The physical and chemical properties of the herbicide cinmethylin (SD 95481)

Cinmethylin (SD 95481), is a novel herbicide developed for the selective pre-emergence control of many annual grass weeds in a wide range of temperate and tropical crops. Representing new herbicide chemistry, cinmethylin is in the cineole family. Cinmethylin is a mobile colourless liquid with a boiling point of 313°C under an inert atmosphere at atmospheric pressure. It has a density of 1015 kg m^?3 and a viscosity of 70–90 mPa s, both at 20°C. It is miscible in all proportions with most organic solvents but has a low solubility, 63 mg litre^?1, in water. It has a vapour pressure of 10.2 mPa (20°C) and the vapour pressure/temperature relationship is given by log_e P(Pa)=28.9–9816/T (K). The n-octanol/water partition coefficient is 6850 and soil organic matter/water sorption coefficient (K_om) ranges between 165 and 235 over the three types of soil used in these studies. Cinmethylin is stable in water over the pH range 3–11. Solutions of cinmethylin in water or solvents are reasonably stable to sunlight, though thin films on a quartz surface photooxidise mainly to an ester within 24 h. This rate can be reduced by the addition of photostabilisers or by sorption onto soil surfaces. In an inert atmosphere cinmethylin is stable to high temperatures, though, in air, oxidation occurs at temperatures above 100°C to give the same product as by photodecay.     

Initial pesticide residues in relation to vapour pressure

Field tests, in which several insecticides were applied at equal rates by ground sprayer to oats, rye and alfalfa, showed that residues 1 h after application were much lower for highly volatile compounds than for those of lower volatility. Varying the distance from spray release to target canopy from 10 to 40 cm did not significantly affect the deposits. Results indicate that applying insecticides with a vapour pressure greater than about 10^?4 mmHg (20°C) in aqueous media is very inefficient.     

Mosquito adulticidal activity of a biosurfactant produced by Bacillus subtilis subsp. subtilis

BACKGROUND: A biosurfactant, surfactin, produced by a strain of Bacillus subtilis subsp. subtilis (VCRC B471), was effective in killing mosquito larval and pupal stages. As it was lethal to the non‐feeding pupal stage, it was presumed that it could kill the adult mosquitoes also. In this study, the adulticidal effect of the biosurfactant was assessed in the laboratory against a malaria vector, Anopheles stephensi. RESULTS: The biosurfactant surfactin, separated from the culture supernatant of the production strain, showed mosquito adulticidal activity when tested as ultralow‐volume (ULV) spray in a Peet‐Grady chamber. Knockdown activity and mortality were found to increase with increasing surfactin dosage. Knockdown dosage (KD) and lethal dosage (LD) were calculated by statistical analysis. The KD₅₀ and KD₉₀ dosages were 10.73 and 26.39 mg m^?3 respectively. The LD₅₀ and LD₉₀ dosages were 16.13 and 39.21 mg m^?3. The average droplet size of B. subtilis surfactin was 17.5 ± 1.07 µm. CONCLUSION: The present study indicates that the biosurfactant surfactin, produced by B. subtilis subsp. subtilis (VCRC B471), is a potential bioadulticide for ULV spray against malaria‐transmitting Anopheles stephensi mosquitoes. This is the first report of a mosquito adulticide from a microbial source. Copyright © 2012 Society of Chemical Industry     

Hydrolysis of the pyrethroid insecticide fenpropathrin in aqueous media

The hydrolysis of [¹⁴C] fenpropathrin ( I ) [(RS)-α-cyano-3-phenoxybenzyl 2,2,3,3-tetramethylcyclopropanecarboxylate] was studied in buffer solutions at pH 1.9–10.4, and in natural river and sea water at 25, 40, 55 and 65°C under laboratory conditions. The hydrolysis of I proceeded predominantly through neutral (pH independent) and base-catalysed processes in the regions below pH 3.9 and above pH 7.0, respectively, whereas both reactions occurred between pH 3.9 and 7.0. The rates of hydrolysis of I in buffer solutions were similar to those in one sample of river and one sample of sea water. If this obtains generally, it may be expected that the half-life of I in natural waters, normally within the range pH 5–9, will range from 1.54 to 1080 days at 40°C, 11.3 to 8520 days at 25°C and, by extrapolation of the data obtained in buffer solutions, 106 to 83 000 days at 10°C. The rate constants for hydrolysis of I in aqueous media can be expressed by: Where log k_N = 9.60–(5.56 × 10³ T^?1) and log k_B = 7.32–(2.56 × 10³ T^?1). The calculated rate constants were in good accord with the observed values in buffer solutions. Cleavage of the ester linkage was more rapid than hydration of the cyano group at any pH and temperature tested.     

