Agricultural weeds may originate from wild populations, but the origination patterns and genetics underlying this transition remain largely unknown. Analysis of weedy-wild paired populations from independent locations may provide evidence to identify key genetic variation contributing to this adaptive shift. We performed genetic variation and expression analyses on transcriptome data from 67 giant ragweed samples collected from different locations in Ohio, Iowa, and Minnesota and found geographically separated weedy populations likely originated independently from their adjacent wild populations, but subsequent spreading of weedy populations also occurred locally. By using eight closely related weedy-wild paired populations, we identified thousands of unique transcripts in weedy populations that reflect shared or specific functions corresponding, respectively, to both convergently evolved and population-specific weediness processes. In addition, differential expression of specific groups of genes was detected between weedy and wild giant ragweed populations using gene expression diversity and gene co-expression network analyses. Our study suggests an integrated route of weedy giant ragweed origination, consisting of independent origination combined with the subsequent spreading of certain weedy populations, and provides several lines of evidence to support the hypothesis that gene expression variability plays a key role in the evolution of weedy species.

1. Introduced seed dispersers can shift seed predation dynamics in native species, impacting native plant establishment and spread. We studied the effect of the non-native earthworm, Lumbricus terrestris , on seed loss dynamics in the large-seeded native annual, Ambrosia trifida (giant ragweed), an expanding agricultural weed whose seeds are heavily predated by mice. Lumbricus terrestris may protect seeds against rodent predation by caching them in its burrows from which seed - lings can emerge unharmed; however, little is known about the ability of earth - worms to compete with rodents

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 19(th) 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.

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

Current recommendations for the control of glyphosate-resistant horseweed [Conyza canadensis(L.) Cronquist var.canadensis] in soybeans [Glycine max(L.) Merr.] consist of comprehensive herbicide programs, which often include herbicide applications outside the soybean growing season. Integration of cover crops with herbicides could potentially improveC. canadensiscontrol and allow for a reduction in herbicide inputs. Two separate field studies were conducted from 2016 through 2018 with the objectives of: (1) determining the effect of planting date and seeding rate of a cereal rye (Secale cerealeL.) cover crop onC. canadensispopulation density and control in the subsequent soybean crop; and (2) determining whether the cover crop could replace a fall herbicide treatment or allow for a reduction in the use of spring-applied residual herbicides. There was no effect of rye planting date, late September versus late October, onC. canadensisdensity in either study. In 2016 to 2017,C. canadensisdensity was greater in the absence of a rye cover crop in both studies, but otherwise not affected by seeding rates of 50 versus 100 kg ha(-1). In the 2017 to 2018 season, the presence of rye resulted in an increasedC. canadensisdensity in the spring residual herbicide study (Study I), and had no effect in the fall herbicide study (Study II).Conyza canadensisdensities were lowest in the treatments where a comprehensive spring residual or fall herbicide treatment had been applied, averaged over rye planting date and seeding rate. Earlier-planted rye at a higher seeding rate produced the most biomass but did not result in lowerC. canadensisdensities. These results suggest that cereal rye planted at a density of 50 kg ha(-1)as a cover crop before no-till soybeans may be sufficient to reduce glyphosate-resistantC. canadensisplant density, but cannot be relied upon to reduce the need for fall herbicide treatments and spring residual programs.

Integrated pest management (IPM) for weeds is considered to be in the early stages of development, especially when compared with insect and disease management. The need to develop IPM principles for weed management will increase as weed population shifts, species adaptation, and environmental impacts of weed control methods threaten the sustainability of agricultural systems. In this paper, we propose a framework for discussion and development of the weed component of IPM. We describe five levels of weed IPM that encompass progressively larger spatial scales and longer time periods, with corresponding changes in goals and complexity of supporting technology and information. The first level consists of the use of a 240single weed management tool at the field level, such as the use of a herbicide as the sole means for weed control. Level II integration incorporates tactical use of multiple tools for weed management, including combinations of herbicides, crop rotation, and mechanical and biological controls, as well as other cultural practices designed to reduce the damage caused by weeds. Level III represents the threshold of much current weed science research, and involves the design of entire cropping systems at the farm and landscape level as a strategy to resist weed invasion, tolerate weed presence, and decrease weed population survival and persistence. Levels IV and V are more speculative because the ecological basis for them is in development. Level IV addresses the management of habitats and landscapes at the ecosystem level to address large scale problems related to weed spread, dispersal, and invasion. At Level V, national trade and environmental policies are considered with respect to their impact on weed populations at a global scale. Approaches that might be taken at the various levels to management of herbicide resistance are described. Research has tended to focus on the first two levels of integration; however, development of IPM principles for weeds will require that attention be given to all levels of integration so that agricultural systems can be designed to more effectively deter and withstand the inevitable presence of weeds. [Article copies available for a fee from The Haworth Document Delivery Service: 1-800-342-9678. E-mail address: getinfo@haworthpressinc.com]

