Carryover Of Residues Research Articles

Combination-Lock SlipChip Integrating Nucleic Acid Sample Preparation and Isothermal LAMP Amplification for the Detection of SARS-CoV-2.

Nucleic acid analysis with an easy-to-use workflow, high specificity and sensitivity, independence of sophisticated instruments, and accessibility outside of the laboratory is highly desirable for the detection and monitoring of infectious diseases. Integration of laboratory-quality sample preparation on a hand-held system is critical for performance. A SlipChip device inspired by the combination lock can perform magnetic bead-based nucleic acid extraction with several clockwise and counterclockwise rotations. A palm-sized base station was developed to assist sample preparation and provide thermal control of isothermal nucleic acid amplification without plug-in power. The loop-mediated isothermal amplification reaction can be performed with a colorimetric method and directly analyzed by the naked eye or with a mobile phone app. This system achieves good bead recovery during the sample preparation workflow and has minimal residue carryover from the lysis and elution buffers. Its performance is comparable to that of the standard laboratory protocol with real-time qPCR amplification methods. The entire workflow is completed in less than 35 min and the device can achieve 500 copies/mL sensitivity. Thirty clinical nasal swab samples were collected and tested with a sensitivity of 95% and a specificity of 100% for SARS-CoV-2. This combination-lock SlipChip provides a promising fast, easy-to-use nucleic acid test with bead-based sample preparation that produces laboratory-quality results for point-of-care settings, especially in home use applications.

Use of the permitted daily exposure (PDE) concept for contaminants of intravitreal (IVT) drugs in multipurpose manufacturing facilities

A toxicological evaluation to determine the product specific permitted daily exposure (PDE) value is an accepted method to determine a safe limit for the carry-over of product residues in multipurpose manufacturing facilities. The PDE calculation for intravitreal (IVT) injection of small and large molecular weight (MW) drugs follows the guiding principles set for systemic administration. However, there are specific differences with respect to the volume administered with IVT administration, pharmacokinetic and pharmacodynamics (PK-PD) parameters and potential for toxicity. In this publication, we have proposed a method to derive PDEIVT in the presence of IVT dose. In the absence of an IVT dose we have a proposed default extrapolationof the systemic PDE for intravenous (IV) administration to the PDEIVT dose by applying a factor of 500 based on comparison of the volume of vitreous humour with the plasma volume, as well as provided examples for PK-PD and toxicity considerations.

Determination and application of the permitted daily exposure (PDE) for topical ocular drugs in multipurpose manufacturing facilities

Limits for the carry-over of product residues should be based on toxicological evaluation such as described in the “Guideline on setting health based exposure limits for use in risk identification in the manufacture of different medicinal products in shared facilities”. The toxicological evaluation should be performed also for locally administered drugs to ensure patient safety. Currently, there is no guidance on setting PDE for ocular drug substances in particular. The purpose of this investigation was to identify and describe a method for calculating a PDE value for topical ocular drugs (PDEocular). As an alternative method, extrapolation of a PDE for systemically administered drugs to a PDEocular is presented. These methods may be applied in cross-contamination risk assessments for manufacturing of topical ocular drugs. Similarly, the methods apply to systemically administered drugs, if their production precedes manufacturing of a topical ocular drug. We have examined pharmacokinetic (PK) properties of topical ocular drugs and compared them to the PK parameters of systemically administered drugs. Furthermore, we examined possible adverse effects of the carry-over in topical ocular drugs at therapeutic doses.

Effect of paste processing on residue levels of imidacloprid, pyraclostrobin, azoxystrobin and fipronil in winter jujube

The changes of imidacloprid, pyraclostrobin, azoxystrobin and fipronil residues were studied to investigate the carryover of pesticide residues in winter jujube during paste processing. A multi-residue analytical method for winter jujube was developed based on the QuEChERS approach. The recoveries for the pesticides were between 87.5% and 116.2%. LODs ranged from 0.002 to 0.1 mg kg–1. The processing factor (Pf) is defined as the ratio of pesticide residue concentration in the paste to that in winter jujube. Pf was higher than 1 for the removal of extra water, and other steps were generally less than 1, indicating that the whole process resulted in lower pesticide residue levels in paste. Peeling would be the critical step for pesticide removal. Processing factors varied among different pesticides studied. The results are useful to address optimisation of the processing techniques in a manner that leads to considerable pesticide residue reduction.

