Herbicide Interactions Research Articles

Metabolically based resistance to the herbicide propanil in Echinochloa species

Abstract Propanil is an acylanilide herbicide introduced in the early 1960s to control dicotyledonous weeds and grasses, including Echinochloa species in cultivated rice. Since then, propanil has been used extensively in rice production in the United States and in several other countries. Propanil is an inhibitor of photosystem II, but rice is tolerant to propanil because of the presence of a high level of aryl acylamidase that catalytically degrades the compound to nonphytotoxic products, i.e., 3,4-dichloroaniline and propionic acid. About 10 yr ago, biotypes of barnyardgrass and junglerice were discovered to be resistant to propanil. The resistance mechanism of these two biotypes has been shown to be elevated levels of aryl acylamidase activity. Various strategies to combat propanil resistance and to more fully understand the biochemistry involved in this resistance have been investigated. These include studies on the interactions of herbicides and other chemicals with propanil, rotation of rice with ot...

Annual Grass Control in Peanut (Arachis hypogaea) with Clethodim and Imazapic1

Field experiments were conducted to evaluate possible interactions of clethodim with imazapic applied as mixtures or sequentially for control of broadleaf signalgrass, fall panicum, goosegrass, and large crabgrass. Imazapic at 70 g ai/ha alone controlled grass weeds inconsistently, whereas clethodim at 140 g ai/ha alone controlled the same weeds at least 99%. Imazapic did not affect broadleaf signalgrass control by clethodim. Reduced control of fall panicum, goosegrass, and large crabgrass was observed when clethodim and imazapic were applied in mixture. Antagonism of clethodim occurred when clethodim was applied 1 d before or up to 3 d after application of imazapic (fall panicum and large crabgrass). Antagonism of goosegrass control was noted when imazapic was applied 3 d before or up to 7 d after application of clethodim. In other experiments, large crabgrass and Texas panicum control by clethodim (70 and 140 g/ha) applied alone or with imazapic (70 g/ ha) or bentazon (1.1 kg ai/ha) plus 2,4-DB (0.28 kg ai/ha) either with or without ammonium sulfate (2.8 kg/ha) was evaluated. Texas panicum control by clethodim was reduced by imazapic regardless of the ammonium sulfate rate. However, large crabgrass control by imazapic was not affected in these experiments. Control of both grasses by clethodim was reduced substantially by bentazon plus 2,4-DB, although in some instances ammonium sulfate improved control when in mixture. Ammonium sulfate improved control by clethodim in some instances irrespective of the broadleaf–sedge herbicide treatments.Nomenclature: Bentazon; clethodim; 2,4-DB; imazapic; 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; Texas panicum, Panicum texanum Buckl. # PANTE.Additional index words: Ammonium sulfate, antagonism, herbicide compatibility, herbicide interaction, sequential application.

Structure effect on the interaction of phenylurea herbicides with model biomembrane as an environmental mobility parameter.

During recent years, intensive use of herbicides has raised increasing concern mainly due to their massive pollution of the environment. As these herbicides are directly or indirectly toxic to a wide range of organisms, their potential for contaminating soil, surface water, and groundwater makes these xenobiotics of special interest from a health and environmental point of view. Knowledge of the mechanisms by which they exert their toxic effects is becoming a need. Because of the herbicides' lipophilicity, a possible site of interaction in the cell is represented by biomembranes. The interaction of four herbicides, difenoxuron, diuron, linuron, and metoxuron, with model membranes constituted of dimyristoylphosphatidylcholine multilamellar vesicles was investigated by the differential scanning calorimetry technique. The aim was to study the effects exerted by an increasing amount of the examined compounds on thermotropic behavior of the model phospholipid membranes and to correlate the obtained results with structural features of the herbicides due to their environmental mobility. Among the herbicides studied, linuron is the most effective in perturbing the ordinate structure of vesicles forming phospholipids, whereas metoxuron is the least effective and the others exert an intermediate effect. Linuron exerts its effect both on the transition temperature of the gel to the liquid crystalline phase and on the enthalpy change. Difenoxuron, diuron, and metoxuron cause a change in the transition temperature but have an insignificant effect on the enthalpy change. The calorimetric results, correlated with the structural features of the herbicides, are consistent with their partition coefficient, log K(ow), suggesting that the more hydrophobic compound character causes a greater liposolubility and consequential cellular absorption with more effectiveness on the membrane order.

