Shawn D. Askew

Weed Efficacy Evaluations for Bromoxynil, Glufosinate, Glyphosate, Pyrithiobac, and Sulfosate'

Thirteen field trials were conducted in 1999 and 2000 to evaluate postemergence (POST) weed control with single applications of bromoxynil at 420 or 560 g ai/ha, glufosinate at 291 or 409 g ai/ha, glyphosate at 1,120 g ai/ha, pyrithiobac at 36 or 72 g ai/ha, or sulfosate at 1,120 g ai/ha. Additional treatments evaluated included two applications with glufosinate at both rates in all possible combinations, two applications of glyphosate, and two applications of sulfosate. Weeds were 2 to 5 cm or 8 to 10 cm tall for annual grass and broadleaf weeds whereas yellow nutsedge and glyphosate-resistant corn were 8 to 10 cm tall. All herbicide treatments controlled 2- to 5-cm common cocklebur, Florida beggarweed, jimsonweed, ladysthumb smartweed, Pennsylvania smartweed, pitted morningglory, prickly sida, redroot pigweed, smooth pigweed, and velvetleaf at least 90%. All herbicide treatments except pyrithiobac at either rate controlled 2- to 5-cm common lambsquarters, common ragweed, and tall morningglory at least 90%; pyrithiobac at the lower rate was the only treatment that failed to control entireleaf and ivyleaf morningglory at least 90%. Bromoxynil and pyrithiobac at either rate controlled 2- to 5-cm sicklepod 33 to 68% whereas glufosinate, glyphosate, and sulfostate controlled ≥99%. Glyphosate and sulfosate applied once or twice controlled hemp sesbania less than 70% and volunteer peanut less than 80%. Bromoxynil and pyrithiobac were the least effective treatments for control of annual grass species and bromoxynil controlled Palmer amaranth less than 80%. Glufosinate controlled broadleaf signalgrass, fall panicum, giant foxtail, green foxtail, large crabgrass, yellow foxtail, seedling johnsongrass, Texas panicum, and glyphosate-resistant corn at least 90% but controlled goosegrass less than 60%. Glyphosate and sulfosate controlled all grass species except glyphosate-resistant corn at least 90%. In greenhouse research, goosegrass could be controlled with glufosinate POST plus a late POST-directed treatment of prometryn plus monosodium salt of methylarsonic acid. Nomenclature: Bromoxynil; glufosinate; glyphosate; monosodium salt of methylarsonic acid; prometryn; pyrithiobac; sulfosate; broadleaf signalgrass, Bracharia platyphylla (Griseb.) Nash #3 BRAPP; common cocklebur, Xanthium strumarium L. # XANST; common lambsquarters, Chenopodium album L. # CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray # IPOHG; fall panicum, Panicum dichotomiflorum Michx. # PANDI; Florida beggarweed, Desmodium tortuosum (Sw.) DC. # DEDTO; giant foxtail, Setaria faberi Herm. # SETFA; goosegrass, Eleusine indica (L.) Gaertn. # ELIEN; green foxtail, Setaria viridis (L.) Beauv. # SETVI; hemp sesbania, Sesbania exaltata (Raf.) Rybd. ex A. W. Hill # SEBEX; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; jimsonweed, Datura stramonium L. # DATST; seedling johnsongrass, Sorghum halepense (L.) Pers. # SORHA; ladysthumb smartweed, Polygonum persicaria L. # POLPE; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; Palmer amaranth, Amaranthus palmeri S. Wats. # AMAPA; volunteer peanut, Arachis hypogaea L. # ARAHY; Pennsylvania smartweed L. # POLPY; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; redroot pigweed, Amaranthus retroflexus L. # AMARE; sicklepod, Senna obtusifolia (L.) Irwin and Barnaby # CASOB; smooth pigweed, Amaranthus hybridus L. # AMACH; tall morningglory, Ipomoea purpurea (L.) Roth # PHBPU; Texas panicum, Panicum texanum Buckl. # PANTE; velvetleaf, Abutilon theophrasti Medicus # ABUTH; yellow foxtail, Setaria glauca (L.) Beauv. # SETLU; yellow nutsedge, Cyperus esculentus L. # CYPES; glyphosate-resistant corn, Zea mays L. ZEAMA. Additional index words: Herbicide-resistant crops, nonselective herbicides, AMACH, AMAPA, AMARE, AMBEL, ARAHY, BRAPP, CASOB, CHEAL, CYPES, DATST, DEDTO, DIGSA, ELEIN, IPOHE, IPOHG, IPOLA, PANDI, PANTE, PHBPU, POLPE, POLPY, SEBEX, SETFA, SETLU, SETVI, SIDSP, SORHA, XANST, ZEAMA. Abbreviations: DAT, days after treatment; POST, postemergence.

