPD-inhibitor resistance in a Nebraska Amaranthus tuberculatus population.

BACKGROUND: Amaranthus tuberculatus is a problematic weed species in Midwest USA agricultural systems. Inhibitors of 4-hydroxyphenylpyruvate dioxygenase (HPPD) are an important chemistry for weed management in numerous cropping systems. Here, we characterize the genetic architecture underlying the HPPD-inhibitor resistance trait in an A. tuberculatus population (NEB). RESULTS: Dose-response studies of an F1 generation identified HPPD-inhibitor resistance as a dominant trait with a resistance factor of 15.0-21.1 based on dose required for 50% growth reduction. Segregation analysis in a pseudo-F2 generation determined the trait is moderately heritable (H2  = 0.556) and complex. Bulk segregant analysis and validation with molecular markers identified two quantitative trait loci (QTL), one on each of Scaffold 4 and 12. CONCLUSIONS: Resistance to HPPD inhibitors is a complex, largely dominant trait within the NEB population. Two large-effect QTL were identified controlling HPPD-inhibitor resistance in A. tuberculatus. This is the first QTL mapping study to characterize herbicide resistance in a weedy species.

Herbicide resistance in Amaranthus tuberculatus†.

Amaranthus tuberculatus is the major weed species in many midwestern US row-crop production fields, and it is among the most problematic weeds in the world in terms of its ability to evolve herbicide resistance. It has now evolved resistance to herbicides spanning seven unique sites of action, with populations and even individual plants often possessing resistance to several herbicides/herbicide groups. Historically, herbicide target-site changes accounted for most of the known resistance mechanisms in this weed; however, over the last few years, non-target-site mechanisms, particularly enhanced herbicide detoxification, have become extremely common in A. tuberculatus. Unravelling the genetics and molecular details of non-target-site resistance mechanisms, understanding the extent to which they confer cross resistance to other herbicides, and understanding how they evolve remain as critical research endeavors. Transcriptomic and genomics approaches are already facilitating such studies, the results of which hopefully will inform better resistance-mitigation strategies. The largely unprecedented level of herbicide resistance in A. tuberculatus is not only a fascinating example of evolution in action, but it is a serious and growing threat to the sustainability of midwestern US cropping systems. © 2020 Society of Chemical Industry.

Metabolic resistance to S-metolachlor in two waterhemp (Amaranthus tuberculatus) populations from Illinois, USA.

BACKGROUND: Two waterhemp (Amaranthus tuberculatus) populations from Illinois demonstrating multiple-resistance to acetolactate synthase (ALS)-, 4-hydroxyphenylpyruvate dioxygenase, and photosystem II (PSII)-inhibiting herbicides (designated CHR and SIR) also displayed reduced sensitivity to very-long-chain fatty acid-inhibiting herbicides, including S-metolachlor. We hypothesized that a physiological mechanism, such as enhanced metabolism, could be responsible for the reduced efficacy of S-metolachlor. RESULTS: Metabolism experiments indicated that resistant populations degraded S-metolachlor more rapidly than sensitive populations and equally as rapidly as corn 2-24 h after treatment (HAT). Resistant waterhemp and corn metabolized 90% (DT90 ) of absorbed S-metolachlor in less than 3.2 h whereas DT90 values for sensitive waterhemp exceeded 6 h. The glutathione S-transferase inhibitor 4-chloro-7-nitrobenzofurazon and cytochrome P450-inhibitor malathion decreased the amount of S-metolachlor metabolized in resistant waterhemp at 4 HAT but not in sensitive waterhemp or corn, and altered the abundance of certain metabolites in resistant waterhemp. CONCLUSION: Results from this research demonstrate that resistance to S-metolachlor in these waterhemp populations is due to enhanced herbicide metabolism relative to sensitive populations. In addition, our results indicate that resistant waterhemp might utilize metabolic pathway(s) more intricate than either sensitive waterhemp or corn based on their metabolite profiles. © 2020 Society of Chemical Industry.

Investigating target-site resistance mechanism to the PPO-inhibiting herbicide fomesafen in waterhemp and interspecific hybridization of Amaranthus species using next generation sequencing.

