Johnsongrass [Sorghum halepense (L.) Pers.] is one of the most problematic perennial grass weed species in row-crop production across the southern United States. Control of this species is especially challenging in organic systems due to a lack of effective options. A field experiment was conducted at the Texas A&M research farm near College Station, TX, from fall 2019 to spring 2021 to evaluate various nonchemical options for managing S. halepense in the fallow season, implemented over 2 yr in the same locations. The treatments included disking once, disking twice, disking + immediate flooding, disking + flush irrigation + flooding, disking twice + flooding after the first frost, periodic mowing, acetic acid treatment, and disking + tarping. Disking + immediate flooding, disking + flush irrigation + flooding, and disking + tarping were the most effective treatments. Compared with the nontreated control plots, these treatments reduced S. halepense aboveground density (<9 plants m−2 vs. 64 plants m−2), aboveground biomass (<80 g m−2 vs. 935 g m−2), rhizome biomass (<4 g m−2 vs. 55 g m−2), rhizome node number (<25 nodes m−2 vs. 316 nodes m−2), and rhizome length (<42 cm m−2 vs. 660 cm m−2). Disking twice + flooding after the first frost did not show a consistent impact. Periodic mowing also reduced S. halepense density (12 plants m−2 vs. 64 plants m−2) and other variables compared with the control plots at the end of the study in spring 2021. Disking alone once or twice each growing season or repeated application of acetic acid failed to control S. halepense. These results indicate that well-timed nonchemical management practices such as tarping and flooding implemented during the winter fallow can be very effective in reducing S. halepense densities.

Several species of Echinochloa P. Beauv., introduced at multiple events, have established themselves as a persistent concern for U.S. rice production. In this review, we highlight the key biological characteristics of economically relevant Echinochloa in U.S. rice production, revisit their historical trajectory, and suggest research directions for their management with special reference to barnyardgrass. Ecologically differentiated Echinochloa species have a distinct association with rice culture methods that have been practiced for the last few decades, barnyardgrass being historically predominant in drill-seeded rice in the mid-South, and early watergrass and late watergrass in water-seeded California rice. However, the emerging evidence challenges the dogma that other Echinochloa species for specific regions are of less importance. Primarily managed by the water-seeding method of rice culture in the early years of the 20th century, Echinochloa species have persisted in the sophisticated U.S. rice culture through the evolution of resistance to herbicides in recent decades. Accumulating knowledge, including those of recent genomic insights, suggests the rapid adaptability of Echinochloa. The last decade has seen a (re)emergence of nonchemical methods as a key component of sustainable management, among which use of harvest weed seed control (HWSC) methods and cover crops in the mid-South and stale-drill seeding in California are being considered as potential methods for managing Echinochloa. In recent years, furrow-irrigated rice has rapidly supplanted a significant proportion of conventionally flooded rice in the mid-South, whereas the propensity for compromised continuous submergence is increasing in California rice. On the cusp of this shift, the question at the forefront is how this will affect Echinochloa interference in rice and how this change will dictate the management efforts. Future research will lead to the development of a clear understanding of the impact of the changing agroecosystems on Echinochloa species and their response to the prospective integrated control interventions.

Ornamental jewelweed (Impatiens glandulifera Royle) is an alien invasive plant in Europe. This annual plant often grows in riparian habitats where herbicides are prohibited. Several studies have reported the negative effect on ecosystem and ecosystem services by this species. However, limited research is published on control measures and the aim of our study was to explore use of hot water and cutting to control I. glandulifera. A lab experiment showed that the lethal water temperature for seed was between 45 and 50 C. In a pot experiment with seeds in soil, emergence of I. glandulifera was reduced by 78% and 93% compared with the untreated control with volumes of hot water (80 C) of 7.2 and 14.5 L m−2, respectively. When treatments were conducted on relatively tall plants (almost 60 cm) in late June, hot water gave significantly better control than cutting. Compared with an untreated control, I. glandulifera cover was reduced by 97% and 79% after hot water and cutting, respectively. Application of hot water to smaller (<40 cm) and less developed plants (BBCH 12–13) in early June and cutting of plants with visible flower buds (mid-July) led to no significant difference in cover. Compared with an untreated control, I. glandulifera cover was reduced by 99% (cut below first node) and 91% (hot water and cut above first node). When relatively tall plants (almost 60 cm) were treated, hot water use was high (31.1 L m−2) and required twice as many work hours (4.8 min m−2) as cutting (2.4 min m−2). When smaller plants (<40 cm) were targeted, work hours and hot water use were reduced to 2.1 min m−2 and 13.7 L m−2, respectively.

