Herbicide Interactions Research Articles

Effect of Lablab purpureus L. cover crop and imidazolinone resistant (IR) maize on weeds in drought prone areas, Kenya

Weeds compete for nutrients and soil moisture resulting to low maize yields in dry lands. A three year field study was initiated in 2009 at Kenya Agricultural and Livestock Research Organization, Kiboko to evaluate the effect of dolichos bean (Lablab purpureus L.) and open pollinated imazapyr herbicide coated imidazolinone-resistant (IR)1 maize on weed species composition, density, and maize yield. Initially, weed species were identified, and then controlled using glyphosate at 1.6 kg ai ha−1. Twenty four plots were marked, each measuring 4 × 5 m. Six treatments 1) IR-maize coated, 2) IR-maize coated + brown dolichos, 3) IR-maize coated + black dolichos 4) IR-maize uncoated, 5) IR-maize uncoated + brown dolichos, 6) IR-maize uncoated + black dolichos were laid out in a randomized complete block design replicated four times. IR-maize was planted at a spacing of 90 × 45 cm and 2 seeds per hole. Weeds were sampled from a one meter squared quadrat 21 and 42 days after planting (DAP). The data was subjected to analysis of variance using Genstat version 12.0. Eighteen (18) weed species were prevalent before the experiment. Interaction of dolichos and herbicide coated IR-maize had no significant (P > 0.05) effect on weed species composition and density. Dolichos significantly (P < 0.05) reduced the density of Portulaca quadrifida L. and Paraknoxia parviflora L., and increased Eleusine indica L. Weed species composition decreased by 14% (21 DAP) and 33% (42 DAP) in plots with dolichos compared to no cover. Maize yields were significantly (P < 0.05) higher in plots with dolichos than without. From the findings, this study recommends dolichos integration with coated IR-for weed management and increased maize yields in drylands.

Corn Response to POST-Applied HPPD-Inhibitor Based Premix Herbicides with In-Furrow and Foliar-Applied Insecticides

In recent years injury has been reported in numerous Tennessee corn fields treated with an organophosphate (OP) insecticide and either a mesotrione- or tembotrione-based herbicide premix. Research was conducted with the objective to determine if corn treated with an in-furrow application of chlorpyrifos or a foliar application of chlorpyrifos or bifenthrin, or a combination of in-furrow and foliar treatment, would be more predisposed to injury when either a premix ofS-metolachlor, mesotrione, and glyphosate (meso premix) or a premix of tembotrione plus thiencarbazone (tembo premix) was applied. The main effects of insecticide or herbicide, the two-way interaction of insecticide by herbicide, and the three-way interaction of herbicide by insecticide by application type of insecticide were all significant for injury as well as yield. When chlorpyrifos was used both in-furrow and foliarly on corn treated with the tembo premix, injury was increased to 56% and yield was reduced 58% compared with corn that had not been treated with that insecticide. This use pattern of chlorpyrifos utilized in-furrow followed by chlorpyrifos applied foliarly with the tembo premix essentially doubled the injury (29 to 56%) and increased yield loss from 41% where chlorpyrifos was only utilized foliarly to 49% when chlorpyrifos was applied in-furrow and foliarly. Corn injury was negligible (&lt; 6%) and yield was similar where the meso premix was examined in combination of both types of insecticide applications. This study clearly demonstrated the phytotoxic interaction between these two herbicide premixes and the OP insecticide chlorpyrifos. Therefore, growers need to be mindful of which herbicides are utilized when OP insecticides are used for insect management.

