Introduction
Waterhemp is one of the most troublesome summer annual broadleaf pigweed species in agronomic crops in the United States (Horak and Loughin Reference Horak and Loughin2000). Native to the U.S. Great Plains region (Waselkov and Olsen Reference Waselkov and Olsen2014), waterhemp is rapidly spreading to the northeastern United States with recent reports from New York and Connecticut (Aulakh et al. Reference Aulakh, Kumar, Westrick, Price and Jhala2025; Kumar et al. Reference Kumar, Aulakh, Stanyard, Hunter, Brown, Sosnoskie and Jhala2025). Waterhemp is a C4 dioecious plant, with male and female flowers on separate plants, and with prolific seed production (Bell and Tranel Reference Bell and Tranel2010). On average, a single female waterhemp plant can produce about 250,000 seeds, though some plants can produce >1 million seeds under noncompetitive growing conditions (Sarangi et al. Reference Sarangi, Irmak, Lindquist, Knezevic and Jhala2016; Sellers et al. Reference Sellers, Smeda, Johnson, Kendig and Ellersieck2003). The unique biological characteristics of waterhemp, including prolonged and extended emergence (May through September), the ability to adapt to a wide range of abiotic stresses, rapid and aggressive growth, and prolific seed production have contributed to its dominance in soybean-based crop rotations (Horak and Loughin Reference Horak and Loughin2000; Rosenbaum and Bradley Reference Rosenbaum and Bradley2013; Sarangi et al. Reference Sarangi, Irmak, Lindquist, Knezevic and Jhala2016; Steckel and Sprague Reference Steckel and Sprague2004a). Waterhemp is a highly aggressive and competitive broadleaf weed species that can cause significant yield losses in soybeans (Glycine max L.) and corn (Zea mays L.) (Bensch et al. Reference Bensch, Horak and Peterson2003; Steckel and Sprague Reference Steckel and Sprague2004b). For instance, soybean yield losses up to 43% have been reported when waterhemp interference persisted until 10 wk after soybean unifoliate expansion (Hager et al. Reference Hager, Wax, Stoller and Bollero2002). In another study, season-long interference of waterhemp reduced soybean yields by 37% to 44% (Steckel and Sprague Reference Steckel and Sprague2004a).
Evolution of herbicide-resistant waterhemp is an increasing challenge for crop producers. Currently, waterhemp populations have been reported in the United States with resistance to seven different classes of herbicides, including inhibitors of acetolactate synthase (ALS), photosystem II (PS II), protoporphyrinogen oxidase (PPO), 4-hydroxyphenylpyruvate dioxygenase (HPPD), 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), very-long-chain fatty acid (VLCFA), and synthetic auxins (Figueiredo et al. Reference Figueiredo, Leibhart, Reicher, Tranel, Nissen, Westra, Bernards, Kruger, Gaines and Jugulam2018; Heap Reference Heap2025; Sarangi et al. Reference Sarangi, Stephens, Barker, Patterson, Gaines and Jhala2019; Shergill et al. Reference Shergill, Barlow, Bish and Bradley2018). Resistance to glyphosate has recently been confirmed in waterhemp populations from Connecticut and New York (Aulakh et al. Reference Aulakh, Kumar, Westrick, Price and Jhala2025; Kumar et al. Reference Kumar, Aulakh, Stanyard, Hunter, Brown, Sosnoskie and Jhala2025). Since its first discovery in 2014, waterhemp populations have been reported from 25 different counties in New York (V. Kumar, personnel communication). Rapid spread of waterhemp in New York and the northeastern United States is possibly linked to contaminated animal feed (such as cottonseed meal and hulls), birdseed, manure from animals fed contaminated feed, or contaminated farm equipment purchased from other parts of the country. Increasing reports of glyphosate-resistant (GR) waterhemp populations in New York warrant the development and deployment of effective alternative programs for its control.
