Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Bladaaltjes in Pioenroos
    Slootweg, G. ; Elberse, I.A.M. ; Bulle, A.A.E. - \ 2011
    nematiciden - plantenparasitaire nematoden - nematodenbestrijding - pesticiden - werkzaamheid - paeonia - aphelenchoides fragariae - veldproeven - gewasbescherming - nematicides - plant parasitic nematodes - nematode control - pesticides - efficacy - paeonia - aphelenchoides fragariae - field tests - plant protection
    Poster met onderzoeksinformatie. In dit onderzoek worden gewasbeschermingsmiddelen getest op hun werking tegen bladaaltjes in pioenrozen.
    Schadelijke aaltjes liggen op de loer : Interview met Leendert Molendijk
    Meijering, Luuk ; Molendijk, L.P.G. - \ 2011
    Boerderij/Akkerbouw 96 (2011)19. - ISSN 0169-0116 - p. E12 - E114.
    nematiciden - gewasbescherming - akkerbouw - bodemkwaliteit - nematodenbestrijding - bodemfactoren - bodempathogenen - grondsterilisatie - nematicides - plant protection - arable farming - soil quality - nematode control - edaphic factors - soilborne pathogens - soil sterilization
    Het aantal percelen waarin schadelijke aaltjes voorkomen neemt langzaam toe. met voldoende kennis en de juiste maatregelen zijn ze goed te beheersen
    Rondje onderzoek bij PPO Lisse (Paul van Leeuwen en Casper Slootweg geïnterviewd)
    Neefjes, H. ; Leeuwen, P.J. van; Slootweg, G. - \ 2010
    Vakblad voor de Bloemisterij 65 (2010)37. - ISSN 0042-2223 - p. 36 - 37.
    tuinbouwbedrijven - bollen - bloementeelt - zantedeschia - bodemmoeheid - paeonia - nematiciden - tulpen - open dagen - market gardens - bulbs - floriculture - zantedeschia - soil sickness - paeonia - nematicides - tulips - open days
    De open dag van PPO Lisse op vrijdag 10 september 2010 gaf inzicht in proeven met bolgewassen. Maar ook (zomer)bloementelers konden er iets van hun gading vinden. Bijvoorbeeld teelt van de grond, herinplantziekte bij pioen, parteren van zantedeschia en fenolen wegvangen bij de tulpenbroei.
    Richtlijnen grondontsmetting Monam/Basamid tegen stengelaaltjes
    Vreeburg, P.J.M. - \ 2010
    nematoda - grondsterilisatie - bloembollen - richtlijnen (guidelines) - nematiciden - nematoda - soil sterilization - ornamental bulbs - guidelines - nematicides
    Verschillende bedrijven en instanties hebben samengewerkt om richtlijnen op te stellen voor de grondontsmetting met Monam/Basamid tegen stengelaaltjes.
    Het effect van granulaten op de aardappelcultivar Karnico en de populatiedynamica van G. pallida op dalgrond
    Schepel, E. ; Schomaker, C.H. ; Molendijk, L.P.G. - \ 2009
    Lelystad : Praktijkonderzoek Plant en Omgeving, Sector Akkerbouw, Groene ruimte en Vollegrondsgroenten - 25
    nematiciden - korrels - plantenparasitaire nematoden - nematodenbestrijding - veldproeven - globodera pallida - akkerbouw - aardappelen - nematicides - granules - plant parasitic nematodes - nematode control - field tests - globodera pallida - arable farming - potatoes
    In 2007 is in een veldproef het effect getoetst van drie doseringen en twee toepassingen van Vydate op de populatiedynamica van het aardappelcysteaaltje Globodera pallida en de opbrengst en kwaliteit van het matig resistente (RV=32% voor de “Rookmaker”-populatie (E400) ras Karnico op dalgrond met een organisch stof gehalte van 15-20%. Het middel is in doseringen van 20 en 40 kg/ha volvelds en 10 kg/ha in de rij toegepast. Het perceel was besmet met 0.1 tot 70 levende juv/g grond.
    Het wortelknobbelaaltje in de biologische glastuinbouw: middelen en systemen
    Wurff, A.W.G. van der - \ 2008
    Gewasbescherming 39 (2008)1. - ISSN 0166-6495 - p. 25 - 25.