Microbe—Chloroacetanilide Herbicide Interaction across Soil Type

An investigation was carried out under laboratory conditions to study the persistence of butachlor applied at recommended dose (2 kg ai/ha) along with its impact on microbial activity as well as growth of colonial bacteria and fungi in alluvial (Typic Haplaquent), lateritic (Typic Haplustalf) and coastal (Typic Haplaquept) soils. Butachlor caused a significant increment in microbial activity following an initial diminution in between 10 to 22 days of incubation depending on the type of soil. The herbicide resulted in a significant shrinkage in bacterial community during later stages of incubation in lateritic and coastal soils in spite of a significant swelling on the 15th day in lateritic and alluvial soils. Fungal community significantly expanded at the initial stage in lateritic soil and during later stages in alluvial soil by the application of butachlor but shriveled during later stages in the lateritic soil, intermediate stage in coastal soil and initial stages in alluvial soil. Alluvial soil reared the highest population of colonial bacteria and exhibited highest microbial activity while coastal soil significantly pressed them down to the lowest. However, lateritic soil was the best niche for fungal community. Co-metabolism was the main phenomenon in butachlor metabolism particularly in coastal soil, though zymogenous microbes including bacteria and fungi also participated in both lateritic and alluvial soil at certain stages. The persistence of butachlor was the lowest in alluvial soil followed by lateritic and coastal soil, respectively. Among the soil types application of butachlor is safe in alluvial soil.

Spectroscopic investigation of the interactions of carbofuran and amitrol herbicides with human serum albumin

In this study, various spectroscopic techniques including UV absorption, fluorescence and synchronous fluorescence spectroscopy were used to examine the interactions of carbofuran (CF) and amitrol (AMT) herbicides with human serum albumin (HSA). The results of spectroscopic experiments illustrated that CF was bound by HSA, on the other hand there was no interaction between HSA and AMT molecules. In HSA–CF system, static quenching mechanism was responsible for the fluorescence quenching of HSA. The Stern–Volmer constant and binding constant decreased with increasing temperature. This means that an increase in temperature reduces the stability of HSA–CF complex. In HSA–CF system, the number of binding site on protein was found to be one. From the thermodynamic parameters, enthalpy change (ΔH) and entropy change (ΔS) were calculated as −22.30kJmol−1 and −10.70Jmol−1K−1, respectively, which indicated that the interaction forces between HSA and CF molecules were mainly hydrogen bonding and van der Waals forces. The conformational change in the protein structure was investigated by synchronous fluorescence spectroscopy. According to the results of synchronous fluorescence analysis, there was a change in the protein structure owing to the interaction of CF with HSA.

Assessment of Envi-Carb™ as a passive sampler binding phase for acid herbicides without pH adjustment

The graphitised carbon solid phase extraction (SPE) sorbent Envi-Carb has been used to fabricate glass fibre filter- Envi-Carb “sandwich” disks for use as a passive sampler for acid herbicides. Passive sampler uptake of a suite of herbicides, including the phenoxyacetic acid herbicides 4-chloro-o-tolyloxyacetic acid (MCPA), 2,4-dichlorophenoxyacetic acid (2,4-D) and 3,6-dichloro-2-methoxybenzoic acid (Dicamba), was achieved without pH adjustment, demonstrating for the first time a suitable binding phase for passive sampling of acid herbicides at neutral pH. Passive sampling experiments with Duck River (Tasmania, Australia) water spiked at 0.5μgL−1 herbicide concentration over a 7d deployment period showed that sampling rates in Duck River water decreased for seven out of eight herbicides, and in the cases of 3,6-dichloro-2-pyridinecarboxylic acid (Clopyralid) and Dicamba no accumulation of the herbicides occurred in the Envi-Carb over the deployment period. Sampling rates for 4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid (Picloram), 2,4-D and MCPA decreased to approximately 30% of the sampling rates in ultrapure water, whilst sampling rates for 2-(4,6-dimethylpyrimidin-2-ylcarbamoylsulfamoyl) benzoic acid, methyl ester (Sulfometuron-methyl) and 3,5,6-Trichloro-2-pyridinyloxyacetic acid (Triclopyr) were approximately 60% of the ultrapure water sampling rate. For methyl N-(2,6-dimethylphenyl)-N-(methoxyacetyl)-D-alaninate (Metalaxyl-M) there was little variation in sampling rate between passive sampling experiments in ultrapure water and Duck River water. SPE experiments undertaken with Envi-Carb disks using ultrapure water and filtered and unfiltered Duck River water showed that not only is adsorption onto particulate matter in Duck River water responsible for a reduction in herbicide sampling rate, but interactions of herbicides with dissolved or colloidal matter (matter able to pass through a 0.2μm membrane filter) also reduces the herbicide sampling rate.