Efficacies of low- to high-volume (960-10 700 litre ha− 1) citrus sprayers for applying petroleum spray oil to control chinese wax scale

Petroleum spray oil (2, 4 and 6% in water) was applied to Valencia orange, Citrus sinensis (L.) Osbeck, for the control of Chinese wax scale, Ceroplastes sinensis del Guercio, using a low-volume ( <2000 litre ha^?1)air-blast (LV AB) sprayer, a low- to high-volume (L-HV) (up to 7000 litre ha^?1) sprayer with four fan-assisted rotary atomiser (FARA) spray heads mounted on a vertical tower, and a high-volume (>7000 litre ha^?1) oscillating boom (HV OB) sprayer. The most effective sprayer was the L-HV FARA sprayer. The most cost-effective treatment was a 20 ml litre^?1 (60 litre oil ha^?1) spray applied at 3000 litre ha^?1 by the L-HV FARA sprayer. It gave mortality equivalent to a standard 20 ml litre^?1, 10 700 litre ha^?1 spray (214 litre oil ha^?1) applied by the HV OB sprayer but with 72% less spray and significantly less oil deposited per cm² of leaf area. Equivalent or significantly (P = 0·05) higher mortality than that given by the 10 700 litre ha^?1 HV OB spray was given by the 40 ml litre^?1, 3000 (120 litre oil ha^?1) and 60 ml litre^?1, 2180 and 3000 litre ha^?1 (130·8 and 180 litre oil ha^?1) L-HV FARA sprays, but the 60 ml litre^?1 sprays deposited more oil per cm² than the 20 ml litre^?1 HV OB spray and were considered to be potentially phytotoxic. The least effective sprayer was the LV AB sprayer, which applied a 60 ml litre^?1 spray (57·6 litre oil ha^?1) at 960 litre ha^?1. Linear relationships were established for Chinese wax scale mortality, transformed using an angular transformation (arcsin proportion), versus log₁₀ spray volume for the 20, 40 and 60 ml litre^?1 sprays applied by L-HV FARA at 1260,2180 and 3000 litre ha^?1, mortality versus log₁₀ μg oil cm^?2 and log₁₀ μg oil versus log₁₀ volume of oil sprayed.     

Efficacy of dose-dependent indigenous microbial insecticides against cotton aphid,Aphis gossypii Glover (Homoptera: Aphididae) at various temperature regimes

Strain selection based on temperature may be warranted when choosing an isolate for development as a microbial control agent. To this end, the effects of three temperature regimes, namely 20, 25 and 30°C, on the virulence of four Beauveria and two Metarhizium isolates against the cotton aphid, Aphis gossypii, were investigated under controlled conditions, 65–70% relative humidity, and a photoperiod of 12:12 (light: dark) hours. The isolates did vary significantly in their activities of efficacy over a range of temperatures. The highest mortality and lowest survival times were observed at 25°C for DLCO41 and at 30°C for DLCO87; while mortality decreased and survival time increased at temperatures of 20°C. Besides the tested fungal isolate DLCO87 had the lowest LC₅₀ value (6.84 × 10⁵ conidia mL^?1) at 30°C. The promising result of this study should enable us to conduct further studies to determine the potential use of the fungus as an agent against Aphis gossypii both in greenhouse and under field conditions.     

Relation between volatility rating and composition of phenoxy herbicide ester formulations

