Wesley J. Everman

Weed control and yield with flumioxazin, fomesafen, and S-metolachlor systems for glufosinate-resistant cotton residual weed management.

Abstract Field studies were conducted near Clayton, Lewiston, and Rocky Mount, NC in 2005 to evaluate weed control and cotton response to preemergence treatments of pendimethalin alone or in a tank mixture with fomesafen, postemergence treatments of glufosinate applied alone or in a tank mixture with S-metolachlor, and POST-directed treatments of glufosinate in a tank mixture with flumioxazin or prometryn. Excellent weed control (> 91%) was observed where at least two applications were made in addition to glufosinate early postemergence (EPOST). A reduction in control of common lambsquarters (8%), goosegrass (20%), large crabgrass (18%), Palmer amaranth (13%), and pitted morningglory (9%) was observed when residual herbicides were not included in PRE or mid-POST programs. No differences in weed control or cotton lint yield were observed between POST-directed applications of glufosinate with flumioxazin compared to prometryn. Weed control programs containing three or more herbicide applications resulted in similar cotton lint yields at Clayton and Lewiston, and Rocky Mount showed the greatest variability with up to 590 kg/ha greater lint yield where fomesafen was included PRE compared to pendimethalin applied alone. Similarly, an increase in cotton lint yields of up to 200 kg/ha was observed where S-metolachlor was included mid-POST when compared to glufosinate applied alone, showing the importance of residual herbicides to help maintain optimal yields. Including additional modes of action with residual activity preemergence and postemergence provides a longer period of weed control, which helps maintain cotton lint yields. Nomenclature: Flumioxazin; fomesafen; glufosinate; pendimethalin; prometryn; S-metolachlor; common lambsquarters, Chenopodium album L. CHEAL; goosegrass, Eleusine indica ELEIN; large crabgrass, Digitaria sanguinalis L. DIGSA; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; pitted morningglory, Ipomoea lacunosa L. IPOLA; cotton, Gossypium hirsutum L.

Critical Period of Weed Interference in Peanut

Field studies were conducted near Lewiston–Woodville and Rocky Mount, NC to evaluate the effects of mixed weed species on peanut yield. A combination of broadleaf and grass weeds were allowed to interfere with peanut for various intervals to determine both the critical timing of weed removal and the critical weed-free period. These periods were then combined to determine the critical period of weed control in peanut. The effects of various weedy intervals on peanut yield were also investigated. The predicted critical period of weed control, in the presence of a mixed population of weeds, was found to be from 3 to 8 wk after planting (WAP). Peanut yield decreased as weed interference intervals increased, demonstrating the need for weed control throughout much of the growing season in the presence of mixed weed populations. Nomenclature: Peanut, Arachis hypogaea L

Weed Control and Yield with Glufosinate-Resistant Cotton Weed Management Systems

Field studies were conducted near Clayton, Goldsboro, Kinston, and Rocky Mount, NC in 2003 to evaluate weed control and cotton response to postemergence (POST) treatments of glufosinate applied alone or in tank mixtures with s-metolachlor, pyrithiobac, or trifloxysulfuron. Late-season control of common lambsquarters, common ragweed, entireleaf morningglory, ivyleaf morningglory, jimsonweed, pitted morningglory, purple nutsedge, and sicklepod with glufosinate early postemergence (EPOST) was ≥90%. The addition of S-metolachlor to glufosinate EPOST improved control of all weeds except sicklepod, ivyleaf morningglory, and entireleaf morningglory. When applied POST, glufosinate provided ≥90% late season control of common lambsquarters, common ragweed, entireleaf morningglory, ivyleaf morningglory, jimsonweed, large crabgrass, pitted morningglory, purple nutsedge, and sicklepod. Control of goosegrass and Palmer amaranth was 81 and 84%, respectively. When pyrithiobac or trifloxysulfuron were added in POST tank mixtures, control of Palmer amaranth improved 6 and 9 percentage points, respectively. Control of goosegrass remained near 80% regardless of herbicide treatment used. The addition of a late post-directed (LAYBY) tank-mixture of glufosinate plus prometryn provided ≥88% late season control of all weeds. Reduced control of goosegrass and Palmer amaranth was observed with the LAYBY tank mixture of glufosinate plus MSMA when compared to other LAYBY tank mixtures. Cotton lint yields in plots receiving any herbicide application were significantly higher than plots receiving no herbicide application for all application timings. Cotton lint yields were ≥ 740 kg/ha where an EPOST was applied and ≥ 680 kg/ha when a POST herbicide was applied. Cotton lint yields were at least 200 kg/ha greater on plots receiving a LAYBY application when compared to plots where no LAYBY treatment was applied. Nomenclature: Glufosinate, MSMA, prometryn, pyrithiobac, S-metolachlor, trifloxysulfuron, common lambsquarters, Chenopodium album L. CHEAL, common ragweed, Ambrosia artemisiifolia L. AMBEL, entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray IPOHG, goosegrass, Eleusine indica ELEIN, ivyleaf morningglory, Ipomoea hederacea Jacq. IPOHE, jimsonweed, Datura stramonium L. DATST, large crabgrass, Digitaria sanguinalis L. DIGSA, Palmer amaranth, Amaranthus palmeri S. Wats AMAPA, pitted morningglory, Ipomoea lacunosa L. IPOLA, purple nutsedge, Cyperus rotundus L. CYPRO, sicklepod, Senna obtusifolia L. Irwin and Barnaby CASOB, cotton, Gossypium hirsutum L

