Herbicide-resistant crops, such as glyphosate-resistant (GR) soybean, allow for broad-spectrum, flexible weed control with minimal crop injury; however, the development of GR weeds, such as horseweed, has forced reliance on alternative herbicides for control of these weeds. While preplant (PP) herbicides provide excellent control of GR-horseweed, there are currently no POST herbicide control options within soybean. The objective of this study was to evaluate the efficacy of dicamba for the control of GR-horseweed when applied PP, POST, and sequentially in dicamba-resistant soybean. Dicamba applied PP at 600 g a.e. ha−1 provided 90 to 100% control of GR-horseweed 8 wk after application (WAA) across three field trials conducted in Ontario in 2011 and 2012. Similarly, sequential applications provided 91 to 100% control. This technology provides a much-needed POST option of dicamba to be applied as a rescue treatment to control weed escapes caused by late emergence or poor initial control following a PP herbicide application.

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.

Field experiments were conducted in 2010 and 2011 at a Mclean County, IL seed corn production field where resistance to foliar-applied 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors was confirmed in waterhemp. Corn herbicides were applied to the soil at 1 and 2 times (1× and 2×, respectively) the recommended field use rate, while soybean herbicides were applied only at 1× the recommended rate. Waterhemp control and density were determined 30 and 60 d after treatment (DAT). In corn, 1× rates of mesotrione, safened and unsafened isoxaflutole formulations, atrazine, and S-metolachlor provided less than 70% control 30 DAT, while control with acetochlor was greater than 80%. One and 2× rates of acetochlor and 2× rates of mesotrione and unsafened isoxaflutole provided the greatest reduction of waterhemp density across years. At 30 DAT in soybean, sulfentrazone, flumioxazin, metribuzin, and pyroxasulfone provided the highest levels of waterhemp control (84 to 92%), as well as the greatest reduction in waterhemp density both years. A dose–response experiment with soil-applied mesotrione was performed under controlled greenhouse conditions using three waterhemp populations: MCR15 (seed collected from the McLean Co. site), NH41 (progeny obtained from the McLean Co. population by an additional generation of mesotrione selection in the greenhouse), and a sensitive (S). Emergence counts 21 DAT revealed higher seedling survival of MCR15 and NH41 at mesotrione rates of 105 g ha−1 or less compared with the sensitive control. Resistant-to-sensitive (R/S) ratios for NH41 and MCR15 were 12.7 and 8.8, respectively. Field results indicate the McLean Co. waterhemp population demonstrates reduced sensitivity to soil-applied HPPD-inhibiting herbicides. This is supported by greenhouse results that demonstrate reduced sensitivity to mesotrione in MCR15 and NH41.

Studies were conducted in 2010 and 2011 to determine the effect of herbicide-based Palmer amaranth management systems in ‘Covington' sweetpotato. Treatments consisted of three herbicide application times. Pretransplant applications were flumioxazin at 107 g ai ha−1, fomesafen at 280 g ai ha−1, flumioxazin at 70 g ha−1 plus pyroxasulfone at 89 g ai ha−1, or no herbicide. A second herbicide application was applied within 1 d after transplanting (DAP) and consisted of S-metolachlor at 800 g ai ha−1, clomazone at 630 g ai ha−1, or no herbicide. Two weeks after planting (WAP) plots received S-metolachlor at 800 g ha−1, metribuzin at 140 g ai ha−1, a tank mix of S-metolachlor at 800 g ha−1 plus metribuzin at 140 g ha−1, hand-weeding followed by (fb) S-metolachlor at 800 g ha−1, or no herbicide. Crop tolerance, Palmer amaranth control, and sweetpotato yield in systems containing fomesafen pretransplant were similar to flumioxazin-containing systems. Systems containing flumioxazin plus pyroxasulfone pretransplant resulted in increased crop stunting and decreased sweetpotato yield in 2010, compared with systems containing flumioxazin or fomesafen, but were similar to systems with flumioxazin or fomesafen in 2011. In 2010, systems containing S-metolachlor applied within 1 DAP resulted in increased sweetpotato injury, similar Palmer amaranth control, and reduced no. 1, jumbo, and total sweetpotato yield, compared with systems with clomazone. In 2011, systems containing clomazone were more injurious to sweetpotato than systems receiving S-metolachlor, but Palmer amaranth control and sweetpotato yield were similar. Systems containing metribuzin 2 WAP resulted in increased sweetpotato injury and Palmer amaranth control (in 2010) but similar no. 1 and total sweetpotato yields, compared with systems containing S-metolachlor at 2 WAP. Hand-weeding fb S-metolachlor provided greater Palmer amaranth control and no. 1 sweetpotato yield than did systems of S-metolachlor without a preceding hand-weeding event in 2010.

