John W. Wilcut

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’.

Reproductive abnormalities in glyphosate-resistant cotton caused by lower CP4-EPSPS levels in the male reproductive tissue

Abstract Glyphosate treatments to glyphosate-resistant (GR) cotton have been associated with poor pollination and increased boll abortion. Anatomical studies were conducted to characterize the effect of glyphosate treatments on the development of male and female reproductive organs of cotton flowers at anthesis. In comparison with nontreated plants, glyphosate applied at both the four-leaf stage postemergence (POST) and at the eight-leaf stage POST directed inhibited the elongation of the staminal column and filament, which increased the distance from the anthers to the receptive stigma tip by 4.9 to 5.7 mm during the first week of flowering. The increased distance from the anthers to the stigma resulted in 42% less pollen deposited on stigmas of glyphosate-treated plants than in nontreated plants. Moreover, pollen from glyphosate-treated plants showed numerous morphological abnormalities. Transmission electron microscopy showed the presence of large vacuoles, numerous starch grains, and less organized pockets of the endoplasmic reticulum containing fewer ribosomes in pollen from glyphosate-treated plants than from nontreated plants. Pollen development in glyphosate-treated plants is likely inhibited or aborted at the vacuolate microspore and vacuolate microgamete stages of microgametogenesis, resulting in immature pollen at anthesis. Although stigmas from glyphosate-treated plants were 1.2 to 1.4 mm longer than those from nontreated plants, no other anatomical differences in stigmas were visibly evident. The presence of the GR 5-enolpyruvylshikimate-3-phosphate synthase (CP4-EPSPS) enzyme from Agrobacterium sp. strain CP4 was quantified in reproductive and vegetative tissues using enzyme-linked immunosorbent assay. The content of CP4-EPSPS in the stigma, anther, preanthesis floral bud (square), and flower petals was significantly less than that in the vegetative leaf tissue. Glyphosate effects on the male reproductive development resulting in poor pollen deposition on the stigma, as well as production of aborted pollen with reduced viability, provide a likely explanation for reports of increased boll abortion and pollination problems in glyphosate-treated GR cotton. Nomenclature: Glyphosate; cotton, Gossypium hirsutum L. ‘Delta Pine & Land 5415RR’, ‘Delta Pine & Land 50’, ‘Delta Pine & Land 90’, ‘SureGrow 125RR’.

CGA-362622 Antagonizes Annual Grass Control with Clethodim1

Abstract: Field and greenhouse experiments were conducted to evaluate clethodim, CGA-362622, mixtures thereof, and sequential treatments for control of broadleaf signalgrass, fall panicum, goosegrass, and large crabgrass. In greenhouse experiments, clethodim alone provided 93 and 100% control of three- to four-leaf goosegrass at the low (105 g ai/ha) and high (140 g/ha) rates, respectively, whereas CGA-362622 did not control grasses in greenhouse or field experiments. Control of six- to eight-leaf goosegrass in the greenhouse with clethodim was 75% for the low rate and 89% for the high rate. Control of goosegrass in greenhouse studies was reduced at least 43 percentage points with CGA-362622 and clethodim at the high rate in mixture compared with control provided by clethodim at the high rate alone. When CGA-362622 and clethodim were applied in mixture in field studies, the effectiveness of the graminicide was decreased from > 97 to < 57% control for all annual grasses. Antagonism of clethodim activity was greater than that of the tank mixture when clethodim was applied 1 d after CGA-362622 on large crabgrass, goosegrass, and fall panicum. Clethodim applied 7 d before or after CGA-362622 controlled the four grass species as well as did clethodim applied alone. When CGA-362622 was applied to goosegrass alone, fresh weight accumulation stopped for a period of 4 d compared with untreated plants. Normal growth resumed after 4 d. Nomenclature: CGA-362622, N-[(4,6-dimethoxy-2-pyrimidinyl)carbamoyl]-3-(2,2,2-trifluoroethoxy)-pyridin-2-sulfonamide sodium salt; clethodim; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash #3 BRAPP; fall panicum, Panicum dichotomiflorum (L.) # PANDI; goosegrass, Eleusine indica (L.) Gaertn. # ELEIN; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA. Additional index words: Antagonism, growth analysis, orthogonal contrasts. Abbreviations: ALS, acetolactase synthase (EC 4.1.3.18); DAT, days after treatment; POST, postemergence.

