Finger weeders were first developed in the 1950s and have since been widely adopted by farmers to improve physical weed control (PWC) within crop rows. Research on finger weeders has largely been comparative, with most studies identifying a top-performing weed control practice among various physical or chemical treatments. Weeding tool performance, however, is often highly variable, affected by tool design and adjustment, soil conditions, and both weed and crop species and size. Finger weeder operating settings have not been systematically tested to determine whether they could optimize tool performance. In this project, field and soil bin experiments examined the effects of finger weeder angle, spacing, and speed on weed control efficacy and weed/crop selectivity. Three finger weeder angles were tested: 108°, which removed soil near the crop; 90°, typical for most commercial tools; and 68°, which moved soil into the crop row. Three spacings and speeds were compared: fingers overlapping (−0.6 cm), touching (0 cm), or spaced apart (2.5 cm); and 4, 7, and 9 km h−1. In both the field and soil bin, finger weeders set at a 68° angle resulted in the greatest efficacy. Decreasing finger spacing and increasing speed improved efficacy in soil bin experiments, as expected, but spacing and speed effects were not detected in the field. The experimental soil bin system shows promise for PWC testing, possibly offering insights that could not be detected in more variable field conditions.

Agricultural weeds remain an important production constraint, with labor shortages and a lack of new herbicide options in recent decades making the problem even more acute. Robotic weeding machines are a possible solution to these increasingly intractable weed problems. Franklin Robotics’ Tertill™ is an autonomous weeding robot designed for home gardeners that relies on a minimalistic design to be cost-effective. The objectives of this study were to investigate the ability of the Tertill to control broadleaf and grass weeds, and based on early observations, experiments were conducted with and without its string-trimmer–like weeding implement. Tertill demonstrated high weed-control efficacy, supporting its utility as a tool for home gardeners. Weeds were best controlled by the combined effect of soil disturbance caused by the action of the robot’s wheels and the actuation of the string trimmer. Despite the regrowth potential of an annual grass due to its meristem location, Tertill maintained low densities of millet in an experimental arena. The simple and effective design of the Tertill may offer insights to inform future development of farm-scale weeding robots. Weed density, emergence periodicity, robot working rate, and robotic weeding mechanisms are important design criteria regardless of the technology used for plant detection.

The long-term success of weed management programs requires that all crops in a rotation receive satisfactory weed control. Band sowing with inter-band hoeing has been proposed as an innovative weed management strategy for grain crops. In the band-sowing system, crops are sown in a broadcast pattern within a band of some chosen width (here we selected 12.7 cm); weeds between bands are controlled with inter-band hoeing, with or without so-called “blind cultivation,” for example, tine harrowing. Alteration of the crop spatial arrangement from typical single-line rows to a more evenly distributed pattern aims to enhance interspecific competition while reducing intraspecific competition. Field experiments, conducted in Maine in 2016 and 2017, compared band sowing with inter-band hoeing to the region’s standard practice of planting in 16.5-cm rows and tine harrowing in four test crops: spring wheat (Triticum aestivum L. ‘Glenn’), oat (Avena sativa L. ‘Colt’), field pea (Pisum sativum L. ‘Jetset’), and flax (Linum usitatissimum L. ‘Prairie Thunder’). Band sowing improved weed control relative to the standard practice, especially in crops with greater competitive ability (wheat and oat). Despite improved weed control, in most cases, yields were unaffected by treatment. While band sowing with hoeing provided improved weed control in multiple crops, further study is warranted to optimize seeding rate, band width, and inter-band width to improve crop yields.

Weeds remain the foremost production challenge for organic small grain farmers in the northeastern United States. Instead of crops sown in narrow, single-line rows, band sowing offers a more uniform spatial arrangement of the crop, maximizing interspecific while reducing intraspecific competition. Weeds in the inter-band zone are controlled by cultivating with aggressive sweeps; tine harrowing can target weeds in both intra- and inter-band zones. Field experiments in Maine and Vermont in 2016 and 2017 evaluated band sowing for improved weed control, crop yield, and grain quality in organic spring barley (Hordeum vulgare L. ‘Newdale’). Specifically, we compared: (1) the standard practice of sowing 16.5-cm rows at a target crop density of 325 plants m−2, (2) narrow-row sowing with increased crop density, (3) wide-row sowing with interrow hoeing, and (4) band sowing both with and (5) without inter-band hoeing. Mustard (Sinapis alba L. ‘Ida Gold’) was planted throughout the experiment as a surrogate weed. Compared with the standard practice, band sowing with hoeing reduced surrogate weed density on average by 45% across site-years. However, effects on weed biomass and yield were inconsistent, perhaps due to suboptimal timing of hoeing and adverse weather conditions. In 1 out of 4 site-years, band sowing with hoeing reduced surrogate weed biomass by 67% and increased crop yield compared with the standard treatment. Results also indicate that band sowing with hoeing may improve 1,000-kernel weight and plump kernel grain-quality parameters.