Commercialization of stacked trait herbicide-tolerant (HT) soybeans (e.g., XtendFlex and Enlist E3 soybeans) provided new postemergence herbicide options (2,4-D for Enlist E3 and dicamba for XtendFlex, and glufosinate for both Enlist E3 and XtendFlex soybean) for controlling GR weed species, including waterhemp (Kniss Reference Kniss2018; Reddy Reference Reddy2001). These technologies offer farmers enhanced weed control options and flexibility (Meyer et al. Reference Meyer, Norsworthy, Young, Steckel, Bradley, Johnson, Loux, Davis, Kruger, Bararpour, Ikley, Spaunhorst and Butts2015, Reference Meyer, Norsworthy, Young, Steckel, Bradley, Johnson, Loux, Davis, Kruger, Bararpour, Ikley, Spaunhorst and Butts2016). However, for GR waterhemp, a tank-mix partner of postemergence herbicides or a two-pass application of herbicides consisting of effective preemergence followed by (fb) a postemergence herbicide is generally considered an effective strategy for season-long control (Meyer et al. Reference Meyer, Norsworthy, Young, Steckel, Bradley, Johnson, Loux, Davis, Kruger, Bararpour, Ikley, Spaunhorst and Butts2015, Reference Meyer, Norsworthy, Young, Steckel, Bradley, Johnson, Loux, Davis, Kruger, Bararpour, Ikley, Spaunhorst and Butts2016; Norsworthy et al. Reference Norsworthy, Ward, Shaw, Llewellyn, Nichols, Webster, Bradley, Frisvold, Powles, Burgos and Witt2012; Willemse et al. Reference Willemse, Soltani, Benoit, Jhala, Hooker, Robinson and Sikkema2021).
Several studies have previously compared the effectiveness of various preemergence, postemergence, or preemergence fb postemergence herbicide treatments to control GR waterhemp in soybeans in the Midwest and other parts of the United States. For instance, sulfentrazone applied preemergence alone or in combinations with chlorimuron, cloransulam, or S-metolachlor provided excellent control (>90%) of waterhemp for about 2 mo (Hager et al. Reference Hager, Wax, Stoller and Bollero2002; Krausz and Young Reference Krausz and Young2003). Two-pass herbicide treatments of alachlor, flumioxazin, S-metolachlor + metribuzin, or sulfentrazone applied preemergence fb a postemergence application of lactofen or acifluorfen resulted in >85% control of GR waterhemp 3 mo after preemergence in Missouri (Legleiter et al. Reference Legleiter, Bradley and Massey2009). Similarly, Sarangi et al. (Reference Sarangi, Sandell, Kruger, Knezevic, Irmak and Jhala2017) reported that S-metolachlor + metribuzin or fomesafen, sulfentrazone + cloransulam, or saflufenacil + imazethapyr + dimethenamid-P applied preemergence fb a late-postemergence application of glyphosate + fomesafen or acifluorfen provided excellent control (91% to 96%) of GR waterhemp in Nebraska. In a recent study, Singh et al. (Reference Singh, Miller, Peters, Naeve and Sarangi2025) reported excellent waterhemp control (≥95%) using acetochlor applied preemergence fb two-pass postemergence applications. These treatments included 2,4-D + glyphosate applied at mid-postemergence, with or without S-metolachlor, 28 d after the late-postemergence application in 2,4-D/glufosinate/glyphosate-resistant soybean.
No previous information exists on the effectiveness of preemergence, postemergence, and preemergence fb postemergence herbicide treatments for controlling GR waterhemp in dicamba-resistant (DR) soybeans under New York soil and weather conditions. In addition, the combined effectiveness of an integrated approach using a preemergence herbicide fb row cultivation (RC) for controlling GR waterhemp remains unknown, particularly in the context of the smaller, more diversified farms in New York compared with those in the Midwest. Therefore, the main objective of this study was to compare various preemergence, postemergence, preemergence fb postemergence herbicide treatments, or preemergence fb RC for GR waterhemp control in DR soybean. We hypothesized that preemergence fb postemergence herbicide applications and preemergence fb RC may provide effective and consistent control of GR waterhemp compared to preemergence- or postemergence-only programs.