Testing the performance of registered herbicides on the control of Campuloclinium macrocephalum (Asteraceae) in South African grasslands

SummaryWe report on the performance of the registered herbicides picloram and metsulfuron‐methyl on the control of Campuloclinium macrocephalum (pompom weed) in grasslands. Herbicide trials in hydric and xeric grasslands were treated for three consecutive years in either summer (February) or autumn (April) and monitored for an additional 3 years after spraying ceased. Uncontrolled factors such as a host‐specific rust, fire and drought were observed from the second year of the study. Metsulfuron‐methyl and picloram did not differ in efficacy according to the timing of applications, but average mortality of marked plants was &lt;80% expected of registered herbicides. Populations of C. macrocephalum in plots were reduced proportionately to the percentage mortality of marked plants. Picloram and metsulfuron‐methyl applied at 252 g a.i. ha−1 and 45 g a.i. ha−1, respectively, were not detectable by gas chromatography in the upper 25 cm of the soil profile during any of the sampling intervals from 0 to 56 days after treatment. Three annual applications of registered herbicide did not reduce C. macrocephalum successfully, and it is estimated that between five (summer) to seven (autumn) annual treatments are required to reduce weed density to &lt;1 plant per plot (25 m2). Future research should focus on rust–herbicide interactions, the role of fire in seedbank management and fire as a treatment that could be integrated with chemical control.

Interaction of Glufosinate with 2,4-D, Dicamba, and Tembotrione on Glyphosate-resistant Amaranthus palmeri

Aims: Glyphosate-resistant Amaranthus palmeri S. Wats. (Palmer amaranth) is a major threat to crops in the southern USA. Experiments were conducted to evaluate differential tolerance to 2,4-D, dicamba, and tembotrione and interaction with glufosinate for glyphosate-resistant (GR) A. palmeri control. Study Design: The differential tolerance experiment was conducted in a randomized complete block design (RCBD) with a split-plot arrangement of treatments with herbicide as mainplot and A. palmeri population as subplot. The herbicide interaction experiment was conducted in RCBD with factorial arrangement of treatments. Place and Duration of Study: University of Arkansas-Fayetteville, USA. Tolerance Original Research Article American Journal of Experimental Agriculture, 4(4): 427-442, 2014 428 experiments were conducted in October–November 2010 and in July–August 2011. Herbicide interaction experiments were conducted in the greenhouse in June–July 2011 and August–September 2011 and in the field in April–August 2012. Methodology: Differential tolerance to alternative herbicides was evaluated using 12 GRA. palmeri populations. Herbicide treatments were 1.06 kg ae/ha 2,4-D, 0.56 kg ae/ha dicamba, and 0.094 kg ai/ha tembotrione. In the herbicide interaction study, glufosinate at 0.18, 0.36, and 0.73 kg ai/ha were mixed with either 0.024, 0.047, and 0.094 kg ai/ha tembotrione; 0.28, 0.56, and 1.12 kg ae/ha 2,4-D; or 0.28 and 0.56 kg ae/ha dicamba. The population used was PRA-C. Results: In the tolerance experiment, 2,4-D at 1x (1.06 kg ae/ha) killed 96-100% of plants per population. Dicamba at 1x (0.56 kg ae/ha) killed 36-94% of plants per population, with survivors sustaining 80-99% injury. Tembotrione at 1x (0.094 kg ai/ha) caused 49-98% mortality per population with survivors incurring 80-99% injury. In the herbicide interaction experiment, mixing half doses of glufosinate and 2,4-D resulted in 100% control of PRA-C in the greenhouse and field. At 1x, glufosinate controlled PRA-C 91% in the field; the addition of 0.5x or 1x of 2,4-D or 1x of dicamba resulted in 100% control. Conclusion: In the field, 2,4-D was most effective on GR-A. palmeri, relative to dicamba and tembotrione. Some populations have a high risk of being selected for resistance to dicamba, glufosinate, and tembotrione. Glufosinate + 2,4-D mixtures were additive and at sublethal doses, synergistic. Most combinations of glufosinate and tembotrione were antagonistic.