Organic vegetable farmers execute weed management using many overall philosophies, including focusing management during the early-season critical period, managing the weed seedbank with a ‘zero seed rain’ strategy, or physically suppressing weeds with plastic or natural mulches. While these strategies vary in their ecological and economic implications, farmers’ reasons for adopting specific weed management approaches, and the related practical implications of each approach remain unclear. To better understand farmer motivations and ecological impacts of broad weed management philosophies, we conducted case studies of four successful organic vegetable farmers with specialization in different management approaches. The farmers were interviewed about their experiences and soil samples were collected for weed community and soil organic matter (SOM) analysis. The farmer who controls weed seedlings primarily during the critical period has appreciated the associated weeding labor savings, but late-season weeds have contributed to a large weed seedbank (38,482 seeds m−2), which is necessitating a change in his management. Conversely, the zero seed rain strategy of another farmer required a large amount of labor in the initial years, but weeding labor requirements have lessened every year due to decreased weed emergence from his diminishing weed seedbank (3065 seeds m−2). Another farmer utilizes plastic mulch in many crops in order to reduce weeding labor during the busy spring planting season. Finally, the farmer that uses natural mulches has high labor costs, but they are offset by the benefits of weed suppression, soil moisture conservation and increases to SOM. The two farmers utilizing mulch had the greatest portion of monocotyledonous weeds, perhaps relating to their morphology allowing them to emerge through the mulch. In ranking management criteria based on their importance, the case study farmers generally valued the criteria that are benefited by their strategy, indicating a strong relationship between their priorities and their management. Overall, there was no ‘best’ weed management strategy, but farmers may benefit from the consideration of how their management priorities match the practical tradeoffs of each strategy.

The northern New England region includes the states of Vermont, New Hampshire, and Maine and encompasses a large degree of climate and edaphic variation across a relatively small spatial area, making it ideal for studying climate change impacts on agricultural weed communities. We sampled weed seedbanks and measured soil physical and chemical characteristics on 77 organic farms across the region and analyzed the relationships between weed community parameters and select geographic, climatic, and edaphic variables using multivariate procedures. Temperature-related variables (latitude, longitude, mean maximum and minimum temperature) were the strongest and most consistent correlates with weed seedbank composition. Edaphic variables were, for the most part, relatively weaker and inconsistent correlates with weed seedbanks. Our analyses also indicate that a number of agriculturally important weed species are associated with specific U.S. Department of Agriculture plant hardiness zones, implying that future changes in climate factors that result in geographic shifts in these zones will likely be accompanied by changes in the composition of weed communities and therefore new management challenges for farmers.

Weed management strategies differ in their ability to control weeds, and often have unique agroecological implications. To provide growers with an improved sense of trade-offs between weed control and ecological effects, we implemented several prominent organic weed management strategies in yellow onion in 2014 and 2015. Strategies included cultivation of weed seedlings during the early, weed-sensitive “critical period” of the crop; frequent cultivation events to ensure “zero seed rain”; and weed suppression with polyethylene or natural mulches. As expected, end-of-season weed biomass and weed seed production were greatest in the critical period system and nearly zero for the zero seed rain system. Weeds were also well controlled in natural mulch systems. Average onion yield per treatment was 50.7 Mg ha−1. In 2014, the critical period system and the polyethylene mulch systems demonstrated yield loss, likely due to weed competition and excessive soil temperature, respectively. Onion soluble solids content was also diminished in these systems in 2014, but bulb firmness was greatest in unmulched systems. Carabid beetles, earthworms, soil compaction, soil nitrate, and microbial biomass were affected by weed management strategy, with natural-mulched systems generally performing most favorably. However, these effects were not substantial enough to affect yield of a subsequent sweet corn crop grown in weed-free conditions. In contrast, sweet corn managed with only early-season cultivations demonstrated yield loss (P=0.004) in plots where the critical period treatment was implemented the prior year, indicating that weed competition resulting from abundant weed seed production in that system was the most influential legacy effect of the weed management strategies.