Spatial patterns of trait variation across a species' range have implications for population success and evolutionary change potential, particularly in range‐expanding and weedy species that encounter distinct selective pressures at large and small spatial scales simultaneously. We investigated intraspecific trait variation in a common garden experiment with giant ragweed (Ambrosia trifida), a highly variable agricultural weed with an expanding geographic range and broad ecological amplitude. Our study included paired populations from agricultural and natural riparian habitats in each of seven regions ranging east to west from the core of the species' distribution in central Ohio to southeastern Minnesota, which is nearer the current invasion front. We observed trait variation across both large‐ and small‐scale putative selective gradients. At large scales, giant ragweed populations from the westernmost locations were nearly four times more fecund and had a nearly 50% increase in reproductive allocation compared to populations from the core. The degree of surface texture on fruits also declined from east to west. Greater fecundity in the west represents a putative trade‐off between fruit size and fruit number across the study region, although no such trade‐off was found across individual plants. This pattern may effectively result in greater propagule pressure closer to the invasion front. At smaller spatial scales, plants from agricultural populations emerged later and were smaller than plants from riparian populations. However, because plants from agricultural populations allocated more biomass to reproduction, total fecundity did not differ across habitats. Our emergence data are consistent with previous observations showing delayed emergence in agricultural compared to natural populations; thus evolutionary change may be predictable as giant ragweed continues spreading into agricultural fields throughout North America. These shifts in life‐history strategy apparently bear no fecundity cost, suggesting that giant ragweed's success can be attributed at least in part to its substantial adaptive potential.

Field studies were conducted in 2011 and 2012 to compare mulch treatments of shredded newspaper, a combination of shredded newspaper plus turfgrass clippings (NP + grass), hardwood bark chips, black polyethylene plastic, and bare soil on weeds, insects, soil moisture, and soil temperature in pumpkins. Newspaper mulch or black plastic reduced total weed biomass ≥90%, and woodchip or NP + grass mulch each reduced total weed biomass 78% compared with bare soil under high rainfall conditions in 2011. In 2012, under low rainfall, all mulches reduced weed biomass 97% or more compared with bare soil. In both years, all mulches resulted in higher squash bug infestations than bare soil. The woodchip, newspaper, and NP + grass mulches retained higher soil moistures than bare soil or black plastic over the course of each growing season, and the woodchip and NP + grass mulches caused greatest fluctuations in soil temperature. Pumpkin yields were abnormally low in 2011 and did not differ among treatments. In 2012, all mulches produced greater total marketable pumpkin fruit weights compared with bare soil, but only black plastic, newspaper, and NP + grass mulches resulted in greater total numbers of marketable pumpkins. Overall results indicate that shredded newspaper or NP + grass mulches may be useful for organic and/or small-scale urban crop producers as sustainable alternatives to black plastic mulch; however, their weed suppression efficacy may require higher application rates with increasing moisture conditions, and they may require greater squash bug control measures than under bare soil conditions.

Giant ragweed has been increasing as a major weed of row crops in the last 30 yr, but quantitative data regarding its pattern and mechanisms of spread in crop fields are lacking. To address this gap, we conducted a Web-based survey of certified crop advisors in the U.S. Corn Belt and Ontario, Canada. Participants were asked questions regarding giant ragweed and crop production practices for the county of their choice. Responses were mapped and correlation analyses were conducted among the responses to determine factors associated with giant ragweed populations. Respondents rated giant ragweed as the most or one of the most difficult weeds to manage in 45% of 421 U.S. counties responding, and 57% of responding counties reported giant ragweed populations with herbicide resistance to acetolactate synthase inhibitors, glyphosate, or both herbicides. Results suggest that giant ragweed is increasing in crop fields outward from the east-central U.S. Corn Belt in most directions. Crop production practices associated with giant ragweed populations included minimum tillage, continuous soybean, and multiple-application herbicide programs; ecological factors included giant ragweed presence in noncrop edge habitats, early and prolonged emergence, and presence of the seed-burying common earthworm in crop fields. Managing giant ragweed in noncrop areas could reduce giant ragweed migration from noncrop habitats into crop fields and slow its spread. Where giant ragweed is already established in crop fields, including a more diverse combination of crop species, tillage practices, and herbicide sites of action will be critical to reduce populations, disrupt emergence patterns, and select against herbicide-resistant giant ragweed genotypes. Incorporation of a cereal grain into the crop rotation may help suppress early giant ragweed emergence and provide chemical or mechanical control options for late-emerging giant ragweed.

