Traditional two-pass weed management strategies need to be compared with new strategies in glyphosate/dicamba-resistant soybean. Weed control, soybean yield, partial profitability and environmental impact (EI) were evaluated in glyphosate/dicamba-resistant soybean using dicamba applied alone or in a tank-mix with dimethenamid-P applied preemergence (PRE). Trials were conducted at three locations during 2014 and 2015. Several PRE herbicides provided excellent control of broadleaf and grass weeds. Dicamba provided > 91% control of broadleaf weeds, and the addition of dimethenamid-P improved grass control. All weed species at the trial locations were controlled > 94% following a postemergence (POST) application of glyphosate. Weed interference reduced soybean seed yield 33% where no herbicide was applied. A single POST application of glyphosate had the lowest EI. Several treatments improved early-season weed control and reduced early-season weed density and biomass compared to glyphosate and had similar EI values. In this study, there was no benefit to yield or partial profit by including a PRE herbicide for weed management; however, the inclusion of multiple modes-of-action in a herbicide program may reduce the selection for herbicide-resistant weeds.
Soybean has been grown in Ontario, Canada since 1881 [
Weed control was greatly simplified when glyphosate-resistant (GR) soybean was commercialized in Ontario in 1997. Glyphosate is a Group 9, non-selective herbicide that controls over 300 weed species [
Two-pass weed management strategies including a pre-plant (PP) or pre-emergence (PRE) residual herbicide followed by a postemergence (POST) herbicide often result in full-season weed control using multiple modes-of-action [
Soybean resistant to both dicamba and glyphosate (DR soybean) will be commercially available for the 2017 growing season. Dicamba is a Group 4, systemic broadleaf herbicide that controls over 40 broadleaf weed species [
It is important to design effective weed management strategies for controlling weeds, but with minimal impact on the environment. Brookes and Barfoot [
Farmers must ensure they are producing an economically sustainable crop in addition to herbicide efficacy, herbicide cost, crop safety, and EI. The commercial release of DR soybean provides additional weed control strategies that need to be compared with traditional two-pass weed management strategies in soybean. The objective of this study was to evaluate herbicide programs for their crop safety, weed control efficacy, profitability, and EI in DR soybean produced with conventional tillage.
Field trials were conducted over a two-year period (2014, 2015) at three sites in southwestern Ontario, Canada. The experiments were located at the University of Guelph―Ridgetown Campus, Ridgetown, Ontario; the Huron Research Station, Exeter, Ontario; and the Woodstock Research Station, Woodstock, Ontario. Location, year, seeding date, and herbicide application dates are presented in
The trials were established in a randomized complete block design (RCBD) with four replications. Treatments are listed in Tables 2-7. Treatments included a weedy (non-treated) and weed-free controls. Weed-free plots were maintained weed-free by applying a tank-mix of imazethapyr (100 g∙ai∙ha−1) plus metribuzin (400 g∙ai∙ha−1) PRE and additional POST applications of glyphosate (900 g∙ae∙ha−1) were made as required. Glyphosate/dicamba-resistant soybean (Roundup Ready 2 XtendTM) was seeded at 400,000 seeds ha−1 in plots that were 3.0 m wide (4 rows spaced 0.75 m apart) and 8 and 10 m long in Ridgetown and Exeter, respectively, and 5.75 and 8 m long in Woodstock in 2014 and 2015, respectively.
Herbicides were applied with a CO2-pressurized backpack sprayer calibrated to deliver 200 L∙ha−1 of spray solution at 210 kPa. A 1.5 m spray boom was used equipped with 4 ultra-low drift nozzles (Hypro ULD 120-02, New Brighton, MN,
Environment | Year | Seeding Date | Application timinga | Herbicide application Date |
---|---|---|---|---|
Ridgetown | 2014 | June 04 | PP | June 04 |
POST | July 02 | |||
2015 | May 20 | PP | May 21 | |
POST | June 25 | |||
Exeter | 2014 | June 01 | PP | June 05 |
POST | July 05 | |||
2015 | May 08 | PP | May 09 | |
POST | June 19 | |||
Woodstock | 2014 | June 05 | PP | June 06 |
POST | July 04 | |||
2015 | May 13 | PP | May 14 | |
POST | June 16 |
aPP application timing represents Pre-Plant and POST represents Post-Emergence.
