The metabolism of [14C]aldicarb in the root of sugar beet plants

Sugar beet plants were grown in the field, after in-furrow application of [¹⁴C]- aldicarb (3 kg of aldicarb ha^?1) at planting. The ripe sugar beet plants were harvested, and the roots were analysed. The roots were fractionated according to a procedure similar to the normal beet-sugar manufacturing process. Expressed as a proportion of the total radioactivity incorporated into the root, the pulp contained 29.7%, the lime cake 9.7%, the crystallised sugar 17.7% (which gave, with the radioactivity found in the sugar in the molasses, a total of 20.7% of the radioactivity in the total sugar), and the molasses, 42.9%. A part of the labelled carbon from the radio- active aldicarb and its metabolites had thus been metabolised and incorporated into sugar molecules. Except for the radioactivity in the sugar and in the lime cake from the processing, the proportion of radioactive non-conjugated organosoluble compounds was very low (2.6%), and perhaps partially corresponded to the very low amount of aldoxycarb (aldicarb sulphone) in the root (less than 0.001 mg of [¹⁴C]-aldicarb equivalents kg^?1 fresh weight). Hydrolysis of the molasses yielded free radioactive 2-methyl-2-(methylsulphinyl)propan-1-ol (3.1%), 2-mesyl-2-methyl-propan-I-ol (8.9%) and 2-mesyl-2-methylpropionic acid (12.0%) which had been conjugated to plant constituents in the root. The corresponding concentrations (expressed as mg of [¹⁴C]aldicarb equivalents kg^?1 fresh weight of root) were 0.004, 0.011, and 0.016, respectively. No aldicarb, aldicarb sulphoxide or aldoxycarb (nor the corresponding nitrile, generated from aldicarb during the fractionation procedure) was liberated by the hydrolysis, indicating the absence of conjugates of these compounds in the root.     

The metabolism of [14C]aldicarb in the leaves of sugar beet plants

Sugar beet plants were grown in the field, after in-furrow application of [¹⁴C]aldicarb (3 kg of aldicarb ha^?1) at planting. The ripe sugar beet plants were harvested, and the blades and petioles of the leaves were analysed separately. In the whole leaves, 15% of the ¹⁴C (all the percentages of ¹⁴C are relative to the total ¹⁴C incorporated into the whole leaves) was insoluble in ethanol+ water (1+1 by volume), 31% was organo-soluble (and thus unconjugated in the leaves), and 54% was water-soluble (mainly conjugated to plant constituents). The weights and concentrations (as aldicarb equivalents) of various identified metabolites of aldicarb, incorporated into the leaves, were determined; no aldicarb, as such, was detected.     

Distribution of the radioactivity in sugar beet plants treated with [14C]aldicarb

Sugar beet plants were grown in the field, after in-furrow application of [¹⁴C]aldicarb (3 kg of aldicarb ha^?1) at planting. Some plants (the growing plants) were harvested 99 days after sowing and the rest (the ripe plants) 196 days after sowing. The percentages of the weights of [¹⁴C]aldicarb equivalents (the total aldicarb plus aldicarb sulphoxide and sulphone, plus all the other metabolites of [¹⁴C]aldicarb which contain ¹⁴C, expressed as aldicarb equivalents) incorporated into the beet plants, relative to the weight applied to the soil, were 2.8 and 1.8, respectively for the growing and ripe plants. The concentrations of [¹⁴C]aldicarb equivalents (mg kg^?1 fresh weight) in the growing and ripe plants, respectively were: blades of the external leaves, 3.16 and 0.93; blades of the internal leaves, 0.63 and 0.68; petioles of the external leaves, 0.51 and 0.26; petioles of the internal leaves, 0.15 and 0.05; crowns, 0.14 and 0.15; roots, 0.16 and 0.13. The proportions of the extractable aldicarb plus aldicarb sulphoxide and aldicarb sulphone determined by gas-liquid chromatography (expressed as aldicarb equivalents) relative to [¹⁴C]aldicarb equivalents, in the external and internal leaf blades of the growing beets, were 56 and 60%, respectively; these values declined to 25 and 19%, respectively in the ripe plants. The proportion was 21 % or less in all other parts of the growing and ripe plants.     