Effects of chlorophenoxy herbicides and their main transformation products on DNA damage and acetylcholinesterase activity.

Persistent pesticide transformation products (TPs) are increasingly being detected among different environmental compartments, including groundwater and surface water. However, there is no sufficient experimental data on their toxicological potential to assess the risk associated with TPs, even if their occurrence is known. In this study, the interaction of chlorophenoxy herbicides (MCPA, mecoprop, 2,4-D and dichlorprop) and their main transformation products with calf thymus DNA by UV-visible absorption spectroscopy has been assessed. Additionally, the toxicity of the chlorophenoxy herbicides and TPs was also assessed evaluating the inhibition of acetylcholinesterase activity. On the basis of the results found, it seems that AChE is not the main target of chlorophenoxy herbicides and their TPs. However, the results found showed that the transformation products displayed a higher inhibitory activity when compared with the parent herbicides. The results obtained in the DNA interaction studies showed, in general, a slight effect on the stability of the double helix. However, the data found for 4-chloro-2-methyl-6-nitrophenol suggest that this transformation product can interact with DNA through a noncovalent mode.

Interactions of simazine, metsulfuron-methyl, and tetracycline with biochars and soil as a function of molecular structure

Biochars are increasingly recognized as effective, inexpensive, and environmentally friendly sorbents for abating organic contaminants. In this study, the sorption and competitive sorption characteristics of simazine (SZ), metsulfuron-methyl (ME), and tetracycline (TC) to corn straw biochars and soil were examined to understand the interactions of herbicides and antibiotics with biochars and the potential role of biochars as engineered sorbents. Biochars were obtained by pyrolyzing corn straw at 400, 500, and 600 °C for 6 h under oxygen-limited conditions and were characterized via elemental analysis, N2-BET surface area determination, 13C nuclear magnetic resonance spectroscopy, and Fourier transform infrared spectroscopy. Soil was collected from North Tanggu Farm in Tianjin, and its organic carbon, cation exchange capacity, and particle size distribution were analyzed. The batch sorption experiments were performed to obtain the sorption isotherms of SZ, ME, and TC to biochars and soil. The biochars that were pyrolyzed at higher temperatures had higher sorption affinities for SZ, ME, and TC, which may be due to the enhancement of hydrophobic interactions, charge transfer (π–π*) interactions, and pore-filling mechanism. The sorption affinities for these compounds to all biochars decreased in the order SZ > TC > ME, indicating that the neutral molecule with a stronger hydrophobicity is more easily adsorbed by biochars. For soil, the decrease of the sorption affinities followed the order TC > SZ > ME due to the high sorption affinity of TC with clays in the soil. Moreover, the sorption affinities of TC by biochars were lower than by soil, indicating that corn straw biochars may be not an ideal sorbent for the immobilization of TC. Biochars were much more effective in sorbing SZ and ME than soil, indicating that corn straw biochars can potentially prevent transport of the herbicides to surface and ground water. Nevertheless, the presence of TC significantly hinders biochar adsorption of SZ and ME, implying that the coexisting contaminants should be considered when developing biochars as engineered sorbents. The observations in this study demonstrated that the sorption of organic contaminants by biochars is dependent on the properties of the biochars and the molecular structures of the contaminants. Corn straw biochars effectively retain SZ and ME and hinder their transportation to surface and ground water; however, the coexisting contaminants should be considered. Our results will be helpful for designing biochars as engineered sorbents for environmental applications.