Absorption, Translocation, and Metabolism of Glufosinate in Transgenic and Nontransgenic Cotton, Palmer Amaranth (Amaranthus palmeri), and Pitted Morningglory (Ipomoea lacunosa)

Abstract Greenhouse studies were conducted to evaluate absorption, translocation, and metabolism of 14C-glufosinate in glufosinate-resistant cotton, nontransgenic cotton, Palmer amaranth, and pitted morningglory. Cotton plants were treated at the four-leaf stage, whereas Palmer amaranth and pitted morningglory were treated at 7.5 and 10 cm, respectively. All plants were harvested at 1, 6, 24, 48, and 72 h after treatment (HAT). Absorption of 14C-glufosinate was greater than 85% 24 h after treatment in Palmer amaranth. Absorption was less than 30% at all harvest intervals for glufosinate-resistant cotton, nontransgenic cotton, and pitted morningglory. At 24 HAT, 49 and 12% of radioactivity was translocated to regions above and below the treated leaf, respectively, in Palmer amaranth. Metabolites of 14C-glufosinate were detected in all crop and weed species. Metabolism of 14C-glufosinate was 16% or lower in nontransgenic cotton and pitted morningglory; however, metabolism rates were greater than 70% in glufosinate-resistant cotton 72 HAT. Intermediate metabolism was observed for Palmer amaranth, with metabolites comprising 20 to 30% of detectable radioactivity between 6 and 72 HAT. Nomenclature: Glufosinate; Palmer amaranth, Amaranthus palmeri S.Wats. AMAPA; pitted morningglory, Ipomoea lacunosa L. IPOLA; cotton, Gossypium hirsutum L.

Absorption, Translocation, and Metabolism of 14C-Glufosinate in Glufosinate-Resistant Corn, Goosegrass (Eleusine indica), Large Crabgrass (Digitaria sanguinalis), and Sicklepod (Senna obtusifolia)

Abstract Greenhouse studies were conducted to evaluate 14C-glufosinate absorption, translocation, and metabolism in glufosinate-resistant corn, goosegrass, large crabgrass, and sicklepod. Glufosinate-resistant corn plants were treated at the four-leaf stage, whereas goosegrass, large crabgrass, and sicklepod were treated at 5, 7.5, and 10 cm, respectively. All plants were harvested at 1, 6, 24, 48, and 72 h after treatment (HAT). Absorption was less than 20% at all harvest intervals for glufosinate-resistant corn, whereas absorption in goosegrass and large crabgrass increased from approximately 20% 1 HAT to 50 and 76%, respectively, 72 HAT. Absorption of 14C-glufosinate was greater than 90% 24 HAT in sicklepod. Significant levels of translocation were observed in glufosinate-resistant corn, with 14C-glufosinate translocated to the region above the treated leaf and the roots up to 41 and 27%, respectively. No significant translocation was detected in any of the weed species at any harvest timing. Metabolites of 14C-glufosinate were detected in glufosinate-resistant corn and all weed species. Seventy percent of 14C was attributed to glufosinate metabolites 72 HAT in large crabgrass. Less metabolism was observed for sicklepod, goosegrass, and glufosinate-resistant corn, with metabolites composing less than 45% of detectable radioactivity 72 HAT. Nomenclature: Glufosinate, goosegrass, Eleusine indica L. Gaertn., large crabgrass, Digitaria sanguinalis L.; sicklepod, Senna obtusifolia (L.) H.S. Irwin & Barneby.; corn, Zea mays L