Disease risk assessment of sugar beet root rot using quantitative real-time PCR analysis of <Emphasis Type="Italic">Aphanomyces cochlioides</Emphasis> in naturally infested soil samples

Sugar beet root rot, caused by the oomycete Aphanomyces cochlioides, is a serious and economically important disease of sugar beets world-wide. Today, disease risk assessment consists of a time-consuming greenhouse bioassay using bait plants. In the present study, a real-time quantitative PCR (qPCR) assay for determination of A. cochlioides DNA in field-infested soil samples was developed and validated using the standard bioassay. The qPCR assay proved to be species-specific and was optimized to give high amplification efficiency suitable for target copy quantification. A high correlation (R² > 0.98, p < 0.001) with pathogen inoculum density was shown, demonstrating the suitability for monitoring soil samples. The limit of detection (LOD) was evaluated in several different soil types and varied between 1 and 50 oospores/g soil, depending on clay content. Soils with a high LOD were characterised as having a low clay content and high content of sand. Varying levels of the A. cochlioides target sequence were detected in 20 of the 61 naturally infested soil samples. Discrepancies between the bioassay and the qPCR assay were found in soils from low- and medium-risk fields. However, the qPCR diagnostic assay provides a potentially valuable new tool in disease risk assessment, enabling sugar beet growers to identify high-risk fields.     

Uptake and residues of aldicarb in sugarbeet leaves

The breakdown of aldicarb and its oxidation products (the sulphoxide and the sulphone, aldoxycarb), under field conditions in 1976, were studied on three different types of soil (a sandy loam, a silt loam and a sandy clay loam that were normally cropped with sugarbeet). Residues were determined in leaves, stems, roots and soil, and related to aphid counts. Higher doses were needed on heavy soils in order to obtain a sufficient concentration in the leaves and thus provide an efficient treatment for aphid control. Weather conditions, especially rainfall, also affected the residue content. At harvest, the sugar beet tops used for fodder can contain residues which vary widely, depending on dosage, soil type and climatic conditions.     

Quantitative reproductive potential of Heterodera schachtii on weeds typical for late summer fallow in sugar beet rotations

In Europe, sugar beet is often produced in a 3‐year rotation with cereals, leaving stubble fields fallow from cereal harvest until primary tillage in autumn in the year prior to sugar beet production. The weed flora on such fields could include host plants of Heterodera schachtii that is one of the most important pests of sugar beet. Crop sequences with non‐hosts and cover cropping with resistant cruciferous hosts during this period have been crucial for its management. Availability of resistant and tolerant sugar beet cultivars could entice growers to forego cover cropping, exacerbating weed problems during the fallow period. The objective of this study was to determine the reproductive potential of H. schachtii on weeds that develop during this period. Under glasshouse conditions, reproduction on 39 plant species was compared with that on oilseed radish and sugar beet of differing nematode host status. In 2 years in field microplots, 18 previously tested species were grown in H. schachtii‐infested soil during the typical fallow period at 60 plants m^?2, and nine of these species were also grown at 180 plants m^?2. There were variable results between years after 8 weeks of growth, but most weeds allowed lower reproduction (<10%) than the susceptible sugar beet; only Stellaria media at 180 plants m^?2 and Thlaspi arvense at both plant densities increased nematodes. Such weed densities may seldom occur under commercial conditions; thus, weed management for nematological considerations during the stubble period may have limited importance.     

The effect of high-level bird-repellent treatment with aldicarb on the germination and development of sugar beets

The effect of high-level treatment with aldicarb on sugar beet seed germination and on sprout growth rate was tested. Ten to 20 mg of Temik 10% granules (1–2 mg aldicarb) per seed was found to be the most appropriate. Due to the slow movement of aldicarb in soils, its absorbance rate from loess soil was found to be highly dependent on the distance between the granules and seeds.     

