Field studies were conducted in 2023 in south-central Texas near Yoakum, south Texas near Castroville, and the High Plains of Texas near New Deal to evaluate sesame’s response to flumiclorac applied postemergence at 0.03, 0.045, or 0.09 kg ha−1. Applications were early postemergence (EPOST), 23 to 32 days after planting (DAP), at the four-leaf pair growth stage or at the four-leaf pair + mid postemergence (MPOST), 45 days later (66 to 77 DAP). Sesame stunting with flumiclorac was evident at all locations and two applications did increase late-season stunting at New Deal and Yoakum. At New Deal, stunting increased with flumiclorac rate. Stunting was more severe (64 to 83%) when evaluated 14 days after EPOSTapplication and decreased thereafter. Yields were not different from the nontreated weed-free control with any flumiclorac rate or application timing. At Yoakum, stunting was most severe 13 day after the EPOST application (48 to 67%). Yields with the EPOST application were not different from the control. All EPOST + MPOST applications reduced yield from the control. At Castroville, stunting was most severe (25 to 39%) 7 days after the EPOST application and decreased as the growing season progressed. Stunting was ≤ 4% when evaluated 62 days after the initial application. Sesame yields decreased as flumiclorac rate increased with sequential applications but not the EPOST-only applications. All application timings reduced yield from the control with the exception of flumiclorac applied EPOST + MPOST at 0.03 kg ha−1. From these results, the use of flumiclorac in sesame poses too great a risk of injury and reduced yields to be a good option.

Palmer amaranth is a summer annual weed native to the southwestern United States and is particularly troublesome across the Cotton Belt. The use of soil-residual herbicides is crucial for cotton producers in the Texas High Plains attempting to achieve early season control of Palmer amaranth and other problematic weeds. A bare-ground field study was conducted in 2022 and 2023 in Halfway, Texas, to evaluate weed control following isoxaflutole + pendimethalin applied preplant incorporated (PPI) or pendimethalin PPI followed by (fb) isoxaflutole applied preemergence alone or combined with seven other cotton residual herbicides, and to determine whether using isoxaflutole PPI would be a useful option for rainfed production systems. In 2022, Palmer amaranth was completely controlled at 28 d after application (DAA) following isoxaflutole + pendimethalin applied PPI fb acetochlor or S-metolachlor applied preemergence, and pendimethalin applied PPI fb isoxaflutole in a tank-mix with diuron, fomesafen, acetochlor, or S-metolachlor applied preemergence. At 42 DAA, PPI treatments that contained isoxaflutole + pendimethalin fb preemergence applications of acetochlor or S-metolachlor, and a PPI treatment with pendimethalin fb isoxaflutole + acetochlor or S-metolachlor applied preemergence increased Palmer amaranth control by ≥12% compared with isoxaflutole + pendimethalin applied PPI fb prometryn applied preemergence and pendimethalin applied PPI fb isoxaflutole + prometryn applied preemergence. In 2023, when assessed at 42 DAA, Palmer amaranth was controlled by >90% with isoxaflutole + pendimethalin applied PPI fb fomesafen or S-metolachlor applied preemergence, and pendimethalin applied PPI fb isoxaflutole applied alone or in a tank-mixture with diuron, fluridone, fomesafen, acetochlor, or S-metolachlor applied preemergence. End-of-season aboveground Palmer amaranth fresh biomass did not vary among treatments in either year. These results suggest that soil-residual control of Palmer amaranth greater than 90% can be achieved for 7 to 9 wk using isoxaflutole-based treatments applied either PPI or preemergence. Furthermore, applying isoxaflutole PPI can be a useful option for achieving early season weed control in cotton production systems.

Field studies were conducted in southwestern Oklahoma (Ft. Cobb) and in south Texas (Yoakum) and the southern High Plains of Texas (Seminole) during the 2019 and 2020 growing seasons to evaluate peanut cultivar tolerance to pyroxasulfone at 0.09 and 0.12 kg ai/ha applied at peanut cracking (CRACK), early postemergence (EPOST), or mid-postemergence (MPOST). No injury from pyroxasulfone was noted at the Texas locations; however, 0 to 4 % stunting (28 to 32 days after treatment) was noted both years in Oklahoma. Pyroxasulfone rate lowered peanut yield only in 2019 at the High Plains location as the untreated check resulted in higher yield than pyroxasulfone at 0.09 kg/ha. The effect of application timing was only evident at the south Texas location in 2019 when the CRACK application produced higher yield than the MPOST application. Peanut grade (SMK+SS) was not affected by pyroxasulfone rate or application timing at Yoakum or Ft. Cobb. Pyroxasulfone rate and application timing had an occasional effect on peanut yield but did not adversely affect quality and has shown to provide excellent control of problem weeds in peanut.