Weed management with CGA-362622, fluometuron, and prometryn in cotton

Abstract An experiment conducted at five locations in North Carolina during 1998 and 1999 evaluated weed management systems in cotton with CGA-362622 and pyrithiobac. Weed management systems evaluated different combinations with or without fluometuron preemergence (PRE) followed by (fb) CGA-362622 early postemergence (EPOST), postemergence (POST), or EPOST + POST; or pyrithiobac EPOST fb prometryn plus MSMA late postemergence directed (LAYBY) or no LAYBY treatment. The weed species evaluated include common ragweed, entireleaf morningglory, pitted morningglory, prickly sida, sicklepod, tall morningglory, and yellow nutsedge. Fluometuron PRE improved the control of all weed species by at least 17 percentage points and increased cotton lint yield compared with the systems that did not use fluometuron PRE. Prometryn plus MSMA LAYBY improved the control of all weed species and increased lint yield compared with the systems that did not use prometryn plus MSMA LAYBY when PRE or POST herbicides were used. Control with CGA-362622 at all application timings was greater than 70% for all weed species evaluated (common ragweed, entireleaf morningglory, pitted morningglory, sicklepod, tall morningglory, and yellow nutsedge), except prickly sida. Control of all three morningglory species and prickly sida was at least 70% with pyrithiobac, whereas control of common ragweed, sicklepod, and yellow nutsedge was lower. The only cotton that yielded over 800 kg ha−1 was treated with fluometuron PRE fb CGA-362622 EPOST, POST, or EPOST + POST fb prometryn plus MSMA LAYBY. Cotton treated with pyrithiobac EPOST gave yields that were similar to those given by cotton treated with CGA-362622 EPOST in systems with fluometuron PRE and less than those given by cotton treated with CGA-362622 EPOST in systems without fluometuron PRE. Early-season injury with CGA-362622 was greater than 60% at Clayton and Rocky Mount in 1998, whereas 12% or less injury was observed at the other locations. Pyrithiobac resulted in 25 to 45% injury at these two locations. No injury was observed 45 d after treatment. Nomenclature: CGA-362622; fluometuron; MSMA; prometryn; pyrithiobac; common ragweed, Ambrosia artemisiifolia L. AMBEL; yellow nutsedge, Cyperus esculentus L. CYPES; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray IPOHG; pitted morningglory, Ipomoea lacunosa L. IPOLA; tall morningglory, Ipomoea purpurea (L.) Roth PHBPU; sicklepod, Senna obtusifolia (L.) Irwin and Barnaby CASOB; prickly sida, Sida spinosa L. SIDSP; cotton, Gossypium hirsutum L. ‘Stoneville 474’.

Economic Evaluation of Diclosulam and Flumioxazin Systems in Peanut (Arachis hypogaea1

Abstract: Field studies were conducted at two locations in North Carolina in 1998 and in 1999 to evaluate weed control and peanut response following diclosulam at 27 g ai/ha preemergence (PRE) or flumioxazin at 87 g ai/ha preemergence (PRE) alone and in systems with postemergence (POST) commercial standards. All plots received a preplant incorporated (PPI) treatment of metolachlor at 1,400 g ai/ha. Metolachlor PPI plus diclosulam or flumioxazin PRE controlled common lambsquarters, common ragweed, entireleaf morningglory, large crabgrass, and yellow nutsedge as well as or better than metolachlor PPI followed by (fb) acifluorfen plus bentazon POST or paraquat plus bentazon early postemergence fb acifluorfen plus bentazon POST. Metolachlor PPI plus diclosulam PRE or flumioxazin PRE controlled ivyleaf morningglory as well as metolachlor PPI fb acifluorfen plus bentazon POST. Metolachlor PPI plus flumioxazin PRE controlled common lambsquarters better than metolachlor PPI plus diclosulam PRE while diclosulam PRE controlled common ragweed better. There was no difference in common lambsquarters control between flumioxazin and diclosulam PRE when POST herbicides were used. There was only one difference in peanut yield and net returns between metolachlor PPI fb either diclosulam or flumioxazin PRE when POST herbicides were used. Nomenclature: Acifluorfen; bentazon; diclosulam; flumioxazin; metolachlor; paraquat; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray # IPOHG; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; large crabgrass, Digitaria sanguinalis L. Scop. # DIGSA; yellow nutsedge, Cyperus esculentus L. # CYPES; peanut, Arachis hypogaea L., ‘NC 7’, ‘NC 10C’. Additional index words: Economic analysis, acifluorfen, bentazon, paraquat. Abbreviations: EPOST, early postemergence; fb, followed by; POST, postemergence; PPI, preplant incorporated; PRE, preemergence.

