Total Herbicide Research Articles

Relationship between temperature and triazinone herbicide activity: I. Herbicide binding to thylakoid membranes

The binding rate of metribuzin, 4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4 H)-one, and its ethylthio analog (ethyl-metribuzin), 4-amino-6-(1,1-dimethylethyl)-3-(ethylthio)-1,2,4-triazin-5(4 H)-one to thylakoid membranes of downy brome ( Bromus tectorum L.), jointed goatgrass ( Aegilops cylindrica Host), and winter wheat ( Triticum aestivum L.) increased as temperature increased from 10 to 30°C. However, total herbicide bound was approximately 20% less at 30°C than at 10 or 20°C. At concentrations ≤0.316 μ M, more metribuzin than ethyl-metribuzin was bound to thylakoid membranes of all three species at 10 to 30°C. Binding constants ( K b ) for ethyl-metribuzin were 1.8 to 2.1 times greater than those for metribuzin for all three species. The reduced binding affinity of ethyl-metribuzin, compared with metribuzin, partially explains its reduced activity at the protoplast and whole plant level. In competitive binding studies, atrazine, 6-chloro- N-ethyl- N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine, metribuzin, and ethyl-metribuzin all competed for a common binding site.

Comparison of Przm and Gleams computer model predictions with field data for alachlor, metribuzin and norflurazon leaching

The ability of the pesticide root zone model (PRZM) and groundwater loading effects of agricultural management systems (GLEAMS) model to simulate movement of three herbicides was evaluated with site-specific soil, environmental, and pesticide data. Field studies examined norflurazon movement in a Dothan loamy sand in which cotton (Gossypium hirsutum L.) was grown, and alachlor and metribuzin movement in an Appling sandy loam. Actual herbicide concentrations were always greatest near the soil surface. The PRZM and GLEAMS computer simulation models accurately predicted the total herbicide present in each profile less than 20 d after application. The models overestimated herbicide movement into the soil profile in later simulations. The model predictions generally agreed with the relative location of alachlor and metribuzin in simulations less than 7 d after herbicide applications, but simulations beyond 7 d after herbicide application deviated from actual concentrations. PRZM accurately predicted that most of the applied norflurazon would remain close to the soil surface 84 d after herbicide application, whereas GLEAMS inaccurately predicted that norflurazon would be located throughout the soil profile, although the predicted depth to the limit of detection by both models was accurate.

Hydrological pathways of metolachlor export from an agricultural watershed

Hydrological pathways of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide] transport from a 5.5 ha−1 corn field in southern Ontario were examined. Metolachlor was applied as an early post-emergence surface broadcast treatment at a rate of 334.1 mg active ingredient m−2. Persistence in soils decreased exponentially following application, with slower dissipation in footslope areas. Metolachlor concentrations in runoff from experimental plots also decreased exponentially with time, and were strongly associated with herbicide levels in surrounding soils. Differences between concentrations and yields in saturation overland flow and Horton overland flow during the monitoring period were controlled by near-stream water table conditions. Total herbicide losses in runoff from the plots were in the order of 1% of applied a.i. Metolachlor was rapidly leached to depths of 1 m, such that peak concentrations and instantaneous metolachlor loads in tile drainage were observed within 14 days following application. Peak concentration in streamflow (125 µg L-1) occurred during the first major runoff event 13 days following application; peak concentrations in succeeding events followed an exponential decay during the growing season. Export of metolachlor from the field was in the order of 1% of applied a.i., with overland flow serving as the dominant transport mechanism from site of application. Near-stream hydrologic conditions may determine whether field exports of herbicide enter receiving water courses.

A Case Study of Herbicide Use

The adoption of herbicide use within Illinois has passed through four stages characterized by methods of application. These stages include an initial stage of POST applications, the PRE stage, the PPI stage, and the most recent stage marked by diversification of application methods. Data from 19 pesticide use surveys conducted in Illinois since 1957 were used to determine trends in pesticide use. Herbicide use has increased from 33% of the corn and 1% of the soybean hectarage treated in 1957 to applications on approximately 97% of all the corn and soybeans in 1990. Total herbicide use in Illinois peaked at 3.0 × 107 kg ai annually in 1982 and declined to 2.1 × 107 kg in 1990. Total herbicide use in Illinois between 1950 and 1990 is estimated at 5.0 × 108 kg ai.