Aims: Studies were conducted to evaluate sesame response to diuron at 1X (1.12 kg ha-1), 2X (2.24 kg ha-1), and 4X (4.48 kg ha-1) the labeled US rate applied at 3- or 4 leaf pair growth stage. Study Design: Treatments consisted of a factorial arrangement of three diuron rates (1.12, 2.24, and 4.48 kg ha-1) and two application timings (3-leaf pair or 4-leaf pair). An untreated check was included in each study with 3-4 replications depending on location. Place and Duration of Study: In south-central Texas near Yoakum (29.2765o N; -97.1237o W) and the High Plains of Texas near New Deal (33.7354o N; -101.7369o W) during the 2022 growing season. Methodology: Sesame variety ‘S-4302’ was seeded 1.0 to 2.0 cm deep under conventionally tilled conditions. Weeds were controlled either by hand-hoeing or with the use of postemegence herbicides. Plot size was two rows (76 cm apart) by 8.9 m at Yoakum and four rows (101 cm apart) by 9.5 m at New Deal. At New Deal, only the two middle rows were sprayed and the other rows were untreated and served as buffers. Sesame was harvested with a small plot combine. An analysis of variance was performed using the ANOVA procedure for SAS to evaluate the significance of herbicides and application timing on sesame response and yield. Fisher’s Protected LSD (0.05) was used for separation of mean differences. Results: Sesame stunting was evident at both locations and increased as diuron rate increased. Stand reductions were noted at Yoakum as diuron at 4.48 kg ha-1 resulted in a 9% stand reduction compared with <1% with diuron at 1.12 or 2.24 kg ha-1. Also, application timing had an effect on sesame growth. Conclusion: Sesame yields decreased as the diuron rate increased at the High Plains location but not the south-central Texas location while application timing had no effect at either location.

Due to the increased adoption of dicamba-tolerant cotton (Gossypium hirsutum L.) and soybean [Glycine max (L.) Merr.], near-by sensitive broadleaf crops such as peanut (Arachis hypogaea L.) are at an increased risk for off-target movement events. Limited data on peanut response to multiple exposure events of reduced rates of glyphosate plus dicamba are available. Therefore, the objective of this study was to determine the impact of multiple exposure events and low rates of glyphosate plus dicamba on peanut yield and grade across multiple locations in the southeast and southwest production regions of the U.S. In 2019/2020, field trials were conducted in seven states (AL, FL, GA, NC, OK, SC, TX). Glyphosate plus dicamba timings were 30 + 60 days after planting (DAP) or 30 + 60 + 90 DAP. Glyphosate plus dicamba rates were 12.6 g ae/ha + 5.6 g ae/ha (1/100X) and 25.2 g ae/ha + 11.2 g ae/ha (1/50X). In the southeast region (AL, FL, GA, NC, SC), peanut yield was not reduced by the 1/100X rate but was reduced 9% by 1/50X rate. Peanut yield was not reduced by any rate or timing in the southwest region (OK, TX). In OK and TX (South), total sound mature kernels were reduced 1% to 4% by the 1/50X rate of glyphosate plus dicamba or when glyphosate plus dicamba was applied 30 + 60 + 90 DAP. Increases in peanut pod malformations (4% to 11%) were observed in GA and NC but this response was not consistent. Multiple off-target exposure events of glyphosate plus dicamba at rates ≤ 1/100X in peanut should not result in significant yield or grade losses but may cause abnormal pod development.