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.     

Fate of the herbicides glyphosate, glufosinate-ammonium, phenmedipham, ethofumesate and metamitron in two Finnish arable soils

The fate of five herbicides (glyphosate, glufosinate-ammonium, phenmedipham, ethofumesate and metamitron) was studied in two Finnish sugar beet fields for 26 months. Soil types were sandy loam and clay. Two different herbicide-tolerant sugar beet cultivars and three different herbicide application schedules were used. Meteorological data were collected throughout the study and soil properties were thoroughly analysed. An extensive data set of herbicide residue concentrations in soil was collected. Five different soil depths were sampled. The study was carried out using common Finnish agricultural practices and represents typical sugar beet cultivation conditions in Finland. The overall observed order of persistence was ethofumesate > glyphosate > phenmedipham > metamitron > glufosinate-ammonium. Only ethofumesate and glyphosate persisted until the subsequent spring. Seasonal variation in herbicide dissipation was very high and dissipation ceased almost completely during winter. During the 2 year experiment no indication of potential groundwater pollution risk was obtained, but herbicides may cause surface water pollution.     

补水移栽对甜菜苗期生长及产量品质的影响

为明晰补水移栽对纸筒育苗甜菜苗期生长及产量品质的影响,研究比较了地下式补水与传统的地上式补水的土壤润湿结构特征,补水量对甜菜苗期地下部根系与地上叶片发育的影响,以及补水移栽在两种土壤条件下的甜菜产量与品质效应。结果表明,地下式补水创造了环裹于秧苗纸筒底部的土壤湿润球,利于向秧苗供水与田间有效保水。随补水量的增加,甜菜苗期侧根数、主根长、主根粗、根鲜重、叶片量、叶面积随之显著增长。在华北寒旱区砂质栗钙土农田,以成活率与壮苗为目标的甜菜移栽补水量为150～200 ml·株^-1、壤质草甸栗钙土农田为100～150 ml·株^-1为宜,较不补水甜菜块根增产68.78%～81.82%,糖产量提高65.57%～81.82%。地下式补水移栽,是提高甜菜成活率的关键;适量补水实现培育壮苗,成为甜菜高产的基础。     

Epidemiology of beet necrotic yellow vein virus in sugar beet at different initial inoculum levels in the presence or absence of irrigation

A field experiment was set up in 1988 to study the development of rhizomania disease of sugar beet at different inoculum levels of beet necrotic yellow vein virus (BNYVV) in soil. Five, tenfold different, inoculum levels were created by addition of the approximate amounts of 0, 0.5, 5, 50 and 500 kg infested soil per ha (the latter corresponding to 0.01% v/v calculated to the tillage layer). A drip irrigation treatment was applied to study the influence of soil moisture on disease. Susceptible sugar beet, cv. Regina, was grown for three consecutive years.In the first year, root symptoms were not observed, but BNYVV-infected plants were detected by ELISA in low numbers at all inoculum levels at harvest. After late drilling in 1989, high numbers of infected plants, up to 90–100% in plots with the highest inoculum level, were detected already in June. Root symptoms were also observed from June onwards. In both these years disease incidence increased in time and was significantly influenced by the initial inoculum level. In the third year, the whole field was heavily diseased, and only for the non-irrigated plots incidence differed for different initial inoculum levels. The expression of symptoms by BNYVV-infected plants was influenced by initial inoculum level, thus by the amount and timing of primary infection.Root weight at harvest was not affected, but sugar content decreased with increasing inoculum level already in 1988, leading to a reduction in sugar yield of 10% at the highest inoculum level. In 1989, both root weight and sugar content decreased progressively with increasing inoculum level, resulting in sugar yield reductions of 11–66% (down to approximately 3000 kg ha^–1) for low to high inoculum levels compared to the control. As the control plots became contaminated, all yields were low in 1990, still showing a decrease with increasing inoculum level in the non-irrigated plots, but an overall mean sugar yield of 3323 kg ha^–1 for the irrigated ones.Sodium and -amino nitrogen content of the root, additional quality parameters determining extractability of sucrose, showed an increase and decrease, respectively, with increasing initial inoculum level already in the first year. The relative differences in contents compared to those from the control were largest for Na content. A significant negative correlation was found between Na (mmol kg^–1 root) and sugar content (% of fresh weight); linear for 1988, exponential for 1989 and 1990.In spring 1989, the infestation of individual plots was assessed using a quantitative bioassay estimating most probable numbers (MPNs) of infective units of BNYVV per 100 g dry soil. The relationship between the MPns determined and root weight, sugar content and sugar yield at harvest could be described by Gompertz curves. The increase in disease incidence with increasing MPN in 1989 was adequately fitted with a logistic equation.     