Reasoned opinion on the modification of the existing MRLs for chlormequat in pears, cereals and commodities of animal origin

In accordance with Article 6 of Regulation (EC) No 396/2005, the United Kingdom (hereafter - evaluating Member State UK (EMS UK)), received an application from the company BASF to modify the existing MRLs for chlormequat in cereals and several commodities of animal origin. The EMS UK proposed to raise MRLs in rye and oat grain and several animal commodities to accommodate the NEU use of chlormequat on cereals. The Netherlands (EMS NL) received an application from Nederlandse Fruittelers Organisatie to maintain the temporary MRL of 0.1 mg/kg for chlormequat in pears until 31 July 2017, in order to accommodate for carry-over of chlormequat residues due to formerly authorized uses on pear trees. The targeted monitoring data provide evidence that, in general, chlormequat residues in pears produced in the Netherlands and Belgium are declining. In 2013 and onwards, 95 % of the samples of pears produced in the Netherlands and Belgium in areas where chlormequat was used in pear orchards before 2003 will contain residues at or below the level of 0.1 mg/kg. The submitted residue trials on cereals indicate that a higher MRL is required for oat and rye grain to support the intended NEU use. The new use on cereals results in a need to raise the existing MRLs for chlormequat in ruminant muscle, liver, kidney, swine kidney and milk. Based on the risk assessment results, EFSA concludes that the temporary MRL for pears and the intended use of chlormequat on rye and oats and the subsequent residues in animal commodities will not result in a consumer exposure exceeding the toxicological reference values and therefore is unlikely to pose a public health concern.

Crop Response to Carryover of Mesotrione Residues in the Field

Two field residue studies were conducted from 2005 to 2007 in Simcoe, Ontario, Canada, to evaluate the effects of mesotrione soil residues on injury, plant dry weight, and yield of sugar beet, cucumber, pea, green bean, and soybean and to verify the potential of reducing a 2-yr field-residue study (conventional residue carryover) to a 1-yr field study (simulated residue-carryover study) by growing these crops in soil treated with reduced rates of mesotrione applied in the same year. There was a significant difference in mesotrione carryover between 2006 and 2007 and differences between years can be explained by differences in soil pH and soil moisture. The conventional and the simulated residue-carryover studies successfully measured mesotrione persistence and rotational crop sensitivity. Both studies showed that sugar beet was the most-sensitive crop with injury, plant dry weight reduction, and yield loss because of mesotrione residues as high as 100%. Green bean was the next most-sensitive crop to mesotrione residues followed by pea, cucumber, and soybean. The simulated residue-carryover study provided a more-rigorous test of rotational crop sensitivity to mesotrione residues than the conventional residue-carryover study, especially at higher rates for the more-sensitive crops. For the other crops, responses to mesotrione residues were similar between the conventional and simulated residue-carryover studies.

Effect of Naturally Contaminated Feed with Aflatoxins on Performance of Laying Hens and the Carryover of Aflatoxin B1 Residues in Table Eggs

The aim of this study was to evaluate the effect of naturally contaminated feed with aflatoxin on performance of laying hens fed for 60 days and the carryover of AFB residues in eggs as well as the stability 1 of AFB in naturally contaminated eggs to boiling process. Forty, 30 weeks old, White Leghorn laying hens 1 were randomly assigned into four experimental groups and after 2 weeks were given naturally contaminated feed containing zero (control), 25, 50 and 100 μg aflatoxin/kg feed. Twenty eggs per treatment were collected on days (1-7); 10; 20, 30, 40, 50 and 60 and submitted to aflatoxin B analysis using ELISA. Average egg 1 production and egg weight were not affected by aflatoxin (P>0.05), while a significant decrease in feed intake (p<0.05) was appeared in the 2 groups fed on 50 and 100 aflatoxin ug/kg feed. Residues of aflatoxin B were 1 detected in eggs at levels that ranged from 0.02 to 0.09 with a mean value of 0.04, 0.05 and 0.07 μg/kg respectively. Aflatoxin B was almost stable in naturally contaminated egg for up to 20 minutes of boiling, so 1 avoiding aflatoxin B transmission into egg appears to be the only practical way to ensure their safety for 1 human consumption. Conclusively, the excretion of aflatoxin B residues in hens' eggs might occur at 1 relatively low concentrations under conditions of long term exposure of laying hens to low level of aflatoxin in naturally contaminated feed with reduction in feed intake started at 50 μg/kg.