Field studies were conducted during the 2017 through 2019 growing seasons in Texas and Oklahoma to determine weed control when using herbicide systems containing the pre-mixture of carfentrazone plus pyroxasulfone (C + P) applied preemergence (PRE), early postemergence-peanut cracking (EPOST), or postemergence (POST). When pendimethalin was not used as a base PRE herbicide treatment, C + P applied PRE controlled Texas millet [Urochloa texana (Buckl.)] ≤75%; however, the addition of pendimethalin to C + P applied PRE increased control to >85%. Palmer amaranth (Amaranthus palmeri S. Wats.) control was >70% with most C + P systems while smellmelon (Cucumis melo L. var. Dudaim Naud.) control was never <97% with any C + P system. Pitted morningglory (Ipomoea lacunose L.) control in systems with C + P applied either PRE or POST was never <79% while ivyleaf morningglory (Ipomoea hederacea Jacq.) control with C + P systems applied PRE varied from 73 to 90%, applied EPOST from 53 to 95%, and POST from 84 to 98%. The use of the premix of C + P provided excellent season—long residual control of several broadleaf weeds including Palmer amaranth, smellmelon, and morningglory spp. This herbicide mixture offers peanut growers another option to control ALS- and glyphosate-resistant Palmer amaranth, which is becoming a major problem in many areas of Texas and Oklahoma.

The continued development of herbicide-resistant weeds, such as Palmer amaranth, represents a growing concern across the United States Cotton Belt. To mitigate this issue, BASF Corp. developed Axant (TM) Flex cotton, the first quadruple-stacked herbicide resistance germplasm to improve the control of troublesome weed species in cotton. Field studies were conducted in 2022 and 2023 at the Texas Tech University Research Farm near New Deal, TX, to evaluate the response of Axant Flex cotton to topramezone applied alone or in combinations when applied to three-leaf cotton (early-postemergence or EPOST) or to seven-leaf cotton (mid-postemergence or MPOST). No difference in cotton stand was observed between isoxaflutole or prometryn preemergence treatments compared to the nontreated control. In 2022, no EPOST treatment caused greater than 6% crop response at 7 and 14 d after application (DAA). When treatments were made to seven-leaf cotton, crop response did not exceed 18% at 7 and 14 DAA. In 2023, crop response was <= 2% at 28 DAA regardless of application timing. No differences in lint yield were observed following any herbicide treatment when compared to the nontreated control in either year. Additionally, fiber length and strength were not adversely affected by treatments containing topramezone EPOST or MPOST in 2022 and 2023. These results support the potential use of topramezone in Axant Flex cotton to help manage troublesome weeds without detrimental effects on yield and fiber quality.

Multiple herbicide-resistant (MHR) kochia [Bassia scoparia (L.) A.J. Scott] is a concern for farmers in the Great Plains. A total of 82 B. scoparia populations were collected from western Kansas (KS), western Oklahoma (OK), and the High Plains of Texas (TX) during fall of 2018 and 2019 (from the various locations), and their herbicide resistance status was evaluated. The main objectives were to (1) determine the distribution and frequency of resistance to atrazine, chlorsulfuron, dicamba, fluroxypyr, and glyphosate; and (2) characterize the resistance levels to glyphosate, dicamba, and/or fluroxypyr in selected B. scoparia populations. Results indicated that 33%, 100%, 48%, 30%, and 70% of the tested B. scoparia populations were potentially resistant (>= 20% survival frequency) to atrazine, chlorsulfuron, dicamba, fluroxypyr, and glyphosate, respectively. A three-way premixture of dichlorprop/dicamba/2,4-D provided 100% control of all the tested populations. Dose-response studies further revealed that KS-9 and KS-14 B. scoparia populations were 5- to 10-fold resistant to dicamba, 3- to 6-fold resistant to fluroxypyr, and 4- to 5-fold resistant to glyphosate as compared with the susceptible (KS-SUS) population. Similarly, OK-10 and OK-11 populations were 10- to 13-fold resistant to dicamba and 3- to 4-fold resistant to fluroxypyr and glyphosate compared with the OK-SUS population. TX-1 and TX-13 B. scoparia populations were 2- to 4-fold resistant to dicamba, and TX-1 was 5-fold resistant to glyphosate compared with the TX-SUS population. These results confirm the first report of dicamba- and fluroxypyr-resistant B. scoparia from Oklahoma and glyphosate- and dicamba-resistant B. scoparia from Texas. These results imply that adopting effective integrated weed management strategies (chemical and nonchemical) is required to mitigate the further spread of MHR B. scoparia in the region.