Evaluation of the Interaction between Glyphosate and Glufosinate

Crops transformed to provide resistance to herbicides with two different mechanisms of action provide new opportunities for control of herbicide-resistant weeds. However, unexpected interactions may develop, especially for herbicides not generally used in tank-mixtures. The objectives of this study were to evaluate weed control and determine herbicide interactions and fluorescence responses with combinations of glyphosate and glufosinate on selected weeds prevalent in Michigan cropping systems. Field studies to determine herbicide interactions resulted in synergism only at 0.84 kg ae ha−1of glyphosate and 0.47 kg ai ha−1glufosinate in 2008. Early synergism (7 d after treatment [DAT]) was observed in the field at several combined rates for common lambsquarters and velvetleaf in 2009, and in the greenhouse for giant foxtail. Differences between years were perhaps due to the effect of environmental conditions on herbicide absorption and translocation. Antagonism was observed in the field in 2009 for velvetleaf, common lambsquarters, and giant foxtail especially at 840 g ae ha−1glyphosate and 118 g ai ha−1glufosinate, 28 DAT. Antagonism was also observed in the greenhouse for giant foxtail and Canada thistle, 28 DAT. Fluorescence measurements on Canada thistle in the greenhouse showed that glufosinate and glufosinate plus glyphosate acted rapidly to quench electron transport of photosystem II (PS II) system of photosynthesis, and the fluorescence characteristics of the glyphosate and glufosinate combinations were indistinguishable from glufosinate alone.

Response of Processing Tomato to Simulated Glyphosate Drift Followed by In-Crop Metribuzin Application

Eight field studies were conducted over a 3-yr period from 2008 to 2010 in Ridgetown, Ontario, Canada, to determine the cumulative stress caused by simulated glyphosate spray drift followed by an in-crop application of metribuzin in processing tomato. As the simulated glyphosate spray drift rate increased so did the degree of injury to the tomatoes. At a simulated spray drift rate of 22.5 g ae ha−1(2.5% of the recommended glyphosate field rate), a 23% decrease in red tomato yield was observed. Yield reductions increased to 88% of the control when 180 g ae ha−1glyphosate (20% of the recommended field rate) was applied. Similarly when simulated spray drift rates were followed 3 to 5 d later with an in-crop application of metribuzin at 250 g ai ha−1, tomato yields decreased by 22 to 85% depending on glyphosate rate applied. A transient synergistic interaction was observed only when 22.5 g ae ha−1glyphosate was followed by metribuzin. The synergistic response was no longer evident by the 28-d injury rating. Herbicide interactions were additive for crop injury, dry weight, fruit counts, and yield when glyphosate spray drift rates of 45, 90, or 180 g ae ha−1were followed by metribuzin.

Interaction of Rice Residue and PRE Herbicides on Emergence and Biomass of Four Weed Species

Studies were conducted in a screenhouse to determine the interaction of rice residue as mulch (0, 3, and 6 t ha−1) and herbicides (nontreated, oxadiazon at 0.5 and 1.0 kg ai ha−1, and pendimethalin at 1.0 and 2.0 kg ai ha−1) on seedling emergence and biomass of barnyardgrass, crowfootgrass, junglerice, and rice flatsedge. Regardless of the residue amount, crowfootgrass and junglerice were effectively controlled by all herbicide treatments. No seedlings of these weed species escaped the herbicides when applied in the presence of residue cover. There was no survival of barnyardgrass seedlings when both herbicides were applied on bare soil (without residue cover); however, some seedlings survived oxadiazon and pendimethalin when applied in the presence of residue cover. For rice flatsedge, the herbicide applications in the presence of residue cover resulted in lower weed control than in the absence of residue. These results suggest that some weed species can escape the application of PRE herbicides in conservation agriculture systems in which residue can bind soil-applied herbicides and result in lower efficacy.