Decline of pesticide residues from barley to malt

The fate of dinitroaniline herbicides (pendimethalin and trifluralin), organophosphous insecticides (fenitrothion and malathion), and pyrimidine (nuarimol) and triazole (myclobutanil and propiconazole) fungicides from barley to malt was determined. Several samples for residue analysis were taken after each stage of malting (steeping, germination and kilning). Pesticide residue analysis was carried out by GC/ITMS in selected ion monitoring mode. Pesticides decline along the process, although in different proportions. The carryover of residues after steeping was 45–85%. A good correlation (r > 0.92) was observed between percentages removed after steeping and the P OW values of pesticides. The amount remaining after malting ranged from 13 to 51% for fenitrothion and nuarimol, respectively. Steeping was the most important stage in the removal of pesticide residues (52%) followed by germination (25%), and kilning (drying and curing, 23%). During malt storage (3 months) the fall in pesticide residues was not significant. Applying the standard first-order kinetics equation (r > 0.95), the half-lives obtained for the pesticides during malt storage varied from 244 to 1533 days for myclobutanil and nuarimol, respectively.

Method for calculating ADI-derived guidance values for drug carryover levels in medicated feeds

There exists the possibility that non-target livestock may receive trace exposure to medications in feed due to residue carryover from previous production runs of medicated feeds at feed mills. We have developed a method by which ADI-Derived Drug Carryover Levels (ADCLs) can be established. It is a practical approach compared to the “zero” levels of residue carryover that may be expected or required by regulatory authorities. The methodology involves application of various safety/uncertainty factors to concentrations of active ingredients (a.i.) already approved for use in medicated feeds for target species. The starting point for each a.i., to be consistent, and to represent the highest possible carryover, is the highest approved concentration for any target animal species, recognizing that this is an approved level based on established ADI and agency review of supporting safety data specific to each a.i. (Hence, these guidance values are characterized to be ‘ADI-derived’.) Safety factors are then applied to account for: (a) interspecies extrapolation, (b) differences in the body weights of target and non-target species (i.e., smaller animals receive higher exposures on a body weight basis for a given dietary concentration), (c) a.i. with clear contraindications for use in certain non-target species (i.e., a priori knowledge of non-target species sensitivity), and (d) withdrawal times (i.e., for a.i. that require a washout period prior to slaughter there is potential exposure to non-target species through other feeds not requiring a washout period). The values of the safety/uncertainty factors range from 1 to 3, 1 to 3.17, 1 to 10, and 1 to 10, for each of conditions (a), (b), (c), and (d), respectively. The “proposed safety factor” to apply to the approved concentration in medicated feed is calculated as the product of the values for each of (a) through (d). The final safety factor is the greater of the proposed safety factor or a default minimum safety factor of 30. ADCLs were calculated for several a.i. and compared to limits of quantitation available for detection of carryover residues in animal feeds. This methodology may be used in its present or modified form in any jurisdiction in which mediated feeds are approved. As a start, this approach has been applied to several example products approved and in use in Canada.