Treatmentab | Rate | AMAREc | AMBEL | CHEAL | POLPE | SETVI |
---|---|---|---|---|---|---|
g∙ai∙ha−1 | % | |||||
Weed-Free Control | 100a | 100a | 100a | 100a | 100a | |
Glyphosate | 900 | 0e | 0g | 0e | 0f | 0h |
Imazethapyr | 100 | 96c | 79de | 90bc | 99abc | 79cde |
Imazethapyr/saflufenacil | 100 | 97abc | 77de | 86cd | 98abcd | 69ef |
Saflufenacil/dimethenamid-p | 245 | 82d | 57f | 65d | 76e | 57f |
Imazethapyr | 75 | 99abc | 91bcd | 97abc | 99ab | 91b |
Metribuzin | 425 | |||||
Chlorimuron | 9 | 98abc | 91bcd | 94abc | 76e | 76de |
Metribuzin | 412 | |||||
Chlorimuron | 9 | 98abc | 87cd | 93bc | 99ab | 90bc |
Imazethapyr | 75 | |||||
Pyroxasulfone | 100 | 98abc | 67ef | 95abc | 98abcd | 87bcd |
Sulfentrazone | 100 | |||||
Dicamba | 600 | 97bc | 99ab | 92bc | 99ab | 20g |
Dimethenamid-p | 544 | 98abc | 89cd | 88c | 85e | 90bc |
Dicamba | 300 | |||||
Metribuzin | 413 | 100ab | 98ab | 99ab | 99ab | 95b |
Imazethapyr | 77 | |||||
Flumioxazin | 96 | |||||
s-metolachlor/metribuzin | 1443 | 97bc | 82cde | 89c | 90cde | 95b |
Pyroxasulfone/flumioxazin | 160 | 100abc | 94bc | 94abc | 88de | 92b |
Means followed by the same letter within a column are not significantly different according to Fisher’s protected LSD test (P = 0.05). aAll PP applications included 900 g∙ae∙ha−1 of glyphosate (Roundup Weathermax 540SL formulation); bAll treatments received a POST application of 900 g∙ae∙ha−1 of glyphosate (Roundup Weathermax 540SL formulation) at the V4 soybean growth stage; cAll data have been pooled across locations and years. Data presented in the table have been backtransformed to the original scale.
Treatmentab | Rate | AMAREc | AMBEL | CHEAL | POLPE | ECHCG | SETVI |
---|---|---|---|---|---|---|---|
g∙ai∙ha−1 | plants m−2 | ||||||
Weedy Control | 12a | 8a | 26a | 6a | 17a | 56a | |
Glyphosate | 900 | 10a | 8ab | 16ab | 6a | 19a | 34ab |
Imazethapyr | 100 | 1b | 6abc | 4cde | 1bcd | 16a | 5defg |
Imazethapyr/saflufenacil | 100 | 0bcd | 4cd | 3def | 1cd | 13abc | 7def |
Saflufenacil/dimethenamid-p | 245 | 1bc | 4cd | 8bc | 2b | 9abcd | 11cd |
Imazethapyr | 75 | 0bcd | 3cde | 1fgh | 0d | 11abc | 4efgh |
Metribuzin | 425 | ||||||
Chlorimuron | 9 | 0bcd | 2de | 2efgh | 1bcd | 14ab | 9cde |
Metribuzin | 412 | ||||||
Chlorimuron | 9 | 0bcd | 5abcd | 4cde | 0d | 10abc | 5defg |
Imazethapyr | 75 | ||||||
Pyroxasulfone | 100 | 0bcd | 5abcd | 1gh | 2bc | 6cde | 4efgh |
Sulfentrazone | 100 | ||||||
Dicamba | 600 | 1b | 1ef | 3defg | 2b | 19a | 23bc |
Dimethenamid-p | 544 | 1bcd | 4bcd | 6cd | 2bc | 4de | 3fgh |
Dicamba | 300 | ||||||
Metribuzin | 413 | 0cd | 1f | 0h | 0d | 7bcde | 2gh |
Imazethapyr | 77 | ||||||
Flumioxazin | 96 | ||||||
s-metolachlor/metribuzin | 1443 | 1bcd | 5abcd | 3def | 1bcd | 4e | 1h |
Pyroxasulfone/flumioxazin | 160 | 0d | 1f | 1gh | 1cd | 4de | 2gh |
Means followed by the same letter within a column are not significantly different according to Fisher’s protected LSD test (P = 0.05). aAll PP applications included 900 g∙ai∙ha−1 of glyphosate (Roundup Weathermax 540SL formulation); bAll treatments received a POST application of 900 g∙ae∙ha−1 of glyphosate (Roundup Weathermax 540SL formulation) at the V4 soybean growth stage; cAll data have been pooled across locations and years. Data presented in the table have been backtransformed to the original scale.