A CIPAC/AOAC test with tomato plants is used to specify the volatility ratings of herbicide ester formulations. This work compares the tomato plant test with an alternative chemical one. The concentrations of esters and the effective molecular weight and density of each formulation were used with the ester vapour pressures to calculate its herbicide vapour pressure as complete, and evaporated formulations. The range was from 28.8 mPa (at 257deg;C) for a mixture of 2,4–D esters to 0–07 mPa (at 25°C) for a 2,4,5–T-(iso-octyl) formulation, as complete formulations, and 35-5 and 0–16 mPa (at 25°C) as evaporated ones. A value of 0–6 mPa (at 25°C) was selected on the basis of the tomato plant test as the cut-off area for low-volatile esters and is recommended to be included in specifications for herbicide esters. Formulations with a herbicide vapour pressure above 3.3 mPa (at 25°C) are high-volatile ones according to the tomato plant test, while between 0–6–3.3 mPa (at 25°C) is a borderline region where the test gives mixed results. Levels of 2,4–D-ethyl and methyl were added to pure 2–ethylhexyl esters of 2,4–D and a 2,4,5–T-(iso-octyl) formulation to find what level of contamination would change the rating of these esters from low to high volatile. Formulations of 2,4–D-(iso-octyl) should not contain more than 11 g litre^?1 2,4–D as methyl ester or 2.0 g litre^?1 2,4–D as ethyl ester. Formulations of 2,4,5–T-(iso-octyl) should not contain more than 26 g litre^?1 2,4–D as methyl ester or 4.7g litre^?1 2,4–D as ethyl ester.     

Effects of different management practices on Portulaca oleracea emergence in soyabean

Portulaca oleracea (common purslane) is a summer annual weed with wide geographic distribution and is problematic in many crops worldwide. Field experiments were conducted to determine the effects of different management practices on P. oleracea emergence in soyabean fields. Two tillage systems [conventional tillage (CT) and no‐till (NT)], three soyabean seeding rates (SR) (200 000, 300 000 and 400 000 seeds ha^?1) and three imazethapyr doses (0, 50, and 100 g a.i. ha^?1 applied pre‐emergence) were considered as experimental factors. Portulaca oleracea emergence was affected by management practices including tillage system, soyabean SR and imazethapyr dose. Conventional tillage required a thermal time (TT) of 195.95 and 221.30 d °C to reach 50% emergence in 2016 and 2017, respectively, while for NT, the respective TT requirements were 182.34 and 203.32 d °C. On increasing soyabean SR from 200 000 to 400 000 seeds ha^?1, the TT requirements for 50% emergence (T₅₀) of P. oleracea also increased. The T₅₀ at the herbicide dose of 100 g a.i. ha^?1 was 193.05 and 220.67 d °C in 2016 and 2017, respectively, while for the non‐herbicide treatment, the respective TT requirements were 165.98 and 202.94 d °C. From an integrated weed management perspective, a combination of CT with a SR of 400 000 seeds ha^?1 and a 100 g a.i. ha^?1 imazethapyr dose not only resulted in the lowest P. oleracea seedling density m^?2 but also caused the longest delay in the time to reach the T₅₀. Findings from our study may facilitate the development of effective P. oleracea management strategies.     

Conversion rates of aldicarb and its oxidation products in soils. II. Aldicarb sulphoxide

The loss of aldicarb sulphoxide was studied in incubation experiments with soil from four plough layers and two deeper layers. The loss during the 111 days of the experiment could be described by first-order kinetics. The half-lives at 15°C ranged from 20 days in a clay loam to 46 days in a peaty sand. The loss of sulphoxide in deeper layers was considerably slower than in the corresponding top layers of a soil profile. In soil from a silty layer at 70–90 cm depth the half-life was about 53 days. In soil from a sand layer at 90–110 cm depth a loss of only about 15% was measured after 111 days of incubation. First-order rate constants for sulphoxide conversion in a clay loam at 6, 15 and 25°C were found to be 0.009, 0.033, and 0.05 day^?1 respectively; in a greenhouse soil these rate constants were 0.0052, 0.019 and 0.04 day^?1 respectively. The fractions of aldicarb sulphoxide that were oxidised to sulphone at 15°C in soil from plough layers were computed to range from 0.52 to 0.76.     

Degradation and adsorption of 14C-MCPA in soil—influence of concentration, temperature and moisture content on degradation