U.S. Grower Views on Problematic Weeds and Changes in Weed Pressure in Glyphosate-Resistant Corn, Cotton, and Soybean Cropping Systems

Abstract Corn and soybean growers in Illinois, Indiana, Iowa, Mississippi, Nebraska, and North Carolina, as well as cotton growers in Mississippi and North Carolina, were surveyed about their views on changes in problematic weeds and weed pressure in cropping systems based on a glyphosate-resistant (GR) crop. No growers using a GR cropping system for more than 5 yr reported heavy weed pressure. Over all cropping systems investigated (continuous GR soybean, continuous GR cotton, GR corn/GR soybean, GR soybean/non-GR crop, and GR corn/non-GR crop), 0 to 7% of survey respondents reported greater weed pressure after implementing rotations using GR crops, whereas 31 to 57% felt weed pressure was similar and 36 to 70% indicated that weed pressure was less. Pigweed, morningglory, johnsongrass, ragweed, foxtail, and velvetleaf were mentioned as their most problematic weeds, depending on the state and cropping system. Systems using GR crops improved weed management compared with the technologies used before the adoption of GR crops. However, the long-term success of managing problematic weeds in GR cropping systems will require the development of multifaceted integrated weed management programs that include glyphosate as well as other weed management tactics. Nomenclature: Glyphosate; foxtail, Setaria spp.; johnsongrass, Sorghum halepense (L.) Pers.; morningglory, Ipomoea spp.; pigweed, Amaranthus spp.; ragweed, Ambrosia spp.; velvetleaf, Abutilon theophrasti Medik.; corn, Zea mays L.; cotton, Gossypium hirsutum L; soybean, Glycine max (L.) Merr

Absorption, translocation, and metabolism of foliar-applied CGA 362622 in cotton, peanut, and selected weeds

Abstract Studies were conducted to evaluate absorption, translocation, and metabolism of 14C-CGA 362622 when foliar applied to cotton, peanut, jimsonweed, and sicklepod. Differential metabolism is the basis for tolerance in cotton and jimsonweed. In addition, cotton absorbs less herbicide compared with the other three species, thus aiding in tolerance. Only jimsonweed translocated appreciable herbicide (25%) out of treated leaves and acropetally to the meristematic tissue where the herbicide was quickly metabolized. No plant species translocated over 2% of applied radioactivity below the treated leaves. Most of the metabolites formed by the four species were more polar than CGA 362622 and averaged 51, 48, 30, and 25% of the radioactivity detected in the treated leaves of cotton, jimsonweed, peanut, and sicklepod, respectively. The half-life of CGA 362622 was estimated to be 0.8, 1.9, 4, and 6 d in treated leaves of cotton, jimsonweed, sicklepod, and peanut, respectively. Nomenclature: CGA 362622, N-[(4,6-dimethoxy-2-pyrimidinyl)carbamoyl]-3-(2,2,2-trifluoroethoxy)-pyridin-2-sulfonamide sodium salt; jimsonweed, Datura stramonium L. DATST; sicklepod, Senna obtusifolia (L.) Irwin and Barnaby CASOB; cotton, Gossypium hirsutum L. ‘Stoneville 474’; peanut, Arachis hypogaea L. ‘NC 10C’.

Absorption and translocation of glyphosate in glyphosate-resistant cotton as influenced by application method and growth stage