Tissue Residues of Diuron in Channel Catfish Ictalurus punctatus Exposed to the Algicide in Consecutive Years

AbstractIn 1999, the United States Environmental Protection Agency granted an emergency exemption under Section 18 of the Federal Insecticide, Fungicide. and Rodenticide Act authorizing the use of the algicide diuron [3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea] to manage cyanobacterial off‐flavors in channel catfish Ictalurus punctcatus. Catfish may remain in ponds for more than one growing season and may therefore be exposed to more than one set of diuron treatments. This study was conducted to determine whether diuron residues in fish carry over from one year to the next and, if so, whether the cumulative exposure causes residues to exceed the tolerance level of 2.0 mg/kg in fillets. Catfish in earthen ponds were exposed to the label‐specified treatment protocol of nine consecutive weekly applications of diuron at 0.01 mg/L in the fall of one year and again the following spring. Diuron concentrations in fillets were below limits of detection (0.05 mg/kg) in all fish (N = 18) prior to the initial diuron treatment series. Immediately after the ninth weekly diuron application in the fall. tissue diuron levels averaged 0.353 mg/kg (pooled SEM = 0.036; range = 0.078–0.724 mg/kg; N= 18). On the day before the second set of diuron treatments 6 mo later. diuron concentrations were below limits of detection in all fish sampled. Immediately after the second set of nine weekly diuron applications, tissue concentrations averaged 0.127 mg/kg (pooled SEM = 0.015; range = not detected to 0.191 mg/kg; N = 18). This study showed that diuron residues in channel catfish were depleted within 2 to 4 mo after exposure to the chemical and there was no carryover of residues in fish from one year to the next. Maximum residue levels in catfish fillets were less than half the tolerance level of 2.0 mg/ kg.

Fate of Insecticide and Fungicide Residues on Barley during Storage and Malting

Agrochemical usage on barley cultivation was investigated to clarify possible chemical residues on malt. Organophosphorous insecticides and azole fungicides were found to be used extensively during the barley head growth stage, when higher residues on barley are of concern. Pesticide applications for barley were carried out in a barley field using some pesticides common in barley cultivation. Mepronil, propiconazole, triadimefon, triflumizole, ethiofencarb, phenthoate, and fenitrothion were used for applications. Their residues after storage and the fate of the residues during malting were determined. More than 80% of residues of phenthoate and fenitrothion (organophosphorous insecticides) remained after two months of storage. The loss of other pesticides was 28–85%, and metabolites of triadimefon and triflumizole increased slightly. The carryover of residues after steeping was 3–50%, and the losses of hydrophilic pesticides were significant. There was a small loss after germination and kilning. These findings suggested that residues of agrochemicals having log Pow values (partition coefficient between n-octanol and water) >2 would remain on malt. One of the critical control points for quality assurance in beer manufacture is therefore to check and control residues of agrochemicals with log Pow values between 2 and 4 used during the barley head-growth stage.

Fate of Agrochemical Residues, Associated with Malt and Hops, During Brewing

A process for predicting the potential for persistence of agrochemical residue levels in beer has been developed. For this, we first developed analytical methods for determining the agrochemical residues in beer, wort, and various by-products during the brewing processes. Second, various types of agrochemicals were spiked during the mashing, wort boiling, or fermentation processes and the residues in the product and in the by-product were determined with the developed method. Agrochemicals added were representative of the typical chemical groups of agrochemicals for which maximum residual levels in barley or hops are regulated by Japanese official law. Third, the potential for the carryover of agrochemical residues into wort and beer was investigated based on their chemical properties such as thermostability, chemical reactivity, and oil/water solubility (which was expressed as log Pow values). It was found that the carryover of agrochemical residues into wort and beer depended on their log Pow values. The carryover percentages into wort or beer of glyphosate (organophosphorus herbicide) having the lowest log Pow value were more than 90% of the amount added to each process. On the other hand, most of the agrochemicals having a high log Pow value, such as pyrethroid pesticides, were detected in the fractions of the spent grains and spent hops. Some amounts of the added agrochemicals were lost during the wort boiling process. On the other hand, no significant reduction was observed during the fermentation process. None of the agrochemicals spiked in the hop pellets were detected in beer because of the loss during boiling and fermentation, though the levels of the spiked agrochemicals were high enough to be detected in beer if no loss of the spiked agrochemicals had occurred. From these results, the process for predicting the potential for the carryover of agrochemical residues in malt or hops into beer on a laboratory scale was proposed, in that the log Pow values of a agrochemical was effectively used as the primary indicator.