Economic evaluation of HADSS™ computer program for weed management in nontransgenic and transgenic cotton

Abstract Field studies were conducted at four locations in North Carolina in 1998 and 1999 to evaluate the use of the Herbicide Application Decision Support System (HADSS™) for weed management in nontransgenic, bromoxynil-resistant, and glyphosate-resistant cotton. Weed management systems included trifluralin preplant incorporated (PPI) plus fluometuron preemergence (PRE) or no soil-applied herbicides. Postemergence (POST) options included bromoxynil, glyphosate, or pyrithiobac early POST (EPOST) followed by (fb) MSMA plus prometryn late postemergence–directed (LAYBY) or herbicide recommendations given by HADSS. Glyphosate-resistant systems provided control equivalent to or better than control provided by bromoxynil-resistant and nontransgenic systems for smooth pigweed, Palmer amaranth, large crabgrass, goosegrass, ivyleaf morningglory, and fall panicum. Trifluralin PPI fb fluometuron PRE fb HADSS POST provided equivalent or higher levels of weed control and yield than trifluralin PPI fb fluometuron PRE fb bromoxynil, glyphosate, or pyrithiobac EPOST fb MSMA plus prometryn LAYBY. The trifluralin PPI fb fluometuron PRE fb HADSS POST systems controlled large crabgrass at Goldsboro and fall panicum better than HADSS POST-only systems in nontransgenic cotton. Cotton yield and net returns in the glyphosate-resistant systems were always equal to or higher than the nontransgenic and bromoxynil-resistant systems. Net returns were higher for the soil-applied fb HADSS POST treatments in 8 of 12 comparisons with HADSS POST systems without soil-applied herbicides. Early-season weed interference reduced cotton lint yields and net returns in POST-only systems. Nomenclature: Bromoxynil; fluometuron; glyphosate; MSMA; prometryn; pyrithiobac; trifluralin; cotton, Gossypium hirsutum L. ‘Deltapine 51’, ‘BXN 47’, ‘Deltapine 5415RR’; fall panicum, Panicum dichotomiflorum Michx. PANDI; goosegrass, Eleusine indica (L.) Gaertn. ELEIN; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. IPOHE; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; smooth pigweed, Amaranthus hybridus L. AMACH.

Cotton (Gossypium hirsutum) and Weed Response to Flumioxazin Applied Preplant and Postemergence Directed1

Separate field experiments were conducted to evaluate weed control and cotton response to flumioxazin in North Carolina. Flumioxazin postemergence directed (PD) at 70 g ai/ha applied alone or mixed with glyphosate or MSMA completely controlled common lambsquarters, common ragweed, entireleaf morningglory, ivyleaf morningglory, Palmer amaranth, pitted morningglory, prickly sida, sicklepod, smooth pigweed, and tall morningglory 4 wk after treatment. Glyphosate at 1,120 g ai/ha controlled sicklepod and entireleaf, ivyleaf, pitted, and tall morningglory less than flumioxazin. Weed-free experiments were conducted to evaluate cotton injury, fresh biomass reduction, and yield response to flumioxazin at 70 g ai/ha preplant (PP) and two rates PD. Nine PP applications were made at various timings between 0 and 10 wk prior to planting. Cotton was stunted 12% initially, and midseason cotton biomass was reduced when flumioxazin was applied at planting in 1 yr. Flumioxazin did not injure 15- or 30-cm–tall cotton when applied PD at 36 or 70 g/ha. Cotton yield differed between years, but was not affected by various flumioxazin treatments compared with commercial standards and nontreated controls. Nomenclature: Flumioxazin; glyphosate; MSMA; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray # IPOHG; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; Palmer amaranth, Amaranthus palmeri S.Wats. # AMAPA; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; sicklepod, Senna obtusifolia Irwin and Banaby # CASOB; smooth pigweed, Amaranthus hybridus L. # AMACH; tall morningglory, Ipomoea purpurea (L.) Roth # PHBPU; cotton, Gossypium hirsutum L. ‘Deltapine 51’, ‘Suregrow 125’. Additional index words: Burn-down application, fresh biomass, injury, LAYBY, stale seedbed. Abbreviations: LAYBY, the last postemergence-directed herbicide application; PD, postemergence directed; POST, postemergence; PP, preplant; PRE, preemergence; WAP, weeks after planting.