    meloidogyne - teelt onder bescherming - vruchtgroenten - nematoda - gewasverliezen - nematiciden - gewasbescherming - biologische landbouw - glastuinbouw - glasgroenten - meloidogyne - protected cultivation - fruit vegetables - nematoda - crop losses - nematicides - plant protection - organic farming - greenhouse horticulture - greenhouse vegetables
    In de biologische en grondgebonden geïntegreerde teelt van groenten onder glas behoren wortelknobbelaaltjes (Meloidogyne spp.) tot de grootste knelpunten. Verliezen lopen op tot veertig procent van de omzet. Onder de biologische vruchtgroenten staat komkommer het zwaarst onder druk omdat resistentie ontbreekt en aaltjesbeheersing nog nauwelijks ontwikkeld is
    Afronding "Vergelijking effectiviteit metam-natrium met cis-dichloorpropeen als grondonsmettingmiddel voor de bestrijding van stengelaaltjes"
    Vreeburg, P.J.M. ; Korsuize, C.A. - \ 2007
    Lisse : PPO Bloembollen en Bomen - 21
    ditylenchus dipsaci - grondsterilisatie - nematiciden - gewasbescherming - bloembollen - ditylenchus dipsaci - soil sterilization - nematicides - plant protection - ornamental bulbs
    Als in een gewas stengelaaltjes (Ditylenchus dipsaci) worden gevonden wordt de grond vastgelegd door de PD omdat het een quarantaine-organisme betreft. Er mogen pas weer vatbare bolgewassen geteeld worden als de grond na bestrijding door de PD is vrijgegeven. Twee met stengelaaltjes besmette percelen werden in 2005 chemisch ontsmet. Na een tweejarige teelt van narcis werd duidelijk dat chemische grondontsmetting tegen stengelaaltjes niet altijd afdoende werkt. Metam-natrium werd op twee wijzen toegepast en vergeleken met cis-trans-dichloorpropeen. Beide middelen werden alleen of met een aanvullende grondbehandeling met dazomet toegepast. Was de aantasting na één jaar teelt nog zeer beperkt, na twee jaar bleek de aantasting echter zeer hevig te kunnen zijn. Bij alle grondontsmettingsbehandelingen was een aantasting aanwezig, dus ook bij de tot en met 2004 geadviseerde cis-trans-dichloorpropeen. Er was een groot verschil tussen de percelen in mate van overleving van stengelaaltjes en in de werking van de toegepaste ontsmettingen. Metam-natrium werkte, indien het direct werd doorgespit, net zo goed als - of slechter dan cis-trans-dichloorpropeen. Metam-natrium werkte bij toepassing via split-application slechter dan bij direct doorspitten. Door een aanvullende behandeling met dazomet door de toplaag, werd de bestrijding beter, maar deze was nog niet afdoende. Het beste alternatief voor het inmiddels niet meer verkrijgbare cis-trans-dichloorpreen is goed doorspitten van metam-natrium gevolgd door een toplaagbehandeling met dazomet, maar dit was op een van de twee percelen volstrekt onvoldoende tegen stengelaaltjes. Stengelaaltjes werden in 2005 aangetroffen in de grondmonsters onder de ontsmette laag. De bolaantasting bleek veelal veel ernstiger te zijn dan bovengronds zichtbaar was. De aantasting één jaar na grondontsmetting kan zo licht zijn dat deze besmetting niet wordt opgemerkt. Omdat de grondontsmetting niet altijd afdoende zal zijn wordt het telen van een stengelaaltjesvatbaar gewas na een grondontsmetting (ook al is die na bemonstering door de PD vrijgegeven), sterk afgeraden. Een extra wachttijd van één of meerdere jaren, zal de nog aanwezige populatie stengelaaltjes verder omlaag brengen, waardoor de kans op een nieuwe aantasting verder wordt verkleind. Als een vatbaar gewas wordt geteeld, bestaat de mogelijkheid dat er een lichte besmetting optreedt die niet wordt herkend en waardoor de stengelaaltjes verder worden verspreid. Mogelijk is dit één van de redenen van de toegenomen aantasting door stengelaaltjes in tulp en de reden waarom een aantasting kan optreden zonder duidelijk aanwijsbare oorzaak. Van metam-natrium en dus ook van dazomet is bekend dat er adaptatie op kan treden, waadoor de werking vermindert. De verspreiding van metam-natrium door de grond is minder goed dan van dichloorpropeen en vereist dus een zorgvuldige toepassing met doorspitten om het middel voldoende goed door de grond te verdelen. In vergelijking met chemische grondontsmetting geeft inunderen mogelijk een zekerder bestrijding omdat door die behandeling ook de diepere grondlaag wordt behandeld. Onderzoek naar de minimale duur van inundatie wordt vanaf 2007 bij PPO uitgevoerd.