Field experiments were conducted in south Texas and the Texas High Plains region during the 2019 and 2020 growing seasons and in Oklahoma in 2020 to evaluate peanut tolerance to norflurazon at 0.56 and 1.12 kg ai/ha applied preemergence (PRE) or early postemergence (EPOST). Weed control with norflurazon applied either preplant incorporated (PPI) or PRE was evaluated in south Texas. Norflurazon at 1.12 kg ai/ha caused more injury than norflurazon at 0.56 kg ai/ha in both years in south Texas, in 2019 in the High Plains region, and in Oklahoma. The EPOST application was more injurious in south Texas but not at the other locations. Peanut yield was only affected in the High Plains in 2020. Norflurazon at 1.12 kg ai/ha applied PRE caused a 25% yield reduction compared to the untreated check. Preplant incorporated applications of norflurazon alone provided 89 to 94% early-season control of Texas millet [Urochloa texana (Buckl.)] and 96 to 100% control of both Palmer amaranth (Amaranthus palmeri L.) and smellmelon (Cucumis melo L.). Norflurazon applied PRE controlled Texas millet 73 to 98%, Palmer amaranth 91 to 98%, and smellmelon 88 to 98% early-season. Late-season weed control was erratic and required the addition of either pendimethalin or ethalfluralin for more consistent weed control. There may be opportunities to utilize norflurazon in peanut in Texas or Oklahoma. However, norflurazon is not a stand-alone herbicide and there is potential for crop injury and yield reductions under certain environments.

Cotton and soybean growers were offered new technologies in 2016, expanding in-crop herbicide options to include dicamba or 2,4-D. Within 3 yr of commercialization, dicamba use in these crops increased 10-fold, and growers began to report Palmer amaranth escapes in dicamba-tolerant production systems in western Tennessee. In 2020, Palmer amaranth seed was collected from eight Tennessee locations where growers witnessed poor control following dicamba. Greenhouse experiments were conducted to evaluate the response of these Palmer amaranth populations to dicamba. In 2021, field experiments were conducted on two tentative dicamba-susceptible populations in Georgia, on three confirmed dicamba-resistant populations in Tennessee, and on a tentative dicamba-susceptible population in Texas to evaluate cotton response following dicamba and to examine if malathion insecticide (a cytochrome P450 inhibitor) would improve weed control and not reduce cotton yield when applied in conjunction with dicamba. Palmer amaranth populations collected in 2020 survived dicamba in the greenhouse at 1, 2, and 4 times the labeled rate. Five Palmer amaranth populations exhibited 15% to 26% survival to the labeled dicamba rate (560 g ha(-1)) in the greenhouse. These findings were reinforced in the field when research on three of those populations in 2021 showed 55% control with the labeled dicamba rate and 69% control with 2 times the labeled rate. This demonstrates that the dicamba resistance allele or alleles were passed between generations. This result was not consistent in the Macon County, GA, or Worth County, GA, locations, where malathion improved dicamba control of 15- to 38-cm-tall Palmer amaranth. Cotton injury was observed when malathion was applied in combination with dicamba. These results further document the evolution of dicamba-resistant Palmer amaranth in Tennessee. Moreover, the nonreversal of resistance phenotype by malathion may suggest that the resistance mechanism is something other than metabolism.

The authors declare no conflicts of interest.

AbstractWith the increase in hectares planted to auxin-resistant cotton, the number of preplant, at-plant, and postplant applications of dicamba and 2,4-D choline to aid in the control of troublesome broadleaf weeds, including glyphosate-resistant Palmer amaranth, has increased. More dicamba and 2,4-D choline applications mean an increased risk of off-target movement. Field studies were conducted in 2019 to 2021 at the Texas Tech University New Deal Research Farm to evaluate dicamba-resistant cotton response to various rates of 2,4-D choline when applied at four growth stages (first square [FS] + 2 wk, first bloom [FB], FB + 2 wk, and FB + 4 wk). Applications of 2,4-D choline were applied at 1,060 (1X), 106 (1/10X), 21 (1/50X), 10.6 (1/100X), 2.1 (1/500X), and 1.06 (1/1000X) g ae ha−1 to Deltapine 1822 XF cotton. Relative to the nontreated control, yield losses were observed in all years at FS + 2 wk and FB from rates of 2,4-D choline ≥ 1/100X. At the FB + 4 wk application, only the 1X rate of 2,4-D choline resulted in a yield reduction in all three years. Micronaire, fiber length, and uniformity were negatively influenced by the 1/10X and 1X rates of 2,4-D choline at various timings in 2019, 2020, and 2021. In addition, short fiber content, neps, and seed coat neps increased where micronaire, fiber length, and uniformity were negatively impacted.

