Bobby R. Golden

Glyphosate-Resistant Italian Ryegrass (Lolium perenne ssp. multiflorum) Control with Fall-Applied Residual Herbicides

Abstract Dense populations of glyphosate-resistant (GR) Italian ryegrass are problematic for spring burndown herbicide programs and crop establishment in the midsouthern United States. Two field studies were conducted to evaluate fall-applied residual herbicides for control of GR Italian ryegrass and to identify the most effective application timing for these herbicides. Fall applications of clomazone at 0.84 and 1.12 kg ai ha−1, pyroxasulfone at 0.16 kg ai ha−1, and S-metolachlor at 1.79 kg ai ha−1 controlled GR Italian ryegrass ≥ 93% 180 d after application. Control from incorporated applications of pendimethalin at 1.59 kg ai ha−1 and trifluralin at 1.68 kg ai ha−1 and surface applications of S-metolachlor at 1.42 kg ha−1 provided control similar to the best treatments. Glyphosate-resistant Italian ryegrass control following clomazone, pyroxasulfone, S-metolachlor, or trifluralin applied in mid September, October, or November exceeded that from fall tillage by 19 to 56% at 90 and 140 d after the last treatment. Pyroxasulfone and S-metolachlor controlled more GR Italian ryegrass following October or November applications compared with those in September at both 90 and 140 d after the last application timing. However, the benefit of delaying clomazone application from October to November was not realized until the last evaluation (140 d after the last treatment). Clomazone, pyroxasulfone, and S-metolachlor offer growers the best opportunity for residual control of GR Italian ryegrass, and control is optimized when these herbicides are applied in November. Nomenclature: Clomazone; glyphosate; pendimethalin; pyroxasulfone; S-metolachlor; trifluralin; Italian ryegrass, Lolium perenne L. ssp. multiflorum (Lam.) Husnot. LOLMU. Resumen Poblaciones densas de Lolium perenne ssp. multiflorum resistente a glyphosate (GR) son problemáticas para los programas de eliminación de vegetación en la primavera y para el establecimiento de cultivos en el centro-sur de los Estados Unidos. Se realizaron dos estudios de campo para evaluar aplicaciones de herbicidas residuales en el otoño para el control de L. perenne GR y para identificar el momento de aplicación más efectivo para estos herbicidas. Aplicaciones en el otoño de clomazone a 0.84 y 1.12 kg ai ha−1, pyroxasulfone a 0.16 kg ai ha−1, y S-metolachlor a 1.79 kg ai ha−1 controlaron L. perenne GR ≥93%, 180 d después de la aplicación. El control a partir de aplicaciones incorporadas de pendimethalin a 1.59 kg ai ha−1 y trifluralin a 1.68 kg ai ha−1 y aplicaciones superficiales de S-metolachlor a 1.42 kg ha−1 brindaron un control similar a los mejores tratamientos. El control de L. perenne GR después de aplicaciones de clomazone, pyroxasulfone, S-metolachlor, o trifluralin, en la mitad de Septiembre, Octubre, o Noviembre, excedieron el control obtenido con labranza en el otoño en 19 a 56%, a 90 a 140 d después del tratamiento. Pyroxasulfone y S- metolachlor aplicados en Octubre o Noviembre controlaron L. perenne GR más que las aplicaciones en Septiembre a 90 y 140 d después del último momento de aplicación. Sin embargo, el beneficio de retrasar la aplicación de clomazone de Octubre a Noviembre no se vio sino hasta la última evaluación (140 d después del tratamiento). Clomazone, pyroxasulfone, y S-metolachlor ofrecen a los productores la mejor oportunidad de control residual de L. perenne GR, y el control se optimiza cuando estos herbicidas se aplican en Noviembre.

Clomazone and Starter Nitrogen Fertilizer Effects on Growth and Yield of Hybrid and Inbred Rice Cultivars

Cultivar and/or application of early-season (starter) nitrogen (N) fertilizer may influence rice tolerance to clomazone. Field studies were conducted to compare the response of hybrid and inbred rice cultivars to applications of clomazone and starter N fertilizer treatments. The inbred cultivar ‘Cocodrie’ and the hybrid cultivar ‘XL723’ were treated with clomazone at 0, 420, or 672 g ai ha-1 immediately after seeding, and starter N fertilizer was applied at 0 or 24 kg N ha-1 when rice reached the two-leaf growth stage. Pooled across clomazone rates and starter N fertilizer treatments, height of Cocodrie 1 week after emergence (WAE) was greater than that of XL723 in 1 of 3 yr. The difference in height between Cocodrie and XL723 resulted from greater clomazone injury 1 WAE on XL723 compared with Cocodrie. No differences in rice height 3 WAE were detected between Cocodrie and XL723 in 2 of 3 yr. when data were pooled across clomazone rates and starter N fertilizer treatments. Injury 3 WAE was similar for Cocodrie across the 3 yr., but injury on XL723 was greater in 1 of 3 yr. Rough rice yield was lower in plots treated with either rate of clomazone where no starter N fertilizer treatment was applied; however, in plots receiving a starter N fertilizer treatment, no effect of clomazone rate on rough rice yield was observed. Clomazone rate did not influence rough rice yield of Cocodrie in any single yr., but rough rice yields of XL723 were lower in plots receiving clomazone compared with plots that received no clomazone in 1 of 3 yr. Therefore, differential susceptibility to clomazone between Cocodrie and XL723 exists based on early-season response and rough rice yield. Starter N fertilizer treatments were beneficial for overcoming yield reductions due to clomazone injury. Nomenclature: Clomazone, rice, Oryza sativa L.