A field study was conducted for the 2014 and 2015 growing season in Arkansas, Indiana, Illinois, Missouri, Ohio, and Tennessee to determine the effect of cereal rye and either oats, radish, or annual ryegrass on the control of Amaranthus spp. when integrated with comprehensive herbicide programs in glyphosate-resistant and glufosinate-resistant soybean. Amaranthus species included redroot pigweed, waterhemp, and Palmer amaranth. The two herbicide programs included were: a PRE residual herbicide followed by POST application of foliar and residual herbicide (PRE/POST); or PRE residual herbicide followed by POST application of foliar and residual herbicide, followed by another POST application of residual herbicide (PRE/POST/POST). Control was not affected by type of soybean resistance trait. At the end of the season, herbicides controlled 100 and 96% of the redroot pigweed and Palmer amaranth, respectively, versus 49 and 29% in the absence of herbicides, averaged over sites and other factors. The PRE/POST and PRE/POST/POST herbicide treatments controlled 83 and 90% of waterhemp at the end of the season, respectively, versus 14% without herbicide. Cover crop treatments affected control of waterhemp and Palmer amaranth and soybean yield, only in the absence of herbicides. The rye cover crop consistently reduced Amaranthus spp. density in the absence of herbicides compared to no cover treatment.

Treerow vegetation abundance and biodiversity were measured in response to six orchard floor management strategies in organic peach in northern Utah for three growing seasons. A total of 32 weed species were observed in the treerow; the most common were field bindweed, dandelion, perennial grasses (e.g., red fescue and ryegrass), clovers, and prickly lettuce. Weed biomass was two to five times greater in unmanaged (living mulch) than in manipulated treatments. Tillage greatly reduced weeds for approximately one month; however, vegetation rebounded midseason. Tillage selected for species adapted to disturbance, such as common purslane and field bindweed. Straw mulch provided equivalent weed suppression to tillage in the early season. Straw required annual reapplication with material costs, labor, and weed-seed contamination (e.g., volunteer grains and quackgrass) as disadvantages. Plastic fabric mulch reduced weeds the most, but had high initial costs and required seasonal maintenance. Weed biomass declined within seasons and across the three years of the study, likely due to tree canopy shading. Neither birdsfoot trefoil nor a perennial grass mixture planted in the alleyways influenced treerow weeds. Our results demonstrate several viable alternatives to tillage for weed management in treerows of organic peach orchards in the Intermountain West.

Effects of nonchemical weed control on weed and seedbank demography in ridge-tilled fields were simulated to examine long-term effects on weed population dynamics. Ridge tillage entails active seedbank management, including removal of much of the seedbank from the crop growth zone (ridge) to the interridge zone (furrow) at planting, and other seedbank manipulations. Dynamics of simulated yellow foxtail and velvetleaf populations were sharply sensitive to the rate of seed removal from the ridge. Variation in winter seed survival, ridge plant demography (emergence, survival, and seed production), and seed survival in the furrow after removal from the ridge also had strong effects on simulated dynamics. To prevent rapid population growth in a simulated corn-soybean rotation, very effective control of seedlings emerging with each crop was necessary to offset seed production from seedlings emerging after ridge rebuilding in corn years. Dynamics of both species were highly sensitive to cultivation efficiency. Effective “rescue” weed control must be available to prevent sharp increases in weed seedbanks during years when cultivation is ineffective.