Field experiments were conducted in 2011 and 2012 in Belle Glade, FL to evaluate the response of sweet corn and weed control to pyroxasulfone on high-organic-matter soils in the Everglades Agricultural Area (EAA) of southern Florida with the use of dose-response curves. Pyroxasulfone was applied PRE at 31.25, 62.5, 125, 250, 500, and 1,000 g ai ha−1 on soil with 80% organic matter. Dose-response curves based on a three-parameter log-logistic model were used to determine pyroxasulfone rate required to provide 90% control (ED90) of spiny amaranth, common lambsquarters, and common purslane in sweet corn. The ED90 values for spiny amaranth, common lambsquarters, and common purslane control were 209, 215, and 194 g ha−1 of pyroxasulfone, respectively, at 21 d after treatment (DAT). At 42 DAT, the ED90 values for spiny amaranth, common lambsquarters, and common purslane control were 217, 271, and 234 g ha−1 of pyroxasulfone, respectively. Sweet corn yield increased with increasing rates of pyroxasulfone. An estimated 214 g ha−1 of pyroxasulfone was required to maintain sweet corn yield at 90% level of the weed-free yield. In addition, pyroxasulfone did not result in sweet corn injury. These results indicate that pyroxasulfone can provide effective weed control in sweet corn on high-organic-matter soils of the EAA.

Fresh market tomato is an important and valuable crop in Florida, accounting for 630 million dollars farm-gate value, which was 45% of the total value of the U.S. crop in 2010. In order to maintain or increase its productivity, labeled herbicide alternatives to methyl bromide are important to limiting seed production of weeds emerging between the raised plasticulture beds. A study was conducted inside a greenhouse where carfentrazone was applied as a drench at 0.03125×, 0.0625×, 0.125×, 0.25×, 0.5×, 1×, 2×, 4×, and 8× and as a subsurface irrigation at 0.0625×, 0.125×, 0.25×, 0.5×, 1×, 2×, 4×, 8×, and 16× rates. The 1× rate equaled the maximum labeled rate of carfentrazone (35.1 g ai ha−1) that would be applied to an area of 0.360 m2. Both the drench and subsurface trials showed an increase in plant injury and reduced growth as the rate of carfentrazone increased. The drench trial, however, was observed to have higher visible injury and greater growth reduction (based on plant measurement) than the subsurface trial, when comparing similar rates. For the 1× rate of carfentrazone in the drench trial vs. the subsurface trial, injury was 66 and 24.5%, respectively. For the 1× rate the tomato plants had estimated growth, based on the curves fit for the data, of 4.8% vs. 39.9% for the drench and subsurface trials, respectively. The subsurface trial better represents what happens in the field when carfentrazone root uptake injury is observed since it is normally observed to be around 10% or less. This still leaves a level of concern; once a 10% injury level in the subsurface trial was estimated to have reduced tomato growth, fruit weight, and total shoot dry weight by 33, 15, and 9.5%, respectively.