Aims: Determine the influence of sequential spray order and role of glufosinate when used in a system with 2,4-D to control Palmer amaranth at two different growth stages. Study Design: Randomized complete block design with three replications. Place and Duration of Study: A fallow, non-crop field at the Texas A&M AgriLife Research and Extension Center, Lubbock, Texas, during the 2018 and 2019 growing seasons. Methodology: Herbicides were applied to 7 to 15 cm and 25 to 30 cm Palmer amaranth with a handheld 1.93m CO2-pressurized backpack calibrated to deliver 140 L ha-1 at 207 kPa. Palmer amaranth control was visually estimated on a scale of 0 (no control) to 100% (complete control) relative to the nontreated control. Palmer amaranth biomass and density were collected 43 and 36 days after the last sequential application for 7 to 15 cm and 25 to 30 cm Palmer amaranth in 2019. Palmer amaranth control, biomass, and density were subjected to analysis of variance and means were separated using Fisher’s Protected LSD at P=.05. Results: 2,4-D choline + glyphosate followed by glufosinate provided the greatest level of Palmer amaranth control for both sizes of Palmer amaranth. Overall, Palmer amaranth control was not influenced by sequential application timing. Biomass and density were not significantly different among treatments. Conclusion: Sequential application order of glufosinate and 2,4-D was not an important factor for Palmer amaranth control. However, due to 2,4-D label restrictions, applying 2,4-D choline + glyphosate followed by glufosinate may be the best option for maximum efficacy.

Aims: Determine sesame response to ethalfluralin at 0.63, 0.84, or 1.05 kg ha-1 in combination with S-metolachlor at 1.07 or 1.42 kg ha-1 applied and incorporated prior to planting. Study Design: Randomized complete-block with 3 replications. Place and Duration of Study: Studies conducted during the 2019 growing season in the Southern High Plains region of Texas near New Deal (33.5818o N, -101.7794o W) and in south Texas near Yoakum (29.2756o N, -97.1226o W). Methodology: At New Deal, two passes (in opposite directions) using a rolling cultivator with mixing wheels was used to incorporate herbicides within one hour of application. Mixing wheels consists of four to six spider gangs approximately 10 to 13 cm long mounted on a gang tube and set to incorporate the herbicide no greater than 2.0 cm. At the Yoakum locations, listed bed tops were cut so that they were no greater than 7 cm tall. At Yoakum 1, after beds were knocked down, herbicides were applied and incorporated approximately 2.0 cm deep with a similar piece of equipment as used at New Deal. At Yoakum 2, only the mixing action of the Monosem® precision planter was used to incorporate herbicides. Results: At Yoakum, Urochloa texana (Buckl.) control with all ethalfluralin plus S-metolachlor treatments when evaluated 31 to 39 DAP was inconsistent and varied from 62 to 95% while Amaranthus palmeri S. Wats control was 98 to 100% and Trianthema portulacastrum L. control was 81 to 99%. At New Deal, only ethalfluralin at 0.84 kg ha-1 + S-metolachlor at 1.42 kg ha-1 did not reduce stand. All treatments caused sesame injury when evaluated 16 and 72 days after planting; only ethalfluralin at 1.05 kg ha-1 + S-metolachlor at 1.42 kg ha-1 reduced yield. At Yoakum, all herbicide treatments reduced yield regardless of incorporation method (mixing wheel vs planter action).

Field experiments were conducted in the south Texas and Texas High Plains area during the 2018 through 2020 growing seasons and in southwestern Oklahoma in 2020 to evaluate runner peanut cultivars (Georgia-13M, Georgia-09B) and the Spanish cultivar (Ole´) tolerance to diclosulam at 0.026 (the manufacture’s recommended use rate) and 0.052 (twice the manufacture’s recommended use rate) kg ai/ha applied preemergence (PRE) or peanut cracking (CRACK). No diclosulam injury was noted in south Texas; however, in the Texas High Plains and Oklahoma locations significant stunting was noted with diclosulam applied PRE especially under sprinkler irrigation. In 2018 at the High Plains location, under furrow irrigation, no peanut stunting was noted. In 2019 and 2020, under sprinkler irrigation, diclosulam at 0.026 and 0.052 kg/ha applied PRE resulted in early-season stunting of 18 to 59% in both Oklahoma and the Texas High Plains. No late-season stunting was noted in Oklahoma; however, up to 20% stunting was still visible at the Texas High Plains location. No yield differences were noted in south Texas or the High Plains region in 2018 or 2020; however, in 2019 at the High Plains location, peanut yield decreased as diclosulam rate increased but application timing had no effect. At the Oklahoma location, application timing and rate effect were noted. Diclosulam applied PRE and the high rate of diclosulam reduced peanut yield. Issues still exist with diclosulam in the southwest peanut growing areas as seen previously in 2000 despite the different varieties planted. There may be opportunities to utilize diclosulam postemergence (POST) since peanut injury was 5% or less and yields were not reduced when applied CRACK.