Cover crop residues are not widely used for weed control because, as a stand-alone tactic, they do not effectively suppress all weeds and their duration of weed control is too short. Field experiments were conducted in 1995 and 1996, under both irrigated and rainfed conditions, to quantify Amaranthus spp., Setaria spp., and soybean emergence and growth in residues of fall-planted, spring-killed barley, rye, triticale, wheat, and hairy vetch. For both weed species, seedling emergence was reduced 3 wk after soybean planting by rye and wheat residues (≥ 2, 170 kg ha−1) in 1996. In 1996, Amaranthus spp. canopy volume was reduced 38 to 71% by residues 3 wk after planting. Likewise, Setaria spp. canopy biomass was reduced 37 to 97% in residues 5 wk after planting over both years. The response comparison index was used to identify frequency by which weed growth was placed at a disadvantage relative to soybean growth. Amaranthus spp. and Setaria spp. growth suppressions 3 to 5 wk after planting indicate potential times for intervention with other integrated weed management tactics such as reduced postemergence herbicide rates and interrow cultivation.

Field experiments were conducted at Vegreville, Alberta, in 1990, 1991, and 1992 to investigate the influence of canola plant density and row spacing (1991 and 1992 only) on interference from Tartary buckwheat. Nonlinear regression equations incorporating both canola and Tartary buckwheat density provided good descriptions of the data. Parameter estimates for both weed and crop density were significant (P < 0.05) but did not differ between row spacings. Where no Tartary buckwheat plants were present, canola yield was little affected by canola plant density. At a given Tartary buckwheat density, canola seed yield increased as canola plant density increased, while Tartary buckwheat shoot weight and seed yield decreased. None of the factors significantly affected canola 1000-seed weight, or oil or protein levels in the canola seed. The results suggest that seeding canola to achieve a density of approximately 200 plants m–2 will significantly reduce the impact of weeds on canola yield, as well as reduce weed biomass and seed yield.

Soybean varieties ‘Ripley’ (semidwarf determinate group IV) and ‘Douglas' (indeterminate group IV) were compared in an interference experiment with common cocklebur. A path analysis model was used to independently estimate interference effects of soybean density on common cocklebur growth and stem diameter, and interference responses of soybean density and seed production to common cocklebur size. Path analysis identified an early period of interference between soybean and common cocklebur, from 40 to 62 d after planting, and a late period, from 63 to 145 d after planting. Late interference measures were independent of early measures, since effects of early interference were statistically removed from estimates of late interference. The semidwarf determinate variety Ripley had early interference effects on common cocklebur 5.3 and 9.5 times greater than those of Douglas in 1987 and 1988, respectively. The Douglas variety had a stronger late interference effect on common cocklebur than Ripley. Soybean varieties were similar in response to common cocklebur interference. Path analysis of crop-weed interference may be useful in breeding crop varieties that suppress weed growth and thus require fewer weed control inputs.

An experiment was conducted on a specially designed hard surface to study the impact of time interval between flaming treatments on the regrowth and flower production of two grass weeds. The goal of this experiment was to optimize the control of annual bluegrass and perennial ryegrass, both species that are very difficult to control without herbicides. Aboveground biomass from 72 plants per treatment was harvested and dry weights were recorded at regular intervals to investigate how the plants responded to flaming. Regrowth of the grasses was measured by harvesting aboveground biomass 2 wk after the second flaming treatments that were implemented at different time intervals. Flaming treatments decreased plant biomass of both species and also the ratio of flowering annual bluegrass plants. However, few plants were killed. The first flaming treatment affected aboveground biomass more than the second flaming treatment. A treatment interval of 7 d provided the greatest reduction in regrowth of perennial ryegrass, whereas the effect of treatment interval varied between the first and second repetitions of this experiment for annual bluegrass. In general, short treatment intervals (3 d) should be avoided, as they did not increase the reduction of aboveground biomass compared with the 7-d treatment interval. Knowledge on the regrowth of grass weeds after flaming treatments provided by this study can help improve recommendations given to road keepers and park managers for management on these weeds.