Giant ragweed is a troublesome weed of increasing importance in the U.S. Corn Belt. This survey of CCAs investigated the association of giant ragweed spread with its historical distribution, local habitat factors, and crop production practices. Earn 0.5 CEUs in Integrated Pest Management by reading this article and taking the quiz at www.certifiedcropadviser.org/certifications/self‐study/779.

Zucchini squash (Cucurbitapepo) has a high pollination demand, and the native, ground-nesting squash bee (Peponapis pruinosa) provides the majority of the crop's pollination requirement in some environments. Squash bees nest directly in crop fields, and nests can be disturbed by tillage and other management operations. Mulches that use municipal waste materials may provide a weed control strategy for squash plantings that is more benign to squash bees than cultivation. Field and greenhouse studies were conducted in 2011 and 2012 to compare the effects of nontillage weed control methods including polyethylene black plastic, woodchips, shredded newspaper, a combination of shredded newspaper plus grass clippings (NP + grass), and bare soil (control) on soil characteristics, squash pollination and fruit production, and squash bee nesting. Woodchips, shredded newspaper, and NP + grass mulch decreased soil temperature, while soils beneath newspaper mulch retained more moisture. Unmarketable, misshapen fruit occurred more frequently in plastic than in the other mulch treatments. No measurable differences in floral resource production or crop pollination were found among treatments, suggesting that misshapen fruit resulted from high soil temperatures in black plastic plots rather than poor pollinator attraction. Squash bee nests were located within bare soil, newspaper, and NP + grass plots, indicating that these mulches did not prevent nesting. NP + grass mulch had a positive effect on plant growth and fruit production, possibly from an addition of plant-available nitrogen or the presence of preferable nesting ground. Shredded newspaper when combined with grass clippings performed as an effective mulch material that improved crop performance with no apparent negative impacts on squash bee nesting or on squash floral resources and pollination.

Giant ragweed (Ambrosia trifida L.) has become one of the most persistent and problematic weeds to farmers and allergy sufferers in North America over the last decades. This study aims to identify and assess the scholarly literature using a bibliometric analysis approach. Based on bibliographic records retrieved from the Web of Science database, the study describes the periodic growth of literature, scientific fields and journals, author productivity and collaborations, institutions and countries, and topical focus and uses article citation analysis to identify the most influential works in this research field during the period of 1903 to 2012.

Giant ragweed germination is delayed by both a physiological dormancy of the embryo (embryo dormancy) and an inhibitory influence of embryo-covering structures (covering structure-enforced [CSE] dormancy). To clarify the roles of embryo and CSE dormancy in giant ragweed seedling emergence timing, we conducted two experiments to address the following objectives: (1) determine changes in germinability for giant ragweed dispersal units (hereafter "involucres") and their components under natural burial conditions, and (2) compare embryo and CSE dormancy alleviation and emergence periodicity between successional and agricultural populations. In Experiment 1, involucres were buried in crop fields at Columbus, OH, periodically excavated, and brought to the laboratory for dissection. Involucres, achenes, and embryos were then subjected to germination assays at 20 C. In Experiment 2, temporal patterns of seedling emergence were determined at a common burial site. Reductions in embryo and CSE dormancy were compared with controlled-environment stratification followed by germination assays at 12 and 20 C, temperatures representative of soil conditions in spring and summer. Results indicated that overwinter dormancy loss involved sequential reductions in embryo and CSE dormancy. CSE dormancy, which may limit potential for fatal germination during fall, was caused by the pericarp and/or embryo-covering structures within the pericarp. In Experiment 2, successional populations emerged synchronously in early spring, whereas agricultural populations emerged throughout the growing season. Levels of embryo dormancy were greater in the agricultural populations than the successional populations, but CSE dormancy levels were similar among populations. In 12 C germination assays, embryo dormancy levels were positively correlated with time required to reach 95% cumulative emergence (run 1: r = 0.81, P = 0.03; run 2: r = 0.76, P = 0.05). These results suggest that late-season emergence in giant ragweed involves high levels of embryo dormancy that prevent germination at low temperatures in spring.

