Katherine M. Jennings

Weed Management in Glufosinate- and Glyphosate-Resistant Soybean (Glycine max)'

Abstract: An experiment was conducted at six locations in North Carolina to compare weed-management treatments using glufosinate postemergence (POST) in glufosinate-resistant soybean, glyphosate POST in glyphosate-resistant soybean, and imazaquin plus SAN 582 preemergence (PRE) followed by chlorimuron POST in nontransgenic soybean. Prickly sida and sicklepod were controlled similarly and 84 to 100% by glufosinate and glyphosate. Glyphosate controlled broadleaf signalgrass, fall panicum, goosegrass, rhizomatous johnsongrass, common lambsquarters, and smooth pigweed at least 90%. Control of these weeds by glyphosate often was greater than control by glufosinate. Mixing fomesafen with glufosinate increased control of these species except johnsongrass. Glufosinate often was more effective than glyphosate on entireleaf and tall morningglories. Fomesafen mixed with glyphosate increased morningglory control but reduced smooth pigweed control. Glufosinate or glyphosate applied sequentially or early postemergence (EPOST) following imazaquin plus SAN 582 PRE often were more effective than glufosinate or glyphosate applied only EPOST. Only rhizomatous johnsongrass was controlled more effectively by glufosinate or glyphosate treatments than by imazaquin plus SAN 582 PRE followed by chlorimuron POST. Yields and net returns with soil-applied herbicides only were often lower than total POST herbicide treatments. Sequential POST herbicide applications or soil-applied herbicides followed by POST herbicides were usually more effective economically than single POST herbicide applications. Nomenclature: Chlorimuron, ethyl 2-[[[[(4-chloro-6-methoxy-2-pyrimidinyl)amino]carbonyl] amino]sulfonyl]benzoate; SAN 582 (proposed name, dimethenamid), 2-chloro-N-[(1-methyl-2-methoxy)ethyl]-N-(2,4-dimethyl-thien-3-yl)-acetamide; fomesafen, 5-[2-chloro-4-(trifluoromethyl)phenoxy]-N-(methylsulfonyl)-2-nitrobenzamide; glufosinate, 2-amino-4-(hydroxymethylphosphinyl) butanoic acid; glyphosate, N-(phosphonomethyl)glycine; imazaquin, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash #2 BRAPP; carpetweed, Mollugo verticillata L. # MOLVE; common lambsquarters, Chenopodium album L. # CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; cutleaf groundcherry, Physalis angulata L. # PHYAN; eclipta, Eclipta prostrata L. # ECLAL; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray # IPOHG; fall panicum, Panicum dichotomiflorum Michx. # PANDI; goosegrass, Eleusine indica (L.) Gaertn. # ELEIN; johnsongrass, Sorghum halepense (L.) Pers. # SORHA; prickly sida, Sida spinosa L. # SIDSP; sicklepod, Senna obtusifolia L. Irwin and Barneby # CASOB; smooth pigweed, Amaranthus hybridus L. # AMACH; tall morningglory, Ipomoea purpurea (L.) Roth # PHBPU; soybean, Glycine max (L.) Merr. ‘Asgrow 5403 LL’, ‘Asgrow 5547 LL’, ‘Asgrow 5602 RR’, ‘Hartz 5566 RR’, ‘Southern States FFR 595’. Additional index words: Herbicide-resistant crops, Liberty Link soybean, nontransgenic soybean, Roundup Ready soybean. Abbreviations: DAT, days after treatment; EPOST, early postemergence; EPSPS, 5-enolpyruvylshikimate-3-phosphate synthase; LPOST, late postemergence; POST, postemergence; PRE, preemergence; THR, transgenic, herbicide-resistant; WAA, weeks after late postemergence application; WAP, weeks after planting.

