Integrated weed management (IWM) can be defined as a holistic approach to weed management that integrates different methods of weed control to provide the crop with an advantage over weeds. It is practiced globally at varying levels of adoption from farm to farm. IWM has the potential to restrict weed populations to manageable levels, reduce the environmental impact of individual weed management practices, increase cropping system sustainability, and reduce selection pressure for weed resistance to herbicides. There is some debate as to whether simple herbicidal weed control programs have now shifted to more diverse IWM cropping systems. Given the rapid evolution and spread of herbicide-resistant weeds and their negative consequences, one might predict that IWM research would currently be a prominent activity among weed scientists. Here we examine the level of research activity dedicated to weed control techniques and the assemblage of IWM techniques in cropping systems as evidenced by scientific paper publications from 1995 to June 1, 2012. Authors from the United States have published more weed and IWM-related articles than authors from any other country. When IWM articles were weighted as a proportion of country population, arable land, or crop production, authors from Switzerland, the Netherlands, New Zealand, Australia, and Canada were most prominent. Considerable evidence exists that research on nonherbicidal weed management strategies as well as strategies that integrate other weed management systems with herbicide use has increased. However, articles published on chemical control still eclipse any other weed management method. The latter emphasis continues to retard the development of weed science as a balanced discipline.

In little over 20 yr, Palmer amaranth has risen from relative obscurity to its current status as one of the most widespread, troublesome, and economically damaging agronomic weeds in the southeastern U.S. Numerous factors have enabled Palmer amaranth to become such a dominant and difficult-to-control weed, including its rapid growth rate, high fecundity, genetic diversity, ability to tolerate adverse conditions, and its facility for evolving herbicide resistance. It is both a serious threat to several U.S. cropping systems and a fascinating model weed. In this paper, we review the growing body of literature on Palmer amaranth to summarize the current state of knowledge on the biology, agricultural impacts, and management of this weed, and we suggest future directions for research.

Weeds are the main constraint in the adoption of zero-till, dry-seeded rice systems because weeds and rice emerge simultaneously in these systems, and there is no standing water at crop establishment to suppress weeds. A study was conducted during the wet season of 2011 and the dry season of 2012 at the International Rice Research Institute to evaluate the performance of different herbicides in mechanized-sown, zero-till dry-seeded rice. Among the treatments evaluated, oxadiazon followed by penoxsulam + cyhalofop followed by one hand-weeding at 42 d after sowing, provided 23 to 35% higher yield than the nontreated control. The yields in the oxadiazon-treated plots were similar to those in the weed-free plots. Some weed species, including eclipta and doveweed, were not controlled by the evaluated herbicides. Therefore, there is a need to evaluate additional herbicides and to integrate them with cultural weed management strategies to manage such problematic weeds.

Field trials were conducted in 2009 and 2010 to investigate the effects of metsulfuron-containing herbicides on tall fescue growth, seedhead production, yield, and forage nutritive value. Several rates of metsulfuron-containing products and picloram plus 2,4-D were applied to a weed-free tall fescue hay field in the early spring vegetative, late spring boot, and late summer dormancy stages of growth. Compared to the nontreated control, applying metsulfuron-containing herbicides to vegetative tall fescue reduced plant height by 13 to 40% whereas boot-stage applications of these same herbicides reduced height by 28 to 45%. Metsulfuron-containing herbicides reduced seedhead density from 14 to 61% when applied to vegetative tall fescue, and from 53 to 88% when applied at the boot stage. Metsulfuron plus 2,4-D plus dicamba (0.01 + 0.40 + 0.14 kg ai ha−1) was the only metsulfuron-containing treatment applied at the vegetative application timing that did not reduce tall fescue seedheads or yield when compared to the nontreated control. Vegetative-stage applications of metsulfuron-containing herbicides reduced tall fescue yields by 33 to 63%, whereas boot-stage applications reduced yields by 15 to 35%. Picloram plus 2,4-D did not reduce tall fescue height, seedhead density, or yield when applied at either timing. Tall fescue crude protein (CP) concentration was greater in response to the vegetative compared to boot-stage herbicide applications, and vegetative-stage applications of metsulfuron-containing herbicides increased CP concentration of tall fescue by 1.5 to 3.4% compared to the nontreated control. Results from these experiments indicate that spring applications of metsulfuron-containing herbicides can be utilized to reduce tall fescue seedhead production and increase CP content of tall fescue pastures and hay fields, but summer applications of these same herbicide treatments will have only limited effects on yield, nutritive values, or seedhead density of tall fescue harvested in the fall or the spring following treatment.