Effect of moisture on quinclorac dissipation in Lethbridge soil

This study examined the dissipation and carry-over of quinclorac residues in a Lethbridge sandy clay loam with 2% organic matter. Experiments were conducted in covered outdoor lysimeters using different simulated rainfall regimes. Quinclorac residues were monitored in the top 10 cm of soil using chemical residue analysis and the activity of carried-over residues assessed by bioassay. Quinclorac dissipation was very slow although, in general, the amount of residue remaining decreased with increased moisture (117–447 mm) applied. Forty-eight weeks after quinclorac application, 85, 66, 52, 49, and 48% of initial residues remained in the very dry, dry, normal, wet and very wet moisture regimes, respectively. Residue persistence could be accurately predicted (r2 = 0.96) using a simple moisture model (% quinclorac remaining = 101% −0.18 × mm cumulative moisture) for up to 300 mm moisture. Quinclorac dissipation was attributed mostly to the residues leaching beyond the 0- to 10-cm soil layer. A separate laboratory experiment showed that 80% of applied quinclorac leached through 9.7-cm deep soil columns when 304 mm of water was applied. The quinclorac residues remaining after 48 wk were biologically available and caused injury to fababeans (Vicia faba L.) under all moisture regimes. Key words: Quinclorac, persistence, moisture effects, leaching, residue carry-over, recropping

Carry-over of granular and emulsifiable concentrate formulations of trifluralin in Saskatchewan

The field persistence of trifluralin from fall treatments of both emulsifiable concentrate (EC) and granular formulations was investigated at two sites in Saskatchewan over a 2-yr period. At both locations, there were no significant differences (P = 0.05) in trifluralin persistence from fall applications of either formulation. In addition, the carryover of trifluralin residues in farmers’ fields following fall and spring applications of EC and granular formulations was monitored at several Saskatchewan locations to determine their persistence under typical farming practices. Trifluralin residue data indicated that following fall applications, the percent carry-over to the first spring was 83 ± 21(15 fields sampled) and 37 ± 15 (28 fields sampled) to the second spring; and that following spring applications, the percent carry-over to the next spring was 33 ± 12 (14 fields sampled). Key words: Field studies, persistence, formulations, trifluralin, herbicide

Formation and persistence of metabolites of imazamethabenz‐methyl in a sandy loam soil