Palmer Amaranth and Large Crabgrass Growth with Plasticulture-Grown Bell Pepper

Field experiments were conducted in 2004 and 2005 at Clemson, SC, and in 2004 at Clinton, NC, to quantify Palmer amaranth and large crabgrass growth and interference with plasticulture-grown bell pepper over multiple environments and develop models which can be used on a regional basis to effectively time removal of these weeds. Experiments at both locations consisted of an early and a late spring planting, with the crop and weeds planted alone and in combination. Daily maximum and minimum air temperatures were used to calculate growing degree days (GDD, base 10 C) accumulated following bell pepper transplanting and weed emergence. Linear and nonlinear empirical models were used to describe ht, canopy width, and biomass production as a function of accumulated GDD. Palmer amaranth reduced bell pepper fruit set as early as 6 wk after transplanting (WATP) (648 GDD), whereas large crabgrass did not significantly reduce fruit set until 8 WATP (864 GDD). Using the developed models and assuming Palmer amaranth and large crabgrass emergence on the day of bell pepper transplanting, Palmer amaranth was predicted to be the same ht as bell pepper at 287 GDD (20 cm tall) and large crabgrass the same ht as bell pepper at 580 GDD (34 cm tall). Nomenclature: Large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA, Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA, bell pepper, Capsicum annuum L. ‘Heritage’

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’.

Sulfentrazone Carryover to Vegetables and Cotton

Abstract Sulfentrazone is commonly used for weed control in soybeans and tobacco, and vegetable crops and cotton are often rotated with soybeans and tobacco. Studies were conducted to evaluate the potential for sulfentrazone to carryover and injure several vegetable crops and cotton. Sulfentrazone was applied PRE to soybean at 0, 210, 420, and 840 g ai/ha before planting bell pepper, cabbage, cotton, cucumber, onion, snap bean, squash, sweet potato, tomato, and watermelon. Cotton, known to be susceptible to sulfentrazone carryover, was included as an indicator species. Cotton injury ranged from 14 to 18% with a 32% loss of yield in 1 of 2 yr when the labeled use rate of sulfentrazone (210 g/ha) was applied to the preceding crop. High use rates of sulfentrazone caused at least 50% injury with yield loss ranging from 36 to 100%. Bell pepper, snap bean, onion, tomato, and watermelon were injured < 18% by sulfentrazone at 840 g/ha. Squash was injured < 3% and < 36% by sulfentrazone at 210 and 840 g/ha, respectively. Yield of these crops was not affected regardless of sulfentrazone rate. Cabbage and cucumber were injured < 13% by sulfentrazone at 210 and 420 g/ha, and yields were not affected. Sulfentrazone at 840 g/ha injured cabbage up to 46% and reduced yield in 1 of 2 yr. Sulfentrazone injured cucumber up to 63% and reduced yield of No. 2 grade fruits. Sulfentrazone at 210 and 420 g/ha injured sweet potato < 6% and did not affect yield. Sulfentrazone at 840 g/ha injured sweet potato 14% and reduced total yield 26%. Our results suggest little to no adverse effect on bell pepper, cabbage, cucumber, onion, snap bean, squash, sweet potato, tomato, or watermelon from sulfentrazone applied at registered use rates during the preceding year. Nomenclature: Sulfentrazone; bell pepper, Capsicum annuum L. ‘Jupiter’ cabbage, Brassica oleracea L. var. capitata ‘Conquest’; cotton, Gossypium hirsutum L. ‘DP-51’; cucumber, Cucumis sativus L. ‘Calypso’; onion, Allium cepa L. var. cepa ‘Tuffball’; snap bean, Phaseolus vulgaris L. ‘Strike’; soybean, Glycine max (L.) Merrill ‘9711’; squash, Cucurbita pepo L. ‘Early Prolific’; sweet potato, Ipomoea batatas (L.) Lam. ‘Beauregard’; tobacco, Nicotiana tabacum L.; tomato, Lycopersicon esculentum Mill. ‘Mountain Spring’; watermelon, Citrullus lanatus (Thumb.) Matsum and Nakai ‘Sangria’

Tolerance of Fresh-Market Tomato to Postemergence-Directed Imazosulfuron, Halosulfuron, and Trifloxysulfuron

Abstract A study was conducted to evaluate the effect of imazosulfuron, halosulfuron, and trifloxysulfuron POST-directed on six fresh-market tomato varieties. Injury 7 d after treatment (DAT) was 3% or less from all treatments, and no injury was observed 28 DAT. Imazosulfuron, halosulfuron, and trifloxysulfuron did not reduce yield relative to the nontreated check. There was no detectable herbicide effect on fruit shape and earliness. Data suggest that imazosulfuron, halosulfuron, and trifloxysulfuron can be applied POST-directed without negatively affecting yield or quality of several fresh-market tomato varieties.