Extirpation or Coexistence? Management of a Persistent Introduced Grass in a Prairie Restoration

Abstract Introduced perennial grasses are one of the greatest constraints to prairie restoration. Herbicides suppress but do not eliminate introduced grasses, so we explored the interaction of herbicide with two additional controls: heavy clipping (to simulate grazing) and competition from native species. A 50‐year‐old stand of the introduced perennial grass Agropyron cristatum (crested wheatgrass) in the northern Great Plains was seeded with native grasses and treated with herbicide annually for 7 years in a factorial experiment. Clipping was applied as a subplot treatment in the final 3 years. Both herbicide and clipping significantly reduced the cover of A. cristatum, but clipping produced an immediate and consistent decrease, whereas herbicide control varied among years. The cover of A. cristatum decreased significantly with increasing cover of a seeded native grass, Bouteloua gracilis (blue grama), suggesting that both top‐down (i.e., grazing) and bottom‐up (i.e., resource competition) strategies can contribute to A. cristatum control. No treatment had any effect on the seed bank of A. cristatum. Even in the most effective control treatments, A. cristatum persisted at low amounts (approximately 5% cover) throughout the experiment. The cover of B. gracilis increased significantly with seed addition and herbicide, and, after 7 years, was similar to that in undisturbed prairie. The total cover of native species increased significantly with clipping and herbicide, and species richness was significantly higher in plots receiving herbicide. Clipping season had no effect on any variable. In summary, no method extirpated A. cristatum, but clipping reduced its cover by 90% and doubled the cover of native species. Extirpation might not be a realistic goal, but relatively simple management allowed coexistence of native species.

Fluorescence characterization of the interaction of Al 3+ and Pd 2+ with Suwannee River fulvic acid in the absence and presence of the herbicide 2,4-dichlorophenoxyacetic acid

In an effort to understand the role of environmental metal ions in the interaction of charged pesticides with humic substances, a fluorescence study of the interaction of the widely-used herbicide 2,4-dichlorophenoxyacetic acid (DCPAA) with Al 3+ and Pd 2+ and Suwannee River fulvic acid (SRFA) was undertaken. Initial fluorescence experiments on binary solutions clearly indicated that both Al 3+ and Pd 2+ strongly interact with both SRFA and DCPAA when alone in solution with the metal ion. Titrations of SRFA with Al 3+ at pH values of 4.0, 3.0 and 2.0 revealed decreased degrees of fluorescence emission enhancement (at λ emission, max=424 nm) with decreasing pH, consistent with the expected loss of rigidity in the SRFA–Al 3+ complexes formed as pH is lowered. In contrast, titrations of SRFA with Pd 2+ at all of these pH values resulted in significant fluorescence quenching. Al 3+ additions to solutions of DCPAA at pH values above the p K a (2.64) of DCPAA resulted primarily in significant changes in the wavelength of maximum emission (without significant quenching or enhancement of emission intensity), while Pd 2+ additions to DCPAA solutions resulted primarily in very significant fluorescence quenching. The DCPAA fluorescence results strongly support the formation of an Al 3+–DCPAA complex at pH values above the p K a of DCPAA. The fluorescence results obtained for solutions of Pd 2+ and DCPAA are best explained by a collisional quenching mechanism, that is, energy transfer from excited DCPAA molecules to Pd 2+ following the collision of these two species in solution. Excitation–emission matrix plots obtained on ternary solutions (at environmentally-relevant pH 4.0) containing SRFA, DCPAA and metal ions (i.e., either Al 3+ or Pd 2+) provides evidence (especially for systems containing Al 3+) for the existence of ternary complexes between fulvic acid species, the herbicide DCPAA and metal ion, suggesting (at least at pH 4.0, where the predominant DCPAA species is negatively-charged) that metal ions may function to “bridge” negatively-charged fulvic acids to negatively-charged pesticides.