Testing aldicarb as a bird repellent in a sprouting sugar beet field

Temik, the granular formulation of aldicarb [2-methyl-2(methylthio) propionaldehyde 0-(methylcarbamoyl) oxime], was placed together with sugar beet seeds during sowing along the rows, at a rate of 1.4 g/m, in a 1.5-ha experimental area within a 6-ha sugar beet field in an arid area with a long history of bird damage. Thirty-three chukar partridges, a major pest of sprouting crops, were observed foraging in the experimental area throughout the 4-week period between sowing and assessment of damage. Damage was restricted to the borders of the field, with a significant difference in level of damage between treated and control plots located along the borders; the size of damaged areas was about five times smaller in the treated plots than in the control plots. The results were interpreted as reflecting the repellent effect of aldicarb absorbed by the sprouts, and as establishment of a conditioned aversion by the chukars to sugar beet sprouts. The high toxicity of the treated sprouts was demonstrated when adult Japanese quail were fed sprouts collected from treated plots.     

Control of Aphis fabae on broad beans (Vicia faba) by the systemic action of gamma-bhc,thionazin and aldicarb

The in-row application of aldicarb granules at 2 lb active ingredient (a.i.)/acre (2·24 kg/ha) at sowing gave complete control of Aphis fabae Scop. on broad beans (Vicia faba L. cv. Seville) up to 7 days before harvest and resulted in a three-fold increase in yield compared with a similar thionazin treatment. Bean plants grown from seeds which were soaked in a gamma-BHC solution at 20 ppm for 24 h prior to planting were protected from this aphid for most of the growing season almost as effectively as with the thionazin treatment. A thin-layer chromatography method was developed for the determination in plants and soil of aldicarb and its two major toxic metabolites, the sulphoxide and sulphone. Gas-liquid chromatography was used to monitor the declining levels of gamma-BHC and thionazin, and simultaneous bioassays were made with Aphis fabae on excised leaf discs from the crop. Analysis of the bean seeds and pods at harvest 90 days after sowing indicated no detectable gamma-BHC, less than 0·01 ppm of thionazin and approximately 0·09 ppm total residue of aldicarb sulphone and sulphoxide. Approximately 22% and 13% of the applied aldicarb, in the form of sulphone and sulphoxide but not the parent compound, remained in the top 6 in (152 mm) of soil at the end of 2 and 4 months respectively. Toxicity studies with Aphis fabae, Acyrthosiphon pisum Harris, and Megoura viciae Buck showed an increasing sensitivity in that order to gamma-BHC at 1 ppm in bean plants. Acute toxicity investigations with feeding Aphis fabae indicated an increasing sensitivity in the order of gamma-BHC < aldicarb sulphone < aldicarb sulphoxide < thionazin < aldicarb. Despite the high acute toxicity of thionazin to Aphis fabae it gave low protection against aphids, possibly owing to its relatively short persistence in both plants and soil when compared with aldicarb.     