    Telen met Toekomst: Kennis over ziekten in de praktijk getoetst
    Kool, S.A.M. de - \ 2007
    BloembollenVisie 2006 (2007)113. - ISSN 1571-5558 - p. 20 - 21.
    bloembollen - sierplanten - narcissus - plantenziekteverwekkende schimmels - schimmelbestrijding - plantenziekteverwekkers - vuur (plantenziektekundig) - tulipa - plantenparasitaire nematoden - nematodenbestrijding - globodera - nematiciden - gewasbescherming - ornamental bulbs - ornamental plants - narcissus - plant pathogenic fungi - fungus control - plant pathogens - blight - tulipa - plant parasitic nematodes - nematode control - globodera - nematicides - plant protection
    Tal van ziekten en plagen spelen de bloembollensector parten. Binnen Telen met toekomst is onder meer gekeken naar de aanpak van schimmels in de narcis 'Tête à Tête, naar vuur in tulp en naar de aanpak van aaltjes. Niet alleen bloembollenaaltjes, maar ook aardappelcystenaaltjes kwamen aan bod
    De invloed van Temik en rooidatum op de vermeerdering van Globodera pallida op het vroege pootardappelras Premiere
    Molendijk, L.P.G. ; Schomaker, C.H. ; Hoek, J. ; Gastel, A.W.W. van - \ 2006
    Wageningen/Lelystad : Praktijkonderzoek Plant en Omgeving (PPO nr. 3250015900) - 24
    pootaardappelen - solanum tuberosum - aardappelen - globodera pallida - plantenparasitaire nematoden - nematiciden - pesticiden - plagenbestrijding - akkerbouw - nematodenbestrijding - seed potatoes - solanum tuberosum - potatoes - globodera pallida - plant parasitic nematodes - nematicides - pesticides - pest control - arable farming - nematode control
    In een proef in 2005 op een praktijkperceel te Firdgum (Friesland) is onderzoek uitgevoerd naar het effect van Temik op de populatiedynamica van Globodera pallida in pootgoedteelt van het vroege ras Premiére, dat vatbaar is voor G. pallida. Temik kon op beide oogsttijdstippen de vermeerdering van G. pallida niet voorkomen, maar heeft de vermeerdering van de aaltjes wel gereduceerd. Geconcludeerd moet worden dat toepassing van Temik in de pootgoedteelt van vatbare rassen de opsporing van besmettingen kan vertragen en dat Temik mogelijk een rol kan spelen bij de beheersing van aardappelmoeheid in rassen met een matige resistentie
    Populatieontwikkeling, schadelijkheid en beheersing van het wortelnecroseaaltje Radopholus similis in Anthurium andreanum in kunstmatige substraten
    Amsing, J.J. ; Stapel, L.H.M. - \ 2001
    Aalsmeer : Proefstation voor Bloemisterij en Glasgroente, Vestiging Aalsmeer (Rapport / Proefstation voor Bloemisterij en Glasgroente 308) - 44
    snijbloemen - anthurium andraeanum - heteroderidae - radopholus similis - nematiciden - populatiedynamica - groeimedia - substraten - kweekmedia - plantenparasitaire nematoden - cut flowers - anthurium andraeanum - heteroderidae - radopholus similis - nematicides - population dynamics - growing media - substrates - culture media - plant parasitic nematodes
    Quantitative studies on the management of potato cyst nematodes (Globodera spp) in The Netherlands
    Been, T.H. ; Schomaker, C.H. - \ 1998
    Agricultural University. Promotor(en): J.C. Zadoks. - S.l. : Been [etc.] - ISBN 9789054859604 - 319
    aardappelen - globodera - plantenparasitaire nematoden - controle - nematiciden - technieken - bemonsteren - detectie - modellen - potatoes - globodera - plant parasitic nematodes - control - nematicides - techniques - sampling - detection - models

