The development of glufosinate-resistant soybean cultivars has created opportunities for use of glufosinate applied postemergence for weed control. Four field experiments were conducted in 2021 and 2022 to ascertain the effect of glufosinate rate and the addition of ammonium sulfate on annual weed control in glyphosate/glufosinate/2,4-D–resistant soybean. An increased glufosinate rate of 500 from 300 g ai ha−1 improved control of common ragweed, common lambsquarters, redroot pigweed, and foxtail species and resulted in decreased density and dry biomass of common lambsquarters and foxtail species. The addition of ammonium sulfate to glufosinate increased control of common lambsquarters, 2 and 8 wk after application (WAA), and of foxtail species, 2, 4, and 8 WAA, but did not improve control of common ragweed and redroot pigweed. Increasing the dose of glufosinate from 300 to 500 g ai ha−1 improves control of common ragweed, redroot pigweed, common lambsquarters, and foxtail species; however, the benefit of the addition of ammonium sulfate to glufosinate is weed species-specific.

Glyphosate-resistant (GR) biotypes of horseweed were first confirmed in southern Ontario in 2010 and have spread across southern Ontario. A total of four field experiments were conducted between 2021 and 2022 to determine GR horseweed control with one- and two-pass herbicide programs in glyphosate/glufosinate/2,4-D-resistant (GG2R) soybean. 2,4-D choline/glyphosate DMA, halauxifen-methyl, and saflufenacil applied preplant (PP) controlled GR horseweed by 59%, 72%, and 78% 8 wk after postemergence (POST) application (WAA-POST); there was no improvement of GR horseweed control when 2,4-D choline/glyphosate DMA was added to saflufenacil; in contrast, there was improved GR horseweed control when saflufenacil was added to 2,4-D choline/glyphosate DMA. Glufosinate and 2,4-D choline/glyphosate DMA applied POST controlled glyphosate-resistant horseweed by 71% and 86%, respectively, 8 WAA-POST. Two-pass herbicide programs of a PP followed by POST application provided greater GR horseweed control than a PP or POST herbicide applied alone. Glufosinate or 2,4-D choline/glyphosate DMA applied POST following 2,4-D choline/glyphosate DMA or halauxifen-methyl applied PP improved GR horseweed control by 29% to 38% and 24%, respectively at 8 WAA-POST. The application of 2,4-D choline/glyphosate DMA applied POST following saflufenacil applied PP improved control by 20% 8 WAA-POST; there was no improvement of GR horseweed control when glufosinate was applied POST following saflufenacil applied PP or when either POST herbicide was applied following saflufenacil + 2,4-D choline/glyphosate DMA applied PP. When used in a two-pass program, 2,4-D choline/glyphosate DMA POST provided 2% to 3% greater control of GR horseweed than glufosinate.

Waterhemp control in Ontario has increased in complexity due to the evolution of biotypes that are resistant to five herbicide modes of action (Groups 2, 5, 9, 14, and 27 as categorized by the Weed Science Society of America). Four field trials were carried out over a 2-yr period in 2021 and 2022 to assess the control of multiple-herbicide-resistant (MHR) waterhemp biotypes in glyphosate/glufosinate/2,4-D-resistant (GG2R) soybean using one- and two-pass herbicide programs. S-metolachlor/metribuzin, pyroxasulfone/sulfentrazone, pyroxasulfone/flumioxazin, and pyroxasulfone + metribuzin applied preemergence (PRE) controlled MHR waterhemp similarly by 46%, 63%, 60%, and 69%, respectively, at 8 wk after postemergence (POST) application (WAA-B). A one-pass application of 2,4-D choline/glyphosate DMA POST provided greater control of MHR waterhemp than glufosinate. Two-pass herbicide programs of a PRE herbicide followed by (fb) a POST-applied herbicide resulted in greater MHR waterhemp control compared to a single PRE or POST herbicide application. PRE herbicides fb glufosinate or 2,4-D choline/glyphosate DMA POST controlled MHR waterhemp by 74% to 91% and by 84% to 96%, respectively, at 8 WAA-B. Two-pass herbicide applications of an effective PRE residual herbicide fb 2,4-D choline/glyphosate DMA POST in GG2R soybean can effectively manage waterhemp that is resistant to herbicides in Groups 2, 5, 9, 14, and 27.

