Stephen L. Meyers

Interference of Palmer Amaranth (Amaranthus palmeri) in Sweetpotato

Abstract Field studies were conducted in 2007 and 2008 at Clinton and Faison, NC, to evaluate the influence of Palmer amaranth density on ‘Beauregard’ and ‘Covington’ sweetpotato yield and quality and to quantify the influence of Palmer amaranth on light interception. Palmer amaranth was established at 0, 0.5, 1.1, 1.6, 3.3, and 6.5 plants m−1 within the sweetpotato row and densities were maintained season-long. Jumbo, number (no.) 1, and marketable sweetpotato yield losses were fit to a rectangular hyperbola model, and predicted yield loss ranged from 56 to 94%, 30 to 85%, and 36 to 81%, respectively for Palmer amaranth densities of 0.5 to 6.5 plants m−1. Percentage of jumbo, no. 1, and marketable sweetpotato yield loss displayed a positive linear relationship with Palmer amaranth light interception as early as 6 to 7 wk after planting (R2  =  0.99, 0.86, and 0.93, respectively). Predicted Palmer amaranth light interception 6 to 7, 10, and 13 to 14 wk after planting ranged from 47 to 68%, 46 to 82%, and 42 to 71%, respectively for Palmer amaranth densities of 0.5 to 6.5 plants m−1. Palmer amaranth height increased from 177 to 197 cm at densities of 0.5 to 4.1 plants m−1 and decreased from 197 to 188 cm at densities of 4.1 to 6.5 plants m−1; plant width (69 to 145 cm) and shoot dry biomass plant−1 (0.2 to 1.1 kg) decreased linearly as density increased. Nomenclature: Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; sweetpotato, Ipomoea batatas L. Lam. ‘Beauregard’ and ‘Covington’ IPOBA

Evaluation of Flumioxazin and S-metolachlor Rate and Timing for Palmer Amaranth (Amaranthus palmeri) Control in Sweetpotato

Abstract Studies were conducted in 2007 and 2008 to determine the effect of flumioxazin and S-metolachlor on Palmer amaranth control and ‘Beauregard’ and ‘Covington’ sweetpotato. Flumioxazin at 0, 91, or 109 g ai ha−1 was applied pretransplant 2 d before transplanting alone or followed by (fb) S-metolachlor at 0, 0.8, 1.1, or 1.3 kg ai ha−1 PRE applied immediately after transplanting or 2 wk after transplanting (WAP). Flumioxazin fb S-metolachlor immediately after transplanting provided greater than 90% season-long Palmer amaranth control. S-metolachlor applied alone immediately after transplanting provided 80 to 93% and 92 to 96% control in 2007 and 2008, respectively. Flumioxazin fb S-metolachlor 2 WAP provided greater than 90% control in 2007 but variable control (38 to 79%) in 2008. S-metolachlor applied alone 2 WAP did not provide acceptable Palmer amaranth control. Control was similar for all rates of S-metolachlor (0.8, 1.1, and 1.3 kg ha−1). In 2008, greater Palmer amaranth control was observed with flumioxazin at 109 g ha−1 than with 91 g ha−1. Sweetpotato crop injury due to treatment was minimal (< 3%), and sweetpotato storage root length to width ratio was similar for all treatments in 2007 (2.5 for Beauregard) and 2008 (2.4 and 1.9 for Beauregard and Covington, respectively). Sweetpotato yield was directly related to Palmer amaranth control. Results indicate that flumioxazin pretransplant fb S-metolachlor after transplanting provides an effective herbicide program for control of Palmer amaranth in sweetpotato. Nomenclature: Flumioxazin; S-metolachlor; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; sweetpotato, Ipomoea batatas L. Lam. ‘Covington’, ‘Beauregard’.