Effect of sodium chloride on herbicide-fluorinated stationary phase association-Evidence of a dual mechanism

The effect of sodium chloride (NaCl) on the mechanism of retention of a series of phenoxypropionic acids has been investigated for the first time by high-performance liquid chromatography (HPLC) with a novel fluorinated stationary phase (FSP). Thermodynamic data relating to retention were determined for a wide range of NaCl concentrations (x). For all the herbicides, the mechanism of retention on the FSP can be divided into two regions of NaCl concentration, depending on whether Cl (region I) or Na+ (region II) has the predominant effect on herbicide-FSP association. This change in the herbicide interaction process was confirmed by an enthalpy-entropy investigation. This dual mechanism was also used to enable better understanding of the process of separation of halogenated molecules on this FSP.

CGA-362622 Antagonizes Annual Grass Control by Graminicides in Cotton (Gossypium hirsutum)1

The effect of CGA-362622 on annual grass control in cotton by clethodim and fluazifop-P and crop response was determined in field studies. CGA-362622 applied postemergence at 5.3 g ai/ha injured cotton up to 34% 1 wk after treatment (WAT). Injury was similar when crop oil concentrate (COC) and nonionic surfactant (NIS) were included. Adding fluazifop-P, but not clethodim, to CGA-362622 increased crop injury. Cotton recovered by 3 WAT. CGA-362622 mixed with fluazifop-P at 210 g ai/ha reduced broadleaf signalgrass and large crabgrass control 60 to 80%. Control was similar with COC or NIS in the mixture. Increasing the fluazifop-P rate to 315 g/ha did not improve control. CGA-362622 mixed with clethodim at 105 g ai/ha reduced control 65 to 80% with NIS and 40 to 65% with COC. Increasing the clethodim rate to 175 g/ha, especially with COC, substantially increased control. However, control was still less than that with clethodim at 105 g/ha. Prometryn plus MSMA postemergence-directed 3 wk after gramincide and CGA-362622 application increased control. Cotton yield was similar with clethodim alone and clethodim at 175 g/ha plus CGA-362622. Yield was reduced 29% by CGA-362622 mixed with fluazifop-P at 350 g/ha. Control was reduced by CGA-362622 applied 1 d before or after clethodim but not 5 d before or after clethodim. Control by fluazifop-P was reduced by CGA-362622 applied 1 or 5 d before or 1 d after the graminicide. Under greenhouse conditions, CGA-362622 and pyrithiobac mixed with clethodim, fluazifop-P, quizalofop-P, or sethoxydim reduced control of large crabgrass. Greater antagonism was noted with CGA-362622 than with pyrithiobac, and with fluazifop-P and quizalofop-P than with clethodim or sethoxydim.Nomenclature: CGA-362622 (proposed common name trifloxysulfuron), N-[(4,6-dimethoxy-2-pyrimidinyl)carbamoyl]-3-(2,2,2-trifluoroethoxy)-pyridin-2-sulfonamid sodium salt; clethodim; fluazifop-P; MSMA; prometryn; pyrithiobac; quizalofop-P; sethoxydim; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash #3 BRAPP; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; cotton, Gossypium hirsutum L. ‘Stoneville BXN 47’.Additional index words: Adjuvants, antagonism, herbicide interactions, herbicide mixtures.Abbreviations: COC, crop oil concentrate; NIS, nonionic surfactant; POST, postemergence; POST-DIR, postemergence directed; WAT, weeks after treatment.