Soybean cyst nematode (SCN) is the most yield-limiting pathogen of soybean in the United States. Henbit is a prevalent winter annual weed species in no-till fields and is reported to be an alternative host of SCN. A greenhouse study was conducted to evaluate how the development of SCN on henbit roots was affected by herbicide mode of action and time of herbicide application. Henbit plants were grown in watertight pots placed in a water bath bench that kept soil temperature constant (27 ± 1 C) during the study. Ten d after transplanting, pots were inoculated with approximately 1,000 SCN eggs. At 7, 14, or 21 d after inoculation (DAI), henbit plants were sprayed with recommended dose of either glyphosate (870 g ae ha−1) or 2,4-D (1,070 g ae ha−1). The experiment was arranged in a randomized complete block design with five replications per treatment, and two experimental runs separated in time. At 28 DAI, the total number of SCN cysts and eggs, and plant shoot and root dry weight per pot were determined. Henbit root and shoot biomass increased as the time of herbicide application was delayed. Glyphosate reduced root biomass more than 2,4-D, but no differences in shoot biomass were detected. The number of SCN cysts per henbit plant and eggs per cyst increased as the herbicide application was delayed from 7 to 21 DAI. Glyphosate reduced the number of cysts found on henbit roots more than 2,4-D, especially at earlier application times. On plants treated with glyphosate, SCN-females produced only half the number of eggs of SCN-females on henbit plants treated with 2,4-D, regardless of time of application. These results indicate that early control of henbit plants, especially with glyphosate, can reduce SCN reproduction potential in SCN infested fields.

Greenhouse and field experiments were conducted to determine whether PRE-applied ethofumesate increased POST spray retention and weed control with glyphosate. In greenhouse studies, ethofumesate was applied PRE at rates from 0 to 224 g ai ha−1 followed by POST treatment with either water or glyphosate (840 g ae ha−1) to which a red dye had been added. Plants were immediately washed and spray retention determined spectrophotometrically. Common lambsquarters retained more glyphosate solution compared to water, regardless of PRE ethofumesate rate. Increasing the rate of PRE ethofumesate increased the POST spray retention of both water and glyphosate. PRE application of ethofumesate increased POST spray retention of water by 114% and glyphosate solution by 18% compared to no ethofumesate treatment as determined by nonlinear regression. Ethofumesate rates of 90 g ha−1 increased POST spray retention to at least 95% of the total observed response. In field studies, common lambsquarters, redroot pigweed, and hairy nightshade densities were all reduced by ethofumesate, although the duration of ethofumesate effect varied by species and ethofumesate application timing. PRE ethofumesate had no significant effect on hairy nightshade density until after POST glyphosate was applied, whereas common lambsquarters densities were most affected by PRE ethofumesate early in the season. Late-season redroot pigweed density was reduced by ethofumesate regardless of application timing.

Approximately 50% of the genetically modified herbicide-resistant corn hectares in the United States are treated only with POST-applied herbicides for weed management. Although a high degree of efficacy can be obtained with POST-applied herbicides, delayed timing of application may result in substantial corn yield loss. Our goal was to characterize on-farm corn–weed communities prior to POST herbicide application and estimate potential corn-yield loss associated with early-season corn–weed competition. In 2008 and 2009, field surveys were conducted across 95 site-years in southern Wisconsin and recorded weed species, density, and height in addition to crop height, growth stage, and row spacing. WeedSOFT® was used to predict corn yield loss. Common lambsquarters, velvetleaf, dandelion, common ragweed, and Amaranthus species were the five most abundant broadleaf weed species across site-years, present in 92, 86, 59, 45, and 44% of all fields, respectively, at mean densities of 19, 3, 3, 4, and 3 plants m−2, respectively. Mean plant heights among these species were 17 cm or less. Grass and sedge species occurred in 96% of fields at a mean density of 25 plants m−2 and height of 7 cm. The mean and median of total weed density across site-years were 96 and 52 plants m−2, with heights of 14 and 13 cm, respectively. Mean predicted corn yield loss was 4.5% with a mean economic loss of $62 ha−1. However, predicted yield loss was greater than 5% on one-third of the site-years, with a maximum of 26%. These results indicate that delayed application of POST herbicides has led to corn yield loss due to early-season weed-crop competition on a substantial number of fields across southern Wisconsin, and suggest that management tactics need to be improved to protect corn yield potential fully.