Response of Sweetpotato Cultivars to S-metolachlor Rate and Application Time

Abstract Studies were conducted in 2008 and 2009 to determine the effect of S-metolachlor rate and application time on sweetpotato cultivar injury and storage root shape under conditions of excessive moisture at the time of application. S-metolachlor at 1.1, 2.2, or 3.4 kg ai ha−1 was applied immediately after transplanting or 2 wk after transplanting (WATP) to ‘Beauregard’, ‘Covington’, ‘DM02-180’, ‘Hatteras’, and ‘Murasaki-29’ sweetpotato. One and three d after S-metolachlor application plots received 1.9 cm rainfall or irrigation. S-metolachlor applied immediately after transplanting resulted in increased sweetpotato stunting 4 and 12 WATP, decreased no. 1 and marketable sweetpotato yields, and decreased storage root length to width ratio compared with the nontreated check. Sweetpotato stunting, no. 1 and marketable yields, and storage root length to width ratio in treatments receiving S-metolachlor 2 WATP were similar to the nontreated check. In 2008, Covington and Hattaras stunting 12 WATP was greater at 2.2 and 3.4 kg ha−1 (11 to 16%) than 1.1 kg ha−1 (1 to 2%). In 2009, S-metolachlor at 3.4 kg ha−1 was more injurious 4 WATP than 2.2 kg ha−1 and 1.1 kg ha−1. While cultivar by treatment interactions did exist, injury, yield, and storage root length to width ratio trends were similar among all cultivars used in this study. Nomenclature: S-metolachlor; sweetpotato, Ipomoea batatas L. Lam. ‘Beauregard’, ‘Covington’, ‘DM02-180’, ‘Hatteras’, and ‘Murasaki-29’.

Effect of PRE and POST Herbicides on Carolina Redroot (Lachnanthes caroliniana) Growth

Abstract Greenhouse studies were conducted in Raleigh, NC to determine Carolina redroot control by selected PRE and POST herbicides labeled for blueberries. Paraquat, glufosinate, glyphosate, and flumioxazin provided some Carolina redroot shoot control 7 d after POST application (DAPOST) ranging from 48 to 74%. Control 25 DAPOST was greatest for hexazinone at 2.2 kg ai ha−1 (90%) followed by glufosinate with 56% control and paraquat and terbacil each with 53% control. Control for most treatments declined between 25 and 63 DAPOST with the exception of glyphosate, which increased to 64%. Carolina redroot shoots per pot were reduced by terbacil, hexazinone at 2.2 kg ha−1, and glyphosate compared with the nontreated check 63 DAPOST. Control of Carolina redroot roots and rhizomes 63 DAPOST ranged from 7 to 68%, with the greatest control provided by terbacil (68%) and hexazinone at 2.2 kg ha−1 (64%). Terbacil and hexazinone at 2.2 kg ha−1 were the only treatments that reduced both shoot and root/rhizome dry weight compared with the nontreated check. Nomenclature: Flumioxazin; glufosinate; glyphosate; halosulfuron-methyl; hexazinone; paraquat, S-metolachlor; terbacil; Carolina redroot, Lachnanthes caroliniana (Lam.) Dandy. Resumen Estudios de invernadero fueron realizados en Raleigh, NC, para determinar el control de Lachnanthes caroliniana con varios herbicidas PRE y POST registrados para uso en arándanos (Vaccinum corymbosum). Paraquat, glufosinate, glyphosate y flumioxazin brindaron control parcial del tejido aéreo de L. caroliniana a 7 días después de la aplicación POST (DAPOST), el cual varió entre 48 y 74%. El mayor control a 25 DAPOST se obtuvo con hexazinone a 2.2 kg ai ha−1 (90%) seguido por glufosinate con 56% y paraquat y terbacil cada uno con 53% de control. Para la mayoría de los tratamientos, el control disminuyó entre 25 y 63 DAPOST, con la excepción de glyphosate, el cual aumentó a 64%. El número de tallos de L. caroliniana por maceta se redujo con terbacil, hexazinone a 2.2 kg ha−1, y glyphosate al compararse con el testigo no-tratado a 63 DAPOST. El control de raíces y rizomas de L. caroliniana a 63 DAPOST varió entre 7 y 68%, obteniéndose el mayor control con terbacil (68%) y hexazinone a 2.2 kg ha−1 (64%). Terbacil y hexazinone a 2.2 kg ha−1 fueron los únicos tratamientos que redujeron el peso seco de tallos y de raíces/rizomas en comparación con el testigo no-tratado.