Nitrogen Fertilization of Soybean Affects Root Growth and Nodulation on Two Soil Types in Mississippi

ABSTRACT Greenhouse studies were conducted to evaluate the influence of nitrogen (N) sources [urea + N-(n-butyl) thiophosphoric triamide, NBPT (urease inhibitor) and polymer-coated urea (PCU)] and rates on soybean root characteristics, nodule formation, and biomass production on two soil types (silt loam and clay) commonly cropped to soybean in Mississippi. About 15% less belowground biomass was produced in clay soil than in silt loam soil directly corresponding to all other root parameters including root length, root area, root diameter, and nodule number. Pooled across N rates, N additions resulted in 19% and 52% decrease in belowground biomass and number of nodules, respectively, across soils compared to soybean receiving no N. The N rate was the most critical factor as it influenced all root growth parameters. Number of nodules were 24% greater with PCU than urea + NBPT. Nitrogen additions and clay soil negatively impacted soybean root growth, nodulation, and belowground biomass production. Abbreviations: Polymer-coated urea, PCU; N-(n-butyl) thiophosphoric triamide, NBPT

The Impact of Simulated Corn Earworm (Lepidoptera: Noctuidae) Damage in Indeterminate Soybean

ABSTRACT Field experiments were conducted in Starkville and Stoneville, MS, during 2012 and 2013 to evaluate fruit removal level and timing on soybean growth, crop maturity, and yield. Fruit removal treatments consisted of 0, 50, and 100% of all fruit removed at specified growth stages (R2, R3, R4, and R5.5). Plant heights were determined at least biweekly from the time damage was imposed until R7. The impact of fruit removal level and timing on crop maturity was determined by estimating the percentage of naturally abscised leaves at 137 days after planting (DAP) when control plots were ∼10–15 d from harvest and the percentage of nonsenesced main stems at 139 DAP. There was no significant impact of fruit removal timing or fruit removal level on plant height or canopy width. Significant delays in crop maturity were observed when fruit removal was imposed at the R5.5 growth stage. Significant reductions in yield and crop value were observed as early as R3 and R4 when 100% of fruit was removed. Both fruit removal levels at R5.5 resulted in a significant reduction in yield and crop value compared with the nontreated control. Indeterminate soybeans appear to have the ability to compensate for some fruit loss during the early to middle reproductive growth stages without delaying maturity. However, severe fruit loss causes increasingly more yield loss as the plant approached maturity. Thresholds and economic injury levels therefore need to be adjusted accordingly to account for the dynamic nature of yield losses and crop maturity delays.

Diversifying Soybean Production Risk Using Maturity Group and Planting Date Choices

Due to the long growing season for soybean production, producers in the Mid-southern US can plant from late March to June. They also have a range of maturity group (MG) choices, affecting the length of the growing season, that are physiologically and economically viable. A producer’s decision of what to plant and when constitutes two potential decision variables that can be freely manipulated to not only maximize profit, but also reduce economic risk. Early maturing MG III and IV soybean cultivars planted early or mid-season typically are highest yielding and thereby the preferred choice of producers. However, planting part of a producer’s acreage at later dates and using later maturing MG VI soybeans may offer producers similar returns (as observed with early planting using early maturing cultivars) at a meaningfully reduced level of risk.

Evaluation of Saflufenacil in Drill-Seeded Rice (Oryza sativa)