Material and Methods
On-farm field experiments were conducted during 2019 and 2020 soybean growing seasons near Waterloo, New York (42.955111°N, -76.895056°W and 42.955194°N, -76.896444°W, respectively). Selected field sites had historically been planted with corn-soybean rotations with known infestations of GR waterhemp. Preliminary greenhouse studies confirmed that waterhemp populations from these sites had survived twice the labelled field-use rate (1,260 g ae ha−1) of glyphosate (B. Brown, personnel communication). However, the status of multiple resistance to any other herbicide site of action was not known in these populations. The soil type at the experimental site in both years was Odessa silt loam, pH 7.5, with 2% organic matter. The seedbed at both field sites was prepared with two passes of a field cultivator in the spring before soybean planting. A dicamba-resistant (Roundup Ready 2 Xtend) soybean variety (Channel 2119R2X, maturity group 2.1) was planted on May 24, 2019, and May 6, 2020, using a seeding rate of approximately 400,000 seeds ha−1 in rows spaced 76 cm apart. A muriate of potash (0-0-60) was applied at a rate of 140 kg ha−1 K2O before tillage, and urea nitrogen (46-0-0) was broadcast at a rate of 112 kg ha−1 nitrogen.
Field studies were established in a randomized complete block design with each treatment replicated four times in each experimental year. Plots were 7.5 m long by 3 m wide. A total of 13 herbicide combinations, including preemergence, postemergence, and preemergence fb postemergence at recommended field use rates, were evaluated each year and compared with nontreated control plots (Table 1). All herbicides were applied with a CO2-pressurized backpack sprayer equipped with AIXR 110015 flat-fan nozzles (TeeJet Technologies, Glendal Heights, IL) calibrated to deliver 140 L ha−1 at 240 kPa. In addition, a treatment containing preemergence fb RC was also evaluated. In-season RC was achieved using a Double Wheel Hoe (Hoss Tools, Norman Park, GA) with two staggered 15 cm sweeps (30 cm effective width). Two passes were made per row so that 60 cm of the 76-cm rows were cultivated. All selected preemergence herbicides were applied on May 27, 2019, and May 8, 2020, whereas RC treatment and postemergence herbicides were applied on July 8, 2019, and June 18, 2020, when waterhemp was 7 to 12 cm tall and soybean was at the V3 to V4 growth stage.
Table 1. Preemergence and postemergence herbicides tested a .
a Abbreviations: fb, followed by; POST, postemergence; PRE, preemergence; RC, row cultivation.
b Manufacturer locations: Albaugh, LLC, Ankeny, IA; Bayer CropScience, St. Louis, MO; Corteva Agriscience, USA, Indianapolis, IN; FMC Corporation, Philadelphia, PA; Loveland Products, Inc., Greenville, MS; Valent, San Ramon, CA.
Data Collection
Data for mean monthly air temperature (C) and total monthly precipitation (mm) during the study periods in 2019, 2020, and the 30-yr average were obtained from a nearby historical weather station (https://www.ncdc.noaa.gov/cdo-web/search). Weather data during both experimental periods are presented in Table 2. Data on waterhemp densities (plants per square meter) were assessed at 6 wk after preemergence and 8 wk after preemergence/2 wk after postemergence by counting the number of waterhemp plants in four 0.25-m2 quadrats placed randomly in the middle two soybean rows of each plot. Data on percent soybean injury (on a scale of 0% to 100%, where 0% = no visible injury and 100% = complete plant death) was also recorded at 6 wk after preemergence and 8 wk after preemergence/2wk after postemergence both years. At 10 wk after preemergence/4 wk after postemergence, waterhemp plants that survived each treatment were clipped at the soil surface using two 0.25-m2 quadrats per plot, placed in paper bags, and oven dried at 65 C for 5 d to obtain shoot dry biomass. Percent reduction of shoot dry biomass was calculated using Equation 1:
$$\eqalign{& Shoot\; dry\; biomass\; reduction\; (\%) \\& \,\,\,\,\,\,\, =\left[{(BNT-BT)}\over{BNT}\right]\times 100 }$$
Table 2. Monthly mean air temperature (C) and total precipitation (mm) during 2019 and 2020 growing seasons near Waterloo, NY.
where BNT is the average shoot dry biomass of waterhemp from the nontreated plot and BT is the shoot dry biomass of waterhemp from a treated plot. At maturity, soybean plants from a 3.3-m row from the middle of the plot were hand harvested, dried, and threshed using a stationary thresher (Almaco, Nevada, IA) to estimate the grain yield (kilograms per hectare). In addition to waterhemp, other weed species, including common lambsquarters and green foxtail, were also sporadically present in test plots in both years; however, due to the non-uniformity of these weed species across test blocks, data on these weed species are not reported.