Impact of herbicide and various soil amendments on soil enzymes activities in a tropical rainfed agroecosystem

A two year study was designed to investigate the activities of soil enzymes namely β-glucosidase, alkaline phosphatase and urease in an agroecosystem under rice–wheat–summer fallow crop rotation receiving herbicide (HC) as Butachlor, either singly or in combination of soil amendments of varying resource quality. Chemical fertilizer (CF), Sesbania shoot (SS), farmyard manure (FYM) and wheat straw (WS), carrying equivalent amount of N were added in combination of HC to soil along with a no input control (CO). Throughout the annual cycle, the activity of β-glucosidase was maximum in HC + WS treatment followed by the decreasing order for HC + FYM > HC + SS > HC + CF > HC > CO plots. Almost similar trend was found for alkaline phosphatase activity throughout the annual cycle. Within the crop cycle, the activities of the two enzymes increased from the vegetative to grain forming stage and then decreased at crop maturity. By contrast, urease activity decreased constantly through the crop cycle for all the treatments except the HC + WS treatment. The interaction of herbicide with soil inputs irrespective of their resource quality compared to single application of herbicide increased activities of all the three enzymes throughout the annual cycle. The activity of β-glucosidase, alkaline phosphatase and urease was influenced by the C:N ratio of the various soil inputs.

Enhanced UV‐B Radiation Increases Glyphosate Resistance in Velvetleaf (Abutilon theophrasti)

Depletion of the ozone layer leads to increasing UV-B radiation on the earth's surface, which may affect weeds and their responses to herbicides. However, the effect of increased UV-B radiation on weeds and the interaction of weeds and herbicides are still obscure. The objective of this study was to compare glyphosate efficacy on velvetleaf that was grown under with and without increased UV-B radiation. Leaf area, dry weight and net photosynthesis of velvetleaf seedlings were adversely affected by increased UV-B radiation. Leaf cuticle wax significantly increased by 28% under increased UV-B radiation. Glyphosate efficacy on velvetleaf, evaluated by shoot dry weight, was significantly decreased by increased UV-B radiation. Exposure to increased UV-B radiation significantly decreased (14)C-glyphosate absorption from 49% to 43%, and also resulted in less (14)C-glyphosate translocation out of treated leaves and less glyphosate accumulation in newly expanded leaves. The decrease in glyphosate efficacy was due to changes in absorption and distribution, which were attributed to increased cuticle wax and decreased photosynthesis caused by increased UV-B radiation. These results suggest that the responses of weeds to herbicides may be affected by increased UV-B radiation, to the extent that higher rates may be required to achieve the desired effects.

Phytotoxicity and antioxidative enzymes of green microalga (Desmodesmus subspicatus) and duckweed (Lemna minor) exposed to herbicides MCPA, chloridazon and their mixtures

In this study, we evaluate the toxicity of MCPA (auxin-like growth inhibitor), chloridazon (CHD) (PSII-inhibitor) and their mixtures to floating plants and planktonic algae. Toxicity of MCPA (4-chloro-2-methylphenoxyacetic acid) and CHD (5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone) was first assessed in two growth inhibition tests with Lemna minor (ISO/DIS 20079) and Desmodesmus subspicatus (ISO 8692). Next, herbicide mixtures at concentrations corresponding to the EC values were used to assess their interactive effects, and the biomarkers were: for duckweed fresh weight, frond area, chlorophyll content and number of fronds, and for algae cell count and cell volume. The 3d EC10 and EC50 values using cell counts of D. subspicatus were 142.7 and 529.1 mg/L for MCPA and 1.7 and 5.1 mg/L for CHD. The 7d EC10 and EC50 values using frond number of L. minor amounted to 0.8 and 5.4 mg/L for MCPA and 0.7 and 10.4 mg/L for CHD. Higher sensitivity of reproductive (number of cells/fronds) than growth processes (cell volume/frond area) to herbicides applied individually and in mixtures was especially pronounced in the responses of Desmodesmus. Herbicide interactions were assessed by the two-way ANOVA and Abbott's formula. Generally, an antagonistic interaction with Lemna was revealed by MCPA and chloridazon, whereas additive effect of both herbicides was observed for Desmodesmus. A significant stimulation of SOD and APX activity by binary mixtures was noted in algal cells mainly after 24 and 48 hours of exposure. The extremely high stimulation of the activity of both enzymes was induced by the combination EC10CHD + EC50MCPA (48 h). Presumably due to oxidative stress, the treatment with CHD at concentration EC50 after 72h was lethal for algae grown in aerated cultures, in contrast to standardized test conditions. Taking into account the consequences of risk assessment for herbicide mixtures we can state that a relatively low toxicity, as well as the lack of significant synergy between MCPA and CHD to non-target plants appears to be the most important result.

