Vipan Kumar

Recent commercialization of herbicide‐resistant (HR) grain sorghum [ Sorghum bicolor (L.) Moench] hybrids, including iGrowth, DoubleTeam, and Inzen enables the use of imazamox, quizalofop, and nicosulfuron, respectively, for annual grass weed control. However, effective season‐long strategies for broad‐spectrum weed control remain lacking. Field studies were conducted in 2021 at Kansas State University Agricultural Research Center near Hays, KS, to evaluate preemergence (PRE) and postemergence (POST) herbicide programs for weed control in these HR sorghum systems. In imazamox‐resistant sorghum, imazamox (79 g ha ^{− 1} ) applied PRE alone or with S ‐metolachlor, PRE S ‐metolachlor followed by ( fb ) POST imazamox, or POST imazamox alone achieved 84%–96% control of green foxtail ( Setaria viridis ) and puncturevine ( Tribulus terrestris ) and reduced total weed biomass by 92%–99%. In quizalofop‐resistant sorghum, PRE atrazine alone or with S ‐metolachlor fb POST quizalofop, alone or tank‐mixed with dicamba, provided 90%–97% green foxtail control. PRE atrazine fb POST quizalofop alone or mixed with 2,4‐D or dicamba controlled puncturevine by 86%–97%. In nicosulfuron‐resistant sorghum, PRE atrazine alone or with S ‐metolachlor fb POST nicosulfuron controlled green foxtail by 88%–93%. PRE atrazine fb POST nicosulfuron plus 2,4‐D or dicamba achieved 84%–95% puncturevine control. Overall, effective PRE and POST programs provided consistent, season‐long control of green foxtail and puncturevine across all three HR sorghum systems.

Widespread evolution of glyphosate resistance among kochia populations is a serious challenge for growers across the North American Great Plains. Dicamba has historically been used to control glyphosate-resistant (Gly-R) kochia. However, the increasing spread of dicamba-resistant kochia and current restrictions on dicamba use (low volatile formulations) warrant alternative herbicide options to control Gly-R kochia. In this context, field-based dose response experiments were conducted in fallow at Kansas State University Agricultural Research Center, Hays, KS, during 2021 and 2022 to determine and compare the effectiveness of 2,4-D, dicamba, and dichlorprop-p applied alone, and in a premixture of 2,4-D/dicamba/dichlorprop-p for controlling Gly-R kochia. Averaged across two years, results indicated that substantially lower doses of 2,4-D, dicamba, and dichlorprop-p were required in a premixture to achieve effective control of Gly-R kochia compared with their standalone applications. Specifically, the ED ₉₀ values for Gly-R kochia control were reduced by 90-, 4-, and 6-times for 2,4-D, dicamba, and dichlorprop-p, respectively, when applied as a premixture. Similarly, achieving 90% biomass reduction required approximately 1021-, 3-, and 4-times lower doses of 2,4-D, dicamba, and dichlorprop-p, respectively, in the premixture than when applied alone. Altogether, these results demonstrated that the premixture of 2,4-D/dicamba/dichlorprop-p can be an effective alternative for managing Gly-R kochia in fallow. The reduced dose requirements in a premixture also suggested potential benefits for resistance management, cost efficiency, and environmental stewardship.