Abstract The influence of herbicide placement and plant growth stage on the absorption and translocation patterns of 14C-glyphosate in glyphosate-resistant cotton was investigated. Plants at four growth stages were treated with 14C-glyphosate on a 5-cm2 section of the stem, which simulated a postemergence-directed spray (PDS) application, or on the newest mature leaf, which simulated a postemergence (POST) application. Plants were harvested 3 and 7 d after treatment and divided into the treated leaf or treated stem, mature leaves, immature leaves and buds, stems, roots, fruiting branches (including the foliage on the fruiting branch), squares, and bolls. The PDS versus POST application main effect on absorption was significant. Absorption of 14C-glyphosate applied to stem tissue was higher in PDS applications than in POST applications. Plants receiving PDS applications absorbed 35% of applied 14C-glyphosate, whereas those receiving POST applications absorbed 26%, averaged over growth stages at application. Absorption increased from the four-leaf growth stage to the eight-leaf stage in POST applications but reached a plateau at the eight-leaf stage. Plants with PDS applications showed an increase in absorption from the four- to eight- to twelve-leaf stages and reached a plateau at the 12-leaf stage. Translocation of 14C-glyphosate to roots was greater at all growth stages with PDS treatments than with POST treatments. Herbicide placement did not affect translocation of 14C-glyphosate to squares and bolls. Squares and bolls retained 0.2 to 3.7% of applied 14C-glyphosate, depending on growth stage. Separate studies were conducted to investigate the fate of foliar-applied 14C-glyphosate at the four- or eight-leaf growth stages when harvested at 8- or 10-leaf, 12-leaf, midbloom (8 to 10 nodes above white bloom), and cutout (five nodes above white bloom, physiological maturity) stages. Thirty to 37% of applied 14C-glyphosate remained in the plant at cutout in four- and eight-leaf treatment stages, respectively. The concentration of 14C-glyphosate in tissue (Bq g−1 dry weight basis) was greatest in mature leaves and immature leaves and buds in plants treated at the four-leaf stage. Plants treated at the eight-leaf stage and harvested at all growth stages except cutout showed a higher concentration of 14C-glyphosate in squares than in other plant tissue. Accumulation of 14C-glyphosate in squares reached a maximum of 43 Bq g−1 dry weight at harvest at the 12-leaf stage. This concentration corresponds to 5.7 times greater accumulation of 14C-glyphosate in squares than in roots, which may also be metabolic sinks. These data suggest that reproductive tissues such as bolls and squares can accumulate 14C-glyphosate at higher concentrations than other tissues, especially when the herbicide treatment is applied either POST or PDS during reproductive stages (eight-leaf stage and beyond). Nomenclature: Glyphosate; cotton, Gossypium hirsutum L. ‘Delta Pine 5415RR’.

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.

Tropic croton interference in cotton

Abstract Studies were conducted to determine the effect of interference between tropic croton (Croton glandulosus) and cotton (Gossypium hirsutum) on plant growth and productivity. Tropic croton height was not affected by weed density, but cotton height decreased with increased weed density 10 wk after planting. Tropic croton biomass per plant was not affected by weed density, but total weed biomass per meter of crop row increased with weed density. Cotton lint yield decreased linearly 2 kg ha−1 with each gram increase in weed dry biomass per meter of row. Percent yield loss–density relationship was described by the rectangular hyperbola model. Estimated coefficients A (maximum yield loss) and I (yield loss per unit density as density approaches zero) were 129.6 ± 42.2 and 35.6 ± 8.0%, respectively, when asymptotic iterations were based on least sums of squares. When A was constrained to 100% yield loss, I was 42.5 ± 5.1%. Results indicated that tropic croton was less competitive with cotton than many weeds but represents an economic threat to cotton growers. Nomenclature: Cotton, Gossypium hirsutum L. ‘Deltapine 51’; tropic croton, Croton glandulosus var. septentrionalis Muell.-Arg. CVNGS.

Palmer Amaranth Interference and Seed Production in Peanut

Studies were conducted to evaluate density-dependent effects of Palmer amaranth on weed and peanut growth and peanut yield. Palmer amaranth remained taller than peanut throughout the growing season and decreased peanut canopy diameter, although Palmer amaranth density did not affect peanut height. The rapid increase in Palmer amaranth height at Goldsboro correspondingly reduced the maximum peanut canopy diameter at that location, although the growth trends for peanut canopy diameter were similar for both locations. Palmer amaranth biomass was affected by weed density when grown with peanut. Peanut pod weight decreased linearly 2.89 kg/ha with each gram of increase in Palmer amaranth biomass per meter of crop row. Predicted peanut yield loss from season-long interference of one Palmer amaranth plant per meter of crop row was 28%. Palmer amaranth seed production was also described by the rectangular hyperbola model. At the highest density of 5.2 Palmer amaranth plants/m crop row, 1.2 billion Palmer amaranth seed/ha were produced. Nomenclature: Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; peanut, Arachis hypogaea L. ‘Perry’.