Cover crops are becoming an increasingly important tool for weed suppression. Biomass production in cover crops is one of the most important predictors of weed suppressive ability. A significant challenge for growers is that cover crop growth can be patchy within fields, making biomass estimation difficult. This study tested ground-based structure-from-motion (SfM) for estimating and mapping cereal rye (Secale cereale L.) biomass. SfM generated 3D point clouds from red, green, and blue (RGB) videos collected by a handheld GoPro camera over five fields in North Carolina during the 2022 to 2023 winter season. A model for predicting biomass was generated by relating measured biomass at termination using a density–height index (DH) from point cloud pixel density multiplied by crop height. Overall biomass ranged from 320 to 9,200 kg ha−1, and crop height ranged from 10 to 120 cm. Measured biomass at termination was linearly related to DH (r2 = 0.813) through levels of 9,000 kg ha−1. Based on independent data validation, predicted biomass and measured biomass were linearly related (r2 = 0.713). In the field maps generated by kriging, measured biomass data were autocorrelated at a range of 5.4 to 42.2 m, and predicted biomass data were autocorrelated at a range of 3.4 to 12.0 m. However, the spatial arrangement of high- and low-performing areas was similar for predicted and measured biomass, particularly in fields with greatest patchiness and spatial correlation in biomass values. This study provides proof-of-concept that ground-based SfM can potentially be used to nondestructively estimate and map cover crop biomass production and identify low-performing areas at higher risk for weed pressure and escapes.

Cover crops are important in organic arable cropping systems because they improve soil fertility and suppress annual weeds in the post-harvest period (the period between cash crops), but their effectiveness against perennial weeds is less clear. This study analyzed outbreaks of perennial weeds in two long-term organic crop rotations with and without cover crops in the period 2011–2022 in Denmark. In addition, the impact of including forage plantain (Plantago lanceolata) in cover crop mixtures on the growth of perennial weeds was studied from 2020 to 2022. P. lanceolata is known to contain secondary metabolites that inhibit nitrification and may influence nitrogen (N) availability. This study found that cover crops did not hinder outbreaks of Cirsium arvense, Sonchus arvensis, Elytrigia repens or other perennial weed species. E. repens actually proliferated more with cover crops whose presence prevented repeated mechanical post-harvest interventions. The crop rotation involving regular cutting of a one-year or two-year green manure crop provided the best management of perennial weeds if repeated post-harvest soil cultivation was also conducted. This could only be done in the absence of cover crops. Mixing P. lanceolata into the cover crop mixtures did not change the outcome of competition between cover crops and perennial weeds in the period between crop harvest in August and November. Instead, P. lanceolata significantly reduced the number of shoots emerging from perennial weeds in the subsequent growing season. The causality of this effect was not further elaborated in the study.

Cereal rye (Secale cereale L.) as a cover crop can be an effective nonchemical tool for waterhemp [Amaranthus tuberculatus (Moq.) Sauer] suppression in crop production. Previous studies have evaluated A. tuberculatus suppression by cereal rye as part of weed management programs but have not investigated the underlying mechanism of suppression by the cover crop. This study aimed to investigate the effect of cereal rye biomass on A. tuberculatus emergence and development, and on soil environmental parameters (temperature, moisture, and light transmittance) that are key triggers of A. tuberculatus germination to elucidate the mechanism of suppression by the cover crop. A dose–response study was conducted under field conditions in Brooklyn and Janesville, WI, from 2021 to 2023. Cereal rye biomass from a fall-planted field was harvested at anthesis in the spring and dried to constant weight at 60 C to provide 0.0, 0.6, 1.2, 2.4, 4.8, 7.2, 9.6, and 12.0 Mg ha−1 of dry biomass that was evenly distributed over 1.9 m−2 plots. Increasing cereal rye biomass reduced A. tuberculatus height, biomass, and density. An average ED50 of 5.2 Mg ha−1 of biomass was needed to reduce A. tuberculatus density by 50%. Low levels of biomass (≤2.38 Mg ha−1) augmented A. tuberculatus density due to an increase in soil moisture underneath the mulch compared with bare soil. Cereal rye biomass decreased the amount of sunlight reaching the soil, which resulted in lower mean soil temperature and temperature amplitude throughout the day (9.3 and 2.7 C temperature amplitude at 0 and 12.0 Mg ha−1, respectively). Prevention of A. tuberculatus germination by this thermal effect is likely the main mechanism of A. tuberculatus suppression from the cereal rye cover crop. Our results support biomass from cereal rye cover crop effectively suppressing A. tuberculatus and contributing to the integrated management of A. tuberculatus.