Drill-seeded rice (DSR) offers several agronomic and environmental advantages over conventional puddled-transplanted rice (PTR), including labor and water savings, reduced cultivation costs, and lower greenhouse gas emissions. Despite these benefits, weed control remains a major bottleneck in the widespread adoption of DSR. Imidazolinone (IMI)-resistant rice, which allows the use of imidazolinone herbicides, has the potential to overcome weed control challenges in DSR and can therefore facilitate the transition from PTR to DSR. However, limited information exists on the effectiveness of IMI herbicide–based weed control programs in drill-seeded IMI-resistant rice in northwestern India. Field experiments were conducted in Karnal, India, from the 2020 through 2023 growing seasons to 1) evaluate the timing and rates of imidazolinone herbicides for effective weed control in IMI-resistant rice under DSR conditions, and 2) assess the potential carryover effects of IMI herbicides on succeeding crops. Results showed that sequential early postemergence applications of imazethapyr followed by (fb) late postemergence applications of either 100 fb 150 g ai ha ⁻¹ or 125 fb 125 g ai ha ⁻¹ ) effectively reduced the biomass of key weed species by 83% to 100%, including barnyardgrass, crowfootgrass, and Chinese sprangletop, and provided yields that were similar to weed-free treatments. These sequential postemergence treatments were consistently more effective than conventional preemergence herbicide applications of oxadiargyl fb a postemergence application of bispyribac-sodium. Sequential preemergence fb postemergence applications of imazethapyr were relatively less effective in controlling weeds and minimizing yield losses compared to sequential postemergence applications. However, in the second and third years, oxadiargyl (90 g ai ha ⁻¹ ) applied preemergence fb imazethapyr (100 g ai ha ⁻¹ ) applied postemergence achieved comparable weed control efficiency to those of sequential postemergence applications of imazethapyr (125 fb 125 g ai ha ⁻¹ ). No phytotoxicity was observed in the succeeding crops of wheat, mustard, chickpea, lentil, and corn from any of the herbicide treatments applied to IMI-resistant rice.

Italian ryegrass [ Lolium perenne ssp. multiflorum (Lam.) Husnot] (referred to as L. multiflorum hereafter) is one of the most problematic grass weeds infesting agronomic and specialty crops across the United States. In 2023 to 2025, inadequate control of L. multiflorum populations (NY_R1, NY_R2, and NY_R3) with glyphosate was reported in Livingston, Ontario, and Genesee counties, New York. This research aimed to (1) confirm and quantify glyphosate resistance in these suspected glyphosate-resistant (GR) populations, (2) evaluate the efficacy of alternative postemergence herbicides, and (3) determine whether EPSPS gene amplification confers glyphosate resistance. A known glyphosate-susceptible (GS) population (AR_S) from Arkansas was included for comparison. Glyphosate dose–response assays indicated that NY_R1, NY_R2, and NY_R3 populations were 13-, 4-, and 5-fold resistant, respectively, relative to the AR_S population. Alternative postemergence herbicides, including clethodim, glufosinate, paraquat, and pinoxaden, provided 96% to 97% control and reduced shoot dry weight by 91% to 97% at 21 d after treatment (DAT). In contrast, nicosulfuron provided reduced control (63% to 74%) and limited biomass reduction (51% to 56%), suggesting possible resistance to acetolactate synthase (ALS)-inhibiting herbicides in three tested populations. Quantitative PCR analysis revealed that NY_R1 and NY_R3 had approximately 30-fold higher EPSPS gene copy numbers than AR_S, indicating gene amplification as a mechanism of glyphosate resistance. This study confirms the first case of GR L. multiflorum associated with EPSPS gene amplification in New York, underscoring the need for integrated, diversified weed management strategies to mitigate its spread.

Palmer amaranth is an increasing concern for producers in the northeastern United States. A new Palmer amaranth population (NY_PA) was identified in a soybean field in Ontario County, New York, in 2024. The main objectives of this research were to 1) confirm whether this NY_PA population is resistant to glyphosate and atrazine, and 2) determine the effectiveness of various postemergence herbicides alone or in mixtures to control it. Along with the NY_PA population, two previously known glyphosate-resistant Palmer amaranth populations from Connecticut (CT_PA) and Kansas (KS_PA), and a known glyphosate-susceptible population from Alabama (AL_SUS) were also evaluated. Results from the quantitative polymerase chain reaction assay revealed that the NY_PA population had an average of 180 copies of the 5-enolpyruvylshikimate-3-phosphate synthase ( EPSPS ) gene with a single EPSPS gene copy in the AL_SUS population. A greenhouse dose-response study revealed that the NY_PA and CT_PA populations had 7-fold to 11-fold resistance to atrazine. Nearly all postemergence herbicides tested, including 2,4-D, dicamba, saflufenacil, glufosinate, and lactofen alone or in mixtures with 2,4-D, dicamba, and glufosinate, provided effective control (90% to 100%) of Palmer amaranth weeds collected in Connecticut, Kansas, and New York. All these postemergence herbicides, alone or in mixtures, reduced shoot dry biomass of all three populations by 82% to 97% compared with plants in nontreated control plots. These results confirm the first report of Palmer amaranth populations from New York and Connecticut with resistance to multiple herbicides (glyphosate and atrazine). Effective postemergence herbicides tested in this research can be used to manage these Palmer amaranth populations.