In recent years, increasing implementation of biological, cultural, and mechanical weed-control methods is desired; however, many of these techniques are not viable in established turfgrass systems. The use of freezing or frost for weed control has previously been researched; however, is not well elucidated. Field and greenhouse experiments were conducted to evaluate liquid carbon dioxide (LCD) for weed control in established turfgrass systems. LCD was applied with handheld prototypes that were modified to reduce the amount of LCD required for weed control. Common annual and perennial turfgrass weeds included common chickweed, corn speedwell, goosegrass, large crabgrass, smooth crabgrass, Virginia buttonweed, and white clover. Turfgrass tolerance was evaluated on the following species: hybrid bermudagrass, Kentucky bluegrass, tall fescue, and zoysiagrass. The final modification allowed for lower output (0.5 kg LCD min−1) when compared with the initial prototype (3 kg LCD min−1). In general, weed control increased as LCD increased. When comparing weed species life cycles, annuals were controlled more than perennials (P < 0.0001) at 14 and 28 d after treatment (DAT). Further, exposure time affected control as white clover, Virginia buttonweed, and large crabgrass control was greater (18, 14, 15%, respectively) from the longer exposure time (30 vs. 15 s), although equivalent amounts of LCD (30 kg m−2) were applied. These data also suggest that plant maturity affects control, as large crabgrass control in one- to two- and three- to four-leaf stages (> 90%) was greater than in the one- to two-tiller stage (< 70%). Turfgrass injury at 7 DAT was unacceptable (> 30%) on all species, but declined to 0% by 28 DAT. These data suggest that LCD has the potential to provide an alternative for weed control of select species where synthetic herbicides are not allowed or desired.

Most farmers now rely on herbicides and, to a lesser extent, cultivation to control weeds in Glycine max in the Midwest. However, the general public is concerned that widely used herbicides will contaminate surface and groundwater. Alternative ways to control weeds in field crops are needed to reduce or prevent herbicide contamination of surface and groundwater. A new between-row-mowing weed management system that consists of band-applied herbicides over crop rows + two or more between-row mowings was tested in G. max over 6 yr in Missouri. Mowing weeds close to the soil surface two or more times between crop rows killed or suppressed annual grass and broadleaf weeds, chiefly Setaria faberi, Ambrosia artemisiifolia, and Amaranthus spp., if properly timed. Shading by crop canopy closure contributed to weed suppression in this weed management system. G. max yield also could not be distinguished from weed-free check plots and was greater than the weedy check plots. Herbicide use was reduced 50% by banding because only 50% of the field area was sprayed. The between-row-mowing weed management system may have use in environmentally sensitive areas to help reduce soil erosion or water contamination by herbicides.

Flaming can be an effective nonselective, nonchemical method of weed control. It has been more effective against broadleaf weeds than grasses. Experiments were conducted with a conveyor bench burner apparatus to evaluate flaming to kill broadleaf and grass seedlings at the 0- to 2- and 2- to 4-leaf stages. Most 0- to 2-leaf green foxtail seedlings were killed when flamed at 2, 4, and 6 km/h conveyor speed. A few plants survived when flamed at 8 km/h. Green foxtail seedlings at the 2- to 4-leaf stage were more tolerant to flaming than 0- to 2-leaf green foxtail, and substantial numbers of plants survived at all flaming speeds except 2 km/h. Barnyardgrass was more tolerant to flaming than green foxtail, and many 0- to 2- and 2- to 4-leaf seedlings survived after flaming. However, fresh weight of the live plants at 14 d after treatment was reduced. Some large crabgrass plants survived flaming at both growth stages. Flaming at 2 km/h reduced seedling number and fresh weight, but there was significant regrowth. Common ragweed was more susceptible to flaming at the 2- to 4-leaf stage than at the 0- to 2-leaf stage. Redroot pigweed and common lambsquarters were susceptible to flaming at both 0- to 2- and 2- to 4-leaf stages.