Abstract Palmer amaranth is the most common and troublesome broadleaf weed species of rice in Mississippi because of the effects of early-season interference and infestations on rice levees, and herbicides for residual or POST control of Palmer amaranth in rice are limited. Three studies were conducted in 2012 and 2013 to evaluate application rates and timings of saflufenacil in rice and to determine the influence of adjuvants when mixed with saflufenacil applied POST. In a PRE study, no injury occurred after saflufenacil PRE, and no control was observed from carfentrazone. Hemp sesbania and Palmer amaranth control increased with increasing saflufenacil rate when applied PRE. Hemp sesbania control with saflufenacil at any rate PRE was ≤ 25% at 35 d after treatment (DAT). Palmer amaranth and ivyleaf morningglory control with saflufenacil at 75 g ai ha−1 PRE was ≥ 94% 35 DAT. In a POST study, rice injury was influenced by application timing and rate of saflufenacil; however, efficacy was not. Rice injury with saflufenacil at 25 g ha−1 and carfentrazone early POST (EPOST) and late POST was similar 7 DAT. Saflufenacil at 50 and 75 g ha−1 EPOST were the most injurious 7 DAT. Control of hemp sesbania and ivyleaf morningglory was similar for all rates of saflufenacil and carfentrazone; however, Palmer amaranth control with saflufenacil at any rate was greater than that of carfentrazone 14 and 28 DAT. In an adjuvant study, rice injury was influenced by adjuvant and saflufenacil rate. Saflufenacil applied alone or in mixture with crop oil concentrate (COC) was least injurious, and saflufenacil at 50 g ha−1 was more injurious than saflufenacil at 25 g ha−1. Saflufenacil applied in combination with any adjuvant provided better control of hemp sesbania and Palmer amaranth than saflufenacil alone. On the basis of this research, saflufenacil should be applied PRE at 50 or 75 g ha−1, depending on weed spectrum, and POST applications should be made at 25 g ha−1 in combination with COC after the two-leaf rice growth stage. Nomenclature: Carfentrazone; saflufenacil; hemp sesbania, Sesbania herbacea (P. Mill.) McVaugh SEBEX; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. IPOHE; Palmer amaranth, Amaranthus palmeri S. Wats AMAPA; rice, Oryza sativa L. Resumen Amaranthus palmeri es la especie de malezas de hoja ancha más común y problemática en arroz en Mississippi debido a sus efectos en la interferencia temprano durante la temporada de crecimiento y sus infestaciones en los diques en los campos de arroz, además hay pocos herbicidas para el control residual y POST de esta maleza en arroz. En 2012 y 2013, se realizaron tres estudios para evaluar la dosis y momentos de aplicación de saflufenacil en arroz y así determinar la influencia de adyuvantes cuando estos se mezclaron con saflufenacil y fueron aplicados POST. En un estudio PRE, no hubo daño después de aplicaciones PRE de saflufenacil, y no se observó control alguno con aplicaciones de carfentrazone. El control de Sesbania herbacea y A. palmeri aumentó con el incremento en las dosis de saflufenacil cuando se aplicó PRE. A cualquier dosis, el control de S. herbacea con saflufenacil PRE fue ≤25% a 35 d después del tratamiento (DAT). El control de A. palmeri e Ipomoea hederacea con saflufenacil a 75 g ai ha−1 PRE fue ≥94% 35 DAT. En un estudio POST, el daño en el arroz fue influenciado por el momento y dosis de aplicación de saflufenacil, sin embargo, la eficacia no lo fue. El daño en el arroz con saflufenacil a 25 g ha−1 y carfentrazone en POST temprana (EPOST) y POST tardía fue similar a 7 DAT. Saflufenacil a 50 y 75 g ha−1 EPOST fueron los tratamientos más dañinos 7 DAT. El control de S. herbacea e I. hederacea fue similar para todas las dosis de saflufenacil y carfentrazone. Sin embargo, el control de A. palmeri con saflufenacil a cualquiera de las dosis fue mayor que el control con carfentrazone 14 y 28 DAT. En un estudio con adyuvantes, el daño al arroz fue influenciado por el adyuvante y la dosis de saflufenacil. Saflufenacil aplicado solo o en mezcla con aceite concentrado de cultivo (COC) causó menos daño, y saflufenacil a 50 g ha−1 causó más daño que saflufenacil a 25 g ha−1. Saflufenacil aplicado en combinación con cualquier adyuvante brindó mejor control de S. herbacea y A. palmeri que saflufenacil solo. Con base en esta investigación, saflufenacil debería ser aplicado PRE a 50 ó 75 g ha−1, dependiendo del espectro de malezas, y las aplicaciones POST deberían hacerse a 25 g ha−1 en combinación con COC y después del estado de crecimiento de dos hojas del arroz.