Common ragweed interference in peanut

Abstract Studies were conducted to evaluate density-dependent effects of common ragweed on weed growth and peanut growth and yield. Common ragweed height was not affected by weed density and peanut canopy diameter. Weed height exceeded peanut height throughout the growing season, indicating that competition for light occurred between the two species. Common ragweed aboveground dry biomass per plant decreased as weed density increased, but total weed dry biomass per meter of crop row increased with weed density. The rectangular hyperbola model described the effect of weed density on percent peanut yield loss. With the asymptote constrained to 100% maximum yield loss, the I coefficient (yield loss per unit density as density approaches zero) was 68.3 ± 12.2%. Common ragweed did not influence the occurrence of tomato spotted wilt virus, early leaf spot (Cercospora arachidicola), southern stem rot (Sclerotium rolfsii), and Cylindrocladium black rot (Cylindrocladium crotalariae). However, as common ragweed density increased, the incidence of late leaf spot (Cercosporidium personatum) increased. Results indicate that common ragweed is one of the more competitive weeds in peanut and a potential economic threat to peanut growers. Nomenclature: Common ragweed, Ambrosia artemisiifolia L. AMBEL; peanut, Arachis hypogaea L. ‘NC 7’.

Glyphosate Systems for Weed Control in Glyphosate-Tolerant Cotton (Gossypium hirsutum)1

Field studies were conducted at three locations in North Carolina to evaluate clomazone preemergence (PRE) in glyphosate-tolerant cotton. Cotton was injured by fluometuron PRE at one location. Clomazone PRE controlled common ragweed, goosegrass, large crabgrass, and prickly sida better than trifluralin preplant incorporated (PPI). Trifluralin controlled Palmer amaranth better than clomazone. The addition of a late post-directed (LAYBY) treatment of cyanazine plus MSMA improved the control of goosegrass. Glyphosate at 0.8 kg ai/ha, used postemergence as needed, controlled tall morningglory and entireleaf morningglory at least 84%. Common ragweed was controlled with all herbicides, except trifluralin PPI. Prickly sida was controlled 94% or greater in glyphosate-containing systems. Cotton yields and net returns were similar for all glyphosate systems, regardless of soil-applied herbicides and LAYBY treatment options. Nomenclature: Clomazone; cyanazine; fluometuron; glyphosate; MSMA; trifluralin; common ragweed, Ambrosia artemisiifolia L. #3 AMBEL; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray # IPOHG; goosegrass, Eleusine indica (L.) Gaertn. # ELEIN; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; Palmer amaranth, Amaranthus palmeri S.Wats # AMAPA; prickly sida, Sida spinosa L. # SIDSP; tall morningglory, Ipomoea purpurea (L.) Roth # PHBPU; cotton, Gossypium hirsutum L. ‘Paymaster 1330RR’, ‘DP5415RR’. Additional index words: Economic analysis, herbicide-resistant crops. Abbreviations: ANS, as needed spray; DAP, days after planting; EPOST, early postemergence; fb, followed by; LAYBY, late post directed; POST, postemergence; POT, postemergence over-the-top; PPI, preplant incorporated; PRE, preemergence.

Selective Creeping Bentgrass (Agrostis stolonifera) Control in Cool-Season Turfgrass

Creeping bentgrass infestations in cool-season turfgrass are unsightly and difficult to control. Field tests were conducted at Stoney Creek Golf Course in Wintergreen, VA, in 2002 and 2003 on a Kentucky bluegrass rough and at the Turfgrass Research Center in Blacksburg, VA, in 2003 on a perennial ryegrass lawn to determine the efficacy of imazaquin, isoxaflutole, and mesotrione for creeping bentgrass control and turfgrass tolerance. Isoxaflutole and mesotrione each applied in two sequential applications at 280 g ai/ha or three sequential applications at 170 or 60 g/ha and imazaquin in two sequential applications at 390 g/ha controlled bentgrass at least 92% 14 wk after initial treatment (WAIT) at all locations. Sequential applications were applied at 2-wk intervals. Isoxaflutole and mesotrione, regardless of rate or sequential treatment, injured turfgrass less than 20% at all rating dates and locations. Imazaquin in two sequential applications at 390 g/ha injured Kentucky bluegrass and perennial ryegrass greater than 50% at all locations 14 WAIT. Results indicate isoxaflutole or mesotrione could be used for selective bentgrass control in Kentucky bluegrass or perennial ryegrass. Nomenclature: Imazaquin; isoxaflutole; mesotrione; creeping bentgrass, Agrostis stolonifera L. #3 AGRST; Kentucky bluegrass, Poa pratensis L. ‘Blacksburg’ and ‘Midnight’; perennial ryegrass, Lolium perenne L. ‘Prosport’. Additional index words: Golf course rough, turfgrass injury, weed control. Abbreviations: SCG, Stoney Creek Golf Course; TRC, Turfgrass Research Center; WAIT, weeks after initial treatment.