Propane flaming could be an effective alternative tool for weed control in organic cropping systems. However, response of major weeds to broadcast flaming must be determined to optimize its proper use. Therefore, field experiments were conducted at the Haskell Agricultural Laboratory, Concord, NE in 2007 and 2008 using six propane doses and four weed species, including green foxtail, yellow foxtail, redroot pigweed, and common waterhemp. Our objective was to describe dose–response curves for weed control with propane. Propane flaming response was evaluated at three different growth stages for each weed species. The propane doses were 0, 12, 31, 50, 68, and 87 kg ha−1. Flaming treatments were applied utilizing a custom-built flamer mounted on a four-wheeler (all-terrain vehicle) moving at a constant speed of 6.4 km h−1. The response of the weed species to propane flaming was evaluated in terms of visual ratings of weed control and dry matter recorded at 14 d after treatment. Weed species response to propane doses were described by log-logistic models relating propane dose to visual ratings or plant dry matter. Overall, response of the weed species to propane flaming varied among species, growth stages, and propane dose. In general, foxtail species were more tolerant than pigweed species. For example, about 85 and 86 kg ha−1 were the calculated doses needed for 90% dry matter reduction in five-leaf green foxtail and four-leaf yellow foxtail compared with significantly lower doses of 68 and 46 kg ha−1 of propane for five-leaf redroot pigweed and common waterhemp, respectively. About 90% dry matter reduction in pigweed species was achieved with propane dose ranging from 40 to 80 kg ha−1, depending on the growth stage when flaming was conducted. A similar dose of 40 to 60 kg ha−1 provided 80% reduction in dry matter for both foxtail species when flaming was done at their vegetative growth stage. However, none of the doses we tested could provide 90% dry matter reduction in foxtail species at flowering stage. It is important to note that foxtail species started regrowing 2 to 3 wk after flaming. Broadcast flaming has potential for control or suppression of weeds in organic farming.

In previous research, use of PRE soil residual herbicides was reduced 50% in no-till corn and soybean by banding herbicides over crop rows followed by mowing weeds growing between rows two times. The research goals were (1) to determine whether such between-row mowing systems adequately controlled weeds and prevented grain yield loss in other competitive field crops, such as no-till grain sorghum, and (2) to compare broadcast herbicide treatments with between-row mowing systems. PRE atrazine plus dimethenamid at relative rates of 0.75× and 1× (where 1× = 1.7 plus 1.3 kg ai/ha, respectively) were band-applied over rows shortly after planting followed by two between-row mowings close to the soil surface. In 2 of 3 yr in Missouri, this system controlled giant foxtail and common waterhemp as well as broadcast herbicides in no-till sorghum. In 2 of 3 yr, between-row mowing systems also prevented yield loss in no-till sorghum as well as both broadcast herbicides at the same rates and the weed-free check.

In previous research, summer annual weeds were successfully controlled in no-till corn with between-row mowing systems that consisted of soil-residual preemergence herbicides banded over corn rows followed by mowing weeds close to the soil surface one or two times later during the growing season. The objective of this research was to determine whether between-row mowing systems could successfully control both winter annual and summer annual weeds as well as broadcast herbicides perform in no-till corn. In two of three years in Missouri, between-row mowing systems controlled and reduced both winter annual and summer annual weed cover and prevented weeds from reducing corn yields. Corn yields for the following no-till weed management systems equaled the weed-free check: winter annual weed control with between-row mowing plus preplant, banded, postemergence-applied glyphosate at 1.1 kg ae/ha and later summer annual weed control with postplant, banded, preemergence-applied atrazine plus S-metolachlor at 2.2 plus 1.8 kg ai/ha followed by between-row mowing. Winter annual weeds growing between rows were controlled with one mowing, and later summer annual weeds were controlled with either one late or “middle” mowing or two mowings (i.e., early and late). Total herbicide use was reduced 50% (i.e., 25 and 25%, respectively) in no-till corn. Commercially acceptable corn stands were needed for between-row mowing systems to adequately control weeds. In one of three years when corn stands were half of those of the other two years, broadcast herbicides performed better than between-row mowing systems in no-till corn.

Cover crops are becoming increasingly common in cotton as a result of glyphosate-resistant Palmer amaranth; hence, a field experiment was conducted in 2009 and 2010 in Marianna, AR, with a rye cover crop used to determine its effects on the critical period for weed control in cotton. Throughout most of the growing season, weed biomass in the presence of a rye cover crop was lesser than that in the absence of a rye cover crop. In 2009, in weeks 2 through 7 after planting, weed biomass was reduced at least twofold in the presence of a rye cover compared with the absence of rye. In 2009, in both presence and absence of a rye cover crop, weed removal needed to begin before weed biomass was 150 g m−2, or approximately 4 wk after planting, to prevent yield loss > 5%. Weed density was less in 2010 than in 2009, so weed removal was not required until 7 wk after planting, at which point weed biomass values were 175 and 385 g m−2 in the presence and absence of a cover crop, respectively.