MCPA was weakly absorbed in soils with 2.4, 3.0 and 2.9% humus. K_d-values were 0.7, 0.9 and 1.0, respectively. In soil, not previously treated with MCPA, the degradation of 0.05 mg kg^?114C-MCPA followed first-order reaction kinetics whereas degradation of 5 mg kg^?1 was only first-order for 2 weeks; exponentially increasing degradation rates followed indicating enrichment of the soil with MCPA decomposers. Degradation was monitored by evolution of ¹⁴CO₂. The influence of temperature on degradation of MCPA (4 mg kg^?1) could initially be described by Q₁₀ values or by the Arrhenius equation. After 1 day of incubation in two field soils Q₁₀ values were 3.3 and 2.9, respectively, between 0°C and 29°C; the activation energies were 87 and 76 kj mol^?1. Exponentially increasing degradation rates followed with doubling times of about 4.0, 1.8, 1.2 and 0.6 days at 6,10, 15 and 21°C, respectively. After 51 days of incubation, at temperatures between 6°C and 29°C, about 60%¹⁴C was evolved in CO₂ and only traces of MCPA were left in the soil. At 0°C and at 40°C only 1% and 10%¹⁴C, respectively, were evolved as CO₂ after 51 days. ¹⁴C-MCPA (4 mg kg^?1) was incubated at moisture contents from that in air-dried soil to 2.3 times field capacity. Optimum for degradation was from 0.6 to 1.2. field capacity. Degradation was very slow where water contents were below the level of wilting point and was nil in air-dried soil. In wet soil degradation was delayed, but even in water-logged soil (2.3 times field capacity) MCPA was decomposed after 4 to 5 weeks at 10°C.     

The effects of temperature and humidity on the toxicity of three organophosphorus insecticides to adult Oryzaephilus surinamensis (L.)

The toxicities, to a laboratory susceptible strain and to a resistant strain of Oryzaephilus surinamensis (L.), of water-dispersible powder formulations of pirimiphos-methyl, fenitrothion or chlorpyrifos-methyl under constant conditions of 25°C and 70% r. h. were compared to the toxicities when the insects were exposed to a diurnal cycle of 12.5–20–12.5°C and 70–50–70% r. h. to simulate grain store conditions in the UK during spring and autumn. All the insecticides were more effective at 25°C and 70% r. h. The LD₅₀ values for the susceptible strain were low, being 4.4 and 1.4 mg m^?2 at 12.5-20°C and 25°C, respectively, for chlorpyrifos-methyl, 18.3 and 4.1 mg m^?2, respectively, for pirimiphos-methyl, and 4.0 and < 1.O mg m^?2, respectively, for fenitrothion. The LD₅₀ values obtained from the two sets of environmental conditions for a resistant strain (484) differed by factors of 1.8 for chlorpyrifos-methyl, 4.8 for pirimiphos-methyl, and 7.3 for fenitrothion. Toxicity studies were also made with chlorpyrifos-methyl under various constant conditions of temperature and humidity from 5–30°C (5°C intervals) and 30, 50, 70 and 90% r. h., and also at O°C and 60% r. h. Chlorpyrifos-methyl was very effective and there was little or no cross resistance to chlorpyrifos-methyl in the resistant strain. From 15 to 30°C, mortality was high, and differences in mortality at the LD₅₀ level for the various humidities were slight, but there was a decrease in mortality with decreasing humidity at any one temperature, in particular, at 5°C, 50 and 70% r. h., and 10°C and 50% r. h. Chlorpyrifosmethyl was more toxic to both strains at the highest humidity (90%) throughout the whole temperature range. The LD₅₀ values for each strain decreased at each temperature as the water vapour concentration was increased. At O°C and 60% r. h., all the insects from both strains died but the cause of death was not clear.     

Effect of environmental factors on herbicidal activity of diphenamid

Diphenamid (N,N-dimethyl-2,2-diphenylacetamide) in an aqueous solution in plastic bottles was partially detoxified when exposed to sunlight for 1 week. Varying spray volumes from 300 to 1,800 I/ha did not have an appreciable effect on the phytotoxicity of diphenamid, sprayed on a coarse or fine soil surface. The marked dissipation of diphenamid which occurred from the soil surface was attributed to photodecomposition and volatilization. Diphenamid phytotoxicity was greater when the first irrigation after spraying was applied in four increments of 100 m³/ha or two increments of 200 m¹/ha than when it was applied in a single 400 m¹/h watering; the latter caused more leaching of the herbicide. The diphenamid fraction leached out of a 4-cm soil layer increased as the organic matter content in the soil decreased, from 25% in peat (22.3% o.m.) to >88% in sandy loam (0.9% o.m.). The herbicidal activity remaining after leaching was lower in sandy loam and in peat than in soil with medium organic matter content (11.6% and 6.2%). Diphenamid degradation rate in soil at 50% field capacity moisture level, increased when temperature was increased from 10° to 30°C. After 4 months of incubation at 10°C, 40-50% of the original herbicide was detoxified, while at 20° and 30°C the loss exceeded 90%. Within the range of day-temperatures of 10° to 40°C in soil and of 10° to 35°C in nutrient solution, diphenamid phytotoxicity to tomato seedlings increased with temperature.     