Statistical Analysis
Data were subjected to ANOVA using the MIXED procedure in SAS software (v.9.3; SAS Institute Inc., Cary, NC). All data were checked for ANOVA assumptions (normality of residuals and homogeneity of variance) using the UNIVARIATE procedure and Shapiro-Wilk tests in SAS, and those assumptions were met. The ANOVA model included all treatments (preemergence, postemergence, or preemergence fb postemergence or preemergence fb RC) as fixed effects, while replications nested within year were considered as random effects. Due to significant year-by-treatment interaction (P < 0.001), data were analyzed separately for each year. Mean separations were obtained using Fisher’s protected LSD test at P < 0.05.
Results and Discussion
No significant crop injury (<2%) was observed with any of the tested herbicide programs in both years (data not shown). The average monthly air temperatures during the study period (May through September) were consistent across both years and ranged from 12 to 23 C with a total precipitation of 525 mm in 2019 and 465 mm in 2020 (Table 2). The weather conditions during the study periods in both years were typical of the region, as evident from the 30-yr average (Table 2). The total precipitation during May (when soybeans were planted and preemergence herbicides were applied) was higher in 2019 (135 mm) than 2020 (77 mm), and the 30-yr average (82 mm) (Table 2).
2019 Growing Season
GR Waterhemp Density. Among all herbicide combinations tested, acetochlor, flumioxazin, acetochlor + fomesafen + metribuzin, carfentrazone + sulfentrazone + metribuzin, chlorimuron + flumioxazin + metribuzin, and S-metolachlor + sulfentrazone + metribuzin applied preemergence significantly reduced the densities of GR waterhemp (1 to 40 plants m−2) at 6 wk after preemergence compared with nontreated weedy check plots (231 plants m−2) (Table 3). These results are consistent with those reported by Meyer et al. (Reference Meyer, Norsworthy, Young, Steckel, Bradley, Johnson, Loux, Davis, Kruger, Bararpour, Ikley, Spaunhorst and Butts2015), that a significant reduction (87% to 94%) occurred in GR waterhemp density when evaluated at 6 to 8 wk after preemergence applications of premixes/tank-mixes containing acetochlor, flumioxazin, metribuzin, S-metolachlor, and fomesafen in bare-ground studies. Similarly, significant reduction in GR waterhemp density (≤35 plants m−2) has also been reported with premixes or tank mixes of chlorimuron, flumioxazin, S-metolachlor, metribuzin, and sulfentrazone compared with nontreated weedy check plots (307 plants m−2) (Sarangi et al. Reference Sarangi, Sandell, Kruger, Knezevic, Irmak and Jhala2017). Furthermore, Legleiter et al. (Reference Legleiter, Bradley and Massey2009) documented that alachlor, flumioxazin, sulfentrazone, and S-metolachor + metribuzin applied preemergence resulted in reduced densities of GR waterhemp (2 to 3 plants m−2) at 4 wk after preemergence compared with nontreated weedy check plots (105 plants m−2). Significant reductions in GR waterhemp densities (77% to 83%) have also been reported with acetochlor applied preemergence to soybean for 3 to 4 wk (Singh et al. Reference Singh, Miller, Peters, Naeve and Sarangi2025; Strom et al. Reference Strom, Jacobs, Seiter, Davis, Riechers and Hager2022). In contrast, moderate reductions in GR waterhemp densities (89 to 103 plants m−2) were observed with metribuzin and carfentrazone + sulfentrazone applied preemergence at 6 wk after preemergence. The least density reduction (228 plants m−2) was observed with cloransulam applied preemergence (Table 3).
Table 3. Effect of various herbicides and row cultivation on density and shoot dry biomass reduction (% of nontreated) of glyphosate-resistant waterhemp, and grain yield of dicamba-resistant soybean in 2019 near Waterloo, NY.
a Abbreviations: fb, followed by; POST, postemergence; PRE, preemergence; RC, row cultivation; WAPOST, weeks after postemergence; WAPRE, weeks after PRE.
b Means following the same lowercase letters within each column indicates no statistical difference according to Fisher’s protected LSD test (P < 0.0001).
