Persistence and biodegradation of vinclozolin in tropical rice soils

The persistence of vinclozolin in three tropical rice soils, widely varying in their physicochemical characteristics, was compared under both non-flooded and flooded conditions. Degradation of the fungicide was more rapid in all the soils under flooded conditions than under non-flooded conditions. Kinetic analysis indicated that the degradation of the fungicide followed a first-order reaction irrespective of soil or water regime. Soil acidity and salinity significantly affected the persistence of the fungicide under non-flooded conditions. The degradation of the dicarboxymide fungicide was enhanced following repeated applications to an alluvial soil under both water regimes, with the enhancement being more marked under flooded conditions. Faster degradation of vinclozolin in mineral salts medium inoculated with non-sterile suspension from retreated alluvial soil indicates the involvement of micro-organisms. 3,5-Dichloroaniline was detected as a metabolite in the degradation of the fungicide in both soil and mineral salts medium. © 1999 Society of Chemical Industry     

Quantitative structure-activity study of herbicidal N-aryl-3,4,5,6-tetrahydrophthalimides and related cyclic imides

The quantitative relationship between structure and inhibitory activity against the root growth of sawa millet of 30 N-aryl-3,4,5,6-tetrahydrophthalimides and 88 related N-aryl cyclic imide compounds (3-aryl-1,5-tetramethylenehydantoins, 4-aryl-1,2-tetramethylenetriazolidine-3,5-diones, and their thiocarbonyl analogs) was analyzed by means of physicochemical parameters of the aryl substituents and regression analysis. The results showed that, in each series of these classes of compounds, the position-specific steric effects of aromatic substituents, as represented by Verloop's STERIMOL values, are highly important in determining the inhibitory potency of the compound.     

Availability and biodegradation of metribuzin in alluvial soils as affected by temperature and soil properties

Herbicide degradation in soils is highly temperature‐dependent. Laboratory incubations and field experiments are usually conducted with soils from the temperate climatic zone. Few data are available for cold conditions and the validation of approaches to correct the degradation rate at low temperatures representative of Nordic environments is scarce. Laboratory incubation studies were conducted at 5, 15 and 28°C to compare the influence of temperature on the dissipation of metribuzin in silt/sandy loam soils in southern and northern Norway and in a sandy loam soil under temperate climate in France. Using ¹⁴C‐labelled metribuzin, sorption and biodegradation were studied over an incubation period of 49 days. Metribuzin mineralisation and total soil organic carbon mineralisation rates showed a positive temperature response in all soils. Metribuzin mineralisation was low, but metabolites were formed and their abundance depended on temperature conditions. The rate of dissipation of ¹⁴C‐metribuzin from soil pore water was strongly dependent on temperature. In Nordic soils with low organic content, metribuzin sorption is rather weak and biodegradation is the most important process controlling its mobility and persistence.     

Measured and computed concentration patterns of propyzamide in field soils

The persistence of propyzamide in soil was studied by analysing soil samples taken at intervals two or three times after application in the spring to experimental fields. Single samples were taken from other fields. 8 to 12 months after autumn application. The concentrations were measured by electron-capture gas chromatography. Persistence is expressed in first-order dissipation rate constants and half-life values. Data were measured and collected on the adsorption of propyzamide on soils, the soil characteristics and the weather conditions. Computations of the mobility of propyzamide in soil were carried out for simplified systems. Results of measurements and computations are compared.     

Further characterization of field resistance in lettuce to Bremia lactucae (downy mildew)

The development of five Bremia lactucae isolates on the field-resistant crisphead lettuce cultivar Iceberg was compared under field conditions with that on the more susceptible crisphead cultivar Ithaca. With each of five isolates, the epidemic developed more rapidly on Ithaca than Iceberg; lesions on Ithaca were more numerous, larger and sporulated more profusely than on Iceberg. There was no evidence for adaptation of isolates to Iceberg, which provides some additional evidence that the resistance of this cultivar could be non-differential (horizontal). There was, however, evidence of non-specific differences between isolates in their quantitative virulence.     