Summary: Résumé: ZusammenfassungThe fate of imazamethabenz‐methyl was studied in a sandy loam soil after application in spring to winter wheat (Triticum aestivum L.). Imazamethabenz‐methyl and its metabolite 2 (2‐(4, 5‐dihydro‐4‐methyl‐4‐(l‐methylethyl)‐5‐oxo‐1H‐imidazol‐2‐yl)‐4‐methylbenzoic acid, in mixture with the 5‐methylbenzoic acid isomer) were further transformed into the metabolites 3 (2‐(4,5‐dihydro‐4‐methyl‐4‐(l‐methylethyl)‐5‐oxo‐1H‐imidazol‐2‐yl)‐l,4‐benzenedicarboxylic acid, in mixture with the 1,5‐benzenedicarboxylic acid isomer), and 4 (1,2,4‐benzenetricarboxylic acid, in mixture with the 1,2,5‐isomer). Meta‐bolites 3 and 4 reached maximum concentration levels in the 0–13 cm layer corresponding to 14–17% and 9–14% of the imazamethabenz‐methyl dose, respectively. These maxima were reached between 105 and 177 days after application. Imazamethabenz‐methyl metabolism was slower in plots treated with organic fertilizers than in untreated plots. After 196 days the concentrations of all metabolites in the 0–13 cm layer had declined to, at most, 0.01 mg kg−1. There was no carry‐over of residues that could be phytotoxic to the next crop. Formation et persistance dés metabolites de l'imazaméthabenz‐méthyl dans un sol sablolimoneux La métabolisation de l'imazaméthabenz‐méthyl a étéétudiée dans un sol sablo‐limoneux après application sur une culture de froment d'hiver (Triticum aestivum L.) L'imazaméthabenz‐méthyl et son métabolite 2 (2‐(4,5‐dihydro‐4‐methyl‐4‐(l‐methylethyl)‐5‐oxo‐−1H‐imidazol‐2‐yl)‐4‐methylbenzoïque acide, en mélange avec 1'isomère 5‐methylbenzoïque acide) sont trans‐formés ultérieurement en métabolites 3 ((2‐(4,5‐dihydro‐4‐methyl‐4‐ (l‐methylethyl)‐S‐ oxo ‐−1H‐imidazol‐2‐yl)‐l,4‐benzenedicarboxylique acide, en mélange avec l'isomère 1,5‐benzenedicar‐boxylique acide) et 4 (1,2,4‐benzenetricarboxy‐lique acide, en mélange avec le 1,2,5‐ isomère). Les concentrations dans la couche de sol de 0–13 cm de profondeur des métabolites 3 et 4 at‐teignent des maximums qui correspondent re‐spectivement à 1,4–17% et 9–14% de la dose initiate en imazamethabenz‐methyl. Ces concentrations maximales sont atteintes entre les 105 et 177 jours qui suivent 1'application. La métabolisation de rimazaméthabenz‐méthyl est plus lente dans les parcelles trailées par des fetilisants organiques, que dans les parcelles non traitées par ces fertilisants. Après 196 jours, les concentrations de tous les métabolites dans la couche de sol de 0–13 cm ont diminué jusqu' à 0.01 mg kg−1 ou moins. Dans ces conditions, en fin de culture il n'est pas resté dans le sol de résidus qui auraient pu être phytotoxiques à la culture suivante. Bildung und Persistenz von Metaboliten des Imazamethabenz‐methyl in einen sandigen Lehmboden Nach der Applikation von Imazamethabenz‐methyl in Winterweizen (Triticum aestivum L.) wurde sein Abbau untersucht. Das Herbizid und seine Metaboliten 2, die isomeren 2‐(4, 5‐Dihydro‐4‐methyl‐4 (1‐methylethyl)‐5‐oxo‐1 Himidazol‐2‐yl)‐und ‐5‐methylbenzoesäure, wurden weiter zu den Metaboliten 3, die isomeren‐1,4‐und‐l,5‐benzendicaboxylsäure, und 4, die isomeren 1,2,4‐ und 1,2,5‐benzentricarboxylsäure, transformiert. Die Metaboliten 3 und 4 hatten ihre höchste Konzentration in 0 bis 13 cm Bodentiefe und entsprachen 14 bis 17 % bzw. 9 bis 14 % der Imazamethabenzmethyl‐Dosis. Diese Maxima wurden zwischen 105 und 177 d nach der Applikation erreicht. In organisch gedüngten Parzellen war der Abbau langsamer als in ungedüngten. Nach 196 d war die Konzentration aller Metaboliten in 0 bis 13 cm Bodentiefe auf höchstens 0,01 mg kg1 zurückgegangen, so daß für die Folgekultur keine phytotoxischen Rückstände mehr vorlagen.

Influence of Application Time on Bioactivity of Imazethapyr in No-tillage Soybean (Glycine max)

Field research was conducted at Arlington, WI, in 1988 and 1989 to determine the influence of application time on weed control and residue carryover with imazethapyr in no-tillage soybean production. Imazethapyr at ≥ 55 g ai ha−1applied early preplant controlled &gt; 90% of the common lambsquarters, velvetleaf, and giant foxtail before no-tillage planting of soybean. Early preplant and sequential treatments with an early preplant component controlled ≥ 88% of all weeds for the entire growing season. Delaying the initial imazethapyr application until immediately after soybean planting reduced weed control compared to the early preplant treatments. Low level of weed control with planting time treatments appeared to be due to a lack of control of common lambsquarters emerged at the time of imazethapyr application and dry weather following imazethapyr application. No soybean injury from imazethapyr was observed and differences in soybean yield appeared to be due to differences in weed control. No significant carryover of imazethapyr was detected through a corn bioassay in the field.