Compared with the nontreated weedy check (160 plants m−2), lower densities of GR waterhemp (2 to 19 plants m−2) were observed with all preemergence and preemergence fb postemergence treatments when evaluated at 8 wk after preemergence/2 wk after postemergence, except for metribuzin, cloransulam, or carfentrazone + sulfentrazone applied preemergence (Table 3). Furthermore, metribuzin and carfentrazone + sulfentrazone applied preemergence also resulted in lower GR waterhemp densities (56 to 78 plants m−2) compared with nontreated plots (160 plants m−2) and cloransulam alone (152 plants m−2). All two-pass strategies, including chlorimuron + flumioxazin + metribuzin applied preemergence fb a postemergence application of lactofen or glyphosate + dicamba or a pass of RC, as well as acetochlor + fomesafen + metribuzin applied preemergence fb a postemergence application of glyphosate + dicamba resulted in significantly lower GR waterhemp densities (2 to 13 plants m−2) (Table 3). These results are consistent with those reported by Spaunhorst et al. (Reference Spaunhorst, Siefert-Higgins and Bradley2014), who obtained excellent control (≥89%) of GR waterhemp with two-pass herbicide strategies that included flumioxazin + chlorimuron applied preemergence fb an early postemergence application of dicamba + glyphosate or dicamba + glyphosate + acetochlor in DR soybean. Postemergence-only treatments, including acetochlor + glyphosate + dicamba and glyphosate + dicamba resulted in slightly lower GR waterhemp densities (118 to 125 plants m−2) compared with nontreated weedy check plots at 8 wk after preemergence/2 wk after postemergence (Table 3). In a multistate field study, Johnson et al. (Reference Johnson, Young, Matthews, Marquardt, Slack, Bradley, York, Culpepper, Hager, Al-Khatib, Steckel, Moechnig, Loux, Bernards and Smeda2010) previously reported 30% to 65% greater control of GR waterhemp with a dicamba + glyphosate mixture compared to sequentially applied glyphosate to dicamba-resistant soybeans.
Shoot Dry Biomass Reduction. Among all tested treatments, acetochlor + fomesafen + metribuzin applied preemergence or two-pass applications of preemergence fb postemergence significantly reduced GR waterhemp shoot dry biomass (≥97% of nontreated) at 10 wk after preemergence/4 wk after postemergence (Table 3). The shoot dry biomass reduction of GR waterhemp was 60% to 85% of nontreated at 10 wk after preemergence/4 wk after postemergence with preemergence treatments of acetochlor, flumioxazin, chlorimuron + flumioxazin + metribuzin, carfentrazone + sulfentrazone + metribuzin, S-metolachlor + sulfentrazone + metribuzin; postemergence-only treatments with acetochlor + glyphosate + dicamba and glyphosate + dicamba; and preemergence fb postemergence treatments consisting of chlorimuron + flumioxazin + metribuzin fb RC. These results are consistent with those reported by Spaunhorst and Bradley (Reference Spaunhorst and Bradley2013), that 55% to 82% fresh biomass reduction of GR waterhemp (7.5 to 30 cm tall) occurred with postemergence-applied glyphosate + dicamba to DR soybean. In contrast, the least shoot dry biomass reduction (16% to 31% of nontreated weed check) of GR waterhemp was observed with preemergence treatments of cloransulam, metribuzin, and carfentrazone + sulfentrazone (Table 3).
Soybean Grain Yield. Consistent with reductions in GR waterhemp densities and shoot dry biomass, two-pass strategies comprising preemergence fb postemergence, or preemergence fb RC, or acetochlor + fomesafen + metribuzin applied preemergence resulted in significantly higher grain yields (2,634 to 2,936 kg ha−1) of DR soybean compared yields from the nontreated weedy check plots (Table 3). Furthermore, soybean grain yield with flumioxazin and S-metolachlor + sulfentrazone + metribuzin applied preemergence as well as glyphosate + dicamba applied postemergence ranged from 1,998 to 2,157 kg ha−1 (Table 3). In contrast, soybean grain yield was highly variable (1,578 to 1,912 kg ha−1) with the rest of the preemergence programs or acetochlor + glyphosate + dicamba applied postemergence, which did not differ from the nontreated weedy check yield (1,387 kg ha−1) (Table 3).