Field experiments were conducted in western Atakora, Benin, to determine the critical time period of weed competition in hand-weeded corn. Weeds were removed until different crop growth stages and then allowed to reemerge. Other treatments began weed control at different growth stages (four-, eight-, and ten-leaf stages and flowering) and were maintained until harvest. One treatment was permanently kept weed-free and one treatment was uncontrolled until harvest. Yields without weed competition ranged from 2.8 to 3.4 t ha−1. As expected, yield loss increased with duration of weed infestation and ranged from 38 to 65% compared to permanent weed-free plots. In three out of four site-years, the critical period for weed control started at the four- to six-leaf stage and continued until ten-leaf stage or flowering of corn. Approximately four hand-weeding applications were required in this critical period of weed control.

Dicamba or 2,4-D will be used POST for the control of weeds in soybean when dicamba- or 2,4-D-resistant soybean are commercialized. The active ingredients of both herbicides are weak acids in solution and may bind to cations present from hard water used as herbicide carrier or from foliar fertilizers added to spray solutions. The objectives of this research were (1) to determine if the efficacy of dicamba or 2,4-D are influenced by divalent cations, namely calcium (Ca), magnesium (Mg), manganese (Mn), and zinc (Zn), in the spray solution, and (2) to determine if adding ammonium sulfate (AMS) to the spray solution can overcome antagonism. The factorial study included five cation solutions (deionized water [dH2O], Ca at 590 mg L−1, Mg at 630 mg L−1, Mn at 4.97 L ha−1, and Zn at 2.33 L ha−1), two herbicide treatments (dicamba or 2,4-D), and two water conditioner treatments (without or with AMS at 20.37 g L−1). Treatments were applied to common lambsquarters, horseweed, and redroot pigweed. Control of horseweed and redroot pigweed increased when AMS was added to the 2,4-D treatments, irrespective of cation solution. Control of common lambsquarters was increased when AMS was added to 2,4-D for only the Ca and Mn cation solution. In contrast to the results obtained with 2,4-D, control of horseweed with dicamba was not influenced by cation solution. Tank-mixing AMS with dicamba increased control of both redroot pigweed and common lambsquarters in the dH2O, Mg, and Mn solutions.

A field experiment was conducted in Boone and Callaway counties in Missouri in 2010 and 2011 to investigate herbicide programs for the management of summer annual grass and broadleaf weeds in soybean resistant to 2,4-D and glufosinate. Results revealed that the addition of 0.56, 0.84, or 1.12 kg ha−1 2,4-D (amine) to either or both POST applications of glufosinate in a two-pass POST herbicide program increased control of common waterhemp compared to two POST applications of glufosinate alone. Similar levels of common cocklebur, giant foxtail, large crabgrass, and barnyardgrass control were achieved with any of the two-pass POST programs that contained 2,4-D compared to two-pass POST programs containing glufosinate alone. Similar control of these species was also achieved with the inclusion of 2,4-D in either the first or second pass of glufosinate. Two-pass programs resulted in the highest levels of weed control (90%). Annual grass and broadleaf weed control was as much as 59% lower when one-pass POST herbicide programs were compared to PRE followed by (fb) POST or two-pass POST programs. However, one-pass POST programs were sufficient to obtain exceptional control of common cocklebur and giant foxtail. Across all site years, soybean yields ranged from 2,680 to 3,100 kg ha−1 for all herbicide treatments, but did not differ statistically. Overall, results from these experiments indicate that compared to glufosinate alone, PRE fb POST or two-pass POST herbicide programs that incorporate 2,4-D amine with glufosinate in 2,4-D–resistant soybean enhance control of common waterhemp, while providing similar levels of control of other summer annual grass and broadleaf weeds.