BACKGROUND: Waterhemp (Amaranthus tuberculatus (Moq.) J. D. Sauer) is one of the most pernicious weeds in cropping systems of the USA due to its evolved resistance against several herbicide sites-of-action, including protoporphyrinogen oxidase inhibitors (PPO-R). Currently, the only source of PPO-R documented in waterhemp is ΔG210 of PPX2. Gene flow may not only lead to a transfer of herbicide-resistant alleles, but also produce a hybrid genotype more competitively fit than one or both parents. However, investigating gene flow of Amaranthus species has been of interest in the past two decades with limited evidence. RESULTS: Here, a high-throughput MiSeq amplicon sequencing method was used to investigate alterations of the PPX2 gene in 146 PPO-R waterhemp populations across five Midwest states of the USA. Five R128 codons of PPX2, novel to waterhemp, were found including AGG (R), GGA (G), GGG (G), AAA (K) and ATA (I). R128G, R128I, and R128K were found in 11, 3, and 2 populations, respectively. R128G and R128I, but not R128K, conferred fomesafen resistance in a bacterial system. Sequence alignment of the R128 region of PPX2 identified a tumble pigweed (Amaranthus albus)-type and Palmer amaranth (Amaranthus palmeri)-type PPX2 allele to be present and widespread in the surveyed waterhemp populations, thus providing strong evidence of gene flow between Amaranthus species. CONCLUSION: Using a next-generation sequencing method, we identified two PPO target-site mutations R128G/I novel to waterhemp and provided evidence of gene flow of Amaranthus species in a large group of screened waterhemp populations from five Midwest states of the USA. © 2019 Society of Chemical Industry.

Inheritance of 4-hydroxyphenylpyruvate dioxygenase inhibitor herbicide resistance in an Amaranthus tuberculatus population from Iowa, USA.

Waterhemp (Amaranthus tuberculatus (Moq.) J.D. Sauer) is a weed prevalent in the Midwest United States and can cause yield losses up to 74% in maize (Zea mays L.) and 56% in soybean (Glycine max (L.) Merr.). An important adaptive trait commonly found in waterhemp is the ability to evolve herbicide resistance and waterhemp populations have evolved resistance to six herbicide sites of action. In 2011, two waterhemp populations were discovered resistant to p-hydroxyphenylpyruvate-dioxygenase (HPPD, EC 1.13.11.27) inhibitor herbicides. We reciprocally crossed a known HPPD-resistant waterhemp population with a known HPPD-susceptible waterhemp population and then intermated the F1 families to established a pseudo-F2 generation. We challenged the parent, F1 and pseudo-F2 generations against four HPPD-inhibiting herbicide rates (mesotrione). Our results suggest the HPPD-resistance trait is polygenic. Furthermore, the number of genes involved with the herbicide resistance increase at higher herbicide rates. These data indicated at least one dominant allele at each major locus is required to confer HPPD herbicide resistance in waterhemp. Using different waterhemp populations and methodologies, this study confirms the reported "complex" HPPD resistance inheritance while providing new information in the response of HPPD-resistant waterhemp to HPPD herbicides.

Inheritance of Mesotrione Resistance in an Amaranthus tuberculatus (var. rudis) Population from Nebraska, USA.

A population of Amaranthus tuberculatus (var. rudis) evolved resistance to 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor herbicides (mesotrione, tembotrione, and topramezone) in Nebraska. The level of resistance was the highest to mesotrione, and the mechanism of resistance in this population is metabolism-based likely via cytochrome P450 enzymes. The increasing number of weeds resistant to herbicides warrants studies on the ecology and evolutionary factors contributing for resistance evolution, including inheritance of resistance traits. In this study, we investigated the genetic control of mesotrione resistance in an A. tuberculatus population from Nebraska, USA. Results showed that reciprocal crosses in the F1 families exhibited nuclear inheritance, which allows pollen movement carrying herbicide resistance alleles. The mode of inheritance varied from incomplete recessive to incomplete dominance depending upon the F1 family. Observed segregation patterns for the majority of the F2 and back-cross susceptible (BC/S) families did not fit to a single major gene model. Therefore, multiple genes are likely to confer metabolism-based mesotrione resistance in this A. tuberculatus population from Nebraska. The results of this study aid to understand the genetics and inheritance of a non-target-site based mesotrione resistant A. tuberculatus population from Nebraska, USA.

Reversing resistance to tembotrione in an Amaranthus tuberculatus (var. rudis) population from Nebraska, USA with cytochrome P450 inhibitors.