    Potatoes are among the most profitable agricultural crops in arable farming in the Netherlands and consequently are grown as frequently as conditions allow. As a result Dutch farmers experienced huge problems with potato cyst nematodes during the last 50 years. In Chapter 1 an outline is presented of the situation of potato cyst nematode control in the 1980's, the problems, possible solutions and the research initiated, of which a part is presented in this thesis.

    In 1984 emphasis was put into research concerning the efficiency of soil fumigation on heavy marine clay soils where the majority of Dutch seed and consumption potatoes are grown. Both laboratory and field experiments were carried out to investigate the efficiency of 1,3 dichloropropene and metam-natrium. This required the processing of thousands of larvae suspensions. One of the most labourious and tedious occupations in nematological research is the counting of individuals of the pathogen.

    In Chapter 2 A GOP-302 image analysis system - Context Vision, Sweden - was used to automate the counting of large numbers of larvae-suspensions of Globodera rostochiensis and G. pallida . These suspensions originated from hatching tests, which were conducted to estimate percentage mortality in field and lab experiments of nematodes exposed to nematicides. The result is called ANECS ( A utomatic NE matode C ounting S ystem), a software program that can count up to 64 compartments with larvae suspensions successively without the aid of an operator. A special object carrier was developed. Images of up to eight object carriers (512 larvae suspensions) can be stored and image analysis can be suspended to off-office hours. The time needed to count one compartment was reduced by 80% to one minute compared to 'manual' labour while the time for probe preparation remained the same. The percentile error is highest at very low larvae densities (<20 per suspension) and is caused by pollution with small fibres carried by air during the handling of the larvae suspensions. This problem can be minimised by setting up clean-laboratory procedures. At least 95% of the larvae originating from hatching tests were recognized and counted. The program can and has been be adapted to count other nematode species or to suit more complicated problems like counting both larvae and eggs in one suspension.

    In Chapter 3 errors due to subsampling and laboratory procedures affecting the expected value and variance of cyst counts were investigated. Several fields, infested with potato cyst nematodes ( Globodera rostochiensis and G. pallida ) were sampled by collecting bulk samples of approximately 70 cores amounting to 1.8 or 2.5 kg soil from a number of square metre plots located in a regular grid pattern over a 0.33 ha area. Bulk samples from five fields, I-V, were thoroughly mixed and from one field, VI, lightly mixed, and subsequently divided into three subsamples of approximately equal weights. Two, sometimes three, subsamples were elutriated separately. Cysts were elutriated by two commercial laboratories, 1 and 2, and separated from the debris and counted at two research laboratories, 0 and 3.

    Random bulk samples from five fields, I-V, were divided into three portion after thoroughly mixing and taken to Laboratory 0, to compare elutriation precision and accuracy of commercial and scientific laboratories and to check the quality of mixing. To this purpose, pairs or triples were divided into classes. The expected value of the variance within pairs was estimated per class and could be described by a distribution function analogue to a negative binomial distribution, but with three in stead of two parameters. Cysts appeared to be randomly distributed in the well mixed samples, resulting in a binomial or trinomial distribution between pairs or triples. The expected values of the coefficient of variation associated with elutriation were 3.6, 9.6 and 5.5% in the Laboratories 0, 1 and 2, respectively. The upper 95% confidence limit,δ 0.95 , of coefficients of variation associated with elutriation in Laboratories 1 and 2, were estimated by the differences in 95% upper limits of coefficients of variation between the Laboratories 1 and 2 on the one hand and Laboratory 0 conversely. This difference,δ 0.95 , ranged from 73% to 42% for Laboratory 1 and from 43% to 19% for Laboratory 2 if 10 to 100 cysts were counted in samples. The consequences of these laboratory errors for the accuracy of sampling methods for both research and extension purposes are discussed.

    Nematicide trials require reliable results concerning the effect caused by the fumigant. The percentage mortality of potato cyst nematodes can be estimated by comparing the hatchability of untreated larvae with that of nematicide treated larvae. In Chapter 4 , research is described to improve the quality of hatching tests. Hatching tests using potato root diffusate are labourious and yield quite variable results. Sources of variability were identified and analysed, and solutions were presented. A method was developed to conduct hatching tests using inert materials so that the total variation at the end of the test is minimized.

    A number of hatching tests was carried out to increase reliability, optimize the method and limit the amount of work. Thus, it was possible to obtain a coefficient of variation ( cv ) of the hatching process which is in accordance with the combined errors expected when a certain number of cysts is treated and eggs are used in a hatching test. An Appendix is provided listing the different errors and ways to calculate and cope with them.

    The results indicate that the hatching process is no longer an important source of variation for the end result. All variation higher than expected could be explained by variation between replications of batches with the same treatment, indicating that small differences in nematicide application cause major differences in the end result. The treatment effect was more important in field experiments than in laboratory experiments.

    The hatching curve could be described adequately by a log-logistic curve with 3 parameters (λfinal number of hatched larvae,αtime,βslope parameter). Addition of a fourth parameter (γ, incubation time) improved the fit of the hatching curve significantly. Using the log-logistic model, final hatch can be predicted with a certain error before the actual hatching test ended, but in general final hatch is underestimated. When an error of 5% is accepted, the length of time required to perform a hatching test of a laboratory experiment can be reduced by 80% for untreated batches and by 40 to 80% for batches treated with nematicides. Acceptable reduction is negatively correlated with the concentration of the fumigant used.