Fluazifop-butyl {(±) butyl 2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, haloxyfop-methyl {methyl-2-[4-[[3-chloro-5-(trifluoromethyl-2-pyridinyl] oxy] phenoxy] propanoic acid}, and sethoxydim {2-[1-(ethoxyimino)-butyl]-5-[2-ethylthio)propyl-3-hydroxy-2-cyclohexen-1-one}exhibited soil herbicidal activity to annual grass species in greenhouse and field experiments. Control of forage sorghum [Sorghum bicolor (L.) Moench. ‘Rox Orange’] with all three herbicides was greater when seeds were planted at or near the soil surface than when planted 2, 4, or 6 cm deep. Imbibition of the herbicides by forage sorghum and soybean [Glycine max (L.) Merr.] seeds did not reduce germination at concentrations of 10-3 M or lower, but forage sorghum seedling survival and vigor were reduced by herbicide concentrations as low as 10-7 M. Fluazifop-butyl, haloxyfop-methyl, and sethoxydim were more phytotoxic when applied to the root zone than the shoot zone. Haloxyfop-methyl exhibited the longest soil residual control in the field followed by fluazifop-butyl and sethoxydim. Haloxyfop-methyl and fluazifop-butyl controlled simulated shattercane [Sorghum bicolor (L.) Moench. ♯3 SORVU] in soybeans with preemergence and early postemergence applications, whereas control from similar applications of sethoxydim was limited and variable.

Field studies were conducted to determine the effect of several herbicides on soybean thrips numbers in soybean. Adult soybean thrips numbers in the preplant-incorporated and preemergent herbicide treatments were observed to be either greater than or equal to, but never less than, numbers in the control plots. Larval soybean thrips numbers were not observed to be affected by the preplant-incorporated or preemergent treatments. The postemergence herbicide treatment of naptalam plus dinoseb consistently reduced both adult and larval soybean thrips numbers. The other postemergent treatments did not affect numbers consistently.

Field studies were conducted in 1996 and 1997 at Belleville and Pawnee, IL, to evaluate single and sequential applications of glufosinate on tolerance of glufosinate-resistant corn and annual weed control. Glufosinate caused 0 to 13% corn injury 7 days after treatment (DAT) and 0 to 6% corn injury 28 DAT. Injury was characterized as stunting with glufosinate. Glufosinate at 400 to 1,200 g ai/ha did not reduce final corn height or grain yield. At Pawnee in both years and at Belleville in 1996, a single application of glufosinate at 400 g/ha controlled giant foxtail, velvetleaf, ivyleaf morningglory, and common lambsquarters 85 to 100%. At Belleville in 1997, sequential applications of glufosinate provided greater weed control (87 to 100%) than a single application (0 to 63%) because of weed emergence after application. Weed control with a single application of glufosinate or with nicosulfuron plus bromoxynil was similar at both locations. Height and grain yield of glufosinate-resistant corn were not different from that of glufosinate-susceptible corn (isoline of glufosinate-resistant corn).

Experiments were conducted to evaluate selective herbicides for yellow and purple nutsedge control in nursery crops. Chlorimuron at 0.03 and 0.06 kg ai ha−1 suppressed yellow and purple nutsedge shoot growth either PRE or POST and did not reduce growth of barberry, Burford holly, Compacta holly, azalea, juniper, or photinia, although shoot tip chlorosis was noted in all species except Burford holly and juniper. Imazaquin at 0.25 and 0.5 kg ha−1 and imazethapyr at 0.06 and 0.21 kg ha−1 reduced growth of azalea. Imazethapyr also reduced growth of barberry, juniper, and photinia. Chlorimuron, imazaquin, and imazethapyr inhibited liriope and daylily growth. Pyridate applied at 1.0 and 2.0 kg ha−1 POST did not control purple nutsedge. Pyridate and flurtamone applied POST did not control yellow nutsedge as effectively as chlorimuron, imazaquin, or imazethapyr. Flurtamone at 0.5 and 1.0 kg ha−1 applied PRE or POST controlled purple nutsedge. Both pyridate and flurtamone visibly injured most nursery crops tested, although plants generally outgrew the damage.