Off-target glyphosate from aerial silvicultural applications,and buffer zones required around sensitive areas

Off-target glyphosate deposits were measured downwind of aerial silvicultural applications which used D8-46 hollow-cone hydraulic nozzles, ‘Micronair’ AU 5000 rotary atomisers, and the ‘Thru Valve Boom’ (030), with volume application rates of 35, 20 and 20 litre ha^?1 respectively, and a glyphosate application rate of 2·1 kg ha^?1. Crosswind spray lines were released 10 m above ground level over a short forest canopy, from a fixed-wing aircraft flying at 45 m s ¹ in atmospheric boundary layers with average wind speeds and air temperatures of 2·2-3·7 m s^?1 and 8-23°C at release height. Ground sheets and artificial foliage clusters were exposed at downwind distances of between 50 and 300 m. Glyphosate deposit measurements at various downwind distances (x) were fitted with non-linear regression lines; deposits were attenuated at rates inversely proportional to x at powers of 1·3-2·3. For a particular trial, deposits on ground sheets and artificial foliage were generally similar, and ranged between 19 and 0·04 mg m^?2 over the sampling distances used. For 100-ha applications the estimated buffer-zone widths around water bodies were less than 50 m, whereas those around non-target vegetation ranged between 75 and 1200 m, depending on the application method and the meteorological conditions.     

Comparative biology and life table of Habrobracon hebetor (Hymenoptera: Braconidae) on Anagasta kuehniella (Lepidoptera: Pyralidae) at five constant temperatures

Habrobracon hebetor Say is an ectoparasitoid that has been used as a control agent of various lepidopteran pests. Temperature-dependent life table and thermal characteristics of H. hebetor are important in understanding the dynamics of host–parasitoid relationships and for optimizing biocontrol programmes. The influence of five constant temperatures (15, 20, 25, 30 and 35 °C) on the biology of H. hebetor when parasitizing Anagasta kuehniella Zeller was studied. The survival rate of immature stages increased from 16.67% to 83.81% as temperature increased from 15 to 30 °C and then decreased at 35 °C. Total development time ranged from 45.70 days at 15 °C to 7.10 days at 35 °C. The lower temperature threshold for immature stages varied slightly around a value of 11–12 °C. The net reproductive rate (R₀) values were significantly different among temperatures and the highest value was found at 30 °C (85.10). The high survival rate and net reproductive rate combined with a relatively short generation time at 30 °C resulted in the intrinsic rate of increase (r_m) being highest (0.312 d^?1) at this temperature. Considering the acquired results, the temperature range between 25 and 30 °C was optimal for H. hebetor.     

Breakdown rates of dimethoate in fruit and vegetable dips

In order to determine the effect of pH and temperature on post-harvest dip solutions of dimethoate (500 mg litre^?1), the half-lives and pseudo first-order rate constants were calculated from measurements at pH 4, 6, 8, 10, 11.5, and at two temperatures 25 and 52°C. The half-lives ranged from 206 days to 39.3 min at 25°C, and from 5.6 days to 205s at 52°C; the rate constants ranged from 3.9 × 10^?8 s^?1 to 2.9 × 10^?4 s^?1 at 25°C, and from 1.4 × 10^?6 s^?1 to 3.4 × 10^?3 s^?1 at 52°C. The results show that the water used in dips should have a pH≤7. The addition of benomyl to the dip solutions at two concentrations (0.5 and 1.0 g litre^?1) had no effect on the half-lives and rate constants. The use of hard and salted waters in dips also showed no major effect. A formula was developed that gives the half-life of the dimethoate as a function of the pH and temperature.     