Treatmentab | Rate | AMAREc | AMBEL | CHEAL | POLPE | ECHCG | SETVI |
---|---|---|---|---|---|---|---|
g∙ai∙ha−1 | plants m−2 | ||||||
Weedy Control | 2.0a | 2.1a | 2.5a | 1.2a | 3.5a | 5.2a | |
Glyphosate | 900 | 2.0a | 2.1a | 2.4a | 1.0ab | 3.8a | 5.2a |
Imazethapyr | 100 | 0.3b | 1.3ab | 0.8bc | 0.2def | 1.9b | 0.9cde |
Imazethapyr/saflufenacil | 100 | 0.1b | 0.8bcde | 0.8bc | 0.2def | 1.4bcd | 0.9cd |
Saflufenacil/dimethenamid-p | 245 | 0.4b | 1.0bcd | 1.9ab | 0.7abc | 1.9b | 1.3c |
Imazethapyr | 75 | 0.1b | 0.6bcdef | 0.2cd | 0.1f | 1.2bcd | 0.5def |
Metribuzin | 425 | ||||||
Chlorimuron | 9 | 0.2b | 0.4def | 0.4cd | 0.2def | 1.6bc | 0.8cdef |
Metribuzin | 412 |
Chlorimuron | 9 | 0.1b | 0.8bcde | 0.6cd | 0.1f | 1.2bcd | 0.7cdef |
---|---|---|---|---|---|---|---|
Imazethapyr | 75 | ||||||
Pyroxasulfone | 100 | 0.1b | 1.0bcd | 0.2cd | 0.5bcd | 1.3bcd | 0.7cdef |
Sulfentrazone | 100 | ||||||
Dicamba | 600 | 0.1b | 0.2ef | 0.1cd | 0.3cdef | 3.8a | 2.8b |
Dimethenamid-p | 544 | 0.1b | 0.5cdef | 0.5cd | 0.5bcde | 0.7d | 0.4def |
Dicamba | 300 | ||||||
Metribuzin | 413 | 0b | 0.1f | 0d | 0f | 1.0bcd | 0.2f |
Imazethapyr | 77 | ||||||
Flumioxazin | 96 | ||||||
s-metolachlor/metribuzin | 1443 | 0.1b | 1.0bc | 0.8bc | 0.2cdef | 0.7d | 0.3ef |
Pyroxasulfone/flumioxazin | 160 | 0b | 0.1f | 0.3cd | 0.1ef | 0.8cd | 0.3def |
Means followed by the same letter within a column are not significantly different according to Fisher’s protected LSD test (P = 0.05). aAll PP applications included 900 g∙ae∙ha−1 of glyphosate (Roundup Weathermax 540SL formulation); bAll treatments received a POST application of 900 g∙ae∙ha−1 of glyphosate (Roundup Weathermax 540SL formulation) at the V4 soybean growth stage; cAll data have been pooled across locations and years. Data presented in the table have been backtransformed to the original scale.