Partial characterization of phytoplasmas associated with lettuce and wild lettuce phyllodies in Iran

Phytoplasmas associated with lettuce phyllody (LP) and wild lettuce phyllody (WLP) in southern Iran were partially characterized by molecular analyses and host-range studies. Agents of both diseases were transmitted by Neoaliturus fenestratus , a leafhopper colonizing lettuce and wild lettuce, to lettuce, wild lettuce, sowthistle and periwinkle, but not to safflower, sunflower, calendula and sesame. Both phytoplasmas induced bud proliferation, virescence, phyllody and witches' broom in infected plants. Total DNA extracted from infected lettuce and wild lettuce or from vector tissues was subjected to PCR using phytoplasma-specific primer pair P1/P7 or nested PCR using P1/P7 followed by R16F2n/R16R2. PCR product of nested PCR (1·2 kbp) was subjected to restriction fragment length polymorphism (RFLP). RFLP analysis of nested PCR product identified the LP, WLP and N. fenestratus -associated phytoplasmas as members of the pigeon pea witches' broom group, 16SrIX. Phylogenetic analysis of the 16S rRNA gene sequence also clustered LP and WLP phytoplasmas with other known members of the 16SrIX group. While no significant differences could be detected between LP and WLP phytoplasmas, both isolates differed from Lebanese wild lettuce phyllody in molecular properties.     

Leaching potential and decomposition of fluroxypyr in Swedish soils under field conditions

The mobility and decomposition of the herbicide fluroxypyr (4-amino-3,5-dichloro-6-fluoro-2-pyridyloxyacetic acid) was studied under field conditions in a sandy soil and a clay soil. Leachate was collected in lysimeters with undisturbed soil (sand) and in tile-drained plots (clay). Soil samples to a depth of one metre were also collected in both soils to characterize the temporal depth distribution of fluroxypyr in the profiles. The herbicide was applied as the I-methylheptyl ester of fluroxypyr at two rates, 187.5 and 375.0 g a.e. ha^?1, representing the normal and double the dose of the compound used for spring cereals. Some lysimeters received supplementary watering. Only two leachate samples (one from each soil) had concentrations of fluroxypyr above the detection limit (1 μg litre^?1), i.e. 2 and 5 μg litre^?1. Both samples were collected within two months after application, when less than 2 mm of drainage had been collected. The methylheptyl ester of fluroxypyr was not found in any of the samples. Fluroxypyr levels above the detection limit in soil (5 μg kg^?1 dry soil), were never found below the topsoil (0.2 m) in the clay profile, while, in the sandy profile, levels just above the detection limit were found occasionally in deeper soil layers. Concentrations were reduced to undetectable or very low levels within three months after spraying.     

Residues of pesticide co-formulants in lettuce and parsley: Identification of decline processes using field trials in different cropping systems

BACKGROUND

Although co-formulants constitute a substantial portion of the total plant protection product (PPP) mass applied to crops, data on residue formation and the behaviour of these substances on plants are scarce. In an earlier study we demonstrated that co-formulants commonly used in PPPs can form considerable residues, i.e., in the low to medium mg/kg range, but normally decline rapidly within few days. In the field trial reported here, we aimed to identify the major decline processes of co-formulants. Residues of co-formulants were therefore monitored in parsley and lettuce grown in an open field as well as under foil tunnels equipped with either an overhead or a drip irrigation system.

RESULTS

Dissipation of three anionic surfactants was markedly faster when crops (parsley and lettuce) were exposed to natural rainfall or irrigation from above compared to drip irrigation. In contrast, the decline of three volatile organic solvents was not affected by rain or irrigation, but was dependent on the crop, with much shorter half-lives in lettuce than in parsley. Furthermore, dilution through plant growth contributed significantly to the reduction of residues over time.