The ethyl ester of fenoxaprop {(±)-2-[4-[(6-chloro-2-benzoxazolyl)oxy] phenoxy] propanoic acid} was applied to rice (Oryza sativa L.) that was heavily infested with barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG] during a 3-yr study. Applications were made to two- to three-leaf, three- to four-leaf, five- to six-leaf, or tillering barnyardgrass. Barnyardgrass control at 9 weeks after final treatment was greater than 90% for all growth stages except the 0.1 kg ai/ha rate applied to three- to four-leaf barnyardgrass in 1983. In 1984, the sequential application of fenoxaprop made at the three- to four-leaf stage controlled more than 95% when rated at 9 weeks. Rates of 0.17 and 0.2 kg ai/ha and the sequential treatment of 0.1 kg ai/ha followed by 0.1 kg ai/ha 7 to 10 days later controlled greater than 90% at 9 weeks when applied to three- to four- and five- to six-leaf barnyardgrass in 1985. In general, barnyardgrass was controlled by fenoxaprop rates greater than 0.1 kg ai/ha when applied to any growth stage evaluated up through the five- to six-leaf stage. However, acceptable control of tillering barnyardgrass was achieved in only 1 of 3 years. Yields were increased due to barnyardgrass control all years with all treatments except those applied at tillering. However, control was sufficient to increase yields over that of the check for all tillering treatments except the 0.1 kg ai/ha rate in 1984 and 1985 and the 0.17 kg ai/ha treatment in 1985.

Field experiments were conducted in 1994 and 1995 to evaluate weed control in imidazolinone-resistant corn with postemergence applications of imidazolinone and sulfonylurea herbicides. Imazethapyr controlled 100% of redroot pigweed, jimsonweed, and eastern black nightshade. Control of fall panicum with imazethapyr was inconsistent, with control ranging from 42 to 85%. Imazethapyr provided less than 55% control of common lambsquarters and 43% of large crabgrass. Imazethapyr plus either atrazine, 2,4-D, or dicamba increased control of common lambsquarters compared to imazethapyr alone. Fall panicum control was > 95% with nicosufluron. CGA-152005 and MON 12000 did not control eastern black nightshade. In 1995, corn yield was greater with the hand-weeded check compared to all herbicide treatments. The greatest return over herbicide cost with imazethapyr was obtained with imazethapyr plus atrazine. Nicosulfuron plus CGA-152005 provided the greatest return over herbicide cost when averaged across years.

Yellow nutsedge is a common and troublesome weed in the nursery industry. A selective postemergence herbicide is not available for yellow nutsedge control in most nursery crops. The effectiveness of MON 12000 for PRE and POST control of yellow nutsedge was evaluated in selected field-grown nursery crops. Preemergence control of yellow nutsedge 4 weeks after treatment (WAT) increased from 68% to 95% as MON 12000 rate increased from 0.03 to 0.28 kg ai/ha. At 9 WAT, control ranged from 16 to 73%. MON 12000 at 0.14 kg/ha provided similar PRE control of yellow nutsedge as metolachlor at 2.2 kg/ha. Four WAT, MON 12000 applied POST at 0.03 kg/ha controlled 73% and controlled 86% with the 0.28 kg/ha rate. MON 12000 at 0.14 and 0.28 kg/ha applied POST controlled yellow nutsedge better than bentazon at 1.12, chlorimuron at 0.01, imazaquin at 0.14, or glyphosate at 3.33 kg/ha. MON 12000 injured the foliage of azalea, crape myrtle, cotoneaster, and Japanese holly. Injury was most severe to cotoneaster. MON 12000 reduced azalea, cotoneaster, and crape myrtle shoot fresh weight compared to hand-weeded plots in at least one study. Metolachlor at 2.2 and 4.5 kg/ha caused little injury to the nursery species tested.

Benazolin (4-chloro-2-oxobenzothiazolin-3-ylacetic acid) formulated as the dimethylamine salt was evaluated for common cocklebur (Xanthium pensylvanicum Wallr.) and prickly sida (Sida spinosa L.) control in soybeans [Glycine max (L.) Merr.] between 1977 and 1979. Benazolin was applied alone or in admixtures with acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}, bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4 (3H)-one 2,2-dioxide], dinoseb (2-sec-butyl-4,6-dinitrophenol) plus naptalam (N-1-naphthylphthalamic acid), and 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] over-the-top of soybeans {V3 to V12 [V(N); vegetative stage with “N” nodes on the main stem beginning with the unifoliolate node]}. Benazolin effectively controlled common cocklebur at rates of 0.2 and 0.4 kg/ha. Soybean tolerance was acceptable even with a repeat application of 0.4 kg/ha. Early-season (July) control was less than late season (August) because it took 2 to 3 weeks for benazolin to kill common cocklebur. Prickly sida control was poor with benazolin even at 0.6 kg/ha. Soybean tolerance and seed yields were higher when soybeans were treated with admixtures of benazolin plus bentazon than with benazolin alone. Antagonism was observed with this admixture for prickly sida and late-season common cocklebur control. Antagonism was eliminated with ratios of benazolin to bentazon of 1 to 3 applied in a single application or a 1 to 1.5 ratio repeated.