Treatmentab | Rate | AMAREc | AMBEL | CHEAL | POLPE | ECHCG | SETVI |
---|---|---|---|---|---|---|---|
g∙ai∙ha−1 | plants m−2 | ||||||
Weed-Free Control | 100a | 100a | 100a | 100a | 100a | 100a | |
Glyphosate | 900 | 96d | 97e | 96e | 96bcd | 97de | 97de |
Imazethapyr | 100 | 99abc | 98de | 99abcd | 100ab | 97cde | 98bcd |
Imazethapyr/saflufenacil | 100 | 99abc | 99cde | 99abcd | 99abcd | 98bcd | 99bc |
Saflufenacil/dimethenamid-p | 245 | 98bcd | 98de | 98de | 96bcd | 96de | 98cde |
Imazethapyr | 75 | 100ab | 99abc | 100ab | 100ab | 97cde | 98bcde |
Metribuzin | 425 | ||||||
Chlorimuron | 9 | 100ab | 99bc | 100ab | 99abcd | 98bcde | 98bcde |
Metribuzin | 412 | ||||||
Chlorimuron | 9 | 100ab | 99bcd | 100abc | 100a | 97cde | 99bcd |
Imazethapyr | 75 | ||||||
Pyroxasulfone | 100 | 100ab | 99bcd | 100ab | 95d | 99abc | 99b |
Sulfentrazone | 100 | ||||||
Dicamba | 600 | 96cd | 99bcd | 98de | 98abcd | 95e | 97e |
Dimethenamid-p | 544 | 98bcd | 99bcd | 98cde | 95cd | 97de | 98bcde |
Dicamba | 300 | ||||||
Metribuzin | 413 | 100a | 100ab | 100a | 100a | 97de | 98bcde |
Imazethapyr | 77 | ||||||
Flumioxazin | 96 | ||||||
s-metolachlor/metribuzin | 1443 | 99abcd | 99cde | 98bcde | 98abcd | 100ab | 99b |
Pyroxasulfone/flumioxazin | 160 | 100ab | 100abc | 100ab | 99abc | 98bcde | 99bc |
Means followed by the same letter within a column are not significantly different according to Fisher’s protected LSD test (P = 0.05). aAll PP applications included 900 g∙ae∙ha−1 of glyphosate (Roundup Weathermax 540SL formulation); bAll treatments received a POST application of 900 g∙ae∙ha−1 of glyphosate (Roundup Weathermax 540SL formulation) at the V4 soybean growth stage; cAll data have been pooled across locations and years. Data presented in the table have been backtransformed to the original scale.
Treatmentab | Rate | AMAREc | AMBEL | CHEAL | POLPE | ECHCG | SETVI |
---|---|---|---|---|---|---|---|
g∙ai∙ha−1 | plants m−2 | ||||||
Weed-Free Control | 100a | 100a | 100a | 100a | 100a | 100a | |
Glyphosate | 900 | 96d | 97e | 96e | 96bcd | 97de | 97de |
Imazethapyr | 100 | 99abc | 98de | 99abcd | 100ab | 97cde | 98bcd |
Imazethapyr/saflufenacil | 100 | 99abc | 99cde | 99abcd | 99abcd | 98bcd | 99bc |
Saflufenacil/dimethenamid-p | 245 | 98bcd | 98de | 98de | 96bcd | 96de | 98cde |
Imazethapyr | 75 | 100ab | 99abc | 100ab | 100ab | 97cde | 98bcde |
Metribuzin | 425 | ||||||
Chlorimuron | 9 | 100ab | 99bc | 100ab | 99abcd | 98bcde | 98bcde |
Metribuzin | 412 | ||||||
Chlorimuron | 9 | 100ab | 99bcd | 100abc | 100a | 97cde | 99bcd |
Imazethapyr | 75 | ||||||
Pyroxasulfone | 100 | 100ab | 99bcd | 100ab | 95d | 99abc | 99b |
Sulfentrazone | 100 | ||||||
Dicamba | 600 | 96cd | 99bcd | 98de | 98abcd | 95e | 97e |
Dimethenamid-p | 544 | 98bcd | 99bcd | 98cde | 95cd | 97de | 98bcde |
Dicamba | 300 | ||||||
Metribuzin | 413 | 100a | 100ab | 100a | 100a | 97de | 98bcde |
Imazethapyr | 77 | ||||||
Flumioxazin | 96 | ||||||
s-metolachlor/metribuzin | 1443 | 99abcd | 99cde | 98bcde | 98abcd | 100ab | 99b |
Pyroxasulfone/flumioxazin | 160 | 100ab | 100abc | 100ab | 99abc | 98bcde | 99bc |
Means followed by the same letter within a column are not significantly different according to Fisher’s protected LSD test (P = 0.05). aAll PP applications included 900 g∙ae∙ha−1 of glyphosate (Roundup Weathermax 540SL formulation); bAll treatments received a POST application of 900 g∙ae∙ha−1 of glyphosate (Roundup Weathermax 540SL formulation) at the V4 soybean growth stage; cAll data have been pooled across locations and years. Data presented in the table have been backtransformed to the original scale.