Narrow row spacing (<76 cm) could improve crop competitiveness, suppress weeds and might provide yield advantage. Many studies have been conducted to evaluate the impact of narrow row spacing; however, no quantitative synthesis of these studies exists. The objectives of this meta-analysis were to (1) quantify the overall effect of narrow row spacing (<76 cm) on weed density, biomass, control, weed seed production, and yield in corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] compared with 76-cm row spacing, and (2) assess the influence of agronomic management decisions (tillage type, weed management, herbicide application frequency and time) on effect of narrow row spacing on weed suppression and corn and soybean yield. We compiled 1,904 pair-wise observations from 35 studies conducted in 12 states in the United States during 1961 to 2018. Averaged across individual observations, narrow row spacing suppressed weed density by 34%, weed biomass by 55%, and weed seed production by 45%, while it improved weed control by 32% and crop yield by 11% compared with 76-cm row spacing. Narrow row spacing in soybean suppressed weed density by 42%, weed biomass by 71%, and increased crop yield by 12% compared with 76-cm row spacing. Although narrow row spacing had a nonsignificant effect on response variables in corn, the number of studies (n = 1 to 6) and observations (n = 1 to 59) addressing each response variable were limited. Tillage type (conventional and reduced) did not influence the response of weed density, control, and seed production in narrow row spacing; however, weed biomass and weed seed production were more greatly reduced with the sequential application of herbicides compared with a single application. Thus, narrow row spacing in soybean can be integrated with other options for management of herbicide-resistant weeds.

Growers have been experimenting with cover crop termination timings to maximize weed suppression and potentially reduce herbicide inputs in soybean [Glycine max (L.) Merr.]. A field study was replicated three times from 2018 through 2021 in South Charleston, OH, to evaluate different management strategies involving a cereal rye (Secale cereale L.) cover crop. The objectives were to determine the effects of cereal rye seeding rate (0, 50, and 100 kg ha−1), management program (preplant, postplant, and delayed), and soybean residual herbicide (flumioxazin + chlorimuron ethyl and no herbicide) on cover crop, weed, and soybean parameters. The preplant program consisted of cereal rye terminated 7 d before planting (DBP) + a postemergence application. The postplant program consisted of cereal rye terminated 7 d after planting (DAP) + a postemergence application. In the delayed program, saflufenacil was applied in April and cereal rye was terminated 21 DAP, and there was no postemergence application. Giant foxtail (Setaria faberi Herrm.) density was reduced by the presence of cereal rye, averaged over other factors, regardless of seeding rate. Cereal rye seeding rate did not affect giant ragweed (Ambrosia trifida L.) density. The delayed management program was generally associated with the lowest weed density, but weed density was often similar in the postplant program. Setaria faberi density was lower in treatments that included a residual herbicide. Residual soybean herbicide use did not affect density of A. trifida. Terminating cereal rye after soybean planting resulted in increased soybean yield in 2019 and reduced yield in 2020, compared with preplant rye termination. These data suggest that adjusting the cereal rye management program may have a greater effect on weed suppression than adjustments to seeding rate. Delaying termination of cereal rye can aid in the suppression of weeds, but a comprehensive herbicide program was necessary to provide adequate (>85%) weed control.

Invasive species control management involves a large amount of plant material. The present work evaluated the allelopathic potential of the invasive species Ulex europaeus L. (Fabaceae) or ‘Gorse’ and its possible use as a bioherbicide, taking advantage of the extracted plant material after control measures, particularly needed in invaded areas. Specifically, we investigated the efficacy of dried plant material from U. europaeus in the control of the adventitious plants, Lolium multiflorum Lam. and Lolium rigidum Gaud., using the Avena sativa L. crop as a case study. We only used vegetative plant parts because it is essential to avoid the dispersion of U. europaeus with its use, especially in invaded areas. A greenhouse pot experiment was conducted, using activated carbon (AC). The target species (L. multiflorum, L. rigidum and A. sativa) were subjected to a mixture of organic substrate with U. europaeus mulch applied pre-emergence and a subsequent application of aqueous extracts from the mulch. Emergence, height and biomass of the target species were determined. After 2 months, we also tested a possible legacy effect of the substrate on the germination of the target species. We noticed a negative effect of U. europaeus mulch on the emergence of L. rigidum, which can be attributable to the allelopathic compounds released from U. europaeus mulch because the effect was non-significant in presence of AC. Conversely, no effect on L. multiflorum or A. sativa was produced by mulch treatments. Nevertheless, the combination of U. europaeus mulch and its extracts demonstrated a phytotoxic effect on the biomass of the crop species A. sativa, and a fertilizing effect on the weeds L. multiflorum and L. rigidum, which is why this use is discouraged. With our results we cannot recommend the use of U. europaeus as a bioherbicide in oat crops, but this study emphasizes the capability of U. europaeus to structure plant communities through the chemic- and bio-properties of its tissues that modifies the soil environment.