POST Control of Carolina Redroot (Lachnanthes caroliniana)

Abstract Greenhouse studies were conducted in 2012 in Raleigh, NC to determine Carolina redroot control by ten POST herbicides. Paraquat and glufosinate provided the greatest control 14 (73 and 64%, respectively) and 25 d (82 and 68%, respectively) after treatment (DAT), but control declined between 25 and 63 DAT (72 and 59%, respectively). Glyphosate provided minimal control 14 DAT (18%), and control increased from 14 to 25 DAT (46%) and 25 to 63 DAT (69%). Control of Carolina redroot roots and rhizomes (roots/rhizomes) was greatest in plants treated with paraquat (91%), glyphosate (88%), glufosinate (73%), hexazinone (62%), diuron (60%). Nontreated Carolina redroot shoot and root/rhizome dry weight were 8.3 and 7.6 g, respectively. Paraquat, glufosinate, glyphosate, and diuron reduced both shoot and root/rhizome dry weight (3.1 and 0.7 g, 5.1 and 2.7 g, 5.4 and 1.0, 5.7 and 1.6 g, respectively). Hexazinone reduced root/rhizome dry weight (2.7 g). Fomesafen reduced shoot dry weight (6.1 g), but did not reduce root/rhizome dry weight. Paraquat, glufosinate, glyphosate, hexazinone, diuron, and clopyralid treatments resulted in reduced incidence of Carolina redroot flowering and anthesis. Nomenclature: Clopyralid; diuron; flumioxazin; fomesafen; glufosinate; glyphosate; halosulfuron-methyl; hexazinone; paraquat; sethoxydim; Carolina redroot, Lachnanthes caroliniana (Lam.) Dandy. Resumen En 2012, se realizaron estudios de invernadero en Raleigh, NC para determinar el control de Lachnanthes caroliniana con diez herbicidas POST. Paraquat y glufosinate brindaron el mayor control 14 d (73 y 64%, respectivamente) y 25 d (82 y 68%, respectivamente) después del tratamiento (DAT), pero el control disminuyó entre 25 y 63 DAT (72 y 59%, respectivamente). Glyphosate brindó un control mínimo 14 DAT (18%), y el control incrementó de 14 a 25 DAT (46%) y 25 a 63 DAT (69%). El control de las raíces y rizomas (raíces/rizomas) de L. caroliniana fue mayor en plantas tratadas con paraquat (91%), glyphosate (88%), glufosinate (73%), hexazinone (62%), diuron (60%). El peso seco del tejido aéreo y raíces/rizomas de L. caroliniana sin tratar fue 8.3 y 7.6 g, respectivamente. Paraquat, glufosinate, glyphosate, y diuron redujeron el peso seco del tejido aéreo y raíces/rizomas (3.1 y 0.7 g, 5.1 y 2.7, 5.4 y 1.0, 5.7 y 1.6 g, respectivamente). Hexazinone redujo el peso seco de raíces/rizomas (2.7 g). Fomesafen redujo el peso seco del tejido aéreo (6.1 g), pero no redujo el peso seco de raíces/rizomas. Los tratamientos con paraquat, glufosinate, glyphosate, hexazinone, diuron, y clopyralid resultaron en una incidencia reducida de floración y antesis de L. caroliniana.