Assessment of Molecular Descriptors Involved in the Sorptive Interactions of Phenoxy-carboxylic Herbicides in Soil Treated with Different Concentrations of Humic Acid

Assessment of Molecular Descriptors Involved in the Sorptive Interactions of Phenoxy-carboxylic Herbicides in Soil Treated with Different Concentrations of Humic Acid

No‐Till Establishment of Rhizoma Peanut

Planting rhizoma peanut (Arachis glabrata Benth.) directly into grass sod may be practical for producers [e.g., cow‐calf (Bos taurus) production, low maintenance roadside or turf situations, wildlife feed, etc.] who do not need the feed value of pure rhizoma peanut stands. The objective of this study was to determine the effects of planter (no‐till vs. conventional sprig planter), ground preparation (undisturbed sod vs. rotovated), planting date (winter vs. summer), and herbicide (glyphosate [N‐(phosphonomethyl) glycine] vs. none) on the establishment and survival of rhizoma peanut. Planter type had no effect on rhizoma peanut establishment. In 1996 there was a planting date × ground preparation × herbicide interaction due to the winter‐planted, rotovated plots without herbicide (0.9 sprouts m−2) having lower sprout counts than any other rotovated treatment at either planting date (>3.4 sprouts m−2). In 1997, only the main effects of planting date and ground preparation and their interaction affected sprout emergence and survival. Final sprout counts were positively correlated with bare ground (r = 0.37). Herbicide suppressed grass in the winter planting only, but did not consistently reduce total ground cover due to increased annual forb cover. There was a ground preparation × herbicide interaction on ground cover of rhizoma peanut (rotovated + herbicide, 22%; rotovated no herbicide, 13%; herbicide not rotovated, 5.9%; and no herbicide not rotovated, 2%). This study indicates that producers can select establishment practices for rhizoma peanut plantings that meet their production goals (clean cultivation establishment for hay production or dairy cattle grazing and sod planting without herbicide for less intensive situations).

Sensitivity of Eleusine indica Callus to Trifluralin and Amiprophosmethyl in Correlation with the Binding of These Compounds to Tubulin

The sensitivity of calluses derived from susceptible and resistant goosegrass (Eleusine indica (L.) Gaertn.) biotypes to dinitroaniline herbicides, which disrupt interphase and mitotic-spindle microtubules, was evaluated. A callus culture derived from the resistant biotype retained resistance to both trifluralin (dinitroaniline herbicide) and amiprophosmethyl (phosphorothioamidate herbicide). The site for the interaction between α-tubulin subunit and dinitroaniline or phosphorothioamidate herbicides was identified by computer simulation. A correlation was found between the level of callus sensitivity to herbicide tested and the pattern of herbicide interaction with α-tubulin.

Use of bacterial biosensors to interpret the toxicity and mixture toxicity of herbicides in freshwater

The dose response relationship between seven commonly used herbicides and four luminescence-based bacterial biosensors was characterised. As herbicide concentration increased the light emitted by the test organism declined in a concentration dependent manner. These dose responses were used to compare the predicted vs. observed response of a biosensor in the presence of multiple contaminants. For the majority of herbicide interactions, the relationship was not additive but primarily antagonistic and sometimes synergistic. These biosensors provide a sensitive test and are able to screen a large volume and wide range of samples with relative rapidity and ease of interpretation. In this study biosensor technology has been successfully applied to interpret the interactive effects of herbicides in freshwater environments.

Broadleaf Weed Control in Corn (Zea mays) and Soybean (Glycine max) with CGA-248757 and Flumiclorac Alone and in Tank Mixtures1