Two populations of Palmer amaranth suspected of being resistant to glyphosate have been reported since 2007 in pecan orchards in Doña Ana County, New Mexico. The objectives of the study were to confirm and evaluate the level of resistance, to evaluate the effectiveness of alternative herbicide mechanisms of action, and to compare the cost of effective alternative herbicides for weed management in pecan orchards. Greenhouse experiments indicated that the resistant populations were able to survive glyphosate at 736 g ae ha−1. Compared with a susceptible (S) population, one of the resistant (R) populations had sevenfold resistance to glyphosate. POST application of 12 herbicides, with five different mechanisms of action, all provided at least 88% control of both R and S populations when applied at their recommended field rates. PRE application of trifluralin and metolachlor also provided more than 99% control of R and S populations. The results of field studies indicated that the financial benefit of season-long weed management with glyphosate, in pecan orchards, was comparable with some of the tested alternative herbicides.

Two field residue studies were conducted from 2005 to 2007 in Simcoe, Ontario, Canada, to evaluate the effects of mesotrione soil residues on injury, plant dry weight, and yield of sugar beet, cucumber, pea, green bean, and soybean and to verify the potential of reducing a 2-yr field-residue study (conventional residue carryover) to a 1-yr field study (simulated residue-carryover study) by growing these crops in soil treated with reduced rates of mesotrione applied in the same year. There was a significant difference in mesotrione carryover between 2006 and 2007 and differences between years can be explained by differences in soil pH and soil moisture. The conventional and the simulated residue-carryover studies successfully measured mesotrione persistence and rotational crop sensitivity. Both studies showed that sugar beet was the most-sensitive crop with injury, plant dry weight reduction, and yield loss because of mesotrione residues as high as 100%. Green bean was the next most-sensitive crop to mesotrione residues followed by pea, cucumber, and soybean. The simulated residue-carryover study provided a more-rigorous test of rotational crop sensitivity to mesotrione residues than the conventional residue-carryover study, especially at higher rates for the more-sensitive crops. For the other crops, responses to mesotrione residues were similar between the conventional and simulated residue-carryover studies.

Grazing experiments were conducted during 2009 and 2010 to investigate the effect of herbicide application and subsequent weed removal on cattle grazing distribution in mixed tall fescue and legume pastures. At each location, herbicide applications were made to one-half of the grazed hectares to remove existing weeds and brush. Weeds and legumes were left nontreated across the remaining half of the grazed hectares at each location. Global positioning system tracking collars were fitted to three beef cows at each site and coordinates from each collar were recorded at 1-h intervals for 3 to 4 mo after herbicide application. At each location, broadleaf weeds were reduced from 1 to 51 kg ha−1, and legumes were completely eliminated in herbicide-treated compared to nontreated portions of the pastures. By the end of the season, the forage grass and legume component of pastures was greater and weed component lower in treated compared to nontreated portions of the pastures. By 3 mo after treatment, the cattle distribution was 1.3 to 5 times greater in herbicide-treated compared to nontreated portions of pastures. Overall, results from these experiments indicate herbicide treatment can increase desirable forage mass and thus modify cattle grazing distribution in pastures.

Field studies were conducted in 2009 and 2010 on established commercial cranberry farms in southeastern Massachusetts to evaluate cranberry vine injury and yield with two rates of dichlobenil (1.8 and 2.7 kg ai ha−1) applied at various growth stages starting in mid-May. Four varieties were evaluated: ‘Ben Lear', ‘Early Black', ‘Howes', and ‘Stevens'. Ben Lear vines exhibited leaf-stress symptoms in both years, and Howes and Stevens vines had leaf symptoms in 1 yr. Data indicated that applications made during periods of flower-part development and growth (jewel through bloom) had the highest injury ratings. Growth stage affected injury ratings by variety and dichlobenil rate in 1 out of 2 yr. In all cases, leaf symptoms abated by the end of the season. No effect on yield (wt of fruit per unit area) was detected for any treatment combination on any variety in either year. Data from the present study support pursuit of future studies and can guide management decisions for dodder control to a limited extent. Longer studies are needed to fully evaluate repeated, annual applications of dichlobenil dispensed during periods of rapid growth on cranberry vine development and yield. Further work is also needed to document the practical use of delayed applications of dichlobenil for dodder management.

