Application of coupled liquid chromatography–mass spectrometry in photolysis studies of the herbicide triflusulfuron‐methyl

The photochemical fate of the herbicide triflusulfuron‐methyl in aqueous solution under UV light (λ > 290 nm) was investigated. Nine photoproducts were detected and tentatively identified by LC/MS and LC/MS/MS analysis. The main routes of degradation involve the cleavage and/or contraction of the sulfonylurea bridge with the elimination of sulfur dioxide, which increases the acidity of the reaction medium. On the basis of the results obtained a photodegradation pathway is proposed. © 2001 Society of Chemical Industry     

Effect of acetochlor treatment on Fusarium wilt and sugar content in melon seedlings

Pretreatment of soil with the herbicide acetochlor at 0.1–1g g^–1 significantly decreased incidence of wilt due toFusarium oxysporum f. sp.melonis in melon seedlings. Glucose, fructose and sucrose increased in leaves of inoculated and uninoculated melon plants following acetochlor treatment. The increase in sugar levels in stems and roots was less pronounced. Light intensity affected sugar content and disease incidence. The percentage of diseased plants was significantly higher in untreated plants grown under 165E m^–2 sec^–1 compared to plants grown under 300E m^–2 sec^–1. Lowering light intensity resulted in reduction of levels of total sugars on the third and sixth day after inoculation. Acetochlor had little or no effect on growth rate or sporulation of the pathogen in culture. The colonization rate of diseased plant stems by the pathogen was similar in herbicide-treated and untreated plants, thus excluding the possibility that disease reduction by the herbicide is related to direct fungitoxicity.Contribution from the Agricultural Research Organization. No. 1560-E, 1995 series.     

Applications of pre-emergent pyroxasulfone,flufenacet and their mixtures with triallate for the control of Bromus diandrus (ripgut brome) in no-till wheat (Triticum aestivum) crops of southern Australia

Four field experiments were conducted over a three-year period in Victoria and South Australia to investigate the effectiveness of pre-emergence (PRE) applications of pyroxasulfone, flufenacet and their mixtures with triallate for the control of Bromus diandrus in spring wheat. Herbicide mixtures of pyroxasulfone plus triallate and flufenacet plus triallate applied PRE to wheat provided consistently high levels of B. diandrus control (≥85%). In contrast, applications of pyroxasulfone and flufenacet applied alone along with trifluralin plus metribuzin (a common farmer practice in southern Australia) provided more variable control of B. diandrus (33–90%). Pyroxasulfone plus triallate treatments had a much lower (≤47 panicles m⁻²) panicle density of B. diandrus than trifluralin plus metribuzin (42–318 panicles m⁻²) and the non-treated control (118–655 panicles m⁻²). PRE herbicides which were safe to spring wheat and provided the greatest level of control of B. diandrus resulted in significantly (P < 0.05) higher grain yields at Culgoa (120%) and Gama (13%) than non-treated wheat (720 and 1740 kg ha⁻¹). Although flufenacet was effective against B. diandrus, crop phytotoxicity at the higher dose (900 g ai ha⁻¹) reduced spring wheat grain yield. Based on these results, PRE pyroxasulfone plus triallate could play an important role in the management of B. diandrus in spring wheat. However, high cost of these herbicides (AUS$35-$70 ha⁻¹) may limit their adoption in low rainfall and low yielding wheat environments in southern Australia where B. diandrus is most prevalent.     

Weed control and autumn-olive affect early growth and survival of black walnut in a hardwood clearcut

Eight years after planting in a hardwood clearcut, black walnut trees in plots with weed control had significantly better survival and were taller and larger in diameter than those in plots without weed control. Planting autumn-olive with walnut also significantly increased height and diameter of the walnuts but did not affect their survival.     