The effect of different dosages of aldicarb on the multiplication at small population densities of Globodera rostochiensis on potato in rotavated and non-rotavated plots

The effect of 0.35, 0.5, 0.7, 1, 1.4 and 2 g aldicarb/m², applied at planting time, on the multiplication of small densities ofGlobodera rostochiensis on potato was investigated in an experiment on sandy loam. The chemical was applied broadcast to the soil and rotavated into the top 15 cm on half the plots of each treatment. The plots were ridged three times, the first time immediately after the planting of the potatoes. Nematodes multiplied at the same rate in the top 20 cm of the soil on rotavated and non-rotavated plots treated with the same dosage of the chemical. The relation between log dosage and probit reduction of the multiplication rate in the top 20 cm after the plots had been levelled was linear between 0.35 g and 1.4 g aldicarb/m². The dosage-increase efficiency was 0.3 probit units per doubling of the dosage and the reduction of the multiplication rate at 0.5 g aldicarb/m² 76%, whereas 2 g aldicarb/m² was not more effective than 1.4 g. However, multiplication rates in the centre of the ridges of rotavated plots were reduced by 96.5% at 1 to 2 g aldicarb/m² but only by about 60% below the furrows and by 60% to 80% below the ridges. The latter reduction was the greater the larger the dosage of the chemical.The observations were in accordance with the supposition that multiplication of nematodes was totally inhibited in the top 20 cm of plots treated with 1.4 g and 2 g aldicarb/m² and that postharvest populations there consisted entirely of non-hatched eggs of the pre-plant population. The poor performance of the chemical in the deeper layers of the soil makes application less effective in reducing population build-up than in preventing yield losses.Samenvatting Het effect van 0,35, 0,5, 0,7, 1, 1,4 en 2 g aldicarb/m², toegediend vlak voor het poten, op de vermenigvuldiging vanGlobodera rostochiensis op aardappel werd onderzocht in een veldproef op zavel. Het middel werd breedwerpig over de oppervlakte van de grond verdeeld. Daarna werd de helft van de met elke dosis behandelde en van de onbehandelde veldjes gefreesd tot 15 cm diepte. Er werd drie maal aangeaard. Er was geen verschil in de vermenigvuldiging van de aaltjes in de bovenste 20 cm van de grond tussen wel en van het middel van probit vermindering van het vermenigvuldigingsgetal van het aaltje ten opzichte van onbehandeld in de bovenste 20 cm van de grond was rechtlijnig tussen 0,35 g en 1,4 g aldicarb/m². Het effect van dosisvergroting was 0,3 probit eenheid per verdubbeling van de dosis en de vermindering van het vermenigvuldigingsgetal bij 0,5 g aldicarb/m² 77%. Het effect van 1,4 g en 2 g aldicarb/m² was gelijk. De resultaten zijn in overeenstemming met de veronderstelling, dat in de met 1,4 en 2 g aldicarb/m² behandelde veldjes de vermenigvuldiging van de aaltjes in de bovenste 20 cm van de grond geheel was verhinderd. Met een voor praktische toepassing aanvaardbare dosis aldicarb kon een sterke vermeerdering van aardappelcystenaaltijes beneden 20 cm onder de oppervlakte van de grond niet worden voorkómen. Daardoor is de bruikbaarheid van dit systemische nematicide (en van overeenkomstige middelen) in een bestrijdingssysteem, dat streeft naar het (zeer) laag houden van dichtheden van aardappelcystenaaltjes, problematisch.     

Correlation between lipid peroxidation and phenolics content in leaves and roots of sugar beet infected with Rhizoctonia solani

The correlation between intensity of lipid peroxidation and changes in antioxidant capacity of sugar beet plants (cv. ‘Drena’) infected with Rhizoctonia solani Kühn isolate (AG 2-2 IIIB group) was studied. Successful inoculation was confirmed by the presence of infection cushions in a cross section of leaf petioles. On the 7^th day of the experiment, phenylalanine ammonia-lyase (PAL; EC. 4.3.1.5) activity was in negative correlation with intensified lipid peroxidation process in leaves of sugar beet plants (r= –0 .99). Also, in leaves and roots of inoculated sugar beet plants, total flavonoids content (35% and 20%, respectively) and 1,1-diphenyl-2-picrylhydrazyl (DPPH)-scavenging activity (80% and 55%, respectively) were significantly reduced. Necrotic processes resulting from R. solani infection of sugar beet plants was followed by induction of plant phenolics metabolism; however, antioxidant capacity of these plants was reduced.     