Tillage is a foundational management practice in many cropping systems. Although effective at reducing weed populations and preparing a crop seedbed, tillage and cultivation can also dramatically alter weed community composition. We examined the impact of soil tillage timing on weed community structure at four sites across the northeastern United States. Soil was tilled every 2 wk throughout the growing season (late April to late September 2013), and weed seedling density was quantified by species 6 wk after each tillage event. We used a randomized complete block design with four replicates for each tillage-timing treatment; a total of 196 plots were sampled. The timing of tillage was an important factor in shaping weed community composition and structure at all sites. We identified three main periods of tillage timing that resulted in similar communities. Across all sites, total weed density tended to be greatest and weed evenness tended to be lowest when soils were tilled early in the growing season. From the earliest to latest group of timings, total abundance decreased on average from 428±393 to 159±189 plants m−2, and evenness increased from 0.53±0.25 to 0.72±0.20. The effect of tillage timing on weed species richness varied by site. Our results show that tillage timing affects weed community structure, suggesting that farmers can manage weed communities and the potential for weed interference by adjusting the timing of their tillage and cropping practices.

Results from the “Potato Ecosystem Project,” a cropping systems study in northern Maine, were used to test the hypothesis that greater reliance on organic nutrient sources and less reliance on synthetic fertilizer sources can benefit weed management efforts. ‘Atlantic’ potato was grown in a 2-yr rotation within a factorial arrangement of three pest management systems, two soil management systems, and both rotation entry points. Weed control in the conventional (CONV) pest management system relied on full rates of herbicides, whereas the biointensive (BIO) system relied exclusively on cultivation. The reduced input (RI) pest management system relied on cultivation in 1991 and 1992 and on 50% of standard herbicide rates plus cultivation from 1993 to 1995. The two soil management systems, unamended (barley/red clover rotation crop; 1× synthetic fertilizer for potato) and amended (pea/oat/hairy vetch green manure rotation crop; manure, compost, and 0.5× synthetic fertilizer for potato) contrasted practices typical for the region to those designed to achieve rapid improvements in soil quality. Midseason weed biomass in potato was dominated by common lambsquarters. In 1991 and 1992, weed biomass in potato was least in the CONV system and did not differ between the RI and BIO systems. In 1993, weeds in both RI and CONV potatoes were effectively suppressed below the level measured in the BIO system. Soil management had no effect on weed biomass from 1991 to 1993 but became an important factor affecting weeds in the BIO system in 1994 and 1995. Weed biomass was 77% lower in 1994 and 72% lower in 1995 in the amended soil management system than in the unamended system. No significant yield loss due to weeds was detected in the 1994 BIO system, but in 1995 yield loss due to weeds was 37% in the unamended system compared to 12% in the amended system. Soil management effects on weeds in the 1994 BIO pest management system carried through to the following season's germinable seed bank. Density of germinable common lambsquarters seed (0 to 10 cm soil depth) in the 1995 BIO system was 4,082 m−2 in the unamended soil management system compared to 1,280 m−2 in the amended soil management system. We suggest that organic amendments and green manure promote a potato crop better able to compete with weeds and that these inputs be considered as potentially important components of integrated weed management systems that have minimal reliance on herbicides.

A rhizotron containing 10 1.5-by 1.2-by 2.4-m chambers and two 1.5-by 1.2-by 1.2-m chambers for plant growth was constructed for teaching purposes at Montana State University. The rhizotron, constructed of pressure-treated plywood and redwood lumber, has a life expectancy of 40 yr and a prorated cost of approximately $100/yr.