Effect of post-planting applications of granulated atrazine and fertiliser on the early growth of Eucalyptus nitens

A factorial experiment was established in a plantation of Eucalyptus nitens in southern Tasmania on a site which had formerly carried native eucalypt forest. Before planting, the site had been cleared of weeds with foliar translocated and pre-emergence herbicides. The first factor of the experiment examined the effects on tree growth of no post-planting weed control, control by hand or with three levels of application of granulated atrazine, 0.9, 1.8 and 8 kg ha^–1. The second factor examined the effects of no fertiliser application or the application of nitrogen as urea at 200 kg ha^–1 N plus triple superphosphate at 120 kg ha^–1 P. Tree growth responses to treatments were examined at 11, 16, 23 and 29 months of age.Fertiliser application increased tree height and diameter growth. Application of atrazine generally reduced height and diameter growth, but this was statistically significant only at the highest rate of application. Growth reduction occurred even though atrazine reduced post-planting weed cover on the site and hence potential competition with the tree crop for site resources. Hand weeding reduced the weed crop on the site even more than atrazine, but this did not increase growth of the tree crop.Given satisfactory establishment practices which include the use of herbicides pre-planting, it was concluded that post-planting weed regeneration was not sufficiently vigorous to warrant post-planting weed control on these sites. The use of atrazine for post-planting weed control could even be deleterious to eucalypts.     

Physionomics and metabolomics-two key approaches in herbicidal mode of action discovery

BACKGROUND: For novel herbicides identified in greenhouse screens, efficient research is important to discover and chemically optimise new leads with new modes of action (MoAs). RESULTS: The metabolic and physiological response pattern to a herbicide can be viewed as the result of changes elicited in the molecular and biochemical process chain. These response patterns are diagnostic of a herbicide's MoA. At the starting point of MoA characterisation, an array of bioassays is used for comprehensive physiological profiling of herbicide effects. This physionomics approach enables discrimination between known, novel or multiple MoAs of a compound and provides a first clue to a new MoA. Metabolic profiling is performed with the use of treated Lemna paucicostata plants. After plant extraction and chromatography and mass spectrometry, changes in levels of approximately 200 identified and 300 unknown analytes are quantified. Check for known MoA assignment is performed by multivariate statistical data analyses. Distinct metabolite changes, which can direct to an affected enzymatic step, are visualised in a biochemical pathway view. Subsequent target identification includes metabolite feeding and molecular, biochemical and microscopic methods. CONCLUSION: The value of this cascade strategy is exemplified by new herbicides with MoAs in plastoquinone, auxin or very‐long‐chain fatty acid synthesis. Copyright © 2011 Society of Chemical Industry     

几种除草剂对花生地杂草小藜的防除效果

50%乙草胺乳油、96%金都尔乳油、12%噁草酮(农思它)乳油、30%噁草.丁草胺乳油4种除草剂对花生地杂草小藜防除效果试验结果表明,2 400 mL/hm2浓度的50%乙草胺和12%噁草酮(农思它)与50%乙草胺混合的除草剂对杂草小藜的防效都在90%以上,且药剂持效期长,对花生无药害,可以在生产上推广使用。     

Influence of straw management, nitrogen fertilization and dosage rates on the dissipation of five sulfonylureas in soil

The dissipation behaviour of metsulfuron-methyl, tribenuron-methyl, thifensulfuron-methyl, triasulfuron and amidosulfuron were studied in soil following post-emergence spring applications to cereal crops. Incorporation or removal of straw and different fertilizer applications had no influence on the disappearance time (DT₅₀) of the herbicides. However, in laboratory trials dissipation of metsulfuron-methyl, triasulfuron and amidosulfuron at higher application rates was accelerated after incorporation of straw into the soil. The addition of straw decreases soil pH thereby causing faster hydrolysis of the compounds. Addition of nitrogen fertilizer increased the half-lives (t_1/2) of the herbicides. Combination of both straw and N fertilizer, however, had no effect. Neither straw nor N influenced the degradation of tribenuron-methyl and thifensulfuron-methyl.
The DT₅₀ of all herbicides investigated varied from 6 to 17 days in the field trials. Except for amidosulfuron, herbicides could not be detected 38–68 days after application. In the laboratory, t_1/2 values were higher than those in the field at 75 days (amidosulfuron), 63 days (metsulfuron-methyl), 35 days (triasulfuron) and 13 days (tribenuron-methyl). Only the t_1/2 of thifensulfuron-methyl was at 29 h faster under laboratory conditions. T_1/2 values of all herbicides were influenced by their initial concentration. The t_1/2 values of amidosulfuron and tribenuron-methyl at 1 mg a.i. kg⁻¹ soil were 2–2.5 times higher than at the recommended field application rate of 42 μg a.i. kg⁻¹ soil.     