Distribution of 14C‐glyphosate in legumes parasitised by Orobanche crenata. Répartition du glyphosate 14C dans des légumes parasités par Orobanche crenata

Summary:Absorption and translocation of 14C‐glyphosate was evaluated under controlled conditions in peas (Pisum sativum L.) and broad beans (Vicia faba L.) parasitised or not by crenate broomrape Orobanche crenata Forsk.). Absorption increased with time up to 12 days after treatment, and reached about 50% of the 14C‐glyphosate applied. Three days after treatment 70–85% of the total herbicide absorbed had been translocated out of the treated leaflet. There was no consistent differ ence in absorption and translocation between infected and non‐infected plants 12 days after treatment. The 14C‐glyphosate concentration in the root system increased with time in broad beans. In peas it remained more or less constant from 3 days after treatment. Generally, pods were stronger sinks for glyphosate than other parts of the plant. Herbicide accumulation in broomrape increased with its growth stage, and the parasite was a much stronger sink for glyphosate than the legume root system.

Uptake by tomato plants of the herbicide [14C] 2,4-D-butyl in the vapour phase

Uptake of [14C-phenyl]2,4-D-butyl by 4- to 6-week-old tomato plants was measured for vapour concentrations in the range 0.3–19 ng litre−1, for an exposure period of 4 h. Calculation of boundary layer thicknesses at the surface of the leaves, and depletion of the vapour concentration due to uptake by the plants, suggested that the plants experienced concentrations very close to the nominal values. Relationships between external vapour concentration and plant uptake, expressed in terms of fresh weight, leaf area, or on a whole plant basis, were linear in all cases. Twenty-four hours after the commencement of exposure, leaves contained 63–93% of the total herbicide in the plant; the proportion retained by the leaves was greater at low vapour concentrations. The largest amount of herbicide was present in leaves from the mid-position on the stem, but in terms of leaf area, the amount was greatest in leaves at the apex and decreased basipetally. It is not known whether this was due to a greater uptake rate per leaf area at the apex, or to translocation. As visible symptoms of phytotoxicity usually develop at the apex, both of these processes, together with the preferential retention of herbicide in leaves at low vapour concentrations, may all contribute to the development of vapour damage.

The influence of soil properties on the rates of degradation of metamitron, metazachlor and metribuzin

AbstractThe rates of degradation of metamitron, metazachlor and metribuzin were measured in 12 mineral soils and the first order rate constants were compared with soil properties by regression analysis. Rates of metamitron degradation were best described by a multiple regression involving the silt content of the soil and the fraction of the total herbicide content which was available in the soil solution. Metazachlor degradation was best described by a multiple regression involving the sand content of the soil, the availability of the herbicide in the soil solution and soil microbial respiration. There was evidence that metribuzin degradation in any one soil was closely related to microbial activity, and rate constants per unit microbial respiration were derived for each soil. These rate constants were best described by a multiple regression involving the Freundlich adsorption constant and the sand content of the soils. The best regression equations for each herbicide were tested against observed degradation rates in an additional group of six soils. The calculated rates compared favourably with those observed for both metamitron and metazachlor, but with metribuzin, there was good agreement with one soil only.

The relationship between the rate of entry of ioxynil and effects on photosynthesis in normal and drought‐stressed Stellaria media

SUMMARYThe entry of 14C‐labelled ioxynil octanoate into leaves of Stellaria media has been measured for plants grown in dry or moist soil. Of the total herbicide applied, 1–3% entered the leaf by 24 h and 2–5% by 72 h after treatment. Entry into moist‐grown plants proceeded at about twice the rate of that into drought‐stressed plants. Despite the limited rate of entry, the inhibitory action of ioxynil octanoate on photosynthetic carbon dioxide exchange was rapid, inhibition within 24 h reaching 70–90% in moist‐grown plants, and 30–70% in dry‐grown plants. Plants grown under moisture stress contained greater concentrations of the pigments chlorophyll a, carotene and lutein (a xanthophyll) than did moist‐grown plants, and ioxynil‐induced breakdown of these pigments was more rapid in moist‐grown plants. It is suggested that these factors contribute to the greater tolerance of drought‐stressed S. media to applications of ioxynil octanoate.The importance of continuous measurements of herbicide action is discussed in relation to the value and interpretation of 14C uptake data.

New carboxyphosphonic and phosphinic acid structures of technical and biological interest

Abstract Carboxyphosphonic and phosphinic acids have recently found applications in the diverse fields of industrial water treatment and pesticides. For example, the acids 1 and 2 are ferrous corrosion inhibitors and scale control agents for circulating industrial water systems, the amino acid 3 is a translocateable total herbicide and the naturally occurring glutamic acid analogue 4 has antibacterial, fungicidal and herbicidal properties. This paper presents a selection of our results on the synthesis of new carboxyphosphonic and phosphinic acids which led to corrosion and scale control agents and structures related to natural products, and their postulated biogenetic precursors.