Clomazone is effective as a chemical fallow herbicide; however, its soil residual properties in the Northern Great Plains are unknown. Clomazone was applied to soil at 0.6, 1.1, and 2.2 kg ai/ha at two locations in Montana in the spring of 1986. Soil samples were taken at each location at monthly intervals for 6 months. Residual levels of the herbicide were estimated by measuring the percent chlorosis by height in oat leaves. Clomazone at 2.2 kg ai/ha applied to a loam soil dissipated to levels below 0.1 mg/kg in 3 months and applied to a silty clay loam soil dissipated to 0.2 mg/kg 6 months after application. Half-lives (t½), determined from first-order rate plots, were 33 and 37 days in the Willow Creek loam and Bozeman silty clay loam, respectively. Thus, clomazone residue from labeled-use rates should not inhibit wheat in a wheat-fallow-wheat cropping system in Montana.

Weed management remains a high priority for organic farmers, whose fieldsgenerally have higher weed density and species diversity than those of theirconventional counterparts. We explored whether variability in farmerknowledge and perceptions of weeds and weed management practices werepredictive of variability in on-farm weed seedbanks on 23 organic farms innorthern New England. We interviewed farmers and transcribed and codedinterviews to quantify their emphasis on concepts regarding knowledge ofecological weed management, the perceived risks and benefits of weeds, andthe perceived risks and benefits of weed management practices. Tocharacterize on-farm weed seedbanks, we collected soil samples from fivefields at each farm (115 fields total) and measured germinable weed seeddensity. Mean weed seed density per farm ranged from 2,775 seeds m−2 to 24,678 seeds m−2 to a soil depth of 10 cm.Farmers most often reported hairy galinsoga and crabgrass species (Digitaria spp.) as their most problematic weeds. Theproportion of the sum of these two most problematic weeds in each farm'sseedbank ranged from 1 to 73% of total weed seed density. Farmer knowledgeand perceptions were predictive of total seed density, species richness, andproportion of hairy galinsoga and crabgrass species. Low seed densities wereassociated with farmers who most often discussed risks of weeds, benefits ofcritical weed-free management practices, and learning from their ownexperience. These farmers also exhibited greater knowledge of managing theweed seedbank and greater understanding of the importance of a long-termstrategy. Targeted education focusing on this set of knowledge and beliefscould potentially lead to improved application and success of ecologicalweed management in the future, thus decreasing labor costs and timenecessary for farmers to manage weeds.

Postdispersal weed seed predation is a significant source of weed mortalityin agroecosystems. The magnitude of seed predation, however, is variable.Understanding the relative importance of factors driving variability in seedpredation rates will increase the potential utility of seed predation tofarmers. We conducted landscape-scale field experiments to quantify andcompare the effects of space, time of sampling, and habitat on weed seedpredation. Seed predation assays, with and without vertebrate exclosures,measured seed predation rates at spatially explicit sample sites across 8.5ha of crop and noncrop habitats on a diversified organic vegetable farm inMaine. Total and invertebrate seed predation averaged 8% and 3% d−1, respectively. Vertebrate seed predators detected bymotion-sensing cameras included small mammals and birds. A ground beetle, Harpalus rufipes, was highly dominant in pitfall traps,comprising 66% of invertebrate seed predators captured within crop fields.Seed predation was randomly distributed in space. However, time of samplingand habitat were highly significant predictors of seed predation. Variancepartitioning indicated that habitat factors explained more variation thandid time of sampling. Total seed predation was greater in crop and riparianforest habitats than in mowed grass, meadow, or softwood forest. Generally,invertebrate seed predation was greatest at sites with an intermediatedegree of vegetative cover, whereas habitat type was the chief bioticdeterminant of vertebrate seed predation rates. These results suggest covercropping and wetland conservation as practices that may bolster seedpredation rates.

Because herbicide and cultivation efficacy is generally density independent, seedling density following these weed control practices will be proportional to the density of germinable seeds in the seedbank. Most farmers would therefore benefit from management practices that reduce seed inputs, increase seed losses, and reduce the probability that remaining seeds establish. Germination, predation, and decay are the primary sources of loss to the seedbank that may respond to management. Farmers have long prepared stale seedbeds in which shallow soil disturbance encourages germination losses. Postdispersal seed predation by vertebrate and invertebrate granivores may cause high rates of seed mortality in a wide range of cropping systems, but seed dispersal asynchronous with predator activity, and seed burial, may limit the overall effect on the seedbank. Although seeds would seem to be an ideal carbon source for soil microorganisms, limited evidence from a study of wild oat suggests that decay may be less responsive to management than germination, and likely predation. A final management objective, supporting a program that aims to reduce seedbank inputs and increase losses, is to reduce the size of the effective seedbank through manipulation of residues and disturbance to reduce the probability of establishment. Incorporation of green manures generally reduces weed establishment, whereas larger-seeded or transplanted crops may better tolerate the residue-mediated changes in the chemical, biological, and physical properties of the soil surface environment. Evidence from no-till systems further support the hypothesis that changes in soil surface conditions may regulate the abundance of “safe sites” for weed establishment, thereby modulating the size of the effective seedbank.