CONCLUSION

In this work we substantiate earlier findings on the magnitude and dissipation of residues of anionic surfactants and solvents representing the most important co-formulant classes. The chosen experimental setup allowed differentiation between decline processes and we confirm that foliar wash-off is a major dissipation process for anionic surfactants. For volatile organic solvents, dissipation appears to depend on the properties not only of the substance but also of the plant (surface). © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Variation in the early development of Bremia lactucae on lettuce cultivars with different levels of field resistance

The early stages of development of Bremia lactucae (lettuce downy mildew) were examined on lettuce cultivars possessing high (Iceberg and Regina di Maggio) and low (Great Lakes and Plenos) levels of field resistance. Germ tubes, appressoria, penetration, primary and secondary vesicles, intercellular hyphae and haustoria were observed 3. 6 and 24 h after inoculation of cotyledons and of leaf discs from adult plants. Differences were observed between cv. Iceberg and susceptible genotypes in the percentage of spores germinating and the incidence and speed of development of infection structures. Secondary vesicles were first observed 24 h and 6 h after inoculation in Iceberg and susceptible genotypes, respectively. The lowest incidence of secondary vesicle formation 24 h after inoculation (48 and/or 43%) was recorded in Iceberg and Regina di Maggio, and the highest incidence (68%) occurred in Plenos. The formation of intercellular hyphae and haustoria was not observed in cv. Iceberg some 24 h after inoculation. There were significant differences in the lengths of germ tubes formed on different cultivars. Those on cv. Iceberg were longer than those formed on susceptible cultivars. The results indicate that the field resistance of B. lactucae may result from mechanisms which are effective in the early stages of infection.     

Field effectiveness of fosetyl-AI against citrus foot rot and brown rot1

The effectiveness of fosetyl-A1 against citrus foot rot caused by Phytophthora citrophthora has been evaluated in a 25-year-old orchard of sweet orange cv. Tarocco, showing severe symptoms of the disease and in a 10-year-old orchard of the clementine-type mandarin cv. Monreal, apparently healthy. All the trees were grafted on sour orange. In both orchards, three sprays at 200 g a.i. per 100 1 were applied in May, July and September for 3 years. The results were evaluated on the basis of yield and fruit quality. Trees of cv. Tarocco had yield increased by 25–44% whereas cv. Monreal yielded 3–16% higher than the unsprayed trees. Fruits of orange cv. Tarocco were collected from trees sprayed with fosetyl-A1 and plunged in a water suspension of P. citrophthora. Fruits treated 11 days before inoculation showed an infection rate of 8.7%) whereas those unsprayed were 77% infected. Fruits inoculated 21 days after the treatment with fosetyl-A1 were 32% infected whereas those unsprayed were 91%, infected. In other trials, trees of volkamer lemon were sprayed with a conidial and mycelial suspension of P. citrophthora at different times after application of fosetyl-A1. The number of infected fruits and leaves in the unsprayed trees was very high (up to total leaf drop) and decreased sharply with the number of sprays (1 to 3).     

小麦植株和麦田土壤莠去津残留气相色谱分析方法研究

本研究确立了乙腈振荡提取、弗罗里硅土SPE小柱净化小麦植株和麦田土壤中莠去津残留样本的前处理方法,建立了柱程序升温、GC-NPD残留样品检测方法.结果表明,优化色谱条件下,莠去津的色谱保留时间为5.97 min,在0.105～54.0 mg/L浓度范围内,莠去津浓度与其色谱峰面积在GC-NPD上线性响应良好,回归方程为Y=38.79X-120.34(R2=0.998 8).莠去津在小麦植株和麦田土壤中0.05～1mg/kg的3个水平的加标回收率均大于75％,各添加水平3次平行测定值的RSD均小于7％.其准确度和精密度均符合农药残留分析的要求.该色谱条件下仪器的最低检出量为0.38 ng,方法的最低检出浓度为0.018 mg/kg(植株)和0.021 mg/kg(麦田土壤),此检测灵敏度可以满足该农药在小麦植株和麦田土壤中残留的定量检测要求.     