Cover crop residue left on the soil surface as organic mulch in no-tillage crop production provides several environmental benefits, including weed suppression. Thus, many farmers who use cover crops attempt to reduce the use of agricultural inputs, especially herbicides. Therefore, our objectives were to study the potential of different cover crop species to suppress weeds and produce an in situ organic mulch and to evaluate the effect of the organic mulch with and without spraying glyphosate on weed suppression for vegetable (tomato [Solanum lycopersicum L.] and broccoli [Brassica oleracea L. var. botrytis]) growth and yield. Five cover crop treatments (sunn hemp [Crotalaria juncea L.], jack bean [Canavalia ensiformis (L.) DC.], pearl millet [Pennisetum glaucum (L.) R. Br.], forage sorghum [Sorghum bicolor (L.) Moench ssp. bicolor], and no cover crop [control]) were used in the main plots; and glyphosate was or was not sprayed on the flattened cover crop in the subplots of this split-plot experimental design. Organic mulch from pearl millet, sorghum, and sunn hemp resulted in lower weed biomass during the early seasons of both tomato and broccoli than mulch from jack bean and no cover crop (control). Spraying glyphosate after roller-crimping reduced weed biomass by 103 g m−2 and 20 g m−2 by 45 and 60 d after transplanting (DATr) of tomato, respectively, and resulted in a better tomato yield compared with not spraying. Glyphosate reduced weed biomass by 110 g m−2 in the early season of broccoli (30 DATr) but did not affect yield. Terminating high-biomass cover crops with a roller-crimper is a promising technique for weed management in vegetable crops that has the potential to reduce or even eliminate the need for herbicide.

With the increasing focus on herbicide-resistant weeds and the lack of introduction of new modes of action, many producers have turned to planting annual cover crops as a method for reducing weed populations. Recent studies have suggested that perennial cover crops such as white clover could be used as living mulch. However, white clover is slow to establish and is susceptible to competition from winter weeds. Therefore, the objective of this study was to determine clover tolerance and weed control in established stands of white clover to several herbicides. Studies were conducted in the fall and winter of 2018 to 2019, and 2019 to 2020, at the J. Phil Campbell Research and Education Center in Watkinsville, GA, and the Southeast Georgia Research and Education Center in Midville, GA. POST applications of imazethapyr, bentazon, or flumetsulam at low and high rates, or in combination with 2,4-D and 2,4-DB, were applied when clover reached the 2- to 3-trifoliate stage. Six weeks after the initial POST application, a sequential application of bentazon and flumetsulam individually, and combinations of 2,4-D, 2,4-DB, and flumetsulam, were applied over designated plots. Clover biomass was similar across all treatments except where it was reduced by sequential applications of 2,4-D + 2,4-DB + flumetsulam in the 2019 to 2020 season, indicating that most treatments were safe for use on establishing living mulch clover. A single application of flumetsulam at the low rate or a single application of 2,4-D + 2,4-DB provided the greatest control of all weed species while minimizing clover injury compared with the nontreated check. These herbicide options allow for control of problematic winter weeds during clover establishment, thereby maximizing clover biomass and limiting canopy gaps that would allow summer weed emergence.

The evolution of herbicide-resistant weeds has resulted in the necessity to integrate nonchemical control methods with chemicals for effective management in crop production systems. In soybean, control of the pigweed species, particularly herbicide-resistant waterhemp and Palmer amaranth, have become predominant concerns. Cereal rye planted as a winter cover crop can effectively suppress early-season weed emergence in soybean, including waterhemp, when planted at a rate of 123 kg ha−1. The objectives of this study were to determine the effects of different cereal rye seeding rates (0, 34, 56, 79, 110, and 123 kg ha−1) on early-season waterhemp suppression and soybean growth and yield. Soybean was planted into fall-seeded cereal rye, which was terminated within 4 d of soybean planting. The experiment was conducted over the 2018, 2019, and 2020 growing seasons in Columbia, Missouri. Effects of cereal rye on early-season waterhemp suppression varied by year and were most consistent at 56 kg ha−1 or higher seeding rates. Linear regression analysis of cereal rye biomass, height, or stand at soybean planting showed inverse relationships with waterhemp emergence. No adverse effects on soybean growth or yield were observed at any of the cereal rye seeding rates relative to plots that lacked cereal rye cover. Result differences among the years suggest that the successfulness of cereal rye on suppression of early-season waterhemp emergence is likely influenced by the amount of waterhemp seed present in the soil seed bank.