The earthworm, Lumbricus terrestris L., caches seeds of the agricultural weed Ambrosia trifida L. in its burrow, providing seeds with a protected overwintering site. Seedlings subsequently emerge from the burrows, resulting in an association of the two species (hereafter “LtAt association”). Although populations of these species frequently co-exist in no-till agricultural fields in the eastern U.S. Corn Belt, an association is not always evident. To identify environmental influences on the LtAt association, 30 no-till agricultural fields were surveyed across the eastern U.S. Corn Belt during spring 2007, 2008 and 2009. The LtAt association occurred across states and soil types, but the strength of the association varied with climate differences during the previous September through March. The strongest environmental driver of LtAt association was frequency of “moderate rain day” (MRD; day that received 12.8–25.3mm of precipitation), with a 1-day increase in MRD frequency increasing the odds of LtAt association by a factor of 1.42. Thus, the potential for L. terrestris to cache seeds and facilitate seedling recruitment is increased by precipitation frequency and amount during September through March. These results highlight the importance of climate variation within a region in driving trophic interactions that regulate weed population dynamics.

Summary Ambrosia trifida L. (giant ragweed), an aggressive weed of US grain crops and indigenous to North America, colonizes no‐tillage crop fields and undisturbed soils despite its large seed size and susceptibility to seed predation. Secondary seed dispersal is critical to seed survival and seedling establishment, yet mechanisms of secondary dispersal are poorly understood for such large‐seeded weedy species. Field experiments were conducted to determine how seed foraging by the European exotic burrowing earthworm Lumbricus terrestris L., affected A. trifida seed burial and seedling recruitment, and to determine seed selectivity by L. terrestris. Earthworms collected and buried over 90% of A. trifida seeds placed on the soil surface at a rate eightfold faster than abiotic seed burial. There was a sixfold higher concentration of seeds in burrows than in surrounding soil and a mean of 127 A. trifida seeds per burrow after a single season of A. trifida seed dispersal. Earthworms buried A. trifida seeds from 0·5 to 22 cm deep and reduced recruitment by 37% compared to seeds buried abiotically and protected from predators, due to burial of some seeds below emergence depth limits. However, seedling biomass was increased by 30%. Earthworms foraged selectively among seeds of 11 large‐seeded species and collected more seeds of A. trifida than of other species. The earthworms buried small (8·5 mm) A. trifida seeds more deeply and reduced their emergence more than large (11·5 mm) A. trifida seeds. Synthesis and applications. The novel interaction of L. terrestris and A. trifida increases seed bank formation of A. trifida. Burrows of L. terrestris provide safe sites for seeds of A. trifida that may increase seedling establishment in environments with a high risk of seed predation. Control measures to prevent reproduction by A. trifida should be increased where L. terrestris is present due to the earthworms’ ability to bury and protect weed seeds. Selective seed caching by this widely distributed earthworm species may change plant community composition in agricultural and natural areas in North America and influence the evolution of seed traits. Land managers should consider the effects of L. terrestris on seedling regeneration of native and exotic plant species in areas undergoing colonization by L. terrestris.

Late-season giant ragweed emergence in Ohio crop fields complicates decisions concerning the optimum time to implement control measures. Our objectives were to develop a hydrothermal time emergence model for a late-emerging biotype and validate the model in a variety of locations and burial environments. To develop the model, giant ragweed seedlings were counted and removed weekly each growing season from 2000 to 2003 in a fallow field located in west central Ohio. Weather data, soil characteristics and geographic location were used to predict soil thermal and moisture conditions with the Soil Temperature and Moisture Model (STM2). Hydrothermal time (θHT) initiated March 1 and base values were extrapolated from the literature (Tb= 2 C, ψb= −10 MPa). Cumulative percent emergence initially increased rapidly and reached 60% of maximum by late April (approximately 400 θHT), leveled off for a period in May, and increased again at a lower rate before concluding in late July (approximately 2,300 θHT). The period in May when few seedlings emerged was not subject to soil temperatures or water potentials less than the θHTbase values. The biphasic pattern of emergence was modeled with two successive Weibull models that were validated in 2005 in a tilled and a no-tillage environment and in 2006 at a separate location in a no-tillage environment. Root-mean-square values for comparing actual and model predicted cumulative emergence values ranged from 8.0 to 9.5%, indicating a high degree of accuracy. This experiment demonstrated an approach to emergence modeling that can be used to forecast emergence on a local basis according to weed biotype and easily obtainable soil and weather data.