Uptake of aminotriazole from humectant-surfactant combinations and the influence of humidity

Uptake of aminotriazole (3-amino-1,2,4-triazole) by bean leaves (Phaseolus vulgaris var. Canadian Wonder) was not greatly influenced by the addition to the spray solution of dimethylformamide (DMF), ethylene glycol and polypropylene glycol 400 (PPG 400) over the concentration range 1.0–50.0 ml litre^?1. However, the addition of polyoxyethylene 20 sorbitan monolaurate (polysorbate 20) (0.2–1.0 g litre^?1) to spray solutions of the above additives and glycerol (5.0 ml litre^?1; except for DMF, 50.0 ml litre^?1) substantially increased uptake to 80–100% in all cases at 50 ± 10% relative humidity (r.h.). Similar penetration figures were recorded when a range of polysorbate surfactants (polysorbate 20, 40, 60, 80 and 85; 0.2 g litre^?1) were applied to spray solutions containing either dimethyl sulphoxide (DMSO) or glycerol (5.0 ml litre^?1). Humidity was found to have a critical effect upon the humectant-surfactant combinations tested, i.e. DMSO + polysorbate 20, ethylene glycol+ polysorbate 20 and PPG + 400-polysorbate 20 (5.0 ml litre^?1+0.2 g litre^?1). With DMSO + polysorbate 20 the following uptake figures were recorded: < 30% r.h., 3.1 %; 45 ± 10% r.h., 86.8%; 55–65% r.h., 48.2 % and 100% r.h., 0.3%. Similar trends were recorded with all three humectant-surfactant combinations. Further studies revealed that the adverse effect of humidity on DMSO-polysorbate mixtures could be at least overcome partially by regulating the DMSO concentration.     

Impact of ant control technologies on insecticide runoff and efficacy

BACKGROUND: Insecticides are commonly used for ant control around residential homes, but post‐treatment runoff may contribute to contamination of surface water in urban watersheds. This study represents the first instance where runoff of insecticides was directly measured after applications around single family residences. During 2007, houses were treated with bifenthrin or fipronil sprays following standard practices. During 2008, pin stream applicators, spray‐free zones and restricting sprays to the house foundation were considered as management options. RESULTS: During 2007, the resulting runoff from the bifenthrin spray in the irrigation water had a mean concentration of 14.9 µg L^?1 at 1 week post‐treatment and 2.5 µg L^?1 at 8 weeks, both high enough to be toxic to sensitive aquatic organisms. In comparison, treatments with bifenthrin granules resulted in no detectable concentrations in the runoff water after 8 weeks. The mean concentration for fipronil used as a perimeter spray was 4.2 µg L^?1 at 1 week post‐treatment and 0.01 µg L^?1 at 8 weeks, with the first value also suggesting a potential for causing acute aquatic toxicity to sensitive organisms. During 2008, insecticide runoff was reduced by using spray‐free zones and pin stream perimeter applications. CONCLUSIONS: It is shown that insecticide runoff from individual home treatments for ants can be measured and used to improve techniques that minimize runoff. The pin stream application and applications limited to the house foundation should be further evaluated for their potential to reduce pesticide runoff from residential homes. Copyright © 2010 Society of Chemical Industry     

Dégradation chimique ou microbiologique des sulfonylurées dans le sol. I. Cas du sulfbméturon méthyle

La Vitesse de transformation du sulfométuron méthyle dans un sol, et en solution au même pH, a été mesurée à différentes temperatures. Aussi bien en solution que dans le sol, la relation d'Arrhénius est bien vérifiée dans la gamme de température étudiée 20°C-75°C. L'énergie d'activation calculée est respectivement de 94 kJ mol^?1 et de 117 kJ mol^?1 dans le sol et en solution. Du fait que la loi d'Arrhénius est vérifiée dans le sol jusqu'à 70°C, un mécanisme de dégradation est proposé: la dégradation chimique. L'analyse des produits formés dans un sol stérile et non stérile a été réalisée a partir du sulfométuron méthyle marqué au ¹⁴C sur le cycle pyrimidine. Dans les deux sols le métabolite principal retrouvé est la 2-amino-4,6-diméthyl-pyrimidine. Aucune différence significative n'est mise en évidence entre le sol sterile et non stérile. Chemical or microbial degradation of sulfonylurea herbicides in soil. I. Sulfometuron methyl The rates of degradation of sulfometuron methyl in a soil and in aqueous solution at the same pH were measured at different temperatures. The Arrhenius relationship was verified between 20°C and 75°C. The calculated activation energy in soil and in solution was 94 kJ mol^?1 and 117 kJ mol^?1, respectively. From the fact that the Arrhenius relationship is followed up to 70°C, it is proposed that the mechanism of degradation in the soil is chemical. Analysis of the metabolites formed in sterile and non-sterile soil was performed using sulfometuron methyl labelled with ¹⁴C in the pyrimidine ring. In both soils the main metabolite isolated was 2-amino-4,6-dimethylpyrimidine. No significant difference has been observed between sterile and non-sterile soils. Chemischer oder mikrobiologischer Abbau von Sulfonylharnstoffen im Boden. I. Sulfometuronmethyl Die Abbaurate von Sulfometuron-methyl wurde in einem Boden und in wäßriger Lösung mit gleichem pH-Wert bei verschiedenen Temperaturen untersucht. Die Gültigkeit der Arrhenius-Gleichung wurde zwischen 20 und 75°C überprüft, mit Aktiviemngsenergien von 94 oder 117 kJ mol^?1 für den Boden bzw. die Lösung. Aus dem linearen Abbau im Boden bis zu 70°C wurde auf chemischen Abbau geschlossen. Bei der Analyse der Abbauprodukte von ¹⁴C-Sulfometuron-methyl (markiert am Pyrimidin-Ring) in sterilisiertem und nicht sterilisiertem Boden wurden keine signifikanten Unterschiede festgestellt und hauptsächlich das 2-Amino-4,6-dimethylpyrimidin gefunden.     

