Formulation selection,and investigation of azadirachtin-A persistence in some terrestrial and aquatic components of a forest environment

Five commercial formulations of azadirachtin-A (AZ-A) Margosan-O^®, Azatin-EC^®, Neem-EC^®, RH-9999 and Neemix^® 4.5, were investigated for their volatilization and washoff potential in laboratory studies. Prior to the investigation, RH-9999 (a wettable powder) was mixed with water to provide an end-use formulation containing 35·6 g AZ-A kg^-1, while the remaining four formulations were investigated without dilution. Volatilization and washoff of AZ-A occurred more from white spruce foliage than from wax-coated glass plates. Neem-EC provided the lowest amount of loss, whereas Margosan-O provided the highest. Physical properties and atomization behaviour of the five formulations indicated that Azatin-EC was highly viscous and caused phase separation in droplets collected on glass plates after atomization in a rotary atomizer. RH-9999, despite its low viscosity, caused phase separation in droplets because of the heterogeneity of the wettable powder formulation. Based on the minimum loss of AZ-A due to volatilization and washoff from spruce foliage, and on the minimum potential for phase separation in droplets after atomization in a rotary atomizer, Neem-EC was considered to be the most appropriate choice for use in field studies to investigate environmental persistence and fate of AZ-A in terrestrial and aquatic matrices of a forest ecosystem. The Neem-EC formulation was sprayed at 40 and 80 g AI ha^-1 over single spruce trees and on litter and soil plots selected in a mixed-wood boreal forest in Ontario, Canada. In addition, outdoor aquaria containing stream water and sediment were also fortified with the formulation at 400 and 800 g AI ha^-1. Persistence of AZ-A was evaluated using one-year-old spruce needles, current-year shoots, spruce bark, litter, soil, stream water and sediment. The duration of persistence varied from 3 to 6 days in terrestrial matrices, whereas it ranged from 8 to 13 days in water, and 2 to 3 days in sediment. The half-life (DT₅₀) values ranged from 10·7 h (for soil) to 71·6 h (for spruce bark) at the lower dosage rate, and from 18·8 h (for litter) to 76·2 h (for bark) at the higher dosage rate. The DT₅₀ value for stream water was about 35 h regardless of the dosage rate applied. The data indicated that AZ-A was appreciably labile and short-lived in different forestry matrices, with low DT₅₀ values. © 1997 SCI     

Persistence and mobility of tebufenozide in forest litter and soil ecosystems under field and laboratory conditions

A field microcosm study was conducted to determine persistence of tebufenozide, an insect growth regulator, in sandy litter and soil. Litter and soil plots (c. 4·5 m² each) were sprayed with an aqueous suspension concentrate formulation of tebufenozide at rates of 35, 70 and 140 g AI ha^-1. Samples were collected at intervals up to 408 days after spraying, and analyzed for tebufenozide residues. The data were subjected to regression analysis and half-life (DT₅₀, the time required for 50% of the initial residues to disappear) values were computed. The DT₅₀ was c. 62 days for both substrates treated with the two lower dosage rates. At the highest dosage rate, the DT₅₀ was 115 days for the litter and c. 52 days for the soil, indicating irregular variations in persistence. Downward movement in soil occurred only in trace amounts, suggesting strong adsorption. Laboratory microcosm studies were conducted to investigate the relative importance of rainfall, exposure to light and volatilization on persistence. Vertical movement occurred in litter and soil (both sandy and clay types) during rainfall. The amount moved increased with the amount of rainfall, but decreased with the rain-free period. The larger the rain droplets, the greater the downward movement. When the rainwater could move laterally along the surface of the substrate (as would occur on a slope), more lateral movement than vertical movement of tebufenozide occurred. The photolysis study indicated that disappearance of tebufenozide was directly related to the duration of exposure to radiation and radiation intensity. Volatilization of tebufenozide depended upon the ambient temperature and the duration of air passing through the substrates. Nonetheless, the amount lost by volatilization was much lower than the amount lost after rainfall or exposure to radiation, thus indicating the greater influence of rainfall and sunlight on persistence. In the laboratory microcosm studies, more tebufenozide was lost from the sandy substrates than from the clay substrates. This behaviour was attributed to the greater adsorptive capacity of the clay substrates, thus providing a greater protection against downward mobility and loss due to radiation. © 1997 SCI     