Field studies were conducted in 1993 and 1994 to evaluate broadleaf weed control in corn with the sulfonylurea herbicide CGA-152005, CGA-152005 was applied at 10 to 50 g ai/ha alone and in combination with 2,4-D, dicamba, or atrazine. No corn injury was observed either year. Metolachlor plus CGA-152005 controlled redroot pigweed, velvetleaf, and common cocklebur 95% or more in 1993 and 1994. Common lambsquarters and ivyleaf morningglory control was dependent on CGA-152005 rate, weed size at application, and growing conditions. In 1994, control of velvetleaf and ivyleaf morningglory with CGA-152005 at 10 or 20 g/ha was less when applied as a tank-mix with atrazine and dicamba compared with when it was applied alone, probably due to antagonism caused by the companion herbicide. Generally, corn yield was related to weed control.

Glyphosate [N-(phosphonomethyl)glycine] toxicity to volunteer wheat (Triticum aestivum L.) and large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] was influenced more by carrier volume than application method. Glyphosate phytotoxicity increased when carrier volume was reduced with both application methods. When compared at equal carrier volumes, there was little difference in volunteer wheat or large crabgrass control when glyphosate was applied with a controlled droplet applicator or flat fan nozzles. Volunteer wheat and large crabgrass control with controlled droplet applicators was influenced by application factors. At a given carrier volume, application factors which yielded larger droplets generally resulted in superior vegetation control.

Common ragweed is an important broadleaf weed in agronomic crops in the northcentral United States. A common ragweed biotype in glyphosate-resistant (GR) soybean production field in southeast Nebraska was not controlled after sequential applications of glyphosate at the labeled rate. The objectives of this study were to confirm GR common ragweed in Nebraska by quantifying the level of resistance in greenhouse and field whole-plant dose-response studies and to evaluate the response of the putative GR common ragweed to POST corn and soybean herbicides. Greenhouse whole-plant dose-response studies confirmed 7- and 19-fold resistance to glyphosate compared to the known glyphosate-susceptible (GS) biotype based on biomass reduction and control estimates, respectively. Field dose-response studies conducted in 2015 and 2016 at the putative GR common ragweed research site suggested that glyphosate doses equivalent to 15- and 40-times the labeled rate (1,260 gaeha–1) were required for 90% control and biomass reduction, respectively. Response of GR common ragweed to POST soybean herbicides in greenhouse studies indicated ≥89% control with acifluorfen, fomesafen, fomesafen plus glyphosate, glyphosate plus dicamba or 2,4-D choline, glufosinate, imazamox plus acifluorfen, and lactofen. POST corn herbicides, including 2,4-D, bromoxynil, diflufenzopyr plus dicamba, glufosinate, halosulfuron-methyl plus dicamba, mesotrione plus atrazine, and tembotrione provided ≥87% control, indicating that POST herbicides with distinct modes of action are available in corn and soybean for effective control of GR common ragweed. Results also suggested a reduced efficacy of the acetolactate synthase (ALS)-inhibiting herbicides tested in this study for control of GR and GS biotypes, indicating further research is needed to determine whether this biotype has evolved multiple herbicide resistance.