Partitioning of etofenprox under simulated California rice‐growing conditions

BACKGROUND: The pyrethroid insecticide etofenprox is of current interest to rice farmers in the Sacramento Valley owing to its effectiveness against the rice water weevil, Lissorhoptrus oryzophilus Kuschel. This study aimed to describe the partitioning of etofenprox under simulated rice field conditions by determining its Henry's law constant (H) (an estimate of volatilization) and organic carbon‐normalized soil–water distribution coefficient (K_oc) at representative field temperatures. A comparison of etofenprox and λ‐cyhalothrin is presented using a level‐1 fugacity model. RESULTS: Experimental determination of H revealed that etofenprox partitioned onto the apparatus walls and did not significantly volatilize; the maximum value of H was estimated to be 6.81 × 10^?1 Pa m³ mol^?1 at 25 °C, based on its air and water method detection limits. Calculated values for H ranged from 5.6 × 10^?3 Pa m³ mol^?1 at 5 °C to 2.9 × 10^?1 Pa m³ mol^?1 at 40 °C, based on estimated solubility and vapor pressure values at various temperatures. Log K_oc values (at 25 °C) were experimentally determined to be 6.0 and 6.4 for Princeton and Richvale rice field soils, respectively, and were very similar to the values for other pyrethroids. Finally, temperature appears to have little influence on etofenprox sorption, as the log K_oc for the Princeton soil at 35 °C was 6.1. CONCLUSION: High sorption coefficients and relatively insignificant desorption and volatilization of etofenprox suggest that its insolubility drives it to partition from water by sorbing to soils with high affinity. Offsite movement is unlikely unless transported in a bound state on suspended sediments. Copyright © 2009 Society of Chemical Industry     

Time,concentration and temperature relationships for phosphine activity in tests on diapausing larvae of Ephestia elutella (Hübner) (Lepidoptera: Pyralidae)

The activity of phosphine against diapausing larvae of Ephestia elutella was shown to depend on several different interactions of duration of exposure, temperature and gas concentration. Using the model proposed by Knight, (C? C₀) × (t? t₀) = k, a constant for mortality, the minimum effective concentration C₀ was raised and the minimum effective exposure t₀ extended as temperatures were increased. The effect of temperature on these thresholds was reduced at higher mortality levels. A range of concentration levels, influenced by temperature, elicited an increase in tolerance at the LD₉₉ level over that evident at higher or lower concentrations. These concentration ranges were 0.9–2-1 mg litre-¹at 25°C,0.7–2.3 mg litre-¹ at 20°C and 0.1–1.5 mg litre-¹ at 15°C. A mathematical model was fitted to relate concentration and time thresholds, mortality and temperature. At the LD₅₀ level, values for t₀ ranged from 2.5 h at 15°C to 5.0 h at 25°C. C₀ values increased from about 0.6 to 7.0 μg litre-¹ over this temperature range. At the LD₉₉ level, t₀ values ranged from 21 to 28 h and C₀ values from 11 to 19 μg litre-¹. Phosphine appeared most effective at each temperature at concentrations from about 40 to 60–100 μg litre-¹.