Camelina is an emerging oilseed crop suitable for biofuel production in dryland cropping systems of the northwestern United States. Currently, camelina growers have limited herbicide options available for weed control. Tolerance of camelina to PRE applications of quinclorac, S-metolachlor, dimethenamid-P, pendimethalin, and pyroxasulfone was evaluated at two locations (Kalispell in 2009 and 2010, and Huntley in 2010 and 2011) in Montana. Susceptibility to each herbicide was determined at three different rates. Quinclorac applied PRE at 280 to 840 g ai ha−1 did not significantly injure camelina, and had no negative effect on plant density, biomass, flowering, and yield at either location. S-Metolachlor at 1,060 to 2,140 g ai ha−1 caused less than 20% injury to camelina, with no reductions in plant density, biomass, and yield compared with the nontreated check. Dimethenamid-P applied at 630 g ai ha−1 did not affect camelina density, biomass, flowering, and yield; however, at the 1,260 g ha−1 rate, injury was as high as 60% (in the coarse-textured Kalispell soil), and plant density and yield were reduced as much as 50 and 31%, respectively, in addition to delayed flowering. Despite causing some visual injury to camelina, crop yield was not reduced by pendimethalin at the 1,060 or 2,130 g ai ha−1 rate. Pyroxasulfone caused significant crop injury, stand loss, and yield reductions, and thus does not appear to be a viable option for weed control in camelina. Camelina plants that exhibited early-season injury showed robust growth and compensatory abilities, with lack of significant effect of herbicides on late-season plant height and biomass at least in one of the two locations. On the baseis of this research, quinclorac was the safest of all herbicides tested in camelina. Dimethenamid-P, S-metolachlor, and pendimethalin also may have an acceptable level of crop safety at lower use rates for possible registration in camelina.

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.

Growth chamber experiments were conducted to assess the effects of foliage-only, soil-only, and foliage-plus-soil placements of amicarbazone on annual bluegrass and creeping bentgrass growth. Evaluated herbicide treatments included amicarbazone at 49 or 147 g ai ha−1, as well as bispyribac-sodium at 74 g ai ha−1 for comparative purposes. Data from this research agree with previous reports of amicarbazone plant uptake. Amicarbazone is absorbed via above- and belowground pathways; however, plant growth is inhibited more by root uptake. Compared to foliage-only amicarbazone placement, soil-only placement more than doubled reductions in aboveground biomass and root mass 56 d after treatment (DAT), whereas no differences were detected between placements including soil contact. Across all evaluated parameters in this research, amicarbazone (49 g ha−1) impacted creeping bentgrass growth similarly to bispyribac-sodium, whereas annual bluegrass growth was inhibited more by amicarbazone, suggesting it provides a more efficacious chemical option for end-user applications.

Downy brome is one of the leading plant pests in winter wheat and no-till spring wheat in many areas of the country. It has recently been studied in North Dakota where it is emerging as a serious crop competitor. Downy brome plants produced up to 60 tillers and more than 7,500 seeds when no control measures were used and densities were less than 2 plants m−2. Experiments focusing on herbicide-application timing identified differences in downy brome control and the grain yield of spring wheat. Regardless of fall or spring application timing, glyphosate applied PRE to wheat completely controlled downy brome in 2007. In 2008, control was not achieved with the earliest glyphosate-application timings because of late-emerging plants. When comparing fall and spring application timings of other herbicides, imazapic provided at least 79% control at each timing and location, resulting in the highest imazamox-resistant spring wheat yield. In general, herbicides performed better when applied in fall than they did when applied in spring. When herbicides were applied POST, imazamox provided the greatest downy brome control and usually caused the largest numerical reduction in downy brome biomass, seed, and stem number. If downy brome was left untreated, regression analysis predicted approximately 2,000 stems m−2 could result in total yield loss of spring wheat.

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.

Three experiments were conducted to evaluate early POST control of yellow woodsorrel using PRE-applied herbicides. In experiment 1, yellow woodsorrel was seeded at two dates in a commercial pine-bark substrate and grown until reaching either the cotyledon–one-leaf (C-1L) or two- to four-leaf (2-4L) growth stage. The herbicides isoxaben, indaziflam, and dimethenamid-p were applied at these growth stages. Two rates of isoxaben and indaziflam provided yellow woodsorrel control (≥ 80% reduction in fresh weight [FW]) when applied at the C-1L stage; however, once yellow woodsorrel reached the 2-4L stage, indaziflam was the only herbicide that provided effective control at both rates tested. Experiments 2 and 3 were similar to experiment 1, except two labeled rates of dithiopyr were also evaluated. In experiment 2, all herbicides evaluated provided ≥ 90% reduction in FW of yellow woodsorrel at the C-1L stage. Although no differences in FW were observed among any of the herbicide treatments when yellow woodsorrel were treated at the 2-4L stage, control ratings indicated that indaziflam provided the most effective yellow woodsorrel control. Experiment 3 results also indicated that isoxaben, indaziflam, and dithiopyr controlled yellow woodsorrel (≥ 95% reduction in FW) when treatments were applied at the C-1L stage, whereas dimethenamid-p reduced shoot FW 70%. When yellow woodsorrel was treated after reaching the 2-4L stage, indaziflam provided the greatest control of any herbicide evaluated.