Winter bentgrass is a common, shallow-rooted perennial weed of lowbush blueberry fields. This unique production system is typically managed on a biannual cycle with blueberry shoot growth and floral bud development occurring in the first year (vegetative year) and berries harvested in the second year (crop year). An experiment was conducted in two commercial blueberry fields to determine the impact of 0, 143, or 286 kg ha−1 of 14–18–10 fertilizer applied in the vegetative year, and fluazifop-P applications in the vegetative, crop, or both years of the biannual production cycle, on winter bentgrass and blueberry growth and yield. Fluazifop-P tended to reduce winter bentgrass biomass at both sites and the vegetative year-herbicide applications had a greater impact on winter bentgrass ground cover than crop-year applications. Total weed biomass following fluazifop-P applications was reduced in the vegetative year but not the crop year due to an increase in broadleaf weed biomass. Grass biomass tended to increase with fertility inputs in the vegetative year. In all years and sites, the application of fertilizers without herbicides increased grass biomass compared to the use of fertilizers combined with herbicides. Blueberry floral bud numbers per stem, flowers per stem, and berry yield tended to increase with vegetative year applications of fluazifop-P, although differences were not significant. These data indicate that winter bentgrass management is best achieved with herbicide applications in the vegetative year and this might result in yield increases, especially if broadleaf weeds also are adequately controlled.

Ground ivy and khakiweed are troublesome broadleaf weeds of warm-season turfgrass. Field studies were conducted in Tennessee (TN) and Texas (TX) from 2008 to 2010 to evaluate the efficacy of sulfentrazone plus metsulfuron and carfentrazone plus metsulfuron tank mixtures compared with metsulfuron alone for control of ground ivy and khakiweed. In TN, sulfentrazone plus metsulfuron and carfentrazone plus metsulfuron provided accelerated control of ground ivy compared with metsulfuron alone. Over a 2-yr period, ground ivy control with metsulfuron at 10, 21, and 42 g ai ha−1 ranged from 0 to 5% 7 d after treatment (DAT) and 12 to 60% 14 DAT. Ground ivy control with mixtures of sulfentrazone plus metsulfuron ranged from 40 to 72% 7 DAT and 87 to 100% 14 DAT. Similarly, carfentrazone plus metsulfuron controlled ground ivy 5 to 32% 7 DAT and 23 to 93% 14 DAT. In TX, carfentrazone plus metsulfuron and sulfentrazone plus metsulfuron controlled khakiweed greater than metsulfuron alone 7 and 14 DAT as well. Few differences in ground ivy and khakiweed control were detected 56 DAT because metsulfuron applied alone at 21 g ai ha−1 controlled both weeds > 77%, similar to each mixture. These data indicate that when applied in mixtures, sulfentrazone and carfentrazone accelerate ground ivy and khakiweed control with metsulfuron but do not affect long-term efficacy.

Five field trials were conducted over a 2-yr period (2007, 2008) at various locations in Ontario to evaluate the tolerance of black, cranberry, kidney, otebo, pink, pinto, small red Mexican (SRM), and white bean to halosulfuron applied PPI, PRE, and POST at 35 and 70 g ai/ha. There was minimal injury (3% or less) with halosulfuron applied PPI or PRE in dry bean. At Exeter and Ridgetown, halosulfuron applied POST at 35 and 70 g/ha caused 3 to 5% and 4 to 8% injury in dry bean, respectively at 1 wk after herbicide application (WAA). The injury was transient with no significant injury at 2 and 4 WAA. At Harrow, halosulfuron POST at 35 and 70 g/ha caused as much as 4% injury at 35 g/ha and 14% injury at 70 g/ha in dry bean. Halosulfuron applied PPI, PRE, and POST at 35 and 70 g/ha caused no decrease in plant height of dry bean except for kidney bean, which was reduced 6% at 70 g/ha, and white bean, which was reduced 3% at both 35 and 70 g/ha. Halosulfuron applied PPI, PRE, and POST at 35 and 70 g/ha caused no decrease in dry bean yield except for kidney bean, which was reduced 9% at 35 g/ha and 10% at 70 g/ha; otebo bean, which was reduced 3% at 70 g/ha; and white bean, which was reduced 7% at both 35 and 70 g/ha. On the basis of these results, there is an adequate margin of crop safety in dry bean to halosulfuron applied PPI or PRE at 35 and 70 g/ha. In addition, there is an adequate margin of crop safety in black, cranberry, pink, pinto, and SRM bean to halosulfuron applied POST at 35 and 70 g/ha. However, further research is required to ascertain the tolerance of kidney, otebo, and white bean to halosulfuron applied POST.