2020 Growing Season
GR Waterhemp Density. Similar to the 2019 growing season, the majority of preemergence herbicides tested in the 2020 growing season, including acetochlor, metribuzin, flumioxazin, chlorimuron + flumioxazin + metribuzin, acetochlor + fomesafen + metribuzin, carfentrazone + sulfentrazone, carfentrazone + sulfentrazone+ metribuzin, and S-metolachlor + sulfentrazone + metribuzin resulted in significantly lower densities of GR waterhemp (1 to 54 plants m−2) at 6 wk after preemergence, compared with weed density in the nontreated weedy check (188 plants m−2) (Table 4). These results are consistent with those reported by Meyer et al. (Reference Meyer, Norsworthy, Young, Steckel, Bradley, Johnson, Loux, Davis, Kruger, Bararpour, Ikley, Spaunhorst and Butts2016), that a significant reduction in GR waterhemp density (77 to 100% of nontreated) was observed at 5 wk after preemergence applications of S-metolachlor or tank mixtures that contained S-metolachlor or metribuzin in combination with 2,4-D. Similarly, Schryver et al. (Reference Schryver, Soltani, Hooker, Robinson, Tranel and Sikkema2017) reported a reduction (87% to 96%) in early-season density of GR waterhemp in soybean at 4 wk after preemergence applications of metribuzin, S-metolachlor + metribuzin, or other premixes containing flumioxazin or sulfentrazone in Ontario, Canada. Slight reductions in GR waterhemp densities (106 to 118 plants m−2) were observed with cloransulam applied preemergence or glyphosate + dicamba applied postemergence at 6 wk after preemergence when compared with nontreated plots (188 plants m−2) (Table 4). It is important to note that several waterhemp populations tested from New York have shown >75% survival when exposed to the field-used rate (11/4 g ha−1) of postemergence-applied chlorimuron/thifensulfuron premix in recent greenhouse study (V. Kumar, personal communication). Therefore, poor control of GR waterhemp with cloransulam applied preemergence observed in this study was probably due to the presence of multiple herbicide resistance to glyphosate and ALS inhibitors. In contrast, no significant differences in GR waterhemp densities were observed between acetochlor + glyphosate + dicamba applied postemergence (161 plants m−2) and nontreated weedy check plots at 6 wk after preemergence. Furthermore, most preemergence (except cloransulam), postemergence, or preemergence fb postemergence strategies, including preemergence fb RC, resulted in lower densities of GR waterhemp (1 to 46 plants m−2) at 8 wk after preemergence/2 wk after postemergence compared with the nontreated weedy check (104 plants m−2). In a recent study conducted in Ontario, Canada, Symington et al. (Reference Symington, Soltani, Kaastra, Hooker, Robinson and Sikkema2024) also reported a lower density (3 to 147 plants m−2) of multiple herbicide–resistant waterhemp at 8 wk after preemergence applications of acetochlor, flumioxazin, metribuzin, or tank mixtures of acetochlor + metribuzin or flumioxazin, or S-metolachlor + metribuzin compared with a nontreated weedy check (882 plants m−2). In contrast, the least reduction in GR waterhemp density (77 plants m−2) was observed 8 wk after preemergence/2 wk after a postemergence application of cloransulam preemergence (Table 4).
Table 4. Effect of various herbicides and row cultivation on density and shoot dry biomass reduction (% of nontreated) of glyphosate-resistant waterhemp, and grain yield of dicamba-resistant soybean in 2020.
a Abbreviations: fb, followed by; POST, postemergence; PRE, preemergence; RC, row cultivation; WAPRE, weeks after PRE; WAPOST, weeks after POST.
b Means following the same lowercase letters within each column indicates no statistical difference according to Fisher’s protected LSD test (P < 0.0001).
Shoot Dry Biomass Reduction. Consistent with density reductions, acetochlor + fomesafen + metribuzin and carfentrazone +sulfentrazone applied preemergence, all two-pass strategies comprising preemergence fb postemergence or preemergence fb RC, and postemergence-only treatments resulted in significant reductions in shoot dry biomass of GR waterhemp (79% to 99% of the nontreated weedy check) at 10 wk after preemergence/4 wk after postemergence (Table 4). The majority of the preemergence-alone treatments provided a moderate reduction (42% to 66% of nontreated) in shoot dry biomass of GR waterhemp at 10 wk after preemergence/2 wk after postemergence. Consistent with density reductions, the least reduction in shoot dry biomass (9% of nontreated) of GR waterhemp was observed when cloransulam applied preemergence (Table 4).