Field studies were conducted to determine the effect of halosulfuron at 0, 13, 26, 39 or 52 g ha−1 applied 10, 22, and 31 d after planting (DAP) on ‘Beauregard' and ‘Covington' sweetpotato. Storage roots were harvested, graded, cured, and stored in controlled environment for 2 mo. Where injury on storage roots was observed, external injury occurred on the surface of the storage root as a blackened area with blistering and internal injury consisted of small red-brown spots inside the sweetpotato storage root. Total yield of sweetpotato with 13 g ha−1 halosulfuron treatment (155,157 kg ha−1) was similar to the nontreated check (162,002 kg ha−1). However, halosulfuron rates above 13 g ha−1 resulted in a reduction of marketable grade roots and total yield of sweetpotato. Regardless of rate and timing of halosulfuron, external and internal injury to Beauregard storage roots was less than 6 and 9%, respectively. No external injury to Covington was observed from all rates of halosulfuron applied POST at 10 DAP. Halosulfuron at 22 DAP to Covington caused greater external injury to storage roots than was observed on the nontreated. Thus, Beauregard appears more tolerant to halosulfuron POST than Covington. To minimize internal or external injury to storage roots of Covington, halosulfuron must be applied within 10 DAP.

Methyl bromide (MBr) has been an industry standard for soil fumigation in a multitude of crops for decades. However, it has been banned by the United Nations Environment Programme, and alternatives to MBr must be implemented to sustain productivity in many vegetable crops that depend on soil fumigation. One alternative that has been implemented in some areas is methyl iodide (MeI). Efficacy of MeI has been demonstrated on many pest species and has been generally similar to MBr. Methyl iodide is a costly material, which has likely limited its adoption. Virtually impermeable film (VIF) and totally impermeable film (TIF) provide greater fumigant retention than low-density and high-density polyethylene film, which can allow for reduced fumigant application rates while maintaining fumigant efficacy. The objectives of this research were to evaluate TIF with reduced rates of shank-applied MeI : chloropicrin (Pic) (50 : 50 w/w) for the control of yellow nutsedge in tomato. Treatments included a standard rate of MeI : Pic (93.3 L ha−1 [178 kg ha−1 broadcast]) under VIF and TIF, three reduced rates (37.3, 56, 74.6 L ha−1 [71.2, 106.8, 142.5 kg ha−1 broadcast, respectively]) under TIF, and a nontreated control under TIF. Results indicate fumigant use rates may be reduced from a standard 93.3 L ha−1 under VIF to 37.3 L ha−1 (60% reduction) under TIF while providing yellow nutsedge control and maintaining tomato yields.

Clovers are commonly included as utility plants within mixed grass swards, such as pastures and roadside right-of-ways. As such, they provide supplemental nitrogen, quality forage, and insect habitat. Yet weed control within mixed swards is often hampered by the lack of selective herbicides that are tolerated by clovers. Differential tolerance of legumes to common row-crop and pasture herbicides has previously been reported, yet little information is available that is specific to clover species. Herbicide injury of clover is often inconsistent, hypothetically due to differential species tolerance. Field and greenhouse experiments were conducted with the objective of testing differential tolerance amongst four clover species. Our experiments suggest varying tolerances amongst clover species and common broadleaf herbicides. Only imazaquin control differed due to species; however, treatment by clover interactions were further demonstrated due to variable reductions in clover height. Imazaquin, 2,4-D, 2,4-DB, and triclopyr height reductions differed due to clover species. Differential clover response to herbicide treatment should be an important consideration when managing mixed grass–clover swards and should be accounted for in future research. On a more practical level, our experiments demonstrate a range of herbicides that effectively control clover species, including atrazine, dicamba, clopyralid, 2,4-D, triclopyr, metsulfuron, and trifloxysulfuron. However, results suggest that 2,4-DB, imazethapyr, and bentazon are candidate herbicides for weed control in scenarios in which clover is a desirable crop.