Replacing tillage with cover crops (CC) for weed management in corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] systems with mechanical weed control has many soil health benefits but in the western Corn Belt, CC establishment after harvest is hampered by cold temperatures, limited labor and few compatible CC species. Spring-planted CC may be an alternative, but information is lacking on suitable CC species. Our objective was to evaluate four spring-planted CC with respect to biomass production and weed suppression, concurrent with CC growth and post-termination. Cover crop species tested were oat (Avena sativa L.), barley (Hordeum vulgare L.), brown mustard [Brassica juncea (L.) Czern.] and yellow mustard (Brassica hirta Moench). They were compared to no-CC treatments that were either tilled pre- and post-planting of soybean (no-CC tilled) or not tilled at all (no-CC weedy). CC were planted in late March to early April, terminated 52–59 days later using an undercutter, and soybean was planted within a week. The experiment had a randomized complete block design with four replications and was repeated for 3 years. Mustards and small grains produced similar amounts of biomass (1.54 Mg ha−1) but mustard biomass production was more consistent (0.85–2.72 Mg ha−1) than that of the small grains (0.35–3.81 Mg ha−1). Relative to the no-CC weedy treatment, mustards suppressed concurrent weed biomass in two out of 3 years, by 31–97%, and small grains suppressed concurrent weed biomass in only 1 year, by 98%.

Six weeks after soybean planting, small grains suppressed weed biomass in one out of 3 years, by 79% relative to the no-CC weedy treatment, but mustards did not provide significant weed suppression. The no-CC tilled treatment suppressed weeds each year relative to the no-CC weedy treatment, on average 87%. The ineffective weed control by CC reduced soybean biomass by about 50% six weeks after planting. While spring-planted CC have the potential for pre-plant weed control, they do not provide adequate early season weed suppression for soybean.

Field experiments were conducted in 2016 and 2017 to evaluate the effects of seeding rate and herbicide programs on weed control and pinto bean yield under irrigation. The experiments comprised a 5 × 5 factorial randomized complete block design with five replications. The weed control treatments comprised a nontreated control, hand-weeded control, EPTC + ethalfluralin PRE, EPTC + ethalfluralin PRE followed by (fb) dimethenamid-P POST at V1, and EPTC + ethalfluralin PRE fb bentazon/imazamox POST. There were five seeding rates ranging from 247,000 to 494,000 seeds ha–1 planted in 19-cm rows. Weed biomass was reduced by 6 kg ha–1 with every additional 1,000 seeds ha–1. EPTC plus ethalfluralin fb either dimethenamid-P or bentazon plus imazamox reduced weed biomass by at least 29% compared to the nontreated control. There was a significant effect of weed control treatment on pinto bean yield (P = 0.0004). However, there was no significant seeding rate (P = 0.42) or seeding rate–by–weed control interaction effect on pinto bean yield (P = 0.38). Pinto bean yield ranged from 3,080 kg ha–1 in the nontreated control to 4,740 kg ha–1 hand-weeded treatment. Increased seeding rate in narrow rows is a cultural practice that can improve weed control in pinto bean but may not necessarily increase yield.

As herbicide-resistant weeds become more problematic, producers will consider the use of cover crops to suppress weeds. Weed suppression from cover crops may occur especially in the label-mandated buffer areas of dicamba-resistant soybean where dicamba use is not allowed. Three cover crops terminated at three timings with three herbicide strategies were evaluated for their effect on weed suppression in dicamba-resistant soybean. Delaying termination until soybean planting or after and using cereal rye or cereal rye + crimson clover increased cover-crop biomass by at least 40% compared to terminating early or using a crimson clover–only cover crop. Densities of problematic weed species were evaluated in early summer before a blanket POST application. Plots with cereal rye had 75% less horseweed compared to crimson clover at two of four site-years. Cereal rye or the mixed cover crop terminated at or after soybean planting reduced waterhemp densities by 87% compared to early termination timings of crimson clover and the earliest termination timing of the mix at one of two site-years. Cover crops were not as effective in reducing waterhemp densities as they were in reducing horseweed densities. This difference was due to a divergence in emergence patterns; waterhemp emergence generally peaks after termination of the cover crop, whereas horseweed emergence coincides with establishment and rapid vegetative growth of cereal rye. Cover crops alone were generally not as effective as was using a high-biomass cover crop combined with an herbicide strategy that contained dicamba and residual herbicides. However, within label-mandated buffer areas where dicamba cannot be used, a cover crop containing cereal rye with delayed termination until soybean planting combined with residual herbicides could be used to improve suppression of horseweed and waterhemp.