In temperate plant communities, seed size is often inversely related to seed longevity at the species level. We tested if the inverse relationship between seed size and seed longevity holds among individuals within populations of Ambrosia trifida L. (Asteraceae), a summer annual agricultural weed in the eastern United States Corn Belt that typically emerges in two successive flushes: one before 1 May and one after 1 May. The effects of maternal phenotype on seed morphology, seed weight, late emergence (emergence after 1 May) and seedbank persistence were determined in two 1-year experiments. All seeds were collected from individuals at weekly intervals for 3 weeks. Sixty seeds per collection were used in the analysis. Despite fluctuating environmental conditions during seed development, seed weight within maternal families remained constant for different maturation times. Differences among families constituted 69% of total variation in seed weight, whereas differences within maternal families composed 31% of the variation in seed weight. Percentage late emergence and percentage seed-bank persistence varied among maternal families. In four maternal families, either 0% or 100% of seedlings emerged after 1 May, but a majority of other maternal families produced seedlings both before and after 1 May. Seed-bank persistence rates ranged from 1 to 51% among maternal families. Percentage late emergence and percentage seed-bank persistence were inversely related to maternal-family mean seed weight in 2006, but not in 2005. These results suggest that the inverse relationship between seed size and seed longevity occurs among individuals of a population, but is affected by the environment.

Giant ragweed is a competitive, allergenic weed that persists in agricultural fields and early successional sites. Field experiments were conducted to determine the effects of seed size and seed burial depth on giant ragweed emergence and seed demise. In a seedling emergence experiment, small (< 4.8 mm in diameter) and large (> 6.6 mm in diameter) seeds were buried 0, 5, 10, and 20 cm in fall 1997, and weed emergence was monitored over the next seven growing seasons. A generalized linear mixed model fit to the cumulative emergence data showed that maximum emergence for both seed sizes occurred at the 5-cm burial depth, where probability of emergence was 19% for small seeds and 49% for large seeds. Emergence probability at the 10-cm burial depth was 9% for small seeds and 30% for large seeds, and no seedlings emerged from the 20-cm burial depth. The model predicted that ≥ 98% of total cumulative emergence was completed after four growing seasons for large seeds buried 5 cm, five growing seasons for small seeds buried 5 cm and large seeds buried 10 cm, and seven growing seasons for small seeds buried 10 cm. Seed size and burial treatment effects on seed demise were tested in a second experiment using seed packets. Rates of seed demise were inversely proportional to burial depth, and the percentage of viable seeds remaining after 4 yr ranged from 0% on the soil surface to 19% at the 20-cm burial depth. Some seeds recovered from the 20-cm burial depth were viable after 9 yr of burial. These results, coupled with previous research, suggest that seed size polymorphism facilitates giant ragweed adaptation across habitats and that a combination of no-tillage cropping practices, habitat modification, and timely weed control measures can reduce its active seed bank in agricultural fields by 90% or more after 4 yr.

Quackgrass [Elytrigia repens (L.) Nevski] (QG) is a troublesome weed in row crop production but has some ideal forage characteristics for pastures. The competitive interactions of QG with other forage species under varying defoliation frequencies are not clearly understood. Our objective was to determine the competitiveness of QG with orchardgrass (Dactylis glomerata L.) (ORG) and/or white clover (Trifolium repens L.) (WC) under 2- or 6-wk cutting frequencies. Two replacement series experiments were conducted in a greenhouse between January and November 2002. Proportional mixtures (100:0, 33:66, 66:33, and 0:100) of QG:ORG and QG:WC, and a 33:33:33 mixture of all three species were established by planting tillers, rhizome shoots, or rooted stolons from ORG, QG, and WC, respectively. Results were similar across duplicate experiments so data were combined for the analysis. Yield for the 6-wk cutting frequency was almost twice that of the 2-wk cutting frequency (P less than or equal to 0.05). No yield differences (P > 0.05) were found among the QG:ORG mixtures at the 6-wk cuttings. A quadratic response (P less than or equal to 0.05) for the QG:WC mixtures under the 6-wk cutting frequency showed 23% greater yield from the two QG:WC mixtures than WC or QG monocultures. Yield of species mixtures did not differ significantly at the 2-wk cutting frequency. We concluded that QG was a productive forage species that yielded best when grown with a complementary species (i.e., WC) rather than with a species likely to compete directly for the same resources (i.e., ORG).