Soybean Grain Yield. Consistent with GR waterhemp suppression (density and biomass), metribuzin, acetochlor + fomesafen + metribuzin, and carfentrazone +sulfentrazone applied preemergence; all two-pass strategies comprising preemergence fb postemergence or preemergence fb RC, and postemergence-only treatments resulted in significantly higher grain yields (3,343 to 4,244 kg ha−1) of dicamba-resistant soybean (Table 4). Soybean grain yield with flumioxazin, acetochlor, chlorimuron + flumioxazin + metribuzin, carfentrazone + sulfentrazone + metribuzin, and S-metolachlor + sulfentrazone + metribuzin applied preemergence ranged from 2,794 to 3,206 kg ha−1, which did not differ from that of the nontreated weedy check (2,765 kg ha−1) (Table 4). The least grain yield was observed with cloransulam applied preemergence (1,599 kg ha−1) (Table 4).
Practical Implications
It is important to note that some of the tested preemergence herbicide premixes containing sulfentrazone (Authority Elite, and Spartan Charge) are currently not labeled for use in New York cropping systems. Information generated from this study may help in further registration of these preemergence herbicides for use in New York soybean production. In addition, the use of low-volatile formulations of dicamba (XtendiMax, Engenia, Fexapan) are no longer legally authorized for use over-the top on DR soybeans. Therefore, some of our results provide pure academic knowledge rather than practicable strategies for GR waterhemp control in DR soybean. But overall, results from this study indicate that two-pass strategies, including preemergence fb postemergence or preemergence fb RC, consistently provided effective control of GR waterhemp. The majority of the preemergence treatments with herbicides belonging to two or more than two sites of action also provided significant control of GR waterhemp during the early growing season in both years. These findings suggest that adoption of these effective preemergence-applied premixes/tank mixes can be used in conjunction with effective postemergence herbicides, which may further help mitigate the spread of GR waterhemp in New York and the northeastern United States (Norsworthy et al. Reference Norsworthy, Ward, Shaw, Llewellyn, Nichols, Webster, Bradley, Frisvold, Powles, Burgos and Witt2012). Furthermore, a preemergence application fb RC effectively controlled GR waterhemp, suggesting the potential use of this nonchemical tool as part of an effective integrated weed management strategy to deplete the seedbank of GR waterhemp.
We recognize that waterhemp has long been a challenging weed in the Midwest and other regions of the United States, and extensive applied research for its control has already been reported. However, waterhemp is a relatively new invasive species for producers in New York, and it has been spreading rapidly across the northeastern United States (Aulakh et al. Reference Aulakh, Kumar, Westrick, Price and Jhala2025; Kumar et al. Reference Kumar, Aulakh, Stanyard, Hunter, Brown, Sosnoskie and Jhala2025). Furthermore, Midwestern states offer more herbicide options for controlling GR waterhemp in soybeans. In contrast, growers in New York have a limited number of registered herbicides that may be used to effectively control GR waterhemp in soybeans. For instance, soil-applied herbicides such as pyroxasulfone (categorized as a Group 15 herbicide by the Weed Science Society of America [WSSA]), sulfentrazone (WSSA Group 14), and isoxaflutole (WSSA Group 27) are not currently registered for use in New York soybean production, whereas these are registered in most Midwestern states. The lack of registration of these active ingredients in New York constrains the range of effective herbicide premixes available for GR waterhemp management. In contrast, Midwestern soybean producers benefit from broader herbicide options that enable more diverse site-of-action rotations, which are critical for delaying the evolution of herbicide resistance. This disparity underscores how regional differences in herbicide registrations can affect management flexibility and long-term resistance-mitigation strategies. In addition, several soybean producers in New York are still relying on a single-pass, glyphosate-based weed control tactics. Information generated through this applied research is critical to support education and outreach efforts aimed at helping New York producers adopt more diversified and effective herbicide strategies for GR waterhemp control.
Acknowledgments
We thank the growers in Seneca County, New York, for providing their field sites and assisting in soybean planting.
Funding
Financial support for this research was provided by the New York Farm Viability Initiative via Grant 19006.
Competing Interests
The authors declare they have no competing interests.
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