The influence of some agricultural practices on soil organisms and plant establishment of sugar beet

In a long term field experiment the influence of crop rotation and the application of insecticides and herbicides on soil arthropods (mesofauna), nematodes, soil fungi and weeds was investigated. Possible changes in numbers of not only pathogenic organisms, but also of predators or parasites of pathogens, could affect seedling establishment and/or yield of sugar beet. In soil samples taken during the spring, high population of the springtailOnychiurus armatus ware detected which caused considerable damage in the first two years. Later also rather severe infestations byAtomaria linearis occurred, probably caused by frequent sugar beet cropping.No significant influence of crop rotation on damage caused by soil arthropods could be detected yet, but in the 1/3 sugar beet and 2/3 winter wheat rotation more micro-arthropods and a higher diversity of species were found than in the blocks with continuous sugar beet growing. In the latter ones the numbers ofHeterodera schachtii increased and in 1980 the tolerance level was exceeded. On the contrary in the 1/3 sugar beet blocksPratylenchus spp. were dominant. Since a number of perennial weeds cannot be controlled sufficiently in sugar beet, some of them created a problem in the 1/1 sugar beet blocks.In the plots not treated with a soil herbicide large numbers of annual weeds provided alternative native food forO. armatus, which resulted in less plant damage. No significant effect of chloridazon on the micro-arthropod fauna could be detected. The insecticides lindane and aldicarb controlledO. armatus andA. linearis partially, and improved seedling emergence and to a lesser extent yield. Both insecticides had a variable effect on the relative abundancy ofCollembola and in addition lindane suppressed numbers ofAcariformes and aldicarb those ofParasitiformes. No negative influence on the species diversity could be detected. All effects did not last long and varied considerably from year to year.Indications were found that, if species ofCollembola, which could act as predators of nematodes, were suppressed, the numbers ofPratylenchus spp. andH. schachtii increased.Samenvatting In een veeljarig proefveld (1976–1979) werd de invloed van de vruchtopvolging en toepassing van insecticiden en herbiciden op bodemarthropoden (mesofauna), nematoden, bodemschimmels en onkruiden onderzocht. Niet alleen mogelijke veranderingen in de aantallen schadeverwekkers, maar ook in de aantallen predatoren en pathogenen van bodemplagen zouden het plantbestand en/of de opbrengst van suikerbieten kunnen beïnvloeden.Gedurende de eerste twee jaar van de proef werden in grondmonsters, die gedurende het voorjaar werden genomen, grote aantallen springstaarten (Onychiurus armatus) aangetroffen, die aanzienlijke schade veroorzaakten. Later kwamen eveneens aantastingen door het bietekevertje (Atomaria linearis) voor, waardoor in meerdere of mindere mate planten wegvielen.Er kon nog geen duidelijke invloed van de vruchtopvolging op de schade door bodemarthropoden worden vastgesteld, maar in de rotatie met 1/3 suikerbieten en 2/3 wintertarwe werden meer micro-arthropoden en een grotere soortenrijkdom gevonden dan in de gedeelten met een continuteelt van suikerbieten. In laatstgenoemde veldjes zijn de aantallen bietecystenaaltjes (Heterodera schachtii) toegenomen, waarbij in 1980 de tolerantiegrens werd overschreden. Daarentegen vond in de veldjes met 1/3 suikerbieten in de rotatie een sterkere vermeerdering vanPratylenchus spp. plaats dan in de continuteelt. Aangezien een aantal wortelonkruiden in suikerbieten niet voldoende kan worden bestreden, veroorzaakten enkele na enige jaren een probleem in de continue bietenteelt.In de veldjes die niet met een bodemherbicide waren behandeld vormden grote aantallen zaadonkruiden een alternatieve voedselbron voorOnychiurus armatus, wat een geringere aantasting van kiemplanten tot gevolg had. Er werd geen aantoonbaar effect van chloridazon op de micro-arthropoden vastgesteld.De insecticiden lindaan en aldicarb konden schade doorOnychiurus armatus enAtomaria linearis slechts gedeeltelijk voorkomen; er werd een duidelijk betere opkomst en soms ook een hogere opbrengst verkregen. Beide insecticiden hadden een wisselende invloed op de relatieve talrijkheid vanCollembola en bovendien onderdrukte lindaan de aantallenAcariformes en aldicarb deParasitiformes. Er kon geen negatieve invloed op de soortenrijkdom worden vastgesteld. Al deze effecten waren niet van langdurige aard en verschilden sterk van jaar to jaar.Er werden aanwijzingen gevonden dat, indien bepaalde soortenCollembola, die als predatoren van nematoden kunnen optreden, werden onderdrukt, de aantallenPratylenchus spp. enHeterodera schachtii toenamen.     