Residues of diflubenzuron and two of its metabolites in a forest ecosystem after control of the pine looper moth,Bupalus piniarius L

Diflubenzuron, 1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)urea was used to control the pine looper population in about 1160 ha of Scots pine stand in eastern Finland in summer 1984. The control measure was effective, resulting in the collapse of the population in the treated area. Residues of diflubenzuron and two of its metabolites, 4-chloroaniline and 4-chlorophenylurea, were determined in water, pine needles, litter, humus, boleti and other wild mushrooms, bilberry (Vaccinium myrtillus L.) and cowberry (Vaccinium vitis-idaea L.) samples taken from this area. In water samples taken from the treated area diflubenzuron was still detected at concentrations of 0.1 μg litre^?1 2 months after application. No diflubenzuron was detected in this area the following year, nor outside the treated area. Neither metabolite was detected at any time. The sum of diflubenzuron and its metabolites in the litter layer was, on average, 0.7mg kg^?1 both 1 week and 1 month after the application. The next year, however, it had increased to 1.4 mg kg^?1. Diflubenzuron and its metabolites were not detected in the humus layer. The amount of diflubenzuron residues in the pine needles was, on average, 3.0 mg kg ^?1 1 day after the application, but in 2 months the level had decreased to 0.2-0.3 mg kg ^?1 or was not detectable. The following year the sum of diflubenzuron and its metabolites in two pine-needle samples was 0.3 and 1.6 mg kg ^?1. The sum of diflubenzuron and its metabolites in wild mushrooms was, on average, 0.07 mg kg ^?1 1 week after the application, but the following year no residues were detected. No residues were found in the boletus samples. The residues of diflubenzuron and its two metabolites in bilberries totalled, on average, 0.2 mg kg ^?1 1 day after the application, and 6 μg kg ^?1 the following year. The sum of diflubenzuron and metabolites in cowberries was, on average, 0.2 mg kg ^?1 1 month after application.     

Persistence of tebufenozide in aquatic ecosystems under laboratory and field conditions

The persistence and dissipation behaviour of tebufenozide, an ecdysone agonist, were investigated: (1) under laboratory conditions in aquatic models set up in glass aquaria, and (2) under field conditions in in-situ aquatic enclosures deployed in a mixed-wood boreal forest lake. Two models were set up in the laboratory study (Study I), which was conducted at constant conditions of temperature, water pH and photoperiod. In Model I, partitioning of tebufenozide from sediment, treated at a concentration of 1400 μg kg^-1, into untreated water was examined. The results showed that the chemical moved very little from the treated sediment into water. The concentration in sediment and water decreased gradually during the 90-day incubation period. Tebufenozide disappeared faster from the top layer of sediment than from the middle and bottom layers. The half-lives of disappearance were 64 days for the top layer but >90 days for the middle and bottom layers respectively. In Model II, partitioning from water, treated at a concentration of 350 μg litre^-1, into untreated sediment was investigated. The results showed that the chemical moved from treated water into sediment due to adsorption. Little vertical downward movement of the adsorbed residues from the top layer of sediment occurred into layers beneath. The adsorbed residues were also not released readily back into water. The concentration in water and sediment decreased gradually during the 90-day incubation period. The half-life of dissipation from water was 67 days. The field microcosm study (Study II), conducted under fluctuating conditions of temperature, water pH and photoperiod, involved application of tebufenozide onto aquatic enclosures at four concentrations of 0·05, 0·10, 0·26 and 0·5 mg litre^-1. This study also showed that the chemical moved downwards from the applied location and was adsorbed onto sediment. The chemical persisted longer in Study II than in Study I. Tebufenozide, being photo-labile, probably degraded faster after constant exposure to light in Study I than after exposure to fluctuating light in Study II. At 90 days after treatment in Study I, only about 55% of the applied material persisted in the sediment, and there was little accumulation. In Study II, the material not only persisted but also was accumulated in the sediment, since at 92 days post-treatment the residues were about 25 times higher than the applied concentration level. Residues in water also decreased more rapidly in Study I than in Study II, because the concentration at 90 days post-treatment was about 41% of the applied value. In Study II, however, about 65% of the applied chemical persisted in water at 92 days post-treatment. While the long persistence of tebufenozide in both the laboratory and field studies was attributable to its low vapour pressure, low water solubility, high octanol/water partition coefficient etc., the differences in the persistence characteristics observed in the two studies were due to the fluctuating environmental conditions and water pH encountered in the field study, compared with the constant environmental conditions and water pH utilized in the laboratory study. © 1997 SCI.     