Sweetpotato Tolerance and Palmer Amaranth Control with Metribuzin and Oryzalin

Field studies were conducted in Clinton, NC in 2007 and 2009 to determine sweetpotato crop response and Palmer amaranth control with metribuzin and oryzalin. Treatments consisted of 140 and 202 g ai ha-1 metribuzin applied immediately after transplanting [0 wk after transplanting (WAP)] or 2 WAP, 560 and 1121 g ha-1 oryzalin 0 WAP, and tank mixes of metribuzin (140 or 202 g ha-1) and oryzalin (560 or 1,121 g ha-1) 0 WAP. At 2 WAP, metribuzin alone applied 0 WAP resulted in greater crop injury (33%) than oryzalin alone (1%), and the tank mix of metribuzin plus oryzalin resulted in greater crop injury (49%) than either herbicide applied alone. Greater crop injury occurred when metribuzin was applied at 202 g ha-1 (54%) than 140 g ha-1 (34%). Levels of injury were similar at 4 WAP (34, 8, and 52% for metribuzin, oryzalin, and the tank mix, respectively). At 4 WAP, injury from metribuzin was greater when it was applied 0 WAP (34%) compared to 2 WAP (18%). By 10 WAP, injury from metribuzin applied at 2 WAP was only 4%. At 4 WAP, Palmer amaranth control was excellent for all treatments and ≥98%. At 10 WAP, control among treatments ranged from 77% to 85%. Palmer amaranth control provided by metribuzin was similar for applications made 0 WAP (78%) and 2 WAP (77%). Oryzalin alone provided similar control (85%) to metribuzin alone 0 WAP, but greater control than the tank mix (77%). Neither metribuzin nor oryzalin rate differed in weed control provided at 10 WAP. Oryzalin 0 WAP and metribuzin 2 WAP provided no. 1 sweetpotato yields equivalent to the hand-weeded check. No. 1 yields of all other treatments were less than the hand-weeded check but greater than the weedy check. Nomenclature: Metribuzin; oryzalin; Palmer amaranth, Amaranthus palmeri S. Wats.; sweetpotato, Ipomoea batatas L. Lam. ‘Beauregard’ and ‘Covington’

An Evaluation of Pre-emergence Metam-Potassium and S-metolachlor for Yellow Nutsedge (Cyperus esculentus) Management in Sweetpotato

Field studies were conducted in 2014 and 2015 at Pontotoc, MS to evaluate combinations of metam-potassium and S-metolachlor for yellow nutsedge control and sweetpotato crop response. Treatments consisted of a factorial of five metam-potassium rates (0, 149, 261, 372, and 484 kg ha-1) by three S-metolachlor rates (0, 0.80, and 1.34 kg ha-1). Additionally, a hand-weeded check was included for comparison. Crop injury was limited to ≤4% at 4 weeks after transplanting (WAP) and was transient. At 2 WAP yellow nutsedge control was 58, 74, and 76% in plots treated with S-metolachlor at 0, 0.80, and 1.34 kg ha-1, respectively. Nutsedge control in all treatments decreased from 2 to 15 WAP. At 15 WAP, S-metolachlor at 0, 0.80, and 1.34 kg ha-1 provided 35, 68, and 70% yellow nutsedge control, respectively. Metam-potassium rate did not influence yellow nutsedge control after transplanting. Sweetpotato yields in the hand-weeded check were 4,640; 22,180; 7,180; 34,000; and 1,360 kg ha-1 for jumbo, no. 1, canner, marketable, and cull grades, respectively. S-metolachlor applied at either 0.80 or 1.34 kg ha -1 provided jumbo, no. 1, and marketable sweetpotato yields equivalent to the hand-weeded check. Canner and cull yields were not influenced by S-metolachlor rate. Metam-potassium rates used in the present study resulted in yields equal to or greater than the hand-weeded check. Nomenclature: Metam-potassium; S-metolachlor; yellow nutsedge, Cyperus esculentus L.; sweetpotato, Ipomoea batatas L. Lam.