The southern United States produces 90% of the nation's cotton, and the Texas High Plains is the largest contiguous cotton producing region. Since 2011, glyphosate-resistant Palmer amaranth has complicated cotton production, and alternatives to glyphosate are needed. Integrating soil residual herbicides into a weed management program is a crucial step to control glyphosate resistant weeds before emergence. The recent development of p-hydroxyphenylpyruvate dioxygenase (HPPD)-resistant cotton by BASF Corporation may allow growers to use isoxaflutole in future weed management programs. In 2019 and 2020, field experiments were conducted in New Deal, Lubbock, and Halfway, Texas, to evaluate HPPD-resistant cotton response to isoxaflutole applied preemergence (PRE) or early postemergence (EPOST) and to determine the efficacy of isoxaflutole when used as part of a season-long weed management program. At the New Deal location, cotton response was observed following the EPOST application, but it never exceeded 10%. Cotton response was greatest following the PRE application in Lubbock in 2019 but did not exceed 14%. In 2020 in Lubbock, cotton was replanted due to severe weather. There was <1% cotton response following the PRE application, and maximum cotton response observed was 9% following EPOST and mid-postemergence (MPOST) applications. Cotton lint yields were not different from those of the nontreated, weed-free control at either location. In non-crop weed control studies in Halfway, all treatments controlled Palmer amaranth >= 94% 21 d after the EPOST application. Twenty-one days after the MPOST treatment, systems with isoxaflutole applied EPOST controlled Palmer amaranth by 88% to 93%, while systems with isoxaflutole PRE controlled Palmer amaranth by 94% to 98%. End-of-season Palmer amaranth control was lowest in the system without isoxaflutole (88%) and when isoxaflutole was used EPOST (88% to 91%). These studies suggest that the use of isoxaflutole in cotton weed management systems may improve season-long control of several troublesome weeds with no adverse effects on cotton yield and quality.

BASF Corp. has developed p-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor-resistant cotton and soybean that will allow growers to use isoxaflutole in future weed management programs. In 2019 and 2020, a multi-state non-crop research project was conducted to examine weed control following isoxaflutole applied preemergence alone and with several tank-mix partners at high and low labeled rates. At 28 d after treatment (DAT), Palmer amaranth was controlled >= 95% at six of seven locations with isoxaflutole plus the high rate of diuron or fluridone. These same combinations provided the greatest control 42 DAT at four of seven locations. Where large crabgrass was present, isoxaflutole plus the high rate of diuron, fluridone, pendimethalin, or S-metolachlor or isoxaflutole plus the low rate of fluometuron controlled large crabgrass >= 95% in two of three locations 28 DAT. In two of three locations, isoxaflutole plus the high rate of pendimethalin or S-metolachlor improved large crabgrass control 42 DAT when compared to isoxaflutole alone. At 21 DAT, morningglory was controlled >= 95% at all locations with isoxaflutole plus the high rate of diuron and at three of four locations with isoxaflutole plus the high rate of fluometuron. At 42 DAT at all locations, isoxaflutole plus diuron or fluridone and isoxaflutole plus the high rate of fluometuron improved morningglory control compared to isoxaflutole alone. These results suggest that isoxaflutole applied preemergence alone or in tank mixture is efficacious on a number of cross-spectrum annual weeds in cotton, and extended weed control may be achieved when isoxaflutole is tank-mixed with several soil-residual herbicides.