Investigations on the metabolic fate of prochloraz in soil under field and laboratory conditions

The degradation of prochloraz in different soils was investigated in field and laboratory experiments. In laboratory degradation experiments in the dark, initial prochloraz concentrations decreased to 30–64% within 56 days, depending on temperature and soil pH. In neutral to basic soils, formation of up to 3.7% of the metabolite prochloraz-urea was observed. The rate of mineralization was strongly pH-dependent, not exceeding 3.2% in the acidic and 18.3% in the neutral to basic soils. Amounts of non-extractable residues ranged from 14 to 31%. Under field conditions, prochloraz disappeared much more rapidly with DT₅₀ values of 11–43 days. The metabolites prochloraz-formylurea and prochloraz-urea were found in significant concentrations. Laboratory experiments with fresh and sterilized soils under UV irradiation confirmed the enhancing effect of light on the formation of the primary metabolite, prochloraz-formylurea. The latter is hydrolysed to prochloraz-urea predominantly by microbial degradation. © 1999 Society of Chemical Industry     

Survival and food choice of the grey field slug (Deroceras reticulatum) on three different seed types under laboratory conditions

In Ireland, the grey field slug (Deroceras reticulatum) is the predominant slug pest species in arable crops. It can cause enormous damage, but the knowledge about its feeding biology is limited.Adult species were reared under laboratory conditions, and the survival, feeding activity, and weight change of slugs when feed on maize, peas, or wheat seeds were investigated. An especially high mortality was experienced in the wheat treatment. It was hypothesised that the high mortality was due to a Fusarium species, however, a Fusarium infection of the wheat seeds was not confirmed. The weight change of the slugs was very variable due to a high egg production of some slugs.     

Survival and food choice of the grey field slug (Deroceras reticulatum) on three different seed types under laboratory conditions

In Ireland, the grey field slug (Deroceras reticulatum) is the predominant slug pest species in arable crops. It can cause enormous damage, but the knowledge about its feeding biology is limited.Adult species were reared under laboratory conditions, and the survival, feeding activity, and weight change of slugs when feed on maize, peas, or wheat seeds were investigated. An especially high mortality was experienced in the wheat treatment. It was hypothesised that the high mortality was due to a Fusarium species, however, a Fusarium infection of the wheat seeds was not confirmed. The weight change of the slugs was very variable due to a high egg production of some slugs.A second experiment examined the food choice and feeding activity of D. reticulatum when offered a choice of the three seed types. Most of the slugs preferred to feed on a mixture of seeds, but the highest feeding activity was recorded on the pea seeds.     