Fluorescence characterization of the interaction Suwannee river fulvic acid with the herbicide dichlorprop (2-(2,4-dichlorophenoxy)propionic acid) in the absence and presence of aluminum or erbium

This study uses fluorescence spectroscopy to better understand the role of environmental metal ions in the interaction of charged herbicides with biochemical degradation product Suwannee River fulvic acid (SRFA). The interactions between the widely-used herbicide dichlorprop (2-(2,4-dichlorophenoxy)propionic acid) (DCPPA) with Al 3+ and the comparative metal Er 3+ were probed at pH 4.0. Fluorescence experiments on binary solutions at pH 4.0 clearly indicated that Al 3+ and Er 3+ strongly interact with both SRFA and DCPPA alone in solution as demonstrated by fluorescence quenching with DCPPA and enhancement with SRFA by Al 3+ and fluorescence quenching of both SRFA and DCPPA fluorescence by Er 3+. Titrating Al 3+ or Er 3+ to SRFA-DCPPA quenched SRFA fluorescence as compared to the SRFA-metal ion binary complexes. Formation constants were determined using the Ryan-Weber model for the titration data. The DCPPA fluorescence results strongly support the formation of DCPPA-Al 3+ and DCPPA-Er 3+ complexes at pH values above the pK a (3.0) of DCPPA. Excitation and emission data obtained on ternary solutions of SRFA-Al 3+-DCPPA and SRFA-Er 3+-DCPPA complexes at pH 4.0 suggest that at this pH where the predominant DCPPA species is negatively-charged, Al 3+ and Er 3+ metal ions may function to “bridge” negatively-charged fulvic acids to negatively-charged pesticides. Fluorescence data collected on UV-irradiated ternary complexes indicate that both metals can also bridge DCPPA interactions with SRFA under those conditions. The results of our studies suggest that creation of a herbicide-free boundary corridor is recommended near mines and runoff areas with metal ions in surface waters to control possible complexation among fulvic acids, DCPPA and metal ions that maintains these molecules in a bioavailable state to plants and animals.

The combined effect of nitrogen and glyphosate on the competitive growth, survival and establishment of Festuca ovina and Agrostis capillaris

In order to study the combined effect of nitrogen and glyphosate on biodiversity in agricultural areas, a replicated long-time field experiment with glyphosate and nitrogen treated plots was set-up. The experiment allowed a quantitative estimation of the effect of glyphosate and nitrogen on competitive growth, survival and establishment of the dominating species during and between growing seasons. It was found that the observed ecological success of Festuca ovina relative to Agrostis capillaris in glyphosate treated plots was primarily due to altered competitive plant growth during the growing season rather than an immediate die back following spraying. Overall, interaction of herbicide and fertilizer on plant competitive growth, survival and establishment were demonstrated, and it was suggested that positive interactions between glyphosate and nitrogen may be important for the ecological success of A. capillaris in field margins. The used method of combining pin-point data and Bayesian state-space competition models may be applied in other ecological studies. For example, the method may be used in predicting the effects of altered weed control strategies on the botanical composition of the agro-ecosystem.