Field studies were conducted in south and the High Plains of Texas as well as in southwestern Oklahoma during the 2014 and 2015 growing seasons to evaluate the effects of glyphosate plus dicamba combinations (1/16 X to 1 X of the 1.68 kg ae ha-1 rate) applied 30, 60, and 90 days after planting (DAP) on Spanish (Oklahoma) and runner (Texas) peanut. Rates were established to evaluate sub-labeled drift and direct application of a 1 X rate. Peanut stunting and death were more prevalent at the 30 and 60 DAP application while peanut were more tolerant of the 90 DAP application. In south Texas, peanut yields were reduced in both years when rates of ¼ X or greater were applied 30 and 90 DAP while rates of 1/8 X or greater reduced yield when applied 60 DAP. At the High Plains location, peanut yields were consistently reduced with rates of ½ X or greater applied 30 and 90 DAP and ¼ X or greater applied 60 DAP. In Oklahoma, peanut yield were consistently reduced with rates of ¼ X or greater applied 30 and 60 DAP and 1/16 X or greater when applied 90 DAP. Peanut grade was more affected by the 60 and 90 DAP application than the 30 DAP application.

Aims: Determine the influence of sequential spray order and role of glufosinate when used in a system with dicamba to control Palmer amaranth at three different growth stages. Study design: Randomized complete block design with four replications Place and duration of Study: A fallow, non-crop field at the Texas A&M AgriLife Research and Extension Center, Lubbock, Texas, during the 2018-2019 growing seasons Methodology: Herbicides were applied to < 10 cm, 10 to 20 cm, and > 30 cm Palmer amaranth with a handheld 1.93m CO2-pressurized backpack calibrated to deliver 140 L ha-1 at 207 kPa. Palmer amaranth control was visually estimated on a scale of 0 (no control) to 100% (complete plant death) relative to the nontreated control. Palmer amaranth biomass and density were taken when all plots reached 50% or less control in 2019. Palmer amaranth control, biomass, and density were subjected to analysis of variance and means were separated using Fisher’s Protected LSD at an alpha of 0.05. Results: Palmer amaranth control decreased as Palmer amaranth size at initial application increased. A difference in efficacy based on herbicide order was observed for < 10 cm Palmer amaranth. Glufosinate followed by dicamba was less effective (76-83%) than dicamba followed by glufosinate (93-96%) at 2 of 4 rating dates following sequential applications in both years. Dicamba + acetochlor followed by glufosinate provided greater Palmer amaranth control than dicamba followed by dicamba at one or more rating dates across all weed sizes. Conclusion: Glufosinate served as a complimentary partner in the dicamba-based system, and additional modes of action will be more effective to slow the development of resistance to group 4 herbicides when compared to repeated use of a group 4 herbicide used alone.

Aims: To determine peanut response and weed control following the use of carfentrazone plus pyroxasulfone (C + P). Study Design: Randomized complete block design with 3-4 reps depending on location. Place and Duration of Study: Studies were conducted during the 2015 and 2016 growing seasons in south Texas near Yoakum (29.276o N, 97.123o W), the High Plains of Texas near Lamesa (32.769o N, 101.977o W) or Brownfield (33.104o N, 102.161o W), and southwestern Oklahoma near Ft. Cobb (35.091o N, 98.275o W). Methodology: Plots were infested with naturally occurring weed populations. Pendimethalin was applied either preplant incorporated (PPI) or preemergence (PRE). Early postemergence (EPOST) applications varied according to weather conditions and peanut growth at each location. Postemergence (POST) treatments were applied 26 to 58 days after planting. Weed control and peanut stunting were visually estimated on a scale of 0 to 100 (0 indicating no control or plant death and 100 indicating complete control or plant death). Results: Peanut stunting with C + P was only noted at the High Plains and Oklahoma locations in 2015 but not 2016. Urochloa texana (Buckl.) control with C + P (PRE) varied from 75 to 93%. POST applications provided inconsistent control. Amaranthus palmeri S. Wats. control with C + P (PRE) was at least 78% season-long while POST applications were inconsistent (24 to 100%). Pendimethalin plus C + P controlled Cucumis melo L. var. Dudaim Naud. at least 80% late-season. Ipomoea hederacea Jacq. control was excellent season-long (> 80%) in 2015 but poor (< 60%) in 2016. Reduced peanut yields were noted with C + P in Oklahoma in 2015 to excessive season-long injury. Conclusion: The premix of C + P has potential for use in peanut especially for control of many small-seeded annual broadleaf weeds that continue to plague many peanut growers across the southwest. For effective broad-spectrum annual weed control season-long, the addition of pendimethalin to PRE applications will be required.