The disappearance and movement of three triazine herhicides and several of their degradation products in soil under field conditions

Several degradation products of the iriazine herbicides atrazine [2-chloro-4-ethylamino-6-isapropylainino-1,3,5-triazine], cyprazine [2-chloro-4-cyclopropylamino-6-isopropylamino-1,3,5-triazine] and cyanazine [2-chloro-4-(l-cyanomethylethyl-amimo)-6-ethylamino-1,3,5-triazine] were monitored over a 3-year period in soil Trom fields under maiTC production. The soils were predominately loamy sands and sandy clay loams. HydroKy-triazines were determined semi-quanlilatively m the soil samples by gaschromalography, after methylation. Their levels ranged Trom 0.05 to 0.5 ppm. The hydroxy-triazines were the predominant triazine residues in the field during ihe spring and autumn, N-de-ethylated atrazine [2-chloro-4-amino-6-iso-propylamino-1,3,5-triazine] persisted at relatively high levels (0.015–0.02 ppm) 12 months after the application of atrazine. Greater proportions of N-de-ethylated atrazine and cyanazine II [2-chloro-4-(1-carbamoyl-1-methyleihylamino)-6-ethyl-amino-s-iriazine] than of atrazine or cyanazine were found to move through the soil profile into subsurface drainage water (1.2–1.6 m depth). Abbau und Transport von drei Triazin-Herbiziden und einiger ihrer Abbauproduk te im Boden unter Feldhedingungen Boden von Maisfeldern wurde über eine Periode von drei Jahren auf Abbauprodukte folgender Triazin-Herbizide unter-suchi: Atrazin [2-Chlor-4-äthylamino-6-isopropylatnino-1,3,5-triazin], Cyprazin [2-Chlor-4-cyclopropylamino-6-isopropyla-mino-1,3,5-(triazin) und Cyanazin [2-Chlor-4-(1-cyanoinethy-läthylamino)-6-äthylamino-1,3,5-triazin], Bei den Böden han-delie es sich hauptsächlich um lehmige Sande und sandig-tonige Lehme Hydroxy-Triazine wurden in den Bodenproben gas-chromatogruphish nach Methylierung. semi-quantitativ be-stimmt. Ihre Konzeniration im Boden betrug zwischen 0.05 und 0.5 ppm. Die Hydroxy-Triazine waren im Frähjahr und Herbst die vorherrschenden Rücksiände, N-desäthylieries Airazin [2-Chlor-4-amino-6-isopropyIamino-1,1,5-triazin] war zwölf Monate nach der Atrazin-Applikation mit relative hohen Kon-zenirationen(0.015–0.02 ppm) vorhanden. Von N-desäthylier-tem Airazin und Cyanazin II [2-Chlor-4-(1 carbamoyl-1–methy-läthylamino)-6-äthylamino-s-triazin] wurden grössere Anteile im Boden in das unterirdische Drainagewasser transportiert (1.2–1.6 m Tiefe) als es für Atrazin oder Cyanazin der Fs Swiir Disparition et migration dans le sol, au champ, de trois triazines herhicides et de plusieurs de leurs produits de dégradalion. Plusieurs produits de dégradation des triazines herbicides suivantes: atrazine (2-chloro-4-éthylamino-6-isopropylamino-1,3,5-triazine) cyprazine (2chloro-4-cyclopropylamino-6-isopropylamino-l,3,5-triazine) et cyanazine (2-chloro-4 (l-cyanométhyléthylamino)-6-éthylamino-l,3,5-triazine) ont été contrölés dans le sol. pendant une période de trois années, dans des champs de maïs en production, Les sols étaient pour la plupart sablo-limoneux et limono-argilo-sableux, Les hydroxy-triazines ont été déterminées semi-quantalivcmeni dans les échantillons de sols, par chroma tographie gazeuse aprés méthy lation, Leursconcen [rations s'étendaienlde0.05à 0.5ppm, Les hydroxy-triazines ont été les résidus les plus imporiants dans le champ au printemps et à I'aulomne, L'alrazine N-dé-éthylée [2-chloro-4-amino-6-isopropylamino-l.3.5-triazine] a persistéà des concentralions rclativemeni élevées (0.015 à 0.02 ppm) douzemois aprés l'application de l'atrazine, Il a été conslaté que des proportions d'atrazine N-dé-éthylée et de cyanazine II [2-ehloro-4(l-carbamoyl-1-méthyléthylamino)-6-éthylamino-1,3,5-triazine] plus importantes que celles de l'atrazine ou de la cyanazine, migraient à travers le profil du sol. dans la subsurface de drainage dc l'eau (1,2 à 1.6 m de profondeur).     