Sweetpotato Response to Simulated Glyphosate Wick Drip

Field studies were conducted in 2009 at Clinton, NC and 2014 at Pontotoc, MS to determine the influence of simulated glyphosate drip on sweetpotato yield and quality. Treatments consisted of three glyphosate solution (140 g ae L−1) drip volumes (0.16, 0.32 and 0.48 ml) by four application timings [(4 wk after transplanting (WAP); 6 WAP; 8 WAP; and 4 WAP followed by (fb) 6 WAP fb 8 WAP]. A non-treated check was included for comparison. Visual sweetpotato injury consisted of chlorosis at the shoot tips approximately 1 wk after treatment fb necrosis and stunting. At 6 WAP and 8 WAP, sweetpotato injury following glyphosate applied 4 WAP was 71 and 65%, respectively. Injury from glyphosate applied 4 WAP fb 6 WAP was 78%. Injury from glyphosate applied 6 WAP was 26% at 8 WAP. In 2009, jumbo, no. 1, canner, and marketable yield of the non-treated check were two to three times greater than glyphosate treatments (0.16, 0.32, 0.48 ml). Likewise, yield of the non-treated check was substantially greater than those treated with 0.16 to 0.48 ml glyphosate solution in 2014. In 2009 and 2014, sweetpotato yield of all grades increased as glyphosate application timing was delayed. In 2009, no. 1 yield from glyphosate 8 WAP (8,210 kg ha−1) was similar to the non-treated check. In 2009, there were no cracked storage roots in the non-treated check. However, sweetpotatoes receiving 0.16 to 0.48 ml glyphosate solution displayed 8 to 17%, 11 to 18%, 5 to 13%, and 11 to 16% cracking (by weight) in jumbo, no. 1, canner, and marketable storage roots, respectively. Compared to the non-treated check, glyphosate applied 4 WAP, 6 WAP, or 4 WAP fb 6 WAP fb 8 WAP had a greater percentage of cracked marketable sweetpotato storage roots. Nomenclature: Glyphosate; sweetpotato, Ipomoea batatas L. Lam. Estudios de campo fueron realizados en 2009 en Clinton, North Carolina y en 2014 en Pontotoc, Mississippi para determinar la influencia de goteo simulado con glyphosate sobre el rendimiento y la calidad de la batata. Los tratamientos consistieron de tres volúmenes de goteo (0.16, 0.32, y 0.48 ml) de solución de glyphosate (140 g ae L−1) y cuatro momentos de aplicación [4 semanas después del trasplante (WAP); 6 WAP; 8 WAP; y 4 WAP seguido por (fb) 6 WAP fb 8 WAP]. Un testigo sin tratamiento fue incluido para fines de comparación. El daño visualmente estimado de la batata consistió de clorosis en los ápices del tejido aéreo de la batata aproximadamente 1 semana después del tratamiento fb necrosis y crecimiento atrofiado. A 6 WAP y 8 WAP, el daño en la batata después de la aplicación de glyphosate 4 WAP fue 71 y 65%, respectivamente. El daño causado por glyphosate aplicado 4 WAP fb 6 WAP fue 78%. El daño con glyphosate aplicado 6 WAP fue 26% a 8 WAP. En 2009, los rendimientos jumbo, no. 1, canner, y comercializable del testigo sin tratamiento fueron dos a tres veces mayores que los tratamientos con glyphosate (0.16, 0.32, y 0.48 ml). De la misma manera, el rendimiento del testigo sin tratamiento fue sustancialmente mayor que el de los tratamientos con glyphosate en soluciones desde 0.16 a 0.58 ml en 2014. En 2009 y 2014, los rendimientos de la batata para todos los grados de calidad aumentaron al retrasarse el momento de aplicación de glyphosate. En 2009, el rendimiento no. 1 después del glyphosate 8 WAP (8,210 kg ha−1) fue similar al testigo sin tratamiento. En 2009, no hubo raíces con fisuras por almacenamiento en el testigo sin tratamiento. Sin embargo, las batatas que recibieron de 0.16 a 0.48 ml de solución de glyphosate mostraron 8 a 17%, 11 a 18%, 5 a 13%, y 11 a 16% de raíces con fisuras (en términos de peso) en raíces almacenadas de jumbo, no. 1, canner, y comercializables, respectivamente. En comparación con el testigo sin tratamiento, glyphosate aplicado 4 WAP, 6 WAP, o 4 WAP fb 6 WAP fb 8 WAP tuvo un mayor porcentaje de raíces de batata comercializables con fisuras.