The role of ferrous ions in the rapid degradation of oxamyl,methomyl and aldicarb in anaerobic soils

The carbamoyloxime pesticides methomyl, oxamyl and aldicarb, together with the oxidation products of aldicarb, are known to break down much more rapidly in certain anaerobic subsoils than in the aerobic topsoils from the same site. Ferrous ions have now been shown to be involved in this reaction. Oxamyl was degraded in aqueous solutions at 30°C containing 250 μg ml^?1 Fe²⁺ with a half-life of about 10 h, independent of pH in the range of 5.65–7.66; the observed products of this reaction were N,N-dimethyl-l-cyanoformamide and methanethiol. These same products, rather than the oximino hydrolysis product observed from degradation in aerobic soils, were rapidly and quantitatively formed from oxamyl in suspensions of anaerobic reduced subsoils (Fe²⁺ concentration 27–41 μg ml^?1 soil water), but oxamyl was rather stable in water-saturated Vredepeel subsoil (Fe²⁺ concentration 0.65 μg ml^?1) in which the redox potential was much higher. Methomyl behaved similarly. The rates of reaction in the suspensions of anaerobic subsoils were greater than expected from the concentrations of Fe²⁺ in the soil water, but most of the Fe²⁺ present in soil was bound to the soil particles by cation exchange and this bound Fe²⁺ may have participated. Breakdown of aldicarb was accelerated both in solutions of Fe²⁺ and in the suspensions of anaerobic reduced subsoils, though the rate enhancement was less than observed with methomyl and oxamyl; 2-methyl-2-methylthiopropionitrile and 2-methyl-2-methylthiopropionaldehyde were the observed products from aldicarb in anaerobic soil but only the former was produced in Fe²⁺ solutions; the corresponding nitriles and aldehydes were also yielded by aldicarb sulphoxide and aldicarb sulphone in the anaerobic, reduced subsoils.     

Plant Host Range of Verticillium longisporum and Microsclerotia Density in Swedish Soils

Verticillium longisporum is a soil-borne fungal pathogen causing vascular wilt of Brassica crops. This study was conducted to enhance our knowledge on the host range of V. longisporum. Seven crop species (barley, oat, oilseed rape, pea, red clover, sugar beet and wheat) and five weed species (barren brome, black-grass, charlock, cleavers and scentless mayweed) all common in southern Sweden were evaluated for infection by response to V. longisporum. Oat, spring wheat, oilseed rape, scentless mayweed and charlock inoculated with V. longisporum in a greenhouse showed stunting to various degrees close to the fully ripe stage. Based on the extent of microsclerotia formation, explants were separated into four groups: for pea and wheat, <5% of the samples had formed microsclerotia; for scentless mayweed, 5–10%; for oat, 10–20%; and for charlock and oilseed rape >80%. The results suggest that plant species outside the Brassicaceae can act as reservoirs of V. longisporum inoculum. Soil inoculum densities in nine fields were monitored over a period of 12 months, which ranged from 1 to 48 cfu g⁻¹ soil. Density of microsclerotia was lowest just after harvest, reaching its maximum six months later. No significant correlation between inoculum density in soil and disease incidence on oilseed rape plants was found. However, the data suggest that a threshold of 1 cfu g⁻¹ soil is needed to cause disease on oilseed rape. Species identification based on microsclerotia morphology and PCR analysis showed that V. longisporum dominated in soil of seven, and V. dahliae in two of the nine fields studied.     