Weed control in Florida citrus is primarily based on herbicides. Saflufenacil, a POST-applied herbicide is recently registered for broadleaf weed control in citrus. Saflufenacil has very limited grass activity; therefore, it should be tank mixed with graminicides or broad-spectrum herbicides to increase the spectrum of weed control. Greenhouse and field experiments were conducted at two locations (Polk County and Orange County, FL) to evaluate the efficacy and potential antagonism or synergy of saflufenacil and sethoxydim applied alone or tank mixed, and various two- and three-way mixes with glyphosate or pendimethalin. The results suggested that tank mixing saflufenacil and sethoxydim had neither synergistic nor antagonistic effect on broadleaf and grass weed control, respectively. Tank mixing pendimethalin with saflufenacil and sethoxydim improved broadleaf and grass weed control and reduced weed density and biomass, compared with saflufenacil or sethoxydim applied alone or tank mixed at 45 and 60 d after treatment (DAT). Glyphosate tank mixed with saflufenacil and sethoxydim provided > 90% control of broadleaf and grass weeds at 15 DAT, reduced density ≤ 8 plants m−2, and reduced biomass < 95 g m−2 at 60 DAT. Glyphosate applied alone was less effective than it was when tank mixed with saflufenacil and sethoxydim or pendimethalin for broadleaf and grass weed control, indicating an additive effect of tank mixture on glyphosate efficacy. It is concluded that saflufenacil can be tank mixed with sethoxydim for control of broadleaf and grass weeds without antagonism on the efficacy of either herbicide; however, tank mixing saflufenacil and sethoxydim with glyphosate or pendimethalin provided long-term, broad-spectrum weed control in Florida citrus.

Common bermudagrass is a problematic weed within tall fescue turfgrass. Field research was conducted from 2010 to 2012 in Knoxville, TN, evaluating the efficacy of sequential applications of topramezone (12.5 and 25 g ha−1), triclopyr (1,120 g ha−1), and mixtures of topramezone + triclopyr for bermudagrass control in tall fescue turf. Sequential applications of fenoxaprop + triclopyr (100 + 1,120 g ha−1) were included for comparison. Three applications of each treatment were applied at 21-d intervals during July, August, and September of 2010 and 2011. Plots were stripped to receive tall fescue interseeding at 0 or 490 kg ha−1 during September 2010 and 2011. Bermudagrass control with topramezone + triclopyr mixtures was greater than topramezone or triclopyr applied alone 14 wk after initial treatment (WAIT) each year. In the second year of this study, topramezone + triclopyr mixtures controlled bermudagrass 27 to 50% compared to 27% for fenoxaprop + triclopyr by 52 WAIT. However, bermudagrass control with topramezone + triclopyr mixtures increased to 88 to 92% by 52 WAIT when accompanied with tall fescue interseeding at 490 kg ha−1. Future research should evaluate effects of interseeding on the efficacy of different herbicides for weed control in cool- and warm-season turf.

Vapor movement of synthetic auxin herbicides can injure desirable plants outside the treatment zone. Vapor movement of the synthetic auxin herbicides aminocyclopyrachlor and aminocyclopyrachlor methyl was compared with that of the relatively volatile herbicide dicamba and the low volatile herbicide aminopyralid with a soybean bioassay under greenhouse and field conditions. Soybean is very sensitive to these active ingredients. Under greenhouse conditions, 82 (61 to 104) mg ae ha−1 of aminocyclopyrachlor, 26 (18 to 33) mg ae ha−1 of aminocyclopyrachlor methyl, 82 (69 to 95) mg ae ha−1 of aminopyralid, and 61 (47 to 75) mg ae ha−1 of dicamba produced an estimated 25% visual soybean phytotoxicity response when soybean was treated POST at the V3 growth stage (GR25 [95% confidence interval]). In field studies, aminocyclopyrachlor, aminocyclopyrachlor methyl, and aminopyralid were applied at 70 g ae ha−1 and dicamba was applied at 560 g ae ha−1 (labeled application rates) to soybean at the V3 growth stage. All herbicides were applied within an enclosed chamber (3 m by 3 m by 1 m) to mitigate movement of spray droplets. The enclosures were removed shortly after spray application and soybean response immediately surrounding the treated area was recorded in each of eight directions approximately 10 d after treatment. On the basis of bioassay responses, relative amount of vapor movement was dicamba > aminocyclopyrachlor methyl > aminopyralid ≈ aminocyclopyrachlor. Vapor movement of aminocyclopyrachlor was very low indicating that the risk of phytotoxic response of sensitive plants due to volatility of aminocyclopyrachlor is negligible.