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 improve C. canadensis control 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 cereale L.) cover crop on C. canadensis population 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, on C. canadensis density in either study. In 2016 to 2017, C. canadensis density 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 increased C. canadensis density in the spring residual herbicide study (Study I), and had no effect in the fall herbicide study (Study II). Conyza canadensis densities 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 lower C. canadensis densities. 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-resistant C. canadensis plant density, but cannot be relied upon to reduce the need for fall herbicide treatments and spring residual programs.

Field experiments were conducted in 2017 and 2018 at two locations in Indiana to evaluate the influence of cover crop species, termination timing, and herbicide treatment on winter and summer annual weed suppression and corn yield. Cereal rye and canola cover crops were terminated early or late (2 wk before or after corn planting) with a glyphosate- or glufosinate-based herbicide program. Canola and cereal rye reduced total weed biomass collected at termination by up to 74% and 91%, in comparison to fallow, respectively. Canola reduced horseweed density by up to 56% at termination and 57% at POST application compared to fallow. Cereal rye reduced horseweed density by up to 59% at termination and 87% at POST application compared to fallow. Canola did not reduce giant ragweed density at termination in comparison to fallow. Cereal rye reduced giant ragweed density by up to 66% at termination and 62% at POST application. Termination timing had little to no effect on weed biomass and density reduction in comparison to the effect of cover crop species. Cereal rye reduced corn grain yield at both locations in comparison to fallow, especially for the late-termination timing. Corn grain yield reduction up to 49% (4,770 kg ha–1) was recorded for cereal rye terminated late in comparison to fallow terminated late. Canola did not reduce corn grain yield in comparison to fallow within termination timing; however, late-terminated canola reduced corn grain yield by up to 21% (2,980 kg ha–1) in comparison to early-terminated fallow. Cereal rye can suppress giant ragweed emergence, whereas canola is not as effective at suppressing large-seeded broadleaves such as giant ragweed. These results also indicate that early-terminated cover crops can often result in higher corn grain yields than late-terminated cover crops in an integrated weed management program.

Cover crops are being increasingly recommended as an integrated approach to controlling glyphosate-resistant Palmer amaranth and other troublesome weeds. Thus, a field experiment was conducted in 2010 through 2012 to evaluate the critical period for weed control (CPWC) in cotton as affected by a cereal rye cover crop and tillage. The management systems evaluated included conventional tillage following winter fallow, conservation tillage (CT) following winter fallow, and CT following a cereal rye cover crop managed for maximum biomass. Throughout most of the growing season, weed biomass in cereal rye cover crop plots was less than the CT winter-fallow system in both years and less than both CT winter fallow and conventional tillage in 2012. The CPWC was shortest in 2010 following conventional tillage; however, in 2012, production system influences on CPWC were less. The presence of the rye cover crop delayed the critical timing for weed removal (CTWR) approximately 8 d compared with fallow treatment both years, while conventional tillage delayed CTWR about 2 wk compared with winter fallow. Relative yield losses in both years did not reach the 5% threshold limit until about 2 wk after planting (WAP) for CT following winter fallow, 3 WAP for CT following a cover crop, and 3.5 WAP following conventional tillage. Thus, CT following winter fallow should be avoided to minimize cotton yield loss.