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 Drip-Applied Herbicides on Yellow Nutsedge (Cyperus esculentus) in Plasticulture

Abstract Greenhouse and field studies were conducted to determine the effect of halosulfuron, imazosulfuron, and trifloxysulfuron applied through drip irrigation on yellow nutsedge. In greenhouse studies, yellow nutsedge control by halosulfuron, imazosulfuron, and trifloxysulfuron was greater (69 to 91%) than the nontreated control (0%). Yellow nutsedge treated with halosulfuron POST had a lower photosynthetic rate (0.6 to 22.6 µmol m−2 s−1) at 4, 7, and 14 d after treatment than the nontreated control (3.3 to 26.2 µmol m−2 s−1). Yellow nutsedge treated with trifloxysulfuron had lower photosynthetic rate and stomatal conductance than the nontreated plants. In field studies at Clinton, NC, yellow nutsedge density increased from treatment (day 0) to 56 d after treatment in all treatments. Increase in yellow nutsedge density was 72 and 95% in drip-applied halosulfuron and imazosulfuron treatments compared with yellow nutsedge density increases of 876% for the same period in the nontreated plots. Yellow nutsedge density increased 69 and 57% at Clinton and Kinston, NC, respectively, in the drip-applied 15 g ha−1 trifloxysulfuron treatment compared with 876% in the nontreated control. In field studies at Clinton and Kinston, NC, suppression of yellow nutsedge emergence in POST and drip-applied herbicide treatments was similar. Emergence of yellow nutsedge was similar in the imazosulfuron POST and the nontreated yellow nutsedge. Based on these studies, drip-applied herbicides may be beneficial as a part of a yellow nutsedge control program, but additional measures, such as a POST herbicide, would be needed for effective control. Drip-applied herbicides may give growers an option for herbicide application after drip irrigation tape and polyethylene mulch have been installed in the current vegetable crops. This application method would also allow herbicide treatment under plastic mulch used for multicropping systems. Nomenclature: Halosulfuron; imazosulfuron; trifloxysulfuron; yellow nutsedge, Cyperus esculentus L.

Eastern black nightshade (Solanum ptycanthum) reproduction and interference in transplanted plasticulture tomato

Abstract Studies were conducted to determine the effect of in-row eastern black nightshade establishment and removal timings in plasticulture tomato on tomato yield loss and nightshade berry production and seed viability. Eastern black nightshade was transplanted at 1, 2, 3, 4, 5, 6, and 12 wk after tomato planting (WAP) and remained until tomato harvest, or was established at tomato planting and removed at 2, 3, 4, 5, 6, 8, and 12 WAP to determine the critical weed-free periods. Eastern black nightshade seed viability increased with berry size and with length of establishment or removal time. The critical weed-free period to avoid viable nightshade seed production was 3–6 WAP. Tomato yield decreased with early weed establishment or with delayed time of weed removal. The critical weed-free period to avoid greater than 20% tomato yield loss for the sum weight of extra large and jumbo grades was 28 to 50 d after tomato transplanting. Nomenclature: Eastern black nightshade, Solanum ptycanthum Dun. SOLPT; tomato, Lycopersicon esculentum.