The use of bendiocarb in ryegrass establishment

AbstractProblems with the establishment of autumn‐reseeded ryegrass can be attributed to a number of causes, one of which is damage by pests, particularly larvae of shoot‐boring flies such as the frit fly (Oscinella frit). In trials over a period of 2 years, bendiocarb has been tested as a seed treatment and as spray and granule formulations for the protection of ryegrass seedlings from pest attack. The trials have included both conventional broadcasting of seed following ploughing of the old sward, and direct drilling following the use of total herbicide. Seed treatments at rates of 10 g a.i. kg−1 of seed and above have given greatly improved plant stands, resulting in yield increases in some trials. Spray and granule applications at 0.5‐1.0 kg a.i. ha−1 have significantly improved establishment at some sites. Bendiocarb has also been tested on spring reseeded leys and although results have been less dramatic than on autumn sowings, significant increases in plant stand were obtained. No evidence of phytotoxicity has been found with any variety of Italian or perennial ryegrass which has been tested, nor with timothy and cocksfoot which have been included in mixtures.

Drummond's Goldenweed and Its Control with Herbicides

Drummond's Goldenweed and Its Control with Herbicides

Absorption and Translocation of Fluridone and Glyphosate in Submersed Vascular Plants

The uptake and translocation of fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone} were examined in sago pondweed (Potamogeton pectinatusL.) and Richardson pondweed [Potamogeton richardsonii(Ar. Benn.) Rydb.]. Root and shoot tissues of both species were isolated from each other with wax barriers and treated individually with 1.0 ppm14C-fluridone. Both tissues bioconcentrated fluridone, but the amount absorbed represented 1% or less of the total herbicide available. Limited root-to-shoot translocation occurred, but shoot-to-root transport was negligible. In contrast to fluridone, highly mobile glyphosate [N-(phosphonomethyl) glycine] translocated from the shoots to the roots in sago pondweed. No metabolism of fluridone was detected in sago pondweed.

Some effects of orchard soil management on sward composition, levels of available nutrients in the soil, and leaf nutrient content of mature ‘Golden Delicious’ apple trees

The effects of soil management practice on sward composition, the levels of available nutrients in the soil and leaf nutrient content of 11-year-old ‘Golden Delicious’ apple trees were examined over a 3-year period. The treatments consisted of: (a) grass sward mown at either 9 cm or 18 cm high, or controlled with the use of grass suppressant maleic hydrazide; (b) total herbicide coverage using simazine/paraquat or terbacil; (c) clean cultivation. Within the tree rows, beneath the tree canopies, the sward was composed of a higher percentage of weeds and grass and a lower percentage of clover than the sward in the alleys. In both areas, the magnitude of the clover component in the sward was in the order: grass suppressant > short grass > long grass. Over the 3 years, the mean dry-matter yield of herbage clippings returned was 11 938 kg ha −1 year −1 in the long-grass treatment, and 9089 kg ha −1 year −1 in the short-grass treatment. This was reflected in the higher amounts of mineral nutrients returned in the herbage clippings from the former treatment. In general, the surface soil (0–10 cm) from grassed plots contained more exchangeable Ca and Mg and less NO 3-N than that from the non-grassed plots. Available P accumulated in the surface layer of the herbicide-treated plots. No significant differences in available nutrients were detected below 10 cm soil depth. Over the 3 years, soil management practice had no measurable effect on tree growth or crop yield. However, in the second and third seasons, trees from grassed plots tended to have lower leaf total N contents than those from non-grassed treatments, while trees from cultivated plots tended to have lower leaf K levels than trees from other plots.

Absorption, Translocation, and Metabolism of 2,4-D and Glyphosate in Hemp Dogbane (Apocynum cannabinum)