Flumioxazin Systems for Weed Management in North Carolina Peanut (Arachis hypogaea) 1

Abstract: A study was conducted to evaluate flumioxazin preemergence (PRE) at 71 and 105 g ai/ha, when used with dimethenamid PRE, dimethenamid preplant incorporated (PPI), or ethalfluralin PPI, for crop injury, weed control, and yield. Peanut injury from treatments including flumioxazin 2 wk after soil-applied treatment (WAST) was less than 2% at two locations and 50 to 67% at a third location. Peanut injury increased with flumioxazin rate. Soil-applied treatments that included flumioxazin at either rate controlled common lambsquarters and prickly sida at least 96 and 89%, respectively. Addition of postemergence (POST) herbicides to any soil-applied program controlled prickly sida and ivyleaf morningglory at least 94 and 98%, respectively. Treatments that included ethafluralin or dimethenamid controlled goosegrass at least 82%. With a few exceptions, peanut yields were not improved by use of POST herbicides. Where peanut injury occurred, increased flumioxazin rate resulted in lower peanut yield when averaged over PPI and POST herbicide treatments. Nomenclature: Dimethenamid; ethalfluralin; flumioxazin; common lambsquarters, Chenopodium album L. #3 CHEAL; goosegrass, Eleusine indica (L.) Gaertn. # ELEIN; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; prickly sida, Sida spinosa L. # SIDSP; peanut, Arachis hypogaea L. ‘NC 7’, ‘NC 10C’. Additional index words: Acifluorfen, bentazon, 2,4-DB, imazapic. Abbreviations: fb, followed by; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; WAPT, weeks after POST treatment; WAST, weeks after soil-applied treatment.

Virginia Market-Type Peanut (Arachis hypogaea) Cultivar Tolerance and Yield Response to Flumioxazin Preemergence1

Abstract: Field studies were conducted in 1996 and 1997 to evaluate response of eight peanut cultivars to flumioxazin applied preemergence (PRE) at 71 g ai/ha. Peanut cultivars evaluated include ‘NC 12C’, ‘NC 7’, ‘VAC 92R’, ‘NC-V 11’, ‘NC 10C’, ‘AT VC 1’, ‘NC 9’, and the experimental breeding line ‘N9001OE’. Visible injury 3 wk after planting in 1996 was 3% or less regardless of cultivar. In 1997, all cultivars were injured 15 to 28% with flumioxazin PRE, except VC 1, which was injured 45%. No visible injury was observed at 5 and 9 wk after planting. Flumioxazin did not influence the incidence of early leaf spot, late leaf spot, southern stem rot, cylindrocladium black rot, or tomato spotted wilt virus. Flumioxazin did not affect percentage of extra-large kernels, sound mature kernels, other kernels, and total yield. Nomenclature: Flumioxazin; peanut, Arachis hypogaea L., ‘NC 12C’, ‘NC 7’, ‘VAC 92R’, ‘NC-V 11’, ‘NC 10C’, ‘AT VC 1’, ‘NC 9’, ‘N9001OE’. Additional index words: Disease interaction, Cylindrocladium crotalariae (Loos) Bell and Sobers, Cercospora arachidicola Hori, Cercosporidium personatum (Berk. and Curt.), Sclerotium rolfsii Sacc., grade parameters, extra-large kernels, sound mature kernels, sound splits, total kernels, other kernels, fancy pods. Abbreviations: CBR, cylindrocladium black rot; DAP, days after planting; ELK, extra-large kernels; PPI, preplant incorporated; PRE, preemergence; SMK, sound mature kernels; SS, sound splits; TMSK, total sound mature kernels; TSWV, tomato spotted wilt virus; WAP, weeks after planting.