Treatmentab | Rate | Yieldc | EI | Partial Profit |
---|---|---|---|---|
g∙ai∙ha−1 | t∙ha−1 | $ ha−1 | ||
Weed-Free Control | 1.82b | |||
Weedy Control | 2.73a | |||
Glyphosate | 900 | 2.58a | 13.8 | 983a |
Imazethapyr | 100 | 2.67a | 15.7 | 944a |
Imazethapyr/saflufenacil | 100 | 2.60a | 15.2 | 925a |
Saflufenacil/dimethenamid-p | 245 | 2.66a | 17.0 | 959a |
Imazethapyr | 75 | 2.77a | 27.3 | 969a |
Metribuzin | 425 |
Chlorimuron | 9 | 2.73a | 25.6 | 969a |
---|---|---|---|---|
Metribuzin | 412 | |||
Chlorimuron | 9 | 2.63a | 15.4 | 932a |
Imazethapyr | 75 | |||
Pyroxasulfone | 100 | 2.75a | 16.2 | |
Sulfentrazone | 100 | |||
Dicamba | 600 | 2.66a | 29.6 | 949a |
Dimethenamid-p | 544 | 2.70a | 28.2 | 949a |
Dicamba | 300 | |||
Metribuzin | 413 | 2.68a | 29.6 | 923a |
Imazethapyr | 77 | |||
Flumioxazin | 96 | |||
s-metolachlor/metribuzin | 1443 | 2.73a | 17.0 | 960a |
Pyroxasulfone/flumioxazin | 160 | 2.65a | 18.0 | 956a |
Means followed by the same letter within a column are not significantly different according to Fisher’s protected LSD test (P = 0.05). aAll PP applications included 900 g∙ae∙ha−1 of glyphosate (Roundup Weathermax 540SL formulation); bAll treatments received a POST application of 900 g∙ae∙ha−1 of glyphosate (Roundup Weathermax 540SL formulation) at the V4 soybean growth stage; cAll data have been pooled across locations and years. Data presented in the table have been backtransformed to the original scale.
United States) spaced 0.5 m apart. Glyphosate (900 g∙ae∙ha−1) was applied POST at the V4 soybean growth stage. This application represented the second herbicide application timing in the two-pass weed control programs evaluated.
Visual assessments of crop injury were made at 2 and 3 weeks after soybean emergence (WAE) using a scale from 0 to 100, where 0 represented no injury and 100 indicated soybean death. Six weed species were evaluated including redroot pigweed, common ragweed, common lambsquarters, lady’s thumb (Persicaria maculosa S.F. Gray), barnyardgrass (Echinochloa crus-galli (L.) P. Beauv.) and green foxtail (Setaria viridis (L.) P. Beauv.). Weed control was rated visually 3 WAE and before the in-crop POST application of glyphosate; ratings were also conducted at 4 and 8 weeks after POST application (WAA). Weed density and aboveground dry weight were determined for each plot at 3 WAE within a randomly selected 1-m2 area. Weeds were placed in paper bags and dried at 60˚C for 7 days and dry weight was recorded. Soybean seed yield and harvest moisture was determined by harvesting the center two rows of each plot with a small plot combine; yields were adjusted to 13% moisture.
Treatment effects were assessed by ANOVA using the PROC MIXED procedure in SAS Version 9.4 (SAS Institute, Cary, NC). Data from each experiment were combined across environment and year because no significant interactions between environment and treatment were detected (P > 0.05). Random effects included environment, block, and treatment by environment; the fixed effect was the herbicide treatment. The significance of variable and fixed effects were confirmed using the Z- and F-test at a P-value of P = 0.05. The assumptions of the ANOVA were confirmed by applying the PROC UNIVARIATE procedure and using the Shapiro-Wilk test for normality together with studentized residual plots. Weed control data were transformed before analysis using an arcsine square root transformation while weed density and dry weight received a log transformation. Yield data were not transformed. Means from transformed data were back-transformed for presentation purposes. Treatment means were separated using Fisher’s protected LSD at P = 0.05.
The EI of each herbicide program was calculated using EIQ values from Kovach et al. [
A partial profit analysis compared the profitability of the herbicide treatments. The profitability of each treatment was determined by subtracting the costs of the herbicide and herbicide application from the gross economic return. Gross returns were determined by multiplying the plot yield by the average Ontario soybean price for the month of October in 2014 and 2015 (Blair Andrews, personal communication, 2016). Annual herbicide costs were calculated based on the herbicide retail prices provided by AGRIS (AGRIS Co-operative Ltd., 2015), and the cost of the herbicide application was based on the Ontario Field Crop Budgets [
There was minimal soybean injury (<5%) observed in this study (data not shown).