Identification of rhizomania-infected soil in Europe able to overcome <Emphasis Type="Italic">Rz1</Emphasis> resistance in sugar beet and comparison with other resistance-breaking soils from different geographic origins

Rhizomania, caused by Beet necrotic yellow vein virus (BNYVV), is vectored by Polymyxa betae. The disease can only be controlled by growing partially resistant sugar beets, which quantitatively reduce virus replication and spread. None of the known major resistance genes (Rz1, Rz2, Rz3), alone or in combination, are able to prevent BNYVV infection entirely. Here we report for the first time the identification of a Spanish soil, containing an A-type BNYVV with RNA 1-4, displaying Rz1 resistance-breaking abilities comparable to soils from the USA and to those from France containing the French (Pithiviers) P-type BNYVV with RNA 5. A resistance test with several soil samples vs. different sugar beet cultivars was conducted under standardised conditions. Sugar beets were analysed after 12 weeks of greenhouse cultivation for taproot weight, BNYVV and relative P. betae content. The soil samples from Spain, France and the USA produced high virus contents and strong rhizomania symptoms in Rz1 plants, indicative of resistance-breaking abilities. In addition, all resistance-breaking soil samples produced detectable virus concentrations in plant lateral roots of the Rz1 + Rz2 cultivar, and plants grown in the Spanish soil sample also had reduced taproot weight and displayed severe rhizomania disease symptoms. Additionally, the main pathogenicity factor P25, responsible for the formation of BNYVV symptoms, showed high sequence variability in the amino acid tetrad at position 67–70. The results suggest the geographically independent selection of BNYVV resistance-breaking isolates following the uniform cultivation of Rz1-containing sugar beet cultivars.     

The effect of root-absorbed PSII inhibitors on Kautsky curve parameters in sugar beet

The effects of the photosystem II inhibitors metamitron and terbuthylazine on the shape of the Kautsky (chlorophyll fluorescence induction) curve were investigated in sugar beet grown in hydroponic culture. The objective of the study was to trace recovery processes following herbicide injury using Kautsky curve parameters. Metamitron is used for selective weed control in sugar beet because it is metabolized in this crop. In contrast, terbuthylazine is toxic to sugar beet. Two hours after treatment, various fluorescence induction curve parameters, such as maximum quantum efficiency (F_V/F_m), the relative changes at the J step (F_vj) and area (the area between the Kautsky curve and maximum fluorescence, F_m), were affected by metamitron at concentration ranges of 70–280 mg active ingredient (a.i.) L^?1 in plants treated at the four‐true‐leaf stage. Shortly after herbicide application, F_v/F_m was more affected by the hydrophilic metamitron [log(K_ow) = 0.83] than by the lipophilic terbuthylazine [log(K_ow) = 3.21], but these differences between compounds were alleviated as metamitron was metabolized and terbuthylazine was not. Terbuthylazine at 1 mg a.i. L^?1 affected sugar beet at the four‐ and six‐true‐leaf stages to the same extent, whereas metamitron at a dose of 140 mg a.i. L^?1 affected much more at four‐ than at the six‐true‐leaf stage. Sugar beet recovered from metamitron injury even at high doses (140 and 280 mg a.i. L^?1). Fluorescence induction curve parameters were similarly affected by terbuthylazine and, although sugar beet recovered from terbuthylazine injury at low doses (<0.2 mg a.i. L^?1), the Kautsky curve was irreversibly affected at higher doses (1–10 mg a.i. L^?1), leading finally to plant death. Older plants were affected later, and recovered sooner, from both herbicides.