南疆杏麦复合类型对间作小麦产量及其构成因素的影响

对南疆杏麦复合系统3种主要复合种植模式中距杏树不同距离小麦的产量及其构成因素进行了研究与分析。结果表明,在南疆杏麦复合系统中,杏麦间作类型对小麦产量影响很大,三种主要杏麦复合种植模式中,宽幅复合种植模式(6 m×3 m6、m×4 m)对小麦产量的影响远小于窄幅复合种植模式(4 m×1.5 m)的影响。间作小麦与杏树的距离愈近,对小麦产量影响愈大,南北走向的复合种植模式,对间作麦区东边的影响远大于西边。不同复合种植模式对小麦产量构成因素的影响中,4 m×1.5 m复合种植模式对小麦穗数和千粒重的影响较大,对穗粒数影响较小;而6 m×3 m6、m×4 m两种复合种植模式对穗数和穗粒数影响最大,对千粒重的影响较小。     

Control of late blight in organic potato production: evaluation of copper-free preparations under field,growth chamber and laboratory conditions

In order to replace copper fungicides in organic potato production, 53 copper-free preparations (CFPs) based on natural compounds, including plant extracts and microorganisms, and five copper preparations were evaluated for their potential to control Phytophthora infestans, the pathogen that causes late blight of potatoes. In in vitro assays, 30% of the CFPs inhibited indirect germination of sporangia, 26% mycelial growth and in growth chamber experiments, 21% efficiently reduced foliar blight of tomato plants. In micro-plot field trials with applications twice a week, the copper preparations were the most effective and reduced foliar blight by 99%. Of the CFPs tested, Oekofluid P, Mycosin and other sulphuric clays, and C-2000 reduced late blight the most, from 63% to 37%. In small-plot trials in 2001, 2002 and 2004, 27 CFPs with different formulations and four copper preparations were examined. In 2004, copper preparations at full and reduced rates and sulphuric clays were applied either weekly or according to the decision support system Bio-PhytoPRE. With Bio-PhytoPRE, copper preparations reduced foliar blight of potatoes by 23–77% and increased tuber yield by 2–28%, depending on the copper rate applied and year. With CFPs, maximal efficacy was 17% and no effect on tuber yield was observed. In vitro and in vivo trials showed that the rainfastness and the persistence of CFPs was low compared with copper preparations. This indicates that the failure of CFPs under field conditions is probably due to a lack of stability under prevailing environmental conditions and not to a lack of efficacy. Until stable formulations for CFPs are developed, an optimised and restricted use of copper fungicides using a decision support system could help to control late blight in organic potato production and to reduce copper input into the environment.     

Lethal and sub-lethal effects of a novel sulfoximine insecticide,sulfoxaflor, against Asian citrus psyllid and its primary parasitoid under laboratory and field conditions

The Asian citrus psyllid, Diaphorina citri Kuwayama, is the most important international pest of citrus because it transmits the bacteria that cause huanglongbing (HLB). HLB limits citrus production globally. We evaluated the toxicity of sulfoxalor against D. citri and its parasitoid, Tamarixia radiata Waterston. Sulfoxaflor was as toxic as imidacloprid to adult D. citri. The LC₅₀ values for sulfoxaflor and imidacloprid were 8.17 and 5.7 µg AI mL^?1, respectively. The LC₅₀ of sulfoxaflor for T. radiata adults was 3.3 times greater than for D. citri adults. Treatment with sulfoxaflor resulted in reduced oviposition, development of nymphs, and emergence of adult D. citri on plants, as compared with controls. The lowest concentration that reduced adult emergence was 0.6 µg AI mL^?1. There was reduced feeding by D. citri adults on leaves treated with sulfoxaflor. The residual toxicity of sulfoxaflor was equivalent to imidacloprid. Under field conditions, formulated sulfoxaflor reduced populations of D. citri compared with untreated controls. Sulfoxaflor is a novel mode of action and is an effective tool for D. citri management.     