1,3,4(2H)-isoquinolinetrione herbicides: Novel redox mediators of photosystem I

A series of 1,3,4(2H)-isoquinolinetriones have been found to be fast-acting post-emergence herbicides, producing symptoms of desiccation. These redox-active compounds are very potent stimulators of the light-dependent consumption of oxygen at photosystem I in isolated chloroplasts. Pulse radiolysis studies on 2-ethyl-1,3,4(2H)-isoquinolinetrione have shown it to have free-radical properties which could enhance the generation of superoxide radicals in plants. Electrochemical studies further support a redox mediator mode of action for the series. The compounds were found to be unstable towards hydrolysis, and this was considered to be a major factor limiting the overall herbicidal effects. Other parameters, related to uptake and/or translocation, which may limit the full expression of the herbicidal activity of certain compounds, are discussed.     

Sublethal Toxicity of the Herbicide Butachlor on the Earthworm Perionyx sansibaricus and its Histological Changes (5 pp)

Goal, Scope and Background   With the advent of the Green Revolution, there has been a quantum leap in the use of synthetic herbicides and pesticides throughout the world to sustain high-yielding crop varieties. Continuous use of these synthetic chemicals leads to loss of soil fertility and soil organisms. Histopathological studies may signal a damaging effect of organisms resulting from prior or ongoing exposure to toxic agents. A large number of studies have reported general histological changes in earthworms. A fewer studies have reported more specific types of histopathological studies in Eisenia foetida, Dendrodrilus rubidus, Lumbricus terrestris, Lumbricus rubellus and Octolasium transpandanum. However, no reports are available on Perionyx sansibaricus. The aim of the present study is (i) to determine the sublethal effects of the herbicide Butachlor on Perionyx sansibaricus on growth and cocoon production, (ii) to evaluate the histological changes in the exposed worms.Methods   The test substrate, namely powdered, dried cow dung, was contaminated with 0.0657, 0.1315 and 0.1973 mg kg–1 of Butachlor, and a control was maintained. Four groups of each 10-test species of Perionyx sansibaricus were used per concentration level (control, 0.0657, 0.1315 and 0.1973 mg kg–1). Various life history parameters such as biomass, cocoon production and histological changes were measured.Results   Worm growth was observed at various exposures over 60 days. While exposing the earthworm to the herbicide, no mortality was observed, not even at a higher dose. At the end of the experiment, the control group had a mean biomass of 0.0831±0.00 mg and, in the exposed group, at herbicide concentrations of 0.1973, 0.1315 and 0.0657 mg kg–1, the mean biomass was found to be 0.0497±0.00 mg, 0.0628±0.00 mg and 0.0781±0.00 mg, respectively. The mean earthworm biomass was found to be decreased with increasing herbicide concentration. Similarly, cocoon production was also reduced by the increasing herbicide concentration. All earthworms in the exposed group were found to have glandular cell enlargement and to be vacuolated. Conclusion   The results clearly indicate that Butachlor can retard the growth and cocoon production in Perionyx sansibaricus. The effect of the herbicide Butachlor can be assessed by the histological observation of the intestinal region, as evidenced by glandular cell enlargement at all the exposed concentrations, which may massively affect food intake and which in turn may indirectly inhibit the earthworm reproductive capacity.Recommendation and Outlook   Risk assessment is normally aimed at the protection of human health and the ecosystem, and the interrelationship of these two areas of protection is easy to perceive. The use of earthworms in risk assessment is to obtain more information on environmental quality and ensure environmental safety. There is an urgent need to test the chemicals causing toxicity to earthworms, because earthworms play a major role in soil fertility as well as acting as a transferring route from the soil to the terrestrial ecosystem.