Broadleaf weed control with postemergence applications of CGA-248757 and flumiclorac applied alone and in tank mixtures was evaluated in greenhouse and field studies. In greenhouse studies velvetleaf, common lambsquarters, redroot pigweed, common ragweed, common cocklebur, eastern black nightshade, and wild mustard shoot weight were reduced by 50% from 0.1, 2.9, 0.9, 1.1, 0.8, 0.4, and 1.2 g/ha of CGA-248757 and 0.7, 3.0, 2.4, 3.3, 3.0, 3.4, and 74.1 g/ha of flumiclorac, respectively. Under greenhouse conditions, tank mixtures of CGA-248757 or flumiclorac with atrazine, bentazon, bromoxynil, dicamba, halosulfuron, imazethapyr, lactofen, primisulfuron plus prosulfuron, or 2,4-D increased velvetleaf, common lambsquarters, redroot pigweed, or common ragweed control 14 d after treatment (DAT) when compared with the control provided by atrazine, bentazon, bromoxynil, dicamba, halosulfuron, imazethapyr, lactofen, primisulfuron plus prosulfuron, or 2,4-D applied alone. In field studies, adding CGA-248757 or flumiclorac to atrazine, bentazon, bromoxynil, dicamba, halosulfuron, imazethapyr, lactofen, CGA-277476, primisulfuron plus prosulfuron, or 2,4-D increased crop injury 3 DAT, but there was no reduction in corn or soybean yields as a result. In corn, tank mixtures of CGA-248757 or flumiclorac plus atrazine, dicamba, or 2,4-D increased velvetleaf control compared with treatments without CGA-248757 or flumiclorac. Tank mixtures of CGA-248757 or flumiclorac with primisulfuron plus prosulfuron increased common lambsquarters control compared with primisulfuron plus prosulfuron alone. Similarly, in soybean CGA-248757 or flumiclorac tank mixtures with bentazon or CGA-277476 increased control of redroot pigweed, and tank mixtures with lactofen increased common lambsquarters control. However, season-long broadleaf control in soybean with bentazon, lactofen, and CGA-277476 tank mixtures with CGA-248757 or flumiclorac did not provide acceptable weed control. Compared with imazethapyr alone the addition of CGA-248757 and flumiclorac improved soybean yield and provided season-long eastern black nightshade, common lambsquarters, redroot pigweed, and common ragweed control.Nomenclature: Atrazine; bentazon; bromoxynil; CGA-248757 (proposed common name fluthiacet), methyl[[2-chloro-4-fluoro-5-[(tetrahydro-3-oxo-1H, 3H-[1,3,4]thiadiazolo[3,4-a]pyridazin-1-ylidene)amino]phenyl]thio]acetate; CGA-277476 (proposed common name oxasulfuron), 2-[[[[(4,6-dimethyl-2-pyrimidinyl)-amino]carbonyl]amino]sulfonyl] benzoic acid, 3-oxetanyl ester; dicamba; flumiclorac; halosulfuron; imazethapyr; lactofen; primisulfuron; prosulfuron; 2,4-D; common cocklebur, Xanthium strumarium L. #3 XANST; common lambsquarters, Chenopodium album L. # CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; corn, Zea mays L. Pioneer 3751, Dekalb 404SR, and Dekalb 493 SR # ZEAMA; eastern black nightshade, Solanum ptycanthum Dun. # SOLPT; redroot pigweed, Amaranthus retroflexus L. # AMARE; soybean, Glycine max (L.) Merr. Conrad # GLYMA; velvetleaf, Abutilon theophrasti Medik. # ABUTH; wild mustard, Brassica kaber (D.C.) L.C. Wheeler # SINAR.Additional index words: Acifluorfen, antagonism, chlorimuron, Digitaria sanguinalis, glyphosate, herbicide interaction, nicosulfuron, protox, Setaria faberi, sethoxydim, Sorghum bicolor, thifensulfuron.Abbreviations: COC, crop oil concentrate; DAP, days after planting; DAT, days after treatment; GR50, 50% growth reduction; NIS, nonionic surfactant; POST, postemergence; protox, protoporphyrinogen oxidase; UAN, 28% urea ammonium nitrate.