Potato producers rely heavily on herbicides for the majority of weed control. However, recent occurrences of herbicide-resistant weed populations and the lack of new herbicide registrations have stimulated interest in alternative strategies. The choice of potato cultivars that can suppress or tolerate weed competition could be a component of an integrated weed management system to reduce reliance on herbicides. The competitive ability of 10 potato cultivars—‘Atlantic’, ‘Bannock Russet’, ‘Dark Red Norland’, ‘Goldrush’, ‘Rodeo’, ‘Russet Burbank’, ‘Russet Norkotah’, ‘Snowden’, ‘Superior’, and ‘Villetta Rose’—was evaluated in 2006 and 2007 in Hancock, WI. Weed competition treatments included (1) weedy throughout the season, (2) weed-free from emergence to 4 wk after emergence (WAE) by hand-weeding, and (3) weed-free by hand-weeding for the entire season. Potato cultivars did not differ in ability to reduce weed biomass. Early-season time of potato emergence and canopy closure, as well as weed competition treatments, were strongly related to potato tuber yield. In general, Bannock Russet yield relative to weed-free controls of the same cultivar was less than that of most other cultivars. Overall, Atlantic, Russet Burbank, Snowden, and Superior yields (relative to weed-free control yields) usually were greater than the yields of other cultivars under weedy conditions. Although the ability to suppress weeds was similar among cultivars, differences in yield among cultivars grown in the presence of weeds suggest differential tolerances of weed competition.

Propane flaming could be an alternative tool for PRE control or suppression of early-emerging weeds in organic and conventional crops. The objective of this study was to test the tolerance of selected early-season weeds to broadcast flaming in no-till systems. Four winter annuals (tansy mustard, henbit, cutleaf evening primrose, and field pennycress), one summer annual (common lambsquarters), and one perennial (dandelion) species were included in the study. Except for dandelion, the response to propane flaming was evaluated at two growth stages. Flaming treatments were applied using an all-terrain-vehicle-mounted flamer moving 4.8 km h−1, and propane pressure was adjusted to deliver doses of 0 (nonflamed control), 22, 34, 48, 67, and 90 kg ha−1. The response of each species to propane doses was described by log-logistic models based on visual ratings of weed control and dry matter reduction. Response to broadcast flaming varied among species and growth stages. Common lambsquarters, tansy mustard, and henbit were more susceptible to flaming than cutleaf evening primrose, field pennycress, and dandelion. On the basis of visual ratings, propane doses between 54 and 62 kg ha−1 effectively controlled (90% control) common lambsquarters at the early growth stage (five-leaf), tansy mustard at both growth stages (nine-leaf and flowering), and henbit (flowering). However, a higher propane dose (> 80 kg ha−1) was necessary to obtain 90% control of common lambsquarters in later growth stage (11-leaf) and early growth stage of henbit (nine-leaf). Cutleaf evening primrose, field pennycress, and dandelion exhibited higher levels of tolerance to broadcast flaming. A 90% control of these species was not achieved even with the highest propane dose (90 kg ha−1) utilized in the study. Results of this study indicate that a single application of broadcast flaming can be an effective tool for controlling tansy mustard, henbit, and common lambsquarters and temporary suppression of cutleaf evening primrose, field pennycress, and dandelion.

Research was conducted to determine the minimum number of between-row mowings necessary to control annual weeds, chiefly giant foxtail and common waterhemp, without corn yield loss. Over 2 yr in Missouri, the between-row mowing systems that were evaluated consisted of a 38-cm band of PRE atrazine plus metolachlor at 2.2 plus 2.2 kg ai/ha applied over corn grown in 76-cm rows shortly after planting followed by one, two, or three between-row mowings close to the soil surface. Based on rated total weed control, between-row total weed cover, and corn yield, the weed-free check was statistically indistinguishable from a treatment in which banded PRE herbicide was followed by only one between-row mowing, late, when weeds were relatively large. When mowed once at 52 to 64 days after planting (DAP), giant foxtail and common waterhemp were greater than 85 cm tall. The yield was not increased by mowing earlier or more than once.