Glyphosate-resistant Corn Interference in Glyphosate-resistant Cotton

Studies were conducted at three locations in North Carolina in 2004 to evaluate density-dependent effects of glyphosate-resistant (GR) corn on GR cotton growth and lint yield. GR corn was taller than GR cotton as early as 25 d after planting, depending on location. A GR corn density of 5.25 plant/m of crop row reduced late season cotton height by 49, 24, and 28% at Clayton, Lewiston–Woodville, and Rocky Mount, respectively, compared to weed-free cotton height. At Clayton, GR corn dry biomass per m crop row and GR corn seed biomass per m of crop row decreased linearly with increasing corn density. The relationship between GR corn and GR cotton yield loss was described by the rectangular hyperbola model with the asymptote (a) constrained to 100% maximum yield loss. The estimated coefficient i (yield loss per unit density as density approaches zero) was 9, 5, and 5 at Clayton, Lewiston–Woodville, and Rocky Mount, respectively. The examined GR corn densities had a significant effect on cotton yield, but not as significant as many other problematic grass and broadleaf weeds. Nomenclature: Glyphosate; corn, Zea mays L., ZEAMX, ‘DKC 69-71RR’; cotton, Gossypium hirsutum L. ‘FM 989RR’, ‘ST 4892RR’.

Potential Corn Yield Losses from Weeds in North America

Crop losses from weed interference have a significant effect on net returns for producers. Herein, potential corn yield loss because of weed interference across the primary corn-producing regions of the United States and Canada are documented. Yield-loss estimates were determined from comparative, quantitative observations of corn yields between nontreated and treatments providing greater than 95% weed control in studies conducted from 2007 to 2013. Researchers from each state and province provided data from replicated, small-plot studies from at least 3 and up to 10 individual comparisons per year, which were then averaged within a year, and then averaged over the seven years. The resulting percent yield-loss values were used to determine potential total corn yield loss in t ha−1 and bu acre−1 based on average corn yield for each state or province, as well as corn commodity price for each year as summarized by USDA-NASS (2014) and Statistics Canada (2015). Averaged across the seven years, weed interference in corn in the United States and Canada caused an average of 50% yield loss, which equates to a loss of 148 million tonnes of corn valued at over U.S.

An Alternative to Multiple Protoporphyrinogen Oxidase Inhibitor Applications in No-Till Cotton

26.7 billion annually. Nomenclature: Corn, Zea mays L.