Repellency of a kaolin particle film to potato psyllid, Bactericera cockerelli (Hemiptera: Psyllidae), on tomato under laboratory and field conditions

BACKGROUND: The potato psyllid, Bactericera cockerelli, is a vector of Candidatus Liberibacter solanacearum, causing several diseases in solanaceous crops. Laboratory and field no‐choice and choice experiments were conducted to evaluate the repellency of kaolin particle film on adults of B. cockerelli on tomato plants that had been sprayed with kaolin particle film on the upper surface only, on the lower surface only and on both leaf surfaces. RESULTS: In no‐choice tests in the laboratory, the numbers of adults on leaves were not different between the kaolin particle film and the water control, regardless of which leaf surface(s) were treated, but numbers of eggs were lower on the leaves treated with kaolin particle film than on those treated with water. In choice tests on plants treated with water/plants treated with kaolin particle film at ratios of 1:1, 6:3 or 8:1, fewer adults and eggs were found on the leaves treated with kaolin particle film than on leaves treated with water. Under field conditions, in caged no‐choice or choice tests, fewer adults, eggs and nymphs were found on plants treated with kaolin particle film than on plants treated with water. In an uncaged test under field conditions, plants sprayed with kaolin particle film had fewer psyllids than those sprayed with water. CONCLUSION: Even though potato psyllid adults could land on plants treated with kaolin particle film when no choice was given, fewer eggs were laid. When given a choice, the psyllids avoided plants treated with kaolin particle film under laboratory and field conditions. Kaolin particle film treatment may be a useful alternative for management of potato psyllids under field conditions. Copyright © 2011 Society of Chemical Industry     

Resistance to Pseudomonas syringae in a collection of pea germplasm under field and controlled conditions

A total of 242 Pisum accessions were screened for resistance to Pseudomonas syringae pv. pisi under controlled conditions. Resistance was found to all races, including race 6 and the recently described race 8. Fifty‐eight accessions were further tested for resistance to P. syringae pv. syringae under controlled conditions, with some highly resistant accessions identified. Finally, a set of 41 accessions were evaluated for resistance to P. syringae pv. pisi and pv. syringae under spring‐ and winter‐sowing field conditions. R2, R3 and R4 race‐specific resistance genes to P. syringae pv. pisi protected pea plants in the field. Resistance sources to race 6 identified under controlled conditions were ineffective in the field. Frost effects were also evaluated in relation to disease response. Results strongly suggest that frost tolerance is effective in lowering the disease effects caused by P. syringae pv. pisi and pv. syringae under frost‐stress conditions, even in the absence of disease resistance genes, although the highest degree of this protection is reached when frost tolerance and disease‐resistance genes are combined in the same genetic background.     

Fumigant distribution in forest nursery soils under water seal and plastic film after application of dazomet, metam-sodium and chloropicrin

Adequate concentration, exposure time and distribution uniformity of activated fumigant gases are prerequisites for successful soil fumigation. Field experiments were conducted to evaluate gas phase distributions of methyl isothiocyanate (MITC) and chloropicrin (CP) in two forest-tree nurseries. Concentrations of MITC and CP in soil air were measured from replicated microplots that received dazomet, metam-sodium and CP. Half of the plots were covered with high-density polyethylene tarp immediately after fumigation; the other half were not covered but received daily sprinkler irrigation for 1 week to create and maintain a water seal. The magnitude of MITC concentrations was similar between nurseries for metam-sodium in both tarp and water seal treatments and for dazomet in the tarp treatment. Consistently greater MITC and CP concentrations were found in the upper 30 cm of soil in the tarped plots compared with the water-sealed plots. Despite potential environmental and economic benefits with the water seal method, tarp covers were more reliable for achieving and maintaining higher MITC and CP concentrations and less prone to variations due to irrigation/rain, soil bulk density and other environmental conditions.     