Effects of Metribuzin Applied Lay-by on Weed Control and Sweetpotato Crop Response

Field studies were conducted at the Pontotoc Ridge-Flatwoods Branch Experiment Station in Pontotoc, MS in 2015 and 2016 to determine the influence of lay-by metribuzin application on weed control and sweetpotato crop response. With the exception of weedy and hand-weeded checks, all plots received flumioxazin at 107 g ai ha-1 pre-transplanting followed by (fb) clomazone at 1,120 g ai ha-1 immediately after transplanting. Lay-by treatments consisted of S-metolachlor (800 g ai ha-1), metribuzin (210 or 315 g ai ha-1), metribuzin (210 g ha-1) plus napropamide (1,120 g ai ha-1), and metribuzin (210 g ha-1) plus S-metolachlor (800 g ha-1). At 4 weeks after transplanting, sweetpotato crop injury was 3 to 15%, but was transient and not evident after 6 (2015) to 8 weeks after transplanting (2016). Season-long weed control was excellent (≥98%) for all herbicide treatments used in the study. Hand-weeded check plots yielded 4,600; 18,350; 28,770; and 1,520 kg ha-1 of jumbo, No. 1, marketable, and cull grades, respectively. Jumbo, No. 1, and marketable yields from all herbicide-containing treatments in the study were greater than the weedy check and similar to the hand-weeded check. For all treatments, the portion of yield graded as cull was similar to the hand-weeded check. Canner yield response differed between years. In general, canner yield was greater in 2016 (8,460 to 10,670 kg ha-1) than 2015 (1,570 to 3,570 kg ha-1). In both years, canner yield in all treatments was similar to the hand-weeded check with one exception: in 2015 sweetpotato receiving metribuzin plus napropamide yielded more canners (3,570 kg ha-1) than the hand-weeded check (2,300 kg ha-1). Nomenclature: Metribuzin; sweetpotato, Ipomoea batatas (L.) Lam.

Weed Control in Southern Highbush Blueberry with S-metolachlor, Flumioxazin, and Hexazinone

Abstract Field studies were conducted in 2010, 2011, and 2012 at a commercial blueberry farm near Burgaw, NC to determine weed control and crop tolerance to S-metolachlor and flumioxazin alone or mixed with hexazinone. Herbicides were applied pre-budbreak and postharvest. Pre-budbreak applications consisted of hexazinone at 1.1 or 2.2 kg ai ha−1, S-metolachlor at 1.4 or 2.8 kg ai ha–1, and flumioxazin at 215 g ai ha–1 alone and tank mixes of hexazinone or flumioxazin plus S-metolachlor. Additional treatments consisted of flumioxazin (215 g ha–1), flumioxazin plus S-metolachlor (1.4 and 2.8 kg ha–1), or hexazinone (1.1 kg ha–1) plus S-metolachlor (1.4 and 2.8 kg ha–1) applied pre-budbreak and followed by (fb) a postharvest application of flumioxazin (215 g ha–1). Herbicide programs containing flumioxazin resulted in greater Maryland meadowbeauty control (73%) 5 to 6 weeks after treatment (WAT) than herbicide programs containing hexazinone at 1.1 or 2.2 kg ha–1 (37% and 39%, respectively). Needleleaf rosette grass control remained ≥94% for all herbicide programs through 2 WAT. Hexazinone at 1.1 kg ha–1 provided greater needleleaf rosette grass control (87%) than flumioxazin (71%) 5 to 6 WAT. Meadowbeauty and needleleaf rosette grass control by all herbicide programs was poor (≤39% and ≤57%, respectively) 16 to 18 WAT. Two weeks after post-harvest applications, herbicide programs receiving a post-harvest flumioxazin application had greater meadowbeauty and needleleaf rosette grass control (78% and 84%, respectively) than those programs without a post-harvest flumioxazin application (43% and 71%, respectively).