Mobility and persistence of isazofos in granular and microencapsulated formulations in two soils,using field lysimeters

Field lysimeters were used to assess the mobility and persistence of microencapsulated and granular formulations of the soil insecticide, isazofos, in Plainfield sand, and the microencapsulated formulation in Vittoria loam soil, using two moisture regimes, rainfall and supplementary watering. Mobility and persistence comparisons were made with an earlier lysimeter study which used emulsifiable concentrate (EC) and granular formulations of isazofos in Plainfield sand. Isazofos mobility in Plainfield sand increased in the following order for the tested formulations: microencapsulated < granular ≦ EC. Atrazine, which was applied as a suspension concentrate to all lysimeters as an internal reference, appeared to exhibit retarded disappearance rates during initial stages of the study when in the presence of granular isazofos in the rainfall treatment. The degradation of isazofos was faster in Vittoria loam than in Plainfield sand for the microencapsulated formulation in the field lysimeters (only formulation tested), and for all three formulations in a laboratory study.     

花生植株、籽粒及田间土壤氟磺胺草醚残留分析方法研究

在前人研究基础上, 确立了花生植株以甲醇、乙二胺-N-丙基硅烷（PSA）和石墨化炭黑（GCB）为基质分散萃取材料, 花生籽粒和田间土壤分别以酸化甲醇和乙腈为分散萃取溶剂, 以PSA为基质净化材料的3类氟磺胺草醚残留样品前处理程序, 建立并优化了花生籽粒、花生植株和田间土壤氟磺胺草醚残留高效液相色谱检测方法。结果显示, 氟磺胺草醚在0.05~10.0 mg/L质量浓度范围内与对应色谱峰积分面积线性响应良好, 回归方程为 y =2.562 8x -0. 006 8（r 2=0.999 8）。在0.05 ~0.5 mg/kg氟磺胺草醚添加范围内, 花生籽粒、植株和田间土壤中的平均回收率为85.6%~113.5%, 相对标准偏差为1.5%~9.7%。花生植株、籽粒和田间土壤中氟磺胺草醚的检出限分别为0.024、0.029和0.031 mg/kg。基质效应试验结果表明, 该样品前处理方法获得的分析样品基质效应不明显, 表明该残留样本前处理方法和样品检测方法简便、高效、经济、可靠, 可满足氟磺胺草醚在花生植株、籽粒及田间土壤中残留的定量检测要求。     

Influence of organic carbon on reductive dechlorination of thiobencarb in California rice field soils

The herbicide thiobencarb is suspected of causing delayed phytotoxicity syndrome (DPS) in rice plants. While the ultimate agent appears to be its dechlorinated product (deschlorothiobencarb), the influence of organic carbon on the formation of deschlorothiobencarb in California rice field soils has not been investigated. Thus, two different soils were compared for their ability to reductively dechlorinate thiobencarb with carbon augmentation: one from the eastern Sacramento Valley, which has historically displayed DPS, and one from the western Sacramento Valley, which has not. Rice straw was homogenized into samples of each soil to produce 0, 0.33 or 2% organic carbon augmentation. During 90-days of anoxic incubation, substantial deschlorothiobencarb production was measured in both soil types. However, only the thiobencarb degradation rate in the eastern valley soil was positively correlated with carbon content. Thus, other characteristics of DPS-resistant soils may limit deschlorothiobencarb formation.     

Interaction between phyllosphere yeasts, aphid honeydew and fungicide effectiveness in wheat under field conditions

Aphid honeydew can reduce fungicide effectiveness against necrotrophic pathogens of wheat under controlled conditions. In 1988 and 1989, field experiments were carried out at different locations in The Netherlands, to assess the interference of honeydew with fungicide effectiveness under field conditions, and to establish whether honeydew consumption by naturally occurring saprophytes could prevent this effect. Different combinations of chemicals were used to create differences in saprophytic population densities and aphid populations, which were expected to result in differences in the amount of honeydew and other nutrients on the leaves. In two of the experiments, Septoria nodorum was the only necrotrophic pathogen present; in the other two the only necrotroph was S. tritici . On several sampling dates, the effect of the fungicides was significantly enhanced by addition of insecticide, most often when the saprophytes were reduced by maneb/anilazine. This effect of insecticide is ascribed to prevention of interference of honeydew with fungicide activity, and not to a direct effect of insecticide, as insecticide alone had no effect on necrosis. On the basis of the fact that interference of honeydew with fungicide activity was most apparent when saprophytic population densities were reduced, it is concluded that the naturally occurring saprophytes can generally prevent the effect of honeydew. The same interactions are likely to occur between other nutrients and fungicides, and it is therefore argued that the naturally occurring saprophytes should be protected by elimination of harmful chemicals.     