Recent reports of glyphosate-resistant (GR) waterhemp pose serious concerns among crop producers in New York. Field experiments were conducted in 2019 and 2020 near Waterloo, New York, to evaluate the effectiveness of preemergence, postemergence, preemergence followed by (fb) postemergence, and preemergence herbicides fb row cultivation (RC) to control glyphosate-resistant (GR) waterhemp in dicamba-resistant (DR) soybean. In 2019, all two-pass herbicide treatments resulted in significantly reduced GR waterhemp densities (2 to 13 plants m ⁻² ) compared with nontreated plots (160 plant m ⁻² ) at 8 wk after preemergence/2 wk after postemergence, reductions in shoot dry biomass (85% to 99% of nontreated), and greater soybean grain yields (2,659 to 2,936 kg ha ⁻¹ ). In addition, flumioxazin, acetochlor, chlorimuron + flumioxazin + metribuzin, acetochlor + fomesafen + metribuzin, carfentrazone + sulfentrazone + metribuzin, and S -metolachlor + sulfentrazone + metribuzin applied preemergence resulted in significant reductions in GR waterhemp density (3 to 19 plants m ⁻² ) and shoot dry biomass (60% to 98% of nontreated). In 2020, most preemergence (except cloransulam), postemergence only, and preemergence fb postemergence herbicide application strategies resulted in lower densities of GR waterhemp (1 to 46 plants m ⁻² ) compared with nontreated plots (104 plants m ⁻² ) at 8 wk after preemergence/2wk after postemergence and lower shoot dry biomass (66% to 99% of nontreated). All two-pass strategies as well as metribuzin, acetochlor + fomesafen + metribuzin, carfentrazone + sulfentrazone applied preemergence resulted in higher grain yields (3,343 to 4,244 kg ha ⁻¹ ). These results conclude that two-pass strategies tested in this research can consistently provide effective control of GR waterhemp in DR soybean in New York.

Greenhouse and field experiments were conducted in Kansas to test various postemergence herbicides for crop safety and weed control in pearl millet. Five pearl millet hybrids were used in greenhouse experiments and three hybrids (Hyb1, Hyb-2k, Hyb-3k) were used in field experiments at two sites. All herbicides were found to be safe (1% to 5% injury) for use on all pearl millet hybrids in both greenhouse and field experiments at 28 d after application (DAA), except imazamox and nicosulfuron, which were noted to cause 22% to 35% injury. At Site 1 at 42 DAA, 2,4-D, dicamba, bromoxynil + pyrasulfotole, 2,4-D + bromoxynil + fluroxypyr, and dicamba + 2,4-D effectively controlled Palmer amaranth by 88% to 91%, and density was reduced to 2 to 4 plants m⁻² compared with 18 plants m⁻² in nontreated control plots. The least control (60% to 65%) and greatest density (8 plants m⁻²) of Palmer amaranth was observed after applications of imazamox and nicosulfuron. In contrast, green foxtail was effectively controlled by 91% to 92%, and density was reduced to just 2 plants m⁻² when imazamox and nicosulfuron were applied, whereas 13 plants m⁻² were recorded in a nontreated control plot at 42 DAA. No weed emergence was observed at Site 2 regardless of treatment, including nontreated plots. High grain yields were recorded (Hyb1, 3,866 to 4,619 kg ha⁻¹; Hyb-2k, 2,222 to 3,699 kg ha⁻¹; and Hyb-3k, 822 to 1,315 kg ha⁻¹) at both sites after applications of 2,4-D + bromoxynil + fluroxypyr. These results highlight that the postemergence herbicides tested in this study, except imazamox and nicosulfuron, can be safely used for weed control in fields of pearl millet.