Fluazifop-P Inhibits Terbacil Metabolism in Strawberry (Fragaria×ananassa)1

We examined the effect of a postemergence application of fluazifop-P on root uptake, translocation, and metabolism of 14C-terbacil in ‘Kent’ strawberry. Fluazifop-P had no effect on uptake of 14C-terbacil from a nutrient solution over 48 h, nor did it affect the proportional distribution of 14C-label in the plants. The 14C-label was readily translocated to the foliage where it tended to accumulate in vascular tissue. Fluazifop-P reduced the overall conversion of 14C-terbacil to metabolites by about 50%. Thin layer chromatography of methanol extracts of leaflets, petioles, crowns, and roots separated the 6-hydroxymethyl derivative, and several unidentified metabolites, including a major water-soluble metabolite at the origin. At least 50% of the latter could be converted to the 6-hydroxymethyl metabolite by β-glucosidase, but other metabolites could be separated in other solvent systems. The levels of metabolites were generally two- to threefold higher in plants treated with terbacil alone than in those pretreated with fluazifop-P. Therefore, we conclude that the interaction observed between these herbicides in the field results from fluazifop-P inhibiting detoxification of terbacil by strawberry.Nomenclature: Fluazifop-P; terbacil; strawberry, Fragaria × ananassa Duchensne ‘Kent’.Additional index words: Herbicide interaction, synergism, root uptake.Abbreviations: GC-ECD, gas chromatography electron capture detection; GC-MSD, gas chromatography mass spectrum detection; HPLC, high-performance liquid chromatography; LSS, liquid scintillation spectrometry; PPFD, photosynthetic photon flux density; SEM, standard error of the mean; TLC, thin layer chromatography.

Sweet Corn (Zea mays) Cultivar Sensitivity to CGA 152005 Postemergence1

Abstract: Field studies were conducted in 1997 and 1998 to evaluate tolerance of nine sweet corn cultivars to CGA 152005 postemergence at 10 and 20 g ai/ha. There was a cultivar by herbicide interaction for visible plant injury, plant height, ear weight, and yield. Sweet corn injury from CGA 152005 increased as rate increased. CGA 152005 at both rates killed ‘DelMonte 2038’. ‘Eliminator’, ‘Reward’, ‘Delectable’, and ‘Reveille’ were injured (10 to 12% plant height reduction), and the remaining cultivars (‘Challenger’, ‘Krispy King’, ‘CNS 710’, and ‘GH 2690’) were tolerant to CGA 152005 at both rates. Nomenclature: CGA 152005 (proposed common name, prosulfuron), 1-(4-methoxy-6-methyl-triazin-2-yl)-3-[2-(3,3,3-trifluoropropyl)-phenylsulfonyl]-urea; sweet corn, Zea mays L. Additional index words: Plant height, crop injury, sulfonylurea. Abbreviations: DAP, days after planting; DAT, days after treatment; OM, organic matter; PRE, preemergence; POST, postemergence; SU, sulfonylurea.

Incorporating CGA-248757 and Flumiclorac into Annual Weed Control Programs for Corn (Zea mays) and Soybean (Glycine max)1