The experimental and theoretical QM/MM study of interaction of chloridazon herbicide with ds-DNA

We report a multispectroscopic, voltammetric and theoretical hybrid of QM/MM study of the interaction between double-stranded DNA containing both adenine–thymine and guanine–cytosine alternating sequences and chloridazon (CHL) herbicide. The electrochemical behavior of CHL was studied by cyclic voltammetry on HMDE, and the interaction of ds-DNA with CHL was investigated by both cathodic differential pulse voltammetry (CDPV) at a hanging mercury drop electrode (HMDE) and anodic differential pulse voltammetry (ADPV) at a glassy carbon electrode (GCE). The constant bonding of CHL–DNA complex that was obtained by UV/vis, CDPV and ADPV was 2.1 × 10 4, 5.1 × 10 4 and 2.6 × 10 4, respectively. The competition fluorescence studies revealed that the CHL quenches the fluorescence of DNA–ethidium bromide complex significantly and the apparent Stern–Volmer quenching constant has been estimated to be 1.71 × 10 4. Thermal denaturation study of DNA with CHL revealed the Δ T m of 8.0 ± 0.2 °C. Thermodynamic parameters, i.e., enthalpy (Δ H), entropy (Δ S°), and Gibbs free energy (Δ G) were 98.45 kJ mol −1, 406.3 J mol −1 and −22.627 kJ mol −1, respectively. The ONIOM, based on the hybridization of QM/MM (DFT, 6.31++G(d,p)/UFF) methodology, was also performed using Gaussian 2003 package. The results revealed that the interaction is base sequence dependent, and the CHL has more interaction with ds-DNA via the GC base sequence. The results revealed that CHL may have an interaction with ds-DNA via the intercalation mode.

Peanut variety response to postemergence applications of carfentrazone-ethyl and pyraflufen-ethyl

Field experiments were conducted in the south Texas and Texas High Plains area in 2005 and 2006 to evaluate peanut variety tolerance to carfentrazone-ethyl and pyraflufen-ethyl. Lactofen was used as the standard. Carfentrazone-ethyl at 0.03 and 0.04 kg ai/ha, pyraflufen-ethyl at 0.003 and 0.004 kg ai/ha, and lactofen at 0.22 kg ai/ha were applied 35 days after planting (DAP) in south Texas and 51–56 DAP in the High Plains area in weed-free plots. Peanut cultivars selected for evaluation were those normally used in each area. In south Texas, Tamrun 96, Tamrun OL 01, and Tamrun OL 02 were evaluated while in the High Plains area, Flavor Runner 458, GP-1, and Tamrun OL 02 were evaluated. No peanut cultivar by herbicide interaction was observed in south Texas but an interaction did occur in the High Plains. In south Texas, peanut stunting was 10% or less with both herbicides and rates. In 2005, carfentrazone-ethyl at 0.04 kg/ha resulted in a yield reduction when compared with the untreated check while in 2006 both rates of carfentrazone-ethyl and the high rate of pyraflufen-ethyl reduced yield compared to the untreated check. No grade differences were noted among herbicide treatments. In the High Plains area, the high dose of both carfentrazone-ethyl and pyraflufen-ethyl caused the greatest peanut injury (at least 25%) compared with lactofen (6% or less). In 2005, the high dose of pyraflufen-ethyl and lactofen reduced yield compared with the untreated check while in 2006 both carfentrazone-ethyl and pyraflufen-ethyl reduced yield compared with the untreated check.

Adsorption of selected herbicides from aqueous solutions on activated carbon

The adsorption of MCPA and 2,4-D on the activated carbon Filtrasorb 300 was studied. The adsorption isotherms of herbicides from aqueous solutions were measured over a wide range of solute concentrations and at different temperatures. The experimental equilibrium data were analyzed by the Langmuir–Freundlich isotherm taking into account the energetic heterogeneity of adsorption system. The effect of temperature and herbicide properties on its uptake was discussed. The thermal analysis was applied in order to find the differences in herbicide interactions with carbon surface. The kinetic dependences were measured and the relations between solute properties and adsorption rate were discussed.