Weed management is a major challenge in pearl millet production. Limited herbicide options available for use with pearl millet further complicates weed control. To fill this knowledge gap, field experiments were conducted during the 2023 and 2024 growing seasons in Hays, Kansas, to investigate eight preemergence herbicides (labeled for use in sorghum production) for crop safety and weed control when applied to three pearl millet hybrids. Averaged across two growing seasons, S-metolachlor applied preemergence alone or in combination with atrazine, mesotrione, or atrazine + mesotrione resulted in >95% injury to all three pearl millet hybrids at 28 d after application (DAA). Visible injury with acetochlor + atrazine applied preemergence ranged from 50% to 96% among hybrids at 28 DAA. Atrazine or mesotrione applied alone or in combination were safe (S-metolachlor, which provided 86% control. The greatest green foxtail control (≥99%) was achieved with mesotrione and acetochlor in combination with atrazine applied preemergence. All three hybrids recorded the highest grain yields (4,370 to 5,870 kg ha⁻¹) with atrazine and mesotrione applied separately, and when they were combined. These results suggested that atrazine, mesotrione, or a mixture of atrazine + mesotrione applied preemergence may be safely used for Palmer amaranth and green foxtail control with newly developed pearl millet hybrids.

Cover crops (CCs) are a component of the integrated weed management strategies for controlling herbicide-resistant weed biotypes. A field study was conducted at Kansas State University Agricultural Research Center near Hays, KS, from 2021 to 2024 to determine the effect of spring-planted CCs in combination with residual herbicide on weed suppression during fallow phase and subsequent wheat yield in a no-till winter wheat (Triticum aestivum L.)–grain sorghum [Sorghum bicolor (L.) Moench]–fallow rotation in the semiarid Central Great Plains (CGP). The study site had a natural seedbank of glyphosate-resistant (GR) kochia [Bassia scoparia (L.) A.J. Scott] and Palmer amaranth (Amaranthus palmeri S. Watson). A mixture of CCs (oats [Avena sativa L.]–barley [Hordeum vulgare L.]–spring peas [Pisum sativum L.]) was spring-planted in no-till sorghum stubbles and terminated at the oats heading stage. Four treatments were tested: (1) weedy fallow (no CC and no herbicide), (2) chemical fallow (no CC but glyphosate + flumioxazin/pyroxasulfone + dicamba), (3) CC terminated with glyphosate, and (4) CC terminated with glyphosate + flumioxazin/pyroxasulfone. Across 3 yr, CC at termination reduced total weed density by 78% to 99% and total weed biomass by 93% to 99% compared with weedy fallow. Weed suppression by the CC terminated with glyphosate plus flumioxazin/pyroxasulfone continued for at least 90 d with reduced total weed density of 52% to 80% and total weed biomass reduction by 70% compared with weedy fallow across 3 yr. No differences in subsequent wheat grain yield between CC treatments and chemical fallow were recorded in 2021 to 2022 and 2022 to 2023; however, in 2023 to 2024, chemical fallow and CC terminated with glyphosate + flumioxazin/pyroxasulfone had greater wheat yield than CC terminated with glyphosate only. These results suggest that integration of spring-planted CC with residual herbicide may help suppress GR B. scoparia and A. palmeri in the CGP.

Waterhemp (Amaranthus tuberculatus) is an economically important broadleaf weed that threatens corn and soybean production across the United States. A waterhemp biotype (CT_Res [resistant biotype from Connecticut]) surviving multiple glyphosate applications was identified from a corn field in Connecticut (CT). Greenhouse and laboratory studies were conducted to (1) confirm glyphosate resistance in CT_Res waterhemp biotype and (2) investigate if the glyphosate resistance in CT_Res biotype is due to target‐site‐based mechanism. Dose‐response studies indicated that CT_Res biotype was 5.8‐fold more resistant to glyphosate compared to a known susceptible biotype (NE_Sus) from Nebraska. No point mutation was detected at Pro₁₀₂ or Thr₁₀₆ positions in the EPSPS gene of the CT_Res biotype. The quantitative polymerase chain reaction assays revealed that one of the three CT_Res waterhemp plants had 3.5‐fold higher EPSPS gene copy number (relative to the housekeeping CPS gene), whereas the other two plants did not reveal EPSPS gene amplification. Obviously, the EPSPS gene amplification partially explains glyphosate resistance in newly identified glyphosate‐resistant waterhemp biotype from CT, indicating that alternative mechanisms might exist. This research reports the first case of glyphosate resistance and EPSPS gene amplification in waterhemp from Connecticut and highlights the need for adoption of diversified weed control strategies to prevent its further spread.