Low recoveries of total applied14C in translocation studies and erratic control of hemp dogbane (Apocynum cannabinumL.) in the field showed a need for a balance-sheet study of absorption, translocation, and metabolism of14C-2,4-D [(2,4-dichlorophenoxy) acetic acid] and14C-glyphosate [N-(phosphonomethyl)glycine]. Total recovery of14C-herbicides applied to hemp dogbane in the laboratory was 97% for 2,4-D and 105% for glyphosate. Of the14C recovered after 12 days in the hemp dogbane, 34 to 55% was parent-2,4-D after 2,4-D treatment, and 93 to 96% was parent glyphosate after glyphosate treatment. Only negligible amounts of14C were lost via volatilization or evolution as14CO2. A broadcast treatment with unlabeled herbicide did not significantly affect subsequent absorption, translocation, or metabolism of either herbicide. Total herbicide absorbed and translocated out of the treated area of the leaf generally increased during the subsequent 12 days for 2,4-D but only 3 days for glyphosate. A greater percentage of the total applied 2,4-D (31 vs. 14%) and glyphosate (14 vs. 8%) was translocated from upper rather than lower leaves of hemp dogbane, respectively. Higher temperatures (30 vs. 25 C) resulted in greater translocation of glyphosate (39 vs. 18%) but not 2,4-D (35 vs. 39%). Higher light intensities resulted in greater accumulations of 2,4-D into roots and of glyphosate into untreated areas of the treated leaf. Autoradiographs showed that both herbicides moved through hemp dogbane in a typical symplastic pattern and accumulated in roots and new leaves.

Effect of trickle irrigation on soil‐applied herbicides*

Summary:The effect of trickle irrigation on the activity, leaching and distribution in the soil of herbicides, was studied in a model specially constructed for simulating trickle irrigation in the field, and also under field conditions.The pattern of movement of a soil‐applied herbicide in the soil under trickle irrigation paralleled, to some extent, that of the trickle water itself, but total herbicide movement was less than that of the water. Both water and herbicide distribution in the soil formed the shape of a hemisphere or cone under the trickle nozzle, the exact shape of which was determined by the soil characteristics (a narrow cone in a light soil and a wide cone in a heavy soil); cone size was determined by the amount of trickle water.Bioassays with susceptible test plants showed that effective weed control could be expected with either simazine or GS‐14259 (2‐t‐butylamino‐4‐ethylamino‐6‐methoxy‐s‐triazine =‘Caragard') only in the areas wetted by the trickle nozzle.The results showed that the pattern of distribution in the soil of simazine and GS‐14259 was similar, but there were quantitative differences in their final spread.

Movement of Fluometuron Across and Through the Soil

AbstractExperiments were conducted to determine the effect of rainfall intensity, antecedent soil moisture, and time and subsequent rainfall on the runoff and leaching of soil‐applied fluometuron [1,1‐dimethyl‐3‐(a,a,a‐trifluoro‐m‐tolyl)urea]. Fluometuron was applied to specially constructed field plots on a 1% slope and a simulated rainfall procedure was used to produce runoff. Runoff water and sediment, as well as vertical soil samples, were collected and analyzed for herbicide concentrations. The highest fluometuron concentrations were found on the sediment portion of the runoff, but the highest losses occurred in the liquid portion of the runoff. These losses were caused by the larger volume of water compared to sediment leaving the plot. The first 3.78 liters of runoff water leaving the plot contained a higher concentration of fluometuron than did a composite of the next 41.6 liters. Antecedent soil moisture had a greater effect on runoff losses than did rainfall intensity. Higher losses occurred when the herbicide was applied to a wet soil than to a dry soil. Fluometuron could not be detected in the runoff water collected 1 month after the first runoff‐producing water application. Total herbicide losses from each experiment were 1% or less of the total amount applied. Fluomeutron was leached to the 5‐ to 10‐cm soil depth with some treatments showing small quantities of herbicide in the 10‐ to 20‐cm layer.

Methodology and analysis for residues of MCP and 2,4,5-T in wheat.

The phenoxy herbicides MCP and 2,4,5-T undergo extensive conjugation with plant constituents. ThereFore, in order to measure total herbicide residues, a method must be used which will extract and hydrolyze such conjugates. The studies reported here showed that heating plant tissue under dilute alkaline conditions is adequate to measure total herbicide residues. Using the alkaline extraction method, it was shown that there were no detectable residues of MCP or 2,4,5-T in the grain of wheat plants treated with these herbicides.

Metabolism of Fenac Herbicide in a Lactating Cow

A study was made of the excretion and metabolism of Fenac herbicide in a lactating cow. At a herbicide level of 5ppm in the feed a gas chromatographic peak with the identical retention time of the major herbicide isomer (2,3,6-trichlorophenylacetic acid) was present in hydrolyzed and unhydrolyzed urine representing, respectively, 52.8% (as the conjugated acid) and 18.6% (as the free acid) of the total herbicide dose. Fenac was absent in milk and feces samples. The herbicide was not degraded when incubated with rumen fluid or the 10,000×g supernatant fraction of beef liver.