Field trials evaluated weed control in corn and soybean with CGA-248757 and flumiclorac. CGA-248757 and flumiclorac were applied to 5-, 45-, and 60-cm-tall velvetleaf. Visual control ratings 7 d after treatment (DAT) indicated the greatest control of velvetleaf in corn with CGA-248757 applied to velvetleaf when 5 or 45 cm tall, whereas the greatest control with flumiclorac occurred when applied to 5-cm-tall velvetleaf. However, ratings 21 DAT to 60-cm-tall velvetleaf indicated velvetleaf control with both herbicides was greatest when applied to plants 45 or 60 cm tall. CGA-248757 or flumiclorac applied postemergence (POST) following metolachlor or metolachlor plus atrazine preemergence (PRE) improved velvetleaf control compared with metolachlor plus atrazine alone. Similarly, tank mixtures of CGA-248757 or flumiclorac with 2,4-D following metolachlor PRE provided greater velvetleaf control compared with metolachlor PRE followed by 2,4-D POST. Velvetleaf control in corn was greater when CGA-248757 or flumiclorac were tank mixed with nicosulfuron plus atrazine or nicosulfuron plus dicamba. In soybean, metolachlor plus metribuzin plus clomazone PRE, metolachlor PRE followed by flumiclorac POST, and metolachlor plus metribuzin PRE followed by CGA-248757 or flumiclorac POST provided greater than 85% control of giant foxtail, common lambsquarters, redroot pigweed, and velvetleaf 56 d after POST treatments (DAPO) in 1997. Additionally, glyphosate applied late postemergence (LPOST) and tank mixtures of glyphosate with CGA-248757 or flumiclorac LPOST provided greater than 90% control of these same weed species in 1997. However, only metolachlor plus metribuzin PRE followed by CGA-248757 or flumiclorac POST and imazethapyr plus CGA-248757 or flumiclorac POST provided greater than 80% giant foxtail, common lambsquarters, redroot pigweed, and velvetleaf control 56 DAPO in 1998.Nomenclature: Atrazine; 2,4-D; CGA-248757 (proposed common name, fluthiacet), methyl[[2-chloro-4-fluoro-5-[(tetrahydro-3-oxo-1H,3H-[1,3,4]thiadiazolo[3,4-a]pyridazin-1-ylidene)amino]phenyl]thio]acetate; clomazone; dicamba; flumiclorac; glyphosate; imazethapyr; metolachlor; metribuzin; nicosulfuron; common lambsquarters, Chenopodium album L. #3 CHEAL; corn, Zea mays L. # ZEAMA; giant foxtail, Setaria faberi Herrm. # SETFA; redroot pigweed, Amaranthus retroflexus L. # AMARE; soybean, Glycine max (L.) Merr. # GLYMA; velvetleaf, Abutilon theophrasti Medik. # ABUTH.Additional index words: Antagonism, herbicide interaction, Protox, bromoxynil, clethodim, oxasulfuron, quizalofop, sethoxydim, ABUTH, AMARE, CHEAL, DIGSA, GLYMA, SETFA, XANST, ZEAMA.Abbreviations: COC, crop oil concentrate; DAP, days after planting; DAPO, days after postemergence treatment; DAT, days after treatment; LPOST, late postemergence; NIS, nonionic surfactant; POST, postemergence; Protox, protoporphyrinogen oxidase; PRE, preemergence; UAN, 28% urea ammonium nitrate.

Imazamox and Diphenylether Herbicide Interactions in Soybean (Glycine max)

The effect of three diphenylether herbicides on the control of green foxtail, kochia, velvetleaf, and ivyleaf morningglory with imazamox in soybean was evaluated in a field study conducted near Manhattan, Kansas in 1997 and 1998. Herbicide treatments were: imazamox at 26 and 44 g ai/ha; acifluorfen and fomesafen each at 140 and 280 g ai/ha; lactofen at 70 and 140 g ai/ha; and tank mixtures of imazamox at both rates with both rates of acifluorfen, fomesafen, and lactofen. Tank mixtures of 26 g/ha imazamox with either rate of acifluorfen, or fomesafen were antagonistic on kochia control, as was 44 g/ha imazamox with 280 g/ha acifluorfen 4 weeks after treatment. Tank mixtures of 26 g/ha imazamox and 280 g/ha acifluorfen or fomesafen were antagonistic on velvetleaf control. The only tank mixture that resulted in reduced ivyleaf morningglory control was 26 g/ha imazamox plus 70 g/ha lactofen. The tank mixture of 26 g/ha imazamox plus 280 g/ ha fomesafen was antagonistic for green foxtail. When a diphenylether herbicide was applied with imazamox, 44 g/ha imazamox resulted in fewer antagonistic interactions than mixtures with 26 g/ha.

Montmorillonite-phenyltrimethylammonium yields environmentally improved formulations of hydrophobic herbicides.

This study aimed to design formulations of hydrophobic herbicides, alachlor and metolachlor, by adsorbing them on the clay mineral montmorillonite preadsorbed by the small organic cation phenyltrimethylammonium (PTMA). An adsorption model that considers electrostatics and specific binding and the possibility of cation adsorption above the cation exchange capacity (CEC) could explain and yield predictions for PTMA adsorption in the presence of NaCl concentrations from 0 to 500 mM. Adsorption of alachlor and metolachlor from aqueous solution on a clay mineral preadsorbed by PTMA was determined by GC and modeled by Langmuir equation. Herbicide interactions with the organoclay were studied by Fourier transform infrared spectroscopy. Leaching of herbicides was determined by a bioassay using a column technique and Setaria viridis as a test plant. The adsorbed amounts of alachlor and metolachlor on montmorillonite preadsorbed by PTMA at a loading of 0. 5 mol/kg (Mont-PTMA0.5) were higher than at a loading up to the CEC, that is, 0.8 mol/kg, and were higher than those obtained by using several other organic cations. Herbicide formulations based on Mont-PTMA0.5 yielded the largest shifts of the infrared peaks of the herbicides. These formulations based on Mont-PTMA0.5 gave slower release and showed improved weed control in comparison with formulations based on other organoclays. These formulations maintained herbicidal activity in the topsoil and yielded the most significant reduction in herbicide leaching.