High-residue cover crops can facilitate organic no-till vegetable production when cover crop biomass production is sufficient to suppress weeds (>8000 kg ha−1), and cash crop growth is not limited by soil temperature, nutrient availability, or cover crop regrowth. In cool climates, however, both cover crop biomass production and soil temperature can be limiting for organic no-till. In addition, successful termination of cover crops can be a challenge, particularly when cover crops are grown as mixtures. We tested whether reusable plastic tarps, an increasingly popular tool for small-scale vegetable farmers, could be used to augment organic no-till cover crop termination and weed suppression. We no-till transplanted cabbage into a winter rye (Secale cereale L.)-hairy vetch (Vicia villosa Roth) cover crop mulch that was terminated with either a roller-crimper alone or a roller-crimper plus black or clear tarps. Tarps were applied for durations of 2, 4 and 5 weeks. Across tarp durations, black tarps increased the mean cabbage head weight by 58% compared with the no tarp treatment. This was likely due to a combination of improved weed suppression and nutrient availability. Although soil nutrients and biological activity were not directly measured, remaining cover crop mulch in the black tarp treatments was reduced by more than 1100 kg ha−1 when tarps were removed compared with clear and no tarp treatments. We interpret this as an indirect measurement of biological activity perhaps accelerated by lower daily soil temperature fluctuations and more constant volumetric water content under black tarps. The edges of both tarp types were held down, rather than buried, but moisture losses from the clear tarps were greater and this may have affected the efficacy of clear tarps. Plastic tarps effectively killed the vetch cover crop, whereas it readily regrew in the crimped but uncovered plots. However, emergence of large and smooth crabgrass (Digitaria spp.) appeared to be enhanced in the clear tarp treatment. Although this experiment was limited to a single site-year in New Hampshire, it shows that use of black tarps can overcome some of the obstacles to implementing cover crop-based no-till vegetable productions in northern climates.

The potential role of fall-seeded cover crops for weed management in edamame [soybean, Glycine max (L.) Merr.] is unknown. Field experiments were conducted over three edamame growing seasons to (1) determine the extent to which cover crop–residue management systems influence edamame emergence while selectively suppressing weed density and biomass, and (2) determine whether cultivars differed in emergence in cover crop–residue management systems. Cover crop treatments included a winter-killed oilseed radish (Raphanus sativus L.), two canola (Brassica napus L.) treatments (early-killed and late-killed), two cereal rye (Secale cereale L.) treatments (early-killed and late-killed), and a bare-soil control. Two spring timings of a cover crop burndown application created the early-killed and late-killed treatments for canola and cereal rye. Twelve soybean cultivars were tested, including 11 edamame cultivars differing in seed size and a grain-type soybean control. Spring residue biomass in cover crop treatments ranged from 438 kg ha−1 for winter-killed radish to 9,003 kg ha−1 for late-killed cereal rye. Cultivars responded similarly to cover crop treatments, and with the exception of late-killed cereal rye, cover crop treatments resulted in similar crop emergence as the bare-soil control. While all cover crop treatments reduced weed biomass 6 wk after planting compared with the bare soil, winter-killed radish and both canola treatments increased weed density. Early-killed cereal rye has potential for weed management in edamame, as evidenced by the fact that the treatment did not interfere with planting or crop establishment, yet reduced weed density 20% and suppressed early-season weed growth 85%.

Wild-proso millet control in furrow-irrigated corn was evaluated in Colorado and Nebraska in 1986 and 1987. No single herbicide alone controlled wild-proso millet all season. In Colorado, EPTC applied preplant incorporated followed by cyanazine plus pendimethalin applied early postemergence controlled 94% of wild-proso millet. Acetochlor applied preemergence followed by cyanazine plus pendimethalin applied early postemergence controlled wild-proso millet better all season (93%) than alachlor (81%) or metolachlor (71%) followed by the same early postemergence strategy. Successful Colorado wild-proso millet management treatments (>85% season-long control) increased corn yields an average of 3260 kg ha-1 compared to the untreated control. To obtain wild-proso millet control of 90% or more in Nebraska in 1986, alachlor, cycloate, EPTC, and metolachlor applied had to be combined with cyanazine plus pendimethalin applied early postemergence. Average corn yields in herbicide-treated areas in Nebraska were 2980 kg ha-1 higher than those recorded in the untreated control.

Rhizobacteria are being evaluated for promotion of plant growth and for biological control of weeds, insects, diseases, and nematodes. Although considerable efforts have been allocated to this approach to biological control, commercial success remains elusive yet intriguing. In this review, the root biology of downy brome and winter wheat is described as an initial model of the information needed for other plant hosts. A limited review of rhizobacteria in disease management is presented to demonstrate the potential and some limitations with rhizobacteria as biocontrol agents. Several techniques are described to improve the survival of a rhizobacterium to suppress downy brome. To achieve success with rhizobacteria in pest management, more information is needed on the root biology of the host plants and the ecology of the rhizobacteria.