Distance-based redundancy analysis (db-RDA), a recently developed ordination technique useful for both multivariate hypothesis testing and data interpretation, was used to evaluate treatment effects on weed communities in a long-term study of alternative potato cropping systems. The experiment consisted of a factorial arrangement of three pest management systems, conventional (CON), reduced input (RI), and biointensive (BIO), two soil management systems (amended vs. unamended), and two crop-rotation entry points. Soil samples collected in the spring of 1998 were subjected to exhaustive germination as a means of characterizing the weed community. Using partial ordinations, each factor in the factorial treatment structure was tested separately, revealing a significant interaction between pest and soil management systems. An ordination diagram of the pest by soil management interaction was used to interpret the results. Weed species that were highly correlated with the first two ordination axes included: common lambsquarters, broadleaf plantain, oakleaf goosefoot, common hempnettle and a complex of the Brassicaceae that included wild mustard, birdsrape mustard, and wild radish. Univariate analyses confirmed the response of these species to the factors examined. The BIO pest management system showed a different response to soil amendments than the other systems. Soil amendments caused an increase in the total weed density in the CON and RI systems, but caused a decrease in the BIO system. Given the need for better multivariate hypothesis testing and data interpretation in many types of weed science research, the use of db-RDA is expected to grow.

Effective in-season weed management options are limited for organic cereal farmers. Two alternatives to current farmer practices are improving efficacy of physical weed control through use of interrow cultivation or increasing the competitive ability of the crop through elevated seeding rates and more uniform spatial planting patterns. It is unknown how these two methods affect yield, quality, and economic returns. Field experiments were conducted in the northeast United States to determine whether the yield gain from increased weed control from these contrasting weed management strategies resulted in increased net returns and how these different systems affected grain quality. Wheat was planted at two seeding rates (400 and 600 plants m−2), in three row spacings (11, 18, and 23 cm). A fourth crop arrangement that approaches a more uniform spatial distribution through a combination of drilling and broadcasting seed was included. For weed control, treatments received tine harrowing. Wheat sown in wide rows also received interrow cultivation. Each system was sown in the presence and absence of condiment mustard, which was sown as a surrogate weed. Increased seeding rate reduced weed density 64% compared to a crop-free check and 30% compared to regional farmers' practices of 18-cm rows and 400 plants m−2. Increased seeding rates lowered grain protein 5% compared to standard seeding rates. Wide rows, in combination with interrow cultivation, reduced weed density 62%, increased yield 16%, and net returns 19% compared to regional organic practices. Significant increases in grain N were limited to weed-free plots. While increased seeding rates improved weed suppression, the high input cost of organic seed make this an unsatisfactory alternative to interrow cultivation and current farmer practices, as yield would need to be. 15 t ha−1 higher at elevated density to offset the extra cost of seed.

Cover crop systems were investigated in 2004 and 2005 for their effects on the activity-density (a function of movement and density) of a promising group of weed biocontrol organisms, the ground beetles collectively known as carabids, with particular emphasis on a beneficial carabid species Harpalus rufipes DeGeer. Marked H. rufipes released into pea/oat–rye/vetch cover crop plots were more than twice as likely to be recaptured within the same plots as beetles released in nonvegetated fallow plots (18 and 8%, respectively). Marked beetles released into fallow plots were more than twice as likely to leave their plots and be recaptured in pea/oat–rye/vetch plots as vice versa (13 vs. 5%), indicating a clear preference for habitat with vegetative cover. Overall recapture rates were not different between treatments. Unmarked H. rufipes activity-density was also higher in pea/oat–rye/vetch compared to fallow plots. Additionally, five cover crop systems, including the fallow and pea/oat–rye/vetch treatments, and two residue management methods (conventional and zone tillage) were investigated from June to August in 2005 for their effects on H. rufipes activity-density. Corn was planted in 2005 into residues of the five cover crop systems grown in 2004. H. rufipes activity-density was higher in zone and conventionally tilled corn planted in pea/oat–rye/vetch residues and conventionally tilled corn planted in red clover/oat residues than in any other cover crop and residue management combination. Pea/oat–rye/vetch cover crop systems are apparently beneficial for H. rufipes during the cover crop year as well as in subsequent crops planted into this cover crop's residues. This system was not the least disturbed system but, based on the number of tillage events, represented a medium level of disturbance among the various systems. Thus, some level of disturbance might be beneficial for H. rufipes, but how and when that soil disturbance occurs requires further research to determine the best means of conserving this species.