Principles of weed science

A comprehensive reference-cum-textbook on fundamentals and principles of weed science. Includes updated information on newer approaches (ecophysiological and biological) in weed management, newer herbicides, bioherbicides, herbicide action mechanisms and transformations in plants, herbicide persistence and behaviour in soil and environment, and interaction of herbicide with other aerochemicals.

Antagonistic Effect of Thiazopyr on Azafenidin to Control Yellow Nutsedge (Cyperus esculentus)1

Greenhouse experiments evaluated azafenidin and thiazopyr applied separately, as a tank mix, or in rapid succession, for preemergence control of yellow nutsedge (Cyperus esculentus) and hairy beggarticks (Bidens pilosa). Average of yellow nutsedge shoot dry weights at 21 and 42 d after treatment (DAT), indicated that azafenidin at 0.28, 0.56, and 1.12 kg ai/ha controlled 70, 86, and 90%, respectively, and thiazopyr at 1.12 kg/ha controlled 10% of yellow nutsedge. However, when thiazopyr at 1.12 kg/ha was tank-mixed with azafenidin at 0.28, 0.56, and 1.12 kg/ha, yellow nutsedge control averaged for 21 and 42 DAT was reduced to 41, 69, and 78%, respectively. Root plus tuber dry weight of yellow nutsedge increased threefold when 1.12 kg/ha thiazopyr was mixed with 0.28 kg/ha azafenidin, compared to azafenidin applied alone at the above rate. When the herbicides were applied sequentially, within minutes of each other, the antagonistic responses were reproduced, independent of the order of herbicide application. Thiazopyr applied at 0.56 and 1.12 kg/ha stimulated the emergence and establishment of hairy beggarticks and antagonized azafenidin for the control of yellow nutsedge based on a mathematical model. Although thiazopyr reduced the preemergence herbicidal efficacy of azafenidin on hairy beggarticks control, antagonism could not be determined because of the stimulatory effects of thiazopyr on hairy beggarticks emergence.Nomenclature: Azafenidin; thiazopyr; hairy beggarticks, Bidens pilosa L. #3 BIDPI; yellow nutsedge, Cyperus esculentus L. # CYPES.Additional index words: Herbicide interaction, stimulation, scarification, antagonism, spanish needles, Bidens alba, Bidens leucantha.Abbreviations: DAT, days after treatment; PRE, preemergence; WAT, weeks after treatment.

Effect of Herbicides on Pepper (Capsicum annuum) Stand Establishment and Yield from Transplants Produced Using Various Irrigation Systems1

Abstract: Studies were conducted in 1996 and 1997 to determine the effect of irrigation systems used to produce transplants on subsequent tolerance of banana and bell pepper (Capsicum annuum) transplants to field-applied herbicides. The irrigation systems were overhead (OH), ebb and flood (EF), and float (F). At 2 and 4 wk, banana and bell pepper injury was greatest from clomazone (1.1 kg/ha) treatments. Banana and bell pepper yield were not influenced by herbicide treatment. Although crop injury was greater in 1997, there was no herbicide or irrigation system interaction with year. OH and EF irrigated banana pepper and OH irrigated bell pepper produced the greatest total yield over two harvests, whereas F irrigated pepper yielded the least. F irrigated bell pepper plants had reduced early total yield and fancy fruits relative to other irrigation treatments. F irrigated plants yielded 32 and 22% less than OH irrigated plants in banana and bell pepper, respectively. Stand counts at 3 wk after planting (WAP...