Tolerance of Tomato to Herbicides Applied through Drip Irrigation

Abstract Greenhouse and field studies were conducted to determine tolerance of tomato to halosulfuron, imazosulfuron, and trifloxysulfuron herbicides applied through drip irrigation. In greenhouse studies, PRE- and POST-applied trifloxysulfuron caused greater tomato injury (14 and 54% injury, respectively) than PRE- and POST-applied halosulfuron (5 and 26% injury, respectively) or imazosulfuron (5 and 23% injury, respectively). All herbicide treatments in the greenhouse studies caused greater injury to tomato than the nontreated. Greater tomato injury was observed in the greenhouse from herbicides applied POST than when soil applied. Tomato injury from POST-applied halosulfuron, imazosulfuron, or trifloxysulfuron followed a linear relationship, with tomato injury increasing with increasing herbicide rate. Tomato photosynthetic rate did not differ among the herbicide treatments (32.7 to 55.0 μmol m−2 s−1) and the nontreated (38.0 to 55.0 μmol m−2 s−1). At 5 to 16 days after treatment (DAT), tomato treated with imazosulfuron POST (0.26 to 0.46 cm s−1) or trifloxysulfuron POST (0.27 to 0.51 cm s−1) had lower stomatal conductance compared to the stomatal conductance of the nontreated tomato (0.65 to 0.76 cm s−1). Chlorophyll content did not differ among treatments at 0 to 6 DAT. At 7 to 12 DAT, tomato treated with imazosulfuron POST (34.0 to 40.1 SPAD) and trifloxysulfuron POST (35.0 to 41.6 SPAD) had lower chlorophyll content compared to the nontreated (39.1 to 48.1 SPAD). In 2008 and 2009 field studies, no tomato injury was observed. Herbicide, herbicide application method, and herbicide rate had no effect on tomato height (73 to 77 cm 14 DAT, 79 to 84 cm 21 DAT) and total fruit yield (62,722 to 80,328 kg ha−1). Nomenclature: Halosulfuron; imazosulfuron; trifloxysulfuron; tomato; Solanum lycopersicum L. Resumen Se realizaron estudios de invernadero y de campo para determinar la tolerancia del tomate a halosulfuron, imazosulfuron y trifloxysulfuron aplicados a travõs de un sistema de riego por goteo. En los estudios de invernadero, trifloxysulfuron aplicado PRE y POST causõ más dańo al tomate (14 y 54%, respectivamente) que halosulfuron aplicado PRE y POST (5 y 26%, respectivamente) o imazosulfuron (5 y 23%, respectivamente). En los estudios de invernadero, todos los tratamientos de herbicidas causaron mayor daño al tomate que el testigo no-tratado. En el invernadero cuando se aplicaron los herbicidas POST, se observõ un mayor daño que cuando se aplicaron al suelo. El daño al tomate causado por halosulfuron, imazosulfuron o trifloxysulfuron aplicados POST siguiõ una relaciõn lineal, incrementándose el daño al tomate conforme incrementõ la dosis del herbicida. La tasa fotosintõtica del tomate no difiriõ entre los tratamientos de herbicidas (32.7 a 55.0 mol m-2 s-1) y el testigo no-tratado (38.0 a 55.0 mol m-2 s-1). De 5 a 16 dúas despuõs del tratamiento (DAT), el tomate tratado con imazosulfuron POST (0.26 a 0.46 cm s-1) o trifloxysulfuron (0.27 a 0.52 cm s-1) tuvo una menor conductancia estomática comparado con el tomate no-tratado (0.65 a 0.76 cm s-1). El contenido de clorofila no difiriõ entre tratamientos de 0 a 6 DAT. De 7 a 12 DAT, el tomate tratado con imazosulfuron POST (34.0 a 40.1 SPAD) and trifloxysulfuron (35.0 a 41.6 SPAD) tuvo un menor contenido de clorofila comparado con el testigo no-tratado (39.1 a 48.1 SPAD). En los estudios de campo en 2008 y 2009, no se observõ ningún daño al tomate. El herbicida, el mõtodo de aplicaciõn del herbicida y la dosis del herbicida no tuvieron efecto sobre la altura del tomate (73 a 77 cm 14 DAT, 79 a 84 cm 21 DAT) y el rendimiento total de fruto (62,722 a 80,328 kg ha-1).