Weed control in white beans is currently limited by the small number of registered herbicides. The tolerance of two white bean cultivars, ‘AC Compass’ and ‘OAC Thunder’, to various postemergence (POST) herbicides at the maximum use rate and twice the maximum use rate for soybean or corn was evaluated at two Ontario locations in 2001 and 2002. Generally, the two cultivars did not differ in their response to the POST herbicides. POST applications of imazamox plus fomesafen, imazamox plus bentazon, and cloransulam-methyl decreased plant height, shoot dry weight, and yield by as much as 29, 41, and 55%, respectively, and increased seed moisture content up to 3.9%. POST applications of thifensulfuron, chlorimuron, and bromoxynil decreased plant height as much as 57%, shoot dry weight by up to 71%, yield as much as 93% and increased seed moisture content up to 15.5%. Based on these results, AC Compass and OAC Thunder white beans do not possess sufficient tolerance to support the registration of imazamox plus bentazon, imazamox plus fomesafen, cloransulam-methyl, thifensulfuron, chlorimuron, and bromoxynil.

Seeds of a suspected glyphosate-resistant giant ragweed biotype from Lauderdale County, TN, were collected from a continuous cotton field in fall 2007 after plants were nonresponsive to multiple glyphosate applications. The objectives of this research were to (1) confirm resistance by quantifying the response of the putative resistant biotype to glyphosate compared to a susceptible biotype from a nonagricultural area, (2) quantify shikimate accumulation over time in both biotypes, and (3) determine the effectiveness of POST-applied herbicides labeled for use in cotton in controlling both biotypes at three growth stages. The susceptible biotype had a 50% lethal dose of 407 g ae/ha of glyphosate compared with 2,176 g/ha for the resistant biotype when treated at the four-node stage, a 5.3-fold level of resistance. The resistant biotype accumulated 3.3- to 9.8-fold less shikimate than the susceptible biotype at 1 to 7 d after treatment. The resistant biotype was less responsive to glyphosate as treatment was delayed past the two-node stage, much more than the susceptible biotype. Glufosinate, MSMA, and diuron controlled both biotypes by at least 90%, regardless of size at application. Prometryn, flumioxazin, carfentrazone-ethyl, fomesafen, and trifloxysulfuron controlled both biotypes by at least 89% when applied at the two-node stage, but control generally diminished with later application timings. Pyrithiobac was not effective in controlling either biotype, regardless of size at application. Hence, there are effective herbicide options for controlling glyphosate-resistant giant ragweed in cotton, and the resistant biotype does not appear to exhibit multiple resistances to other herbicides.

Herbicide-resistant kochia is an increasing concern for growers in the northwestern United States. Four suspected glyphosate-resistant (Gly-R) kochia accessions (referred to as GIL01, JOP01, CHES01, and CHES02) collected in fall 2012 from four different chemical-fallow fields in northern Montana were evaluated. The objectives were to confirm and characterize the level of glyphosate resistance in kochia accessions relative to a glyphosate-susceptible (Gly-S) accession and evaluate the effectiveness of various POST herbicides for Gly-R kochia control. Whole-plant dose–response experiments indicated that the four Gly-R kochia accessions had 7.1- to 11-fold levels of resistance relative to the Gly-S accession on the basis of percent control ratings (I50 values). On the basis of shoot dry weight response (GR50 values), the four Gly-R kochia accessions exhibited resistance index (R/S) ratios ranging from 4.6 to 8.1. In a separate study, the two tested Gly-R accessions (GIL01 and JOP01) showed differential response (control and shoot dry weight reduction) to various POST herbicides 21 d after application (DAA). Paraquat, paraquat + linuron, carfentrazone + 2,4-D, saflufenacil alone or with 2,4-D, and bromoxynil + fluroxypyr effectively controlled (99 to 100%) and reduced shoot dry weight (88 to 92%) of the GIL01 accession, consistent with the Gly-S kochia accession; however, bromoxynil + MCPA and bromoxynil + pyrasulfotole provided 76% control and 83% shoot dry weight reduction of the GIL01 accession and were lower compared with the Gly-S accession. The JOP01 accession exhibited lower control or shoot dry weight reduction to all herbicides tested, except dicamba, diflufenzopyr + dicamba + 2,4-D, paraquat + linuron, and bromoxynil + pyrasulfotole, compared with the Gly-S or GIL01 population. Furthermore, paraquat + linuron was the only treatment with ≥ 90% control and shoot dry weight reduction of the JOP01 kochia plants. Among all POST herbicides tested, glufosinate was the least effective on kochia. This research confirms the first evolution of Gly-R kochia in Montana. Future research will investigate the mechanism of glyphosate resistance, inheritance, ecological fitness, and alternative strategies for management of Gly-R kochia.