BACKGROUND: A population of Amaranthus tuberculatus (var. rudis) was confirmed resistant to 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibitor herbicides (mesotrione, tembotrione, and topramezone) in a seed corn/soybean rotation in Nebraska. Further investigation confirmed a non-target-site resistance mechanism in this population. The main objective of this study was to explore the role of cytochrome P450 inhibitors in restoring the efficacy of HPPD-inhibitor herbicides on the HPPD-inhibitor resistant A. tuberculatus population from Nebraska, USA (HPPD-R). RESULTS: Enhanced metabolism via cytochrome P450 enzymes is the mechanism of resistance in HPPD-R. Amitrole partially restored the activity of mesotrione, whereas malathion, amitrole, and piperonyl butoxide restored the activity of tembotrione and topramezone in HPPD-R. Although corn was injured through malathion followed by mesotrione application a week after treatment, the injury was transient, and the crop recovered. CONCLUSION: The use of cytochrome P450 inhibitors with tembotrione may provide a new way of controlling HPPD-inhibitor resistant A. tuberculatus, but further research is needed to identify the cytochrome P450 candidate gene(s) conferring metabolism-based resistance. The results presented here aid to gain an insight into non-target-site resistance weed management strategies. © 2017 Society of Chemical Industry.

Confronting herbicide resistance with cooperative management.

BACKGROUND: Resistance of pathogens and pests to antibiotics and pesticides worldwide is rapidly reaching critical levels. The common-pool-resource nature of this problem (i.e. whereby the susceptibility to treatment of target organisms is a shared resource) has been largely overlooked. Using herbicide-resistant weeds as a model system, we developed a discrete-time landscape-scale simulation to investigate how aggregating herbicide management strategies at different spatial scales from individual farms to larger cooperative structures affects the evolution of glyphosate resistance in common waterhemp (Amaranthus tuberculatus). RESULTS: Our findings indicate that high-efficacy herbicide management strategies practiced at the farm scale are insufficient to slow resistance evolution in A. tuberculatus. When best practices were aggregated at large spatial scales, resistance evolution was hindered; conversely, when poor management practices were aggregated, resistance was exacerbated. Tank mixture-based strategies were more effective than rotation-based strategies in most circumstances, while applying glyphosate alone resulted in the poorest outcomes. CONCLUSIONS: Our findings highlight the importance of landscape-scale cooperative management for confronting common-pool-resource resistance problems in weeds and other analogous systems. © 2018 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Evaluating the potential for weed seed dispersal based on waterfowl consumption and seed viability.

BACKGROUND: Migratory waterfowl have often been implicated in the movement of troublesome agronomic and wetland weed species. However, minimal research has been conducted to investigate the dispersal of agronomically important weed species by waterfowl. The two objectives for this project were to determine what weed species are being consumed by ducks and snow geese, and to determine the recovery rate and viability of 13 agronomic weed species after passage through a duck's digestive system. RESULTS: Seed recovered from digestive tracts of 526 ducks and geese harvested during a 2-year field study had 35 020 plants emerge. A greater variety of plant species emerged from ducks each year (47 and 31 species) compared to geese (11 and 3 species). Viable seed from 11 of 13 weed species fed to ducks in a controlled feeding study were recovered. Viability rate and gut retention times indicated potential dispersal up to 2900 km from the source depending on seed characteristics and variability in waterfowl dispersal distances. CONCLUSIONS: Study results confirm that waterfowl are consuming seeds from a variety of agronomically important weed species, including Palmer amaranth, which can remain viable after passage through digestive tracts and have potential to be dispersed over long distances by waterfowl. © 2017 Society of Chemical Industry.

Managing the evolution of herbicide resistance.

BACKGROUND: Understanding and managing the evolutionary responses of pests and pathogens to control efforts is essential to human health and survival. Herbicide-resistant (HR) weeds undermine agricultural sustainability, productivity and profitability, yet the epidemiology of resistance evolution - particularly at landscape scales - is poorly understood. We studied glyphosate resistance in a major agricultural weed, Amaranthus tuberculatus (common waterhemp), using landscape, weed and management data from 105 central Illinois grain farms, including over 500 site-years of herbicide application records. RESULTS: Glyphosate-resistant (GR) A. tuberculatus occurrence was greatest in fields with frequent glyphosate applications, high annual rates of herbicide mechanism of action (MOA) turnover and few MOAs field(-1) year(-1) . Combining herbicide MOAs at the time of application by herbicide mixing reduced the likelihood of GR A. tuberculatus. CONCLUSIONS: These findings illustrate the importance of examining large-scale evolutionary processes at relevant spatial scales. Although measures such as herbicide mixing may delay GR or other HR weed traits, they are unlikely to prevent them. Long-term weed management will require truly diversified management practices that minimize selection for herbicide resistance traits.