Western salsify has recently formed dense stands in Conservation Reserve Program (CRP) lands in north-central Montana. Our objective was to test the effects of various herbicide treatments and mowing on western salsify and associated vegetation in CRP lands. Six herbicide treatments and one mowing treatment were applied at three sites in 2010. Herbicide treatments included combinations of glyphosate, 2,4-D, dicamba, and/or metsulfuron-methyl applied when western salsify was either in the rosette or early flowering stage. Mowing was applied at the early flowering stage. Herbicide treatments reduced western salsify and increased perennial grass at one of the three sites, which was the site most dominated by western salsify. When dicamba (0.14 kg ae ha−1) plus 2,4-D (0.48 kg ae ha−1) was applied at the rosette stage, western salsify adult plant density and biomass were reduced to zero and perennial grass biomass increased by 108% in 2010. In 2011, western salsify adult plant density was lower across all herbicide treatments compared to the mowed and nontreated plots. Annual grass density increased by up to 400% when herbicide applications including metsulfuron-methyl were applied at the early flowering stage. Mowing did not control western salsify. Results suggest dicamba plus 2,4-D applied at the rosette stage can provide effective control of western salsify and increase perennial grasses without stimulating the emergence of annual grasses.

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.

Dermatitis from poison ivy is an important health problem, and considerable effort is devoted to the control of this virulent weed. Triclopyr, metsulfuron, and two fixed-ratio tank mixtures of triclopyr and metsulfuron were evaluated across a series of rates for poison ivy control. The objective was to test whether tank mixtures are more effective than triclopyr alone. Triclopyr, metsulfuron, and 9 : 1 and 8 : 2 (by weight) mixtures of these two herbicides, respectively, were applied at eight rates to 1-yr old, pot-grown poison ivy plants. Rates ranged in phytotoxicity from none to death. Percentage of control as determined from plant fresh weight reduction relative to a nontreated control was determined at 1 and 4 mo after treatment (MAT). Data were subjected to ANOVA followed by nonlinear regression. Rates required for 95% control at 1 MAT, control of regrowth at 4 MAT, and the costs of these treatments were determined for the herbicides applied alone and the mixtures. Triclopyr alone and metsulfuron alone were consistently the least and the most expensive treatments, respectively. The mixtures were intermediate to these extremes.

Inputs, including herbicides, used in crop production may create negative environmental impacts. One solution to minimize these adverse effects is the adoption of integrated weed management (IWM) with the intention of reducing herbicide use. This study, conducted in 2010, estimates the willingness of farmers to pay for the adoption of more effective weed management methods. Results suggest that the willingness to pay (WTP) for IWM is greater than the WTP for other weed management methods, including chemical weed management and chemical and mechanical weed management. This study also identified a number of factors that influence the adoption of IWM on wheat farms in Iran using a multinomial logit model. Total annual income, area under irrigated wheat, wheat yield loss due to weeds, perennial nature of the weeds, and having awareness of weed resistance to herbicides had a positive effect on the adoption of IWM practices. However, having rain-fed (dryland) wheat cultivation and a larger number of plots on the farm had a negative influence on the choice of IWM.