Distribution and persistence of emamectin benzoate at efficacious concentrations in pine tissues after injection of a liquid formulation

In an earlier paper the authors reported the creation of a novel emamectin benzoate 40 g litre(-1) liquid formulation (Shot Wan Liquid Formulation). The injection of this formulation exerted a preventative effect against the pine wilt disease caused by the pine wood nematode, Bursaphelenchus xylophilus (Steiner & Buhrer) Nickle, and this effect lasted for at least 3 years. The present study was carried out to show experimentally that the marked effect of this formulation was due to the presence and persistence in pine tissues of sufficient amounts of emamectin benzoate to inhibit nematode propagation. A cleanup procedure prior to quantitative analysis of emamectin benzoate by fluorescence HPLC was devised. The presence of the compound in concentrations sufficient to inhibit nematode propagation in the shoots of current growth and its persistence for 3 years explained the marked preventative effect. Non-distribution of emamectin benzoate in some parts of the lower trunk suggested that the formulation should be injected at several points for large trees in order to distribute the compound uniformly to lower branches.     

Persistence and binding of DDT and gamma-HCH in a sandy loam soil under field conditions in Delhi,India

Persistence and binding capacity of [¹⁴C]p, p′-DDT and [¹⁴C]y-HCH were studied for one year in a sandy loam soil of Delhi, India, after surface treatment during monsoon, winter and summer seasons under field conditions. Both DDT and HCH dissipated more rapidly under the Indian subtropical climate than reported for temperate regions. In all three seasons, both insecticides dissipated most rapidly during the initial 60 days. However, in the final six months there was very little change in the residue levels. After one year, the final soil burden of DDT varied from 33 to 36% and of HCH from 14 to 15% of the initial concentrations in the different experiments. HCH bound more with the soil as, out of the total residues present after one year, more than 75% of HCH was in bound form compared with only 24% of DDT. The observed time for 50% initial dissipation of DDT ranged from 60 to 120 days, while in the case of HCH it varied from 30 to 45 days. However, the rate of loss of residues which persisted for more than 6 months was equivalent to a half-life of between 500 and 10000 days for DDT, and between 700 and 2000 days for HCH, thus illustrating the very long persistence of aged residues. Since degradation of both insecticides was apparently minimal, the data indicate that dissipation of DDT and HCH was largely due to volatilisation.     

Control of Tobacco mosaic virus by PopW as a result of induced resistance in tobacco under greenhouse and field conditions

In a previous study, we isolated a new harpin protein, PopW, from the bacterium Ralstonia solanacearum ZJ3721 that can induce a hypersensitive response in tobacco, Nicotiana tabacum, leaves. In the current study, we demonstrate that, in a greenhouse experiment, PopW induced tobacco-acquired resistance against the Tobacco mosaic virus (TMV) with a biocontrol efficacy of 80.9 to 97.4% at a concentration as low as 25 μg/ml in both PopW-treated and neighboring leaves. The resistance induced by PopW is systemic acquired resistance mediated by salicylic acid, which was certified by the development of resistance being accompanied by the expression of the pathogenesis-related-1 gene (PR1) 8 h after PopW was sprayed onto the tobacco leaves. In addition, hydrogen peroxide began to accumulate 10 h after PopW spraying, peaking at 24 h with a maximum concentration of 1.97 μM/g fresh weight. The activities of phenylalanine ammonia lyase (EC4.3.1.5), polyphenoloxidase (EC1.14.18.1), and peroxidase (EC1.11.1.7) also increased, peaking at different times in the PopW-treated tobacco leaves. PopW also reduced the level of TMV disease in field trials with a biocontrol efficacy of 45.2%. Furthermore, PopW both increased tobacco yield (by 30.4 more than in control plants) and improved tobacco foliar quality, with an increase of 50.2% in the number of first-class tobacco leaves from treated compared with untreated plants. All of these results indicate that the new harpin protein PopW has the potential to be an effective biocontrol agent against TMV in tobacco.     