Nitrogen Release from Weed Residue

Abstract Glyphosate-resistant (GR) Palmer amaranth is a widespread problem in southeastern cotton production areas. Herbicide programs to control this weed in no-till cotton commonly include flumioxazin applied with preplant burndown herbicides approximately 3 wk before planting followed by fomesafen applied PRE and then glufosinate or glyphosate applied POST. Flumioxazin and fomesafen are both protoporphyrinogen oxidase (PPO) inhibitors. Multiple yearly applications of PPO inhibitors in cotton, along with widespread use of PPO inhibitors in rotational crops, raise concerns over possible selection for PPO resistance in Palmer amaranth. An experiment was conducted to determine the potential to substitute diuron for one of the PPO inhibitors in no-till cotton. Palmer amaranth control by diuron and fomesafen applied PRE varied by location, but fomesafen was generally more effective. Control by both herbicides was inadequate when timely rainfall was not received for activation. Palmer amaranth control was more consistent when programs included a preplant residual herbicide. Applied preplant, flumioxazin was more effective than diuron. Programs with diuron preplant followed by fomesafen PRE were as effective as flumioxazin preplant followed by fomesafen only if fomesafen was activated in a timely manner. Programs with flumioxazin preplant followed by diuron PRE were as effective as flumioxazin preplant followed by fomesafen PRE at all locations, regardless of timely activation of the PRE herbicide. As opposed to flumioxazin preplant followed by fomesafen PRE, which exposes Palmer amaranth to two PPO-inhibiting herbicides, one could reduce selection pressure by using flumioxazin preplant followed by diuron PRE without sacrificing Palmer amaranth control or cotton yield. Nomenclature: Diuron; flumioxazin; fomesafen; glufosinate; glyphosate; Palmer amaranth, Amaranthus palmeri S. Wats.; cotton, Gossypium hirsutum L. Resumen Amaranthus palmeri resistente a glyphosate (GR) es un problema ampliamente diseminado en las áreas de producción de algodón en el sureste de Estados Unidos. Los programas de herbicidas para el control de esta maleza en algodón bajo labranza cero incluyen flumioxazin aplicado con herbicidas para quema total en pre-siembra, aproximadamente 3 semanas antes de la siembra seguido de fomesafen aplicado PRE y después glufosinate o glyphosate aplicados POST. Flumioxazin y fomesafen son ambos inhibidores de protoporphyrinogen oxidase (PPO). Aplicaciones anuales múltiples de inhibidores PPO en algodón, además del amplio uso de inhibidores PPO en cultivos rotacionales, genera preocupación sobre la posible selección de resistencia a herbicidas inhibidores de PPO en A. palmeri. Se realizó un experimento para determinar el potencial de sustituir diuron por uno de los inhibidores PPO en algodón bajo labranza cero. El control de A. palmeri con diuron y fomesafen aplicados PRE varió según la localidad, pero fomesafen fue generalmente más efectivo. El control brindado por ambos herbicidas fue inadecuado cuando no se recibió lluvia en el momento necesario para su activación. El control de A. palmeri fue más consistente cuando los programas incluyeron un herbicida residual pre-siembra. Al aplicarse pre-siembra, flumioxazin fue más efectivo que diuron. Los programas con diuron pre-siembra seguidos de fomesafen PRE fueron tan efectivos como flumioxazin pre-siembra seguido de fomesafen solamente si fomesafen fue activado en el momento adecuado. Los programas con flumioxazin pre-siembra seguidos de diuron PRE fueron tan efectivos como flumioxazin pre-siembra seguido de fomesafen PRE en todas las localidades, sin importar el momento de activación del herbicida PRE. En contraste a programas con flumioxazin pre-siembra seguido de fomesafen PRE, los cuales exponen a A. palmeri a dos herbicidas inhibidores PPO, uno podría reducir la presión de selección al usar flumioxazin pre-siembra seguido de diuron PRE sin sacrificar el control de A. palmeri o el rendimiento del algodón.

Weed Management in North Carolina Peanuts (Arachis Hypogaea) with S-metolachlor, Diclosulam, Flumioxazin, and Sulfentrazone Systems

Abstract Weed residues can impact nitrogen (N) cycling in agro-ecosystems that primarily utilize POST weed control. Quantifying this potential N source or sink may influence weed control and fertilization practices. A laboratory experiment measured the rate and quantity of N release from common lambsquarters, common ragweed, and giant foxtail. Weeds were grown in the field at four N rates (0, 67, 134, or 202 kg N ha−1) and collected at two weed heights (10 or 20 cm) to give a range of residue chemical composition. Residue chemical composition parameters of carbon ∶ N (C ∶ N) ratio and total N, nitrate-N, acid detergent fiber, and neutral detergent fiber concentration were measured and correlated with N release. Nitrogen release from weed residue mixed with soil was determined over a 12-wk period. Nitrogen was released from all weed residues at 12 wk. Prior to 12 wk, N was immobilized by giant foxtail grown with no N application. Prior to 4 wk, N was immobilized by 20-cm weeds grown with no N application. Nitrogen release from weed residue was negatively correlated with C ∶ N ratio. Weed residue with a C ∶ N ratio of < 19 (weeds grown with N application and 10-cm weeds) released 25 to 45% total N concentration within 2 wk and may contribute N within the growing season. Weed residue with a C ∶ N ratio > 19 (giant foxtail and 20-cm weeds grown with no N) initially immobilized N and may not contribute N within the growing season. Nomenclature: Common lambsquarters, Chenopodium album L. CHEAL; common ragweed Ambrosia artemisiifolia L. AMBEL; giant foxtail, Setaria faberi Herrm. SETFA; corn, Zea mays L.