There were six dominant weed species in this study including redroot pigweed, common ragweed, common lambsquarters, lady’s thumb, barnyardgrass, and green foxtail. Barnyardgrass emerged later in the season so no data are presented for the 3 WAE evaluation timing. There were no weeds at the time of soybean seeding because of secondary tillage before seeding. The glyphosate-only treatment received a POST application of glyphosate (900 g∙ae.∙ha−1); consequently, the level of weed control was equal to the weedy check prior to the POST application.
Herbicides applied PRE alone or in-combination with others provided good to excellent early season weed control prior to the POST application of glyphosate. At 3 WAE, saflufenacil/dimethenamid-p (245 g∙ai∙ha−1) provided the lowest numeric control and controlled redroot pigweed, common ragweed, common lambsquarters, lady’s thumb and green foxtail 82, 57, 65, 76 and 57%, respectively (
Herbicide programs evaluated provided >80% control of broadleaved and grass weed species 3 WAE at most study sites, which is similar to the results reported in previous studies evaluating PRE or PP herbicide applications in soybean [
Herbicide tank-mixes applied PRE reduced broadleaf and grass weed density and biomass 3 WAE (
All PRE followed by glyphosate POST weed management programs provided >95% weed control 4 WAA where glyphosate (900 g∙ai∙ha−1) was applied POST in V4 soybean (
The two-pass weed control programs controlled annual broadleaf and grass weeds similarly at 4 and 8 WAA. Across all treatments, the control of broadleaved and grass was 95% to 100% and 94% to 99%, respectively (
Weed interference in the weedy control reduced soybean yield 33% compared to the weed-free control (
There was no difference in partial profit among herbicide programs. All herbicide treatments produced similar partial profits. Glyphosate was the lowest cost weed management program and was 33% of the cost of the second lowest cost weed management program. The low cost of glyphosate combined with only one application cost contributes to why this treatment demonstrated the highest partial profit in this study. It is important to note, however, that if a single POST application of glyphosate was not applied in a timely matter, soybean would be exposed to a longer period of early-season weed interference, potentially causing greater yield losses which may result in lower partial profits. Additionally, in fields where higher weed pressures exist, or where one or more difficult-to-control or GR weeds are present, glyphosate may not adequately control the weed population, which could also contribute to greater yield losses and lower partial profits. The development of glyphosate resistant weeds is a topic of concern; from a stewardship perspective, a herbicide program consisting only of glyphosate should be avoided to reduce the risk of selecting for GR weed biotypes. Since there were no differences in partial profits between the glyphosate-only herbicide program and other two-pass weed control programs with multiple modes-of-action, it is recommended that a two-pass weed control program be employed.
The environmental impact of the herbicide programs included in this study ranged from 13.8 to 29.6 (
Generally, two-pass weed control programs provided excellent grass and broadleaved weed control and controlled weeds early in the growing season during the CWFP. Although there were differences in early-season weed control among the herbicide treatments, weeds were controlled by the follow-up POST application of glyphosate. Although past research demonstrates the importance of early weed control during the CWFP, differences in soybean seed yield were not detected. Partial profits were similar among the herbicide treatments. Because of the similarities in yield and partial profit among the treatments, soybean producers may find it attractive to use a single application of glyphosate as their weed control program of choice; however, there are several risks of utilizing a single mode-of-action. Dicamba provided excellent broadleaf weed control, and when combined with a grass herbicide, grass weeds were also controlled. Herbicide programs that contained dicamba resulted in soybean yields and partial profits similar to current industry standards. The use of dicamba in DR soybean will provide control of troublesome broadleaf weeds in soybean, and its importance as a soybean herbicide will increase as the presence of GR broadleaf weeds increases across Ontario.
Underwood, M.G., Soltan, N., Hooker, D.C., Robinson, D.E., Vink, J.P., Swanton, C.J. and Sikkema, P.H. (2017) Weed Control, Environmental Impact, and Net-Profit of Two-Pass Weed Management Strategies in Dicamba-Resistant Soybean (Glycine max) Using Conventional Tillage. American Journal of Plant Sciences, 8, 3414-3428. https://doi.org/10.4236/ajps.2017.813229