Virus impact at the interface of an ancient ecosystem and a recent agroecosystem: studies on three legume-infecting potyviruses in the southwest Australian floristic region

The southwest Australian floristic region (SWAFR) is an internationally recognized 'hot spot' of global biodiversity and has an endangered flora. It represents a unique interface between an ancient ecosystem and a recent agroecosystem, providing the opportunity to investigate encounters where the recipient of the virus is an introduced crop and the donor a native plant and vice versa. Phylogenetic analysis of the virus coat-protein genes was used to study isolates of three potyviruses representing different 'new encounter' scenarios at this interface. The incidence, symptomatology, host range, non-persistent aphid transmission and considerable genetic diversity of the first indigenous virus described from the SWAFR, where it infects the native legume Hardenbergia comptoniana , and its potential to damage lupin, a locally important, newly introduced cultivated grain legume, was studied. The name Hardenbergia mosaic virus is proposed for this virus. Two other examples of 'new encounter' scenarios involving other legume-infecting potyviruses studied were: Passion fruit woodiness virus , which has been found only in Australasia, where it damages recently introduced species of Passiflora and legumes; and Bean yellow mosaic virus, which is not indigenous to Australia and was introduced recently to the SWAFR, where it infects a number of introduced legumes, but also damages the local native legume Kennedia prostrata . Isolates of the former had considerable genetic diversity consistent with the virus being indigenous, while isolates of the latter virus from K. prostrata had a low genetic diversity consistent with recent arrival. This research illustrates how introduced viruses can damage indigenous plants and indigenous viruses can damage introduced cultivated plants within this unique ecosystem, and how human activities can facilitate damaging 'new encounters' between plants and viruses.     

Performance of three endophytic actinomycetes in relation to plant growth promotion and biological control of <Emphasis Type="Italic">Pythium aphanidermatum</Emphasis>, a pathogen of cucumber under commercial field production conditions in the United Arab Emirates

In the current study, the performance of three endophytic actinomycetes identified as Actinoplanes campanulatus, Micromonospora chalcea and Streptomyces spiralis previously shown to reduce seedling damping-off, and root and crown rots of mature cucumber (Cucumis sativus) caused by Pythium aphanidermatum in pots under greenhouse conditions were further evaluated to determine their potential as biological control agents and as plant growth promoters in the field under the conditions of commercial production of cucumbers in the United Arab Emirates (UAE). When applied individually or in combination to cucumber seedlings, the three isolates significantly promoted plant growth and yield and reduced seedling damping-off and root and crown rots of mature cucumber plants. Individually the performance level of S. spiralis was relatively the best followed by A. campanulatus and then by M. chalcea. The three isolates (which were not inhibitory to each other) performed better, both as biological control agents as well as plant growth promoters, when applied together than when they were inoculated individually. The ability of these three isolates to colonize the internal tissues of roots, stems and leaves under field conditions, and to persist up to 8 weeks after seedling inoculation, showed that they can easily adapt to an endophytic habit systemically within healthy cucumber plants. As the three endophytic actinomycete isolates also colonized the rhizosphere and showed outstanding rhizosphere competency it is clear that they are facultative and not obligate endophytes. The success with the three inoculants indicated that they could well be used in place of the fungicide metalaxyl which is currently recommended for the management of Pythium diseases in the UAE. This is the first successful field use of endophytic actinomycetes as promising plant growth promoters and biological control agents against Pythium diseases of cucumber.