Legume green manures have been used for millennia as sources of N for succeeding crops, but they are also sources of phytotoxic compounds that may selectively influence the performance of crop and weed species. To determine whether substitution of legume green manure for synthetic N fertilizer could enhance crop yield while suppressing weed growth, we conducted a field experiment in which common bean and wild mustard were sown in monocultures and mixtures. Three soil management treatments were employed: red clover residue, ammonium nitrate fertilizer (84 kg N ha−1), and a control that received neither red clover nor ammonium nitrate. In the absence of wild mustard, bean seed yield was equivalent in the red clover and ammonium nitrate treatments, where yields were 11 to 26% greater, respectively, than in the control. When bean grew in competition with wild mustard, its seed yield was as high (1995 and 1996) or higher (1994) with red clover residue than with ammonium nitrate. Averaged over bean competition treatments, wild mustard biomass production was 37% lower with red clover residue than with ammonium nitrate in 1994, 53% lower in 1995, and equivalent in these two treatments in 1996. Bean seed yield and wild mustard biomass production were strongly correlated with whole-plant N content and more weakly correlated with leaf area duration. Of the variation observed in wild mustard seed production, 89 to 93% was predicted by the variation in wild mustard biomass. The results of this study indicate that substitution of red clover green manure for ammonium nitrate fertilizer can be compatible with bean production goals and can contribute to the management of wild mustard.

Two broad aims drive weed science research: improved management and improvedunderstanding of weed biology and ecology. In recent years, agriculturalweed research addressing these two aims has effectively split into separatesubdisciplines despite repeated calls for greater integration. Although someexcellent work is being done, agricultural weed research has developed avery high level of repetitiveness, a preponderance of purely descriptivestudies, and has failed to clearly articulate novel hypotheses linked toestablished bodies of ecological and evolutionary theory. In contrast,invasive plant research attracts a diverse cadre of nonweed scientists usinginvasions to explore broader and more integrated biological questionsgrounded in theory. We propose that although studies focused on weedmanagement remain vitally important, agricultural weed research wouldbenefit from deeper theoretical justification, a broader vision, andincreased collaboration across diverse disciplines. To initiate change inthis direction, we call for more emphasis on interdisciplinary training forweed scientists, and for focused workshops and working groups to developspecific areas of research and promote interactions among weed scientistsand with the wider scientific community.

The rapid expansion of the plant bioeconomy is creating strong economic incentives to distribute novel plant material, including transgenic cultivars, exotic species, and species that were formerly constrained to small geographical areas, at large geographical scales. Such introductions carry with them the risk of invasive spread of the introduced species (Simberloff and Alexander 1998). Deployment of plant species for biofuel production offers a clear example of the benefits and risks associated with the new bioeconomy (Raghu et al. 2006).

In a measure aimed at reducing U.S. dependence upon foreign petroleum reserves for energy production, President Bush announced the Advanced Energy Initiative (AEI) in his 2006 State of the Union address. This initiative provides federal funding and guidelines for the development of renewable energy sources, including plant biofuels. The objectives of the AEI, though admirable, have the potential to create a conflict with Executive Order 13112, which states that “[Federal agencies shall] not authorize, fund, or carry out actions that it believes are likely to cause or promote the introduction or spread of invasive species in the United States or elsewhere unless, pursuant to guidelines that it has prescribed, the agency has determined and made public its determination that the benefits of such actions clearly outweigh the potential harm caused by invasive species; and that all feasible and prudent measures to minimize risk of harm will be taken in conjunction with the actions.”