Comparison of solvent systems for extracting herbicide residues from weathered field soils

The extraction from several field soils of the four herbicides benzoylprop-ethyl, nitrofen, profluralin, and tri-allate applied at least 6 months previously was compared using six solvent systems. The residues extracted were quantified using gas chromatographic techniques. Similar recoveries were achieved using 30% aqueous acetonitrile or acetonitrile + water + glacial acetic acid mixtures. The presence of the acetic acid was found to increase residues extracted only in the case of tri-allate. Methanol and 10% aqueous acetonitrile were slightly less efficient in recovering residues from the weathered field soils whereas acetone tended to be a poor solvent for the extraction of the chemicals studied.     

Studies on resistance to beet western yellows virus in lettuce (Lactuca sativa) and the occurrence of field sources of the virus

An effective method based on glasshouse and field procedures was developed for screening commercial cultivars and other lettuce types for resistance to beet western yellows virus (BWYV). Field experiments in 1985, 1986 and 1987 showed that lettuce cultivars varied in their reaction to BWYV, but no high levels of resistance were identified in the main commercial types. Crisp types generally showed milder symptoms than butterhead or cos types, but individual butterhead cultivars were identified with resistance equal to the best crisp types. The highest levels of resistance were identified in Batavian type cultivars and extreme resistance or possible immunity was found in Lactuca perennis and L. muralis . BWYV caused yield reductions in some cultivars as high as 63% and reduced maturation by up to 38%, in others. There was no correlation between chlorotic leaf symptom severity and yield reduction.
BWYV was isolated from a range of weed and non-lettuce host species growing near affected lettuce crops. Isolates of BWYV obtained from infected lettuce and brassicas appeared to be similar. They infected sugar beet with difficulty but caused no symptoms, and could only be detected by ELISA serology.     

Occurrence of Polyscytalum pustulans, Phoma foveata and Fusarium solani var. coemleum in field soils in Scotland

The effectiveness of various methods for detecting three fungal potato pathogens was compared with artificially infested soil, naturally infested tuber-borne soil and field soil. In the spring of 1985 and 1986 field soils from 30 farms in north-east Scotland were sampled just before planting a seed potato crop and 6 months after harvesting such a crop. The minimum statutory gap between crops is 5 years. Polyscytalum pustulans was recovered from 32 out of 60 field soil samples taken 6 months after harvest while from fields sampled in the spring before a potato crop was planted the fungus was isolated from 10 out of 30 soils in 1985 and five out of 30 in 1986. Phoma foveata was isolated from only one out of 60 pre-planting soil samples but Fusarium solani var. coeruleum was recovered from eight of these soils.
Microplant bait plants were grown over 3 years at an experimental farm near Edinburgh in various fields at different intervals after a previous potato crop. Contamination by P . pustulans was not related to interval after potatoes between 1 - 7 years. No contamination was recorded in fields where potatoes had not been grown for more than 30 years.     

吡虫啉在生菜中的吸收迁移及转化行为

为了探究吡虫啉在植物中的吸收转运规律,本研究选择生菜为研究对象,将其在含有1 mg/kg吡虫啉的水培液中持续暴露120 h,利用超高效液相色谱-三重四极杆质谱检测吡虫啉及其5种代谢物在生菜不同部位动态吸收变化和转运分布规律.结果表明,吡虫啉在叶部富集程度明显高于根部,当达到吸收稳定状态时,吡虫啉在叶部富集程度约为根部的...