Injury and Yield Response of Selected Crops to Imazaquin and Norflurazon Residues

Field studies were conducted in 1987, 1988, and 1989 to evaluate the effects of freshly applied residual levels (simulated residue carryover) of imazaquin and norflurazon on the growth and yield of corn, cotton, grain sorghum, rice, and wheat. Studies ware conducted on five soils, and concentrations of herbicides were determined at crop planting. Crop injury ratings were recorded 4 wk after emergence, and yields were measured at the end of each growing season. In simulated residue carryover studies, corn and grain sorghum injury occurred and yields were reduced when norflurazon concentrations were 450 ng g-1soil or greater. Rice yields were reduced at norflurazon concentrations of 710 ng g-1. Corn, cotton, and wheat heights and yields were reduced when imazaquin concentrations were 13 ng g-1, 13 ng g-1, and 45 ng g-1soil, respectively for crops. Comparisons between simulated carryover and actual carryover were made for corn and cotton grown in imazaquin treated fields as well as for corn grown in a norflurazon treated field.

Effects of Tillage on Trifluralin Residue Carryover Injury to Corn (Zea mays)

Trifluralin was evaluated at 1.1, 2.2, and 4.5 kg/ha in 1983 and 1984 at two locations in Iowa for residue carryover injury to corn the following seasons. Three methods of seedbed preparation (no-till, moldboard, and chisel plowing) for corn planting were also examined. There was no effect on corn growth at the 1.1 kg/ha rate of trifluralin. Averaged over the four experiments, reductions in corn height of 8 and 24% were observed 5 weeks after planting at 2.2 and 4.5 kg/ha, respectively. The relative degree of stunting due to trifluralin decreased as the growing season progressed. Early-season carryover injury was more severe in reduced tillage than in moldboard plow treatments in the 1983-84 Nashua experiment. Moldboard and chisel plowing reduced the concentration of trifluralin in the 0- to 7.5-cm zone of the soil profile by 62 and 31%, respectively, when compared to no-till. No yield reductions were observed at the 1.1 or 2.2 kg/ha rate of trifluralin. In 1984, grain yields were reduced by 8 and 16% at Ames and Nashua, respectively, by the 4.5 kg/ha trifluralin rate.

A Corn (Zea mays L.) Bioassay Technique for Measuring Chlorsulfuron Levels in Three Saskatchewan Soils

Chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carboxyl]benzenesulfonamide} has recently been registered for the control of several broadleaf weeds in spring wheat (Triticum aestivum L.), durum wheat (Triticum durum Desf.), and barley (Hordeum vulgare L.) in western Canada. Residue carryover of this herbicide can cause injury to subsequent sensitive crops. A bioassay technique based on growth of pregerminated corn roots was used to detect levels of chlorsulfuron as low as 0.125 ppb in three Saskatchewan soils. Confidence levels of 95% were established. These confidence bands allowed the detection of chlorsulfuron levels within a minimum and maximum variation of 3.1 and 11.5% of root development.

Persistence of Selected Insecticides in Subtropical Soil after Repeated Biweekly Applications over Two Years1

The persistence of heptachlor, triazophos, and fenvalerate in subtropical soil was studied over a 3-year period. Each insecticide was applied biweekly for 2 years to field soil and to three distinct soil types confined in wooden boxes and placed in the field. Insecticide residues in the top 15 cm soil layer were monitored from the initiation of the experiment and until 1 year after application was discontinued. Insecticide residues did not accumulate in the soil between May and October, but their concentrations increased gradually after October. High concentrations were recorded from January until April, after which they declined rapidly. No carryover of insecticide residues was noted from year to year. Precipitation and temperature appeared to influence degradation which was faster from May through October (avg precipitation 1545 mm; mean temp 28.1°C), than from November to April (avg precipitation 226 mm; mean temp 19.8°C). Soils confined in boxes had greater residue concentrations especially of heptachlor than did field soil in situ. Except for heptachlor epoxide, there was practically no movement of insecticide residues below the 0–15 cm soil layer. Application of heptachlor, triazophos and fenvalerate mixture did not result in any change in the persistence rates of individual insecticides over the rates observed when such chemicals were applied individually.