Effect of Fall-Applied Residual Herbicides on Rice Growth and Yield

Abstract Glyphosate-resistant (GR) Italian ryegrass is one of the most troublesome weeds in Mississippi row crop production. Fall-applied residual herbicide applications are recommended for control of GR Italian ryegrass. However, carryover of residual herbicides applied in fields for rice production can have a negative impact on rice performance. Field studies were conducted in Stoneville, MS, to determine the effects of fall-applied residual herbicides on rice growth and yield. Herbicide treatments included suggested use rates (1 × ) of clomazone at 840 g ai ha-1, pyroxasulfone 170 g ai ha-1, S-metolachlor 1,420 g ai ha-1, and trifluralin 1,680 g ai ha-1, and two times (2 × ) the suggested use rates in the fall before rice seeding. Pooled across application rate, pyroxasulfone, S-metolachlor, and trifluralin injured rice to an extent 28% to 36% greater than clomazone 14 d after emergence (DAE). Rice seedling density and height 14 DAE and rice maturity were negatively affected by all fallapplied herbicides except clomazone. Applications at 2 × rates reduced rough rice yields in plots treated with pyroxasulfone, S-metolachlor, and trifluralin compared with clomazone. Pyroxasulfone applied at the 2 × rate reduced rough rice yield 22% compared with the 1 × rate. Rough rice yield was 90% or greater of the nontreated control in plots treated with either rate of S-metolachlor, and these were comparable with rough rice yields from plots treated with both rates of trifluralin and the 1 × rate of pyroxasulfone. Early-season injury and reductions in seedling density and height 14 DAE, would preclude even 1 × applications of pyroxasulfone, S-metolachlor, and trifluralin from being viable options for residual herbicide treatments targeting GR Italian ryegrass in the fall before rice seeding. Of the herbicides evaluated, only clomazone should be utilized as a fall-applied residual herbicide treatment targeting GR Italian ryegrass before seeding rice. Nomenclature: Clomazone; S-metolachlor; trifluralin; pyroxasulfone; rice, Oryza sativa L.; Italian ryegrass, Lolium perenne ssp. multiflorum (Lam.) Husn

Utilization of Saflufenacil in a Clearfield® Rice (Oryza sativa) System

Abstract Research was conducted in Mississippi in 2012 and 2013 to compare the efficacy of saflufenacil to other broadleaf herbicides applied in mixtures with imazethapyr in a Clearfield rice system. Saflufenacil at 50 g ai ha−1, carfentrazone at 35 g ai ha−1, a prepackaged mixture of halosulfuron plus thifensulfuron at 35 plus 4 g ai ha−1, and a prepackaged mixture of propanil plus thiobencarb at 2,240 plus 2,240 g ai ha−1 were applied in mixture with imazethapyr at 70 g ai ha−1 early-POST (EPOST) to rice in the one- to two-leaf stage or late-POST (LPOST) to rice in the four-leaf to one-tiller stage. No differences in injury among the broadleaf herbicides or between application timings were detected at any evaluation. Imazethapyr combined with propanil plus thiobencarb or saflufenacil provided the greatest control of barnyardgrass 7 and 14 d after treatment (DAT). Hemp sesbania, ivyleaf morningglory, and Palmer amaranth control was greatest and similar for imazethapyr combined with carfentrazone, propanil plus thiobencarb, and saflufenacil; however, rough rice yield was greatest for imazethapyr combined with propanil plus thiobencarb or saflufenacil. Propanil plus thiobencarb or saflufenacil can be used in a Clearfield rice system to achieve optimum weed control and highest rice yields. Nomenclature: Carfentrazone, halosulfuron, imazethapyr, propanil, saflufenacil, thifensulfuron, thiobencarb; barnyardgrass, Echinochloa crus-galli (L.) Beauv ECHCG, hemp sesbania, Sesbania herbacea (P. Mill.) McVaugh SEBEX; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. IPOHE; Palmer amaranth, Amaranthus palmeri S. Wats AMAPA; rice, Oryza sativa L. ‘CL151′. Resumen En 2012 y 2013 se realizó una investigación en Mississippi, para comparar la eficacia de saflufenacil con la de otros herbicidas para malezas de hoja ancha aplicados en mezcla con imazethapyr, en sistemas de arroz Clearfield. Se aplicó saflufenacil a 50 g ai ha−1, carfentrazone a 35 g ai ha−1, y una mezcla de pre-empacada de propanil más thiobencarb a 2,240 más 2,240 g ai ha−1, en mezcla con imazethapyr a 70 g ai ha−1, en POST temprano (EPOST) a arroz en el estadio de una a dos hojas o en POST tardío (LPOST) a arroz en el estadio de cuatro hojas al primer hijuelo. No se detectaron diferencias en daño entre los herbicidas para hoja ancha ni entre momentos de aplicación en ninguna de las evaluaciones. Imazethapyr combinado con propanil más thiobencarb o saflufenacil brindó el mayor control de Echinochloa crus-galli 7 y 14 d después del tratamiento (DAT). El control de Sesbania herbacea, Ipomoea hederacea, y Amaranthus palmeri fue mayor o similar para imazethapyr combinado con carfentrazone, propanil más thiobencarb, y saflufenacil. Sin embargo, el rendimiento del arroz en granza fue mayor para imazethapyr combinado con propanil más thiobencarb o saflufenacil. Propanil más thiobencarb o saflufenacil puede ser usado en sistemas de arroz Clearfield para alcanzar un control de malezas óptimo y los mayores rendimientos del arroz.