Field studies were conducted in 2011 and 2012 at the Horticultural Crops Research Station near Clinton, NC, to determine ‘Covington' sweetpotato tolerance to S-metolachlor rate and application timing. Treatments were a factorial arrangement of four S-metolachlor rates (0, 1.1, 2.2, or 3.4 kg ai ha−1) and six application timings (0, 2, 5, 7, 9, or 14 d after transplanting [DAP]). Immediately following application, 1.9 cm of irrigation was applied to individual plots. Sweetpotato injury was minimal for all treatments (≤ 10%). No. 1 grade sweetpotato yield displayed a negative linear response to S-metolachlor rate, and decreased from 25,110 to 20,100 kg ha−1 as S-metolachlor rate increased from 0 to 3.4 kg ha−1. Conversely, no. 1 sweetpotato yield displayed a positive linear response to S-metolachlor application timing and increased from 19,670 to 27,090 kg ha−1 as timing progressed from 0 to 14 DAP. Total marketable sweetpotato yield displayed a quadratic response to both S-metolachlor application rate and timing. Total marketable yield decreased from 44,950 to 30,690 kg ha−1 as S-metolachlor rate increased from 0 to 3.4 kg ha−1. Total marketable yield increased from 37,800 to 45,780 kg ha−1 as application timing was delayed from 0 to 14 DAP. At 1.1 kg ha−1S-metolachlor, sweetpotato storage root length to width ratio displayed a quadratic relationship to application timing and increased from 1.87 to 2.23 for applications made 0 to 14 DAP. At 2.2 kg ha−1 of S-metolachlor, sweetpotato length to width ratio displayed a quadratic response to application timing, increased from 1.57 to 2.09 for 0 to 10 DAP, and decreased slightly from 2.09 to 2.03 for 10 to 14 DAP. Application timing did not influence length to width ratio of sweetpotato storage roots for those plots treated with S-metolachlor at either 0 or 3.4 kg ha−1.

Methyl bromide (MBr) was widely used as a soil fumigant to manage pests in the planting bed prior to transplanting fresh market tomato; however, it has been banned by the United Nations Environment Programme. Alternatives to MBr must be implemented to sustain productivity in fresh market tomato. Dimethyl disulfide plus chloropicrin (DMDS : Pic) is a fumigant alternative to methyl bromide for the management of yellow nutsedge and other soil-borne pests in tomato. Fumigant costs, environmental concerns, and risk mitigation measures encourage reduced fumigant application rates. Virtually impermeable film (VIF) and totally impermeable film (TIF) provide greater fumigant retention than low density and high density polyethylene film, VIF and TIF 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 DMDS : Pic (79 : 21 w/w) for the control of yellow nutsedge in tomato. Treatments included a standard rate of DMDS : Pic (468 L ha−1) under VIF and TIF, a high rate (561 L ha−1) under VIF, three reduced rates (187 L ha−1, 281 L ha−1, and 374 L ha−1) under TIF, and a nontreated control under TIF and VIF. Results indicated rates may be reduced from a standard 468 L ha−1 under VIF to 187 L ha−1 (67% reduction) under TIF while maintaining yellow nutsedge control and tomato yields. In addition, the results indicated that nontreated TIF managed yellow nutsedge better than nontreated VIF because of decreased penetration of the mulch by yellow nutsedge.

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.

Turfgrass weed scientists commonly use visual ratings (VR) to assign a numerical value to a turfgrass or weed response. These ratings lack quantifiable numerical values and are considered subjective. Alternatives to VR, including line intersect analysis (LIA) and digital image analysis (DIA), have been used to varying extents in turfgrass research. Alternatives can be expensive, labor intensive, and can require extensive calibration and increased time for data acquisition. Minimal research has been conducted evaluating rating methods used in turfgrass weed science. Trials were conducted in 2007 and 2008 to evaluate ratings methods used to quantify large crabgrass populations as influenced by tall fescue mowing height (2.5, 5.1, 7.6, and 10.2 cm). Percent large crabgrass cover was assessed utilizing VR, LIA, and DIA to determine if differences existed among evaluation methods. Pairwise comparisons, Pearson's correlation, and linear regression were performed to compare evaluations. All rating methods were significantly correlated to one another. Differences of large crabgrass cover estimates existed between LIA and DIA data at all mowing heights and between VR and DIA data at the 7.6 and 10.2 cm mowing heights in 2007. Authors believe that shadows produced by the turf canopy at higher (≥ 7.6 cm) mowing heights increased DIA estimates of large crabgrass cover. At trial initiation in 2007, researchers did not capture calibration images because the methodology to eliminate a shadow influence using a standard digital image had not been published. Additional DIA calibration in 2008 corrected for canopy shadows, and no differences were observed in large crabgrass cover between all evaluation methods indicated by nonsignificance pairwise comparisons and estimated regression parameters. These data indicate VR are no different than LIA or DIA in estimating large crabgrass cover as affected by tall fescue mowing height.