    Hatching tests with cysts originating from field experiments are unsuitable for prediction using a time limited data set. In cyst batches from the field compound hatching curves could be distinguished in 4 out of 6 fields, indicating that the soil samples contained at least two fractions of cysts with different hatching responses. Prediction would cause a significant underestimation of final hatch and consequently an overestimation of mortality.

    Because of its high vapour pressure, 1,3-dichloropropene is primarily used on marine clay soils. In Chapter 5 a laboratory experiment is described investigating the two stereo-isomeres of 1,3-dichloropropene for their efficiency in killing nematodes. Batches of increasing numbers of Globodera rostochiensis cysts were exposed to a range of concentrations of the (E)- and (Z)-isomers of 1,3-dichloropropene. The cysts were of identical origin. Temperature during treatment was 10 oC, humidity 100% and time of exposure 8 days. The integrals of concentration time products ( CT ) created were 0, 3, 7, 14, 31, 60, 125, 242, and 437μg/ml·day for the (E)-isomer and 0, 3, 16, 59, 240, and 419μg/ml·day for the (Z)-isomer. Survival was estimated with hatching tests 1.5, 3, and 7 months after treatment.

    The relationship between dosage of (E)-isomer and numbers of hatchable nematodes followed a log-logistic equation at all hatching dates. Hatchability, and therefore lethal dosages, increased as hatching tests were more delayed. Seven months after treatment, practically all treated nematodes had recovered and hatchability of treated and untreated nematodes was the same. A log-logistic relationship was also found for dosage (Z)-isomer and numbers of hatchable nematodes 1.5 month after treatment. When hatching tests of nematodes treated with the (Z)-isomer were delayed till 3 and 7 months after treatment, the results were better explained by a compound model, assuming two independent log-logistic effects, one stimulating hatch at low dosages and one reducing hatch at all dosages. Only the (Z)-isomer of 1,3-dichloropropene was effective as a nematicide.

    Chapter 6 presents research concerning the efficiency of standard doses of 1,3 dichloropropene in fields with a high silt content. Three fields of marine clay soil were fumigated with 150 l/ha 1,3-dichloropropene (DD) (Teleone II TM, Shell 95 TM). On three dates after application, concentrations of Z- and E- 1,3-dichloropropene were measured per 5 cm layer of soil to a depth of 40 cm and integrals of concentration time products were calculated. When the fumigant was no longer detectable, a top soil treatment with either 150 l/ha metam-sodium or 180 kg/ha dazomet (active compound methyl isothiocyanate) was applied, followed immediately by autumn ploughing. Soil samples were taken before and after fumigation and after the top soil treatment to extract potato cyst nematodes (PCN). Survival was determined by means of hatching tests. Mortalities after the DD treatment, defined as 100 - % survival, were estimated per 5 cm layer of soil to a depth of 30 cm to construct dosage response curves. Fumigation with DD killed 48, 48 and 72% of the PCN per field, respectively. Accelerated breakdown of DD by microorganisms accounted for the two lower mortality rates.

    The additional top soil treatment with metam-sodium increased mortality to 90% or more. Dazomet, however, was less effective (53 and 80%) considering that twice as much of the active compound was applied as in the metam-sodium treatment. Multiplication of hatched larvae originating from the injection layer after the DD treatment was 25% less than that from untreated plots. This was caused by a lower fraction of larvae developing into cysts. PCN could be retrieved from soil layers as deep as 80 cm below the surface. Fumigation reached only a fraction of the infested soil, down to 25-30 cm. The infestation foci were so small compared to the standard minimum area fumigated (1 ha) that 90% of the active compound would be wasted on non-infested soil. Soil fumigation, whether or not combined with an additional top soil treatment, will seldom be profitable. Monitoring for infestation foci is recommended.

    As soil fumigation was not a viable option to keep potato cyst nematodes in check on heavy marine clay soils, another way of control had to be found. Research was focussed at the development of sampling methods for the detection of small infestation foci with high reliability (≥90% probability of detection). Precautionary soil fumigation can be avoided, the area where a control measure has to be applied can be minimized to the actual infestation, and detection occurs so early that (partially) resistant potato cultivars can be grown without significant yield reduction as population densities are still low.

    Research in the Flevopolders yielded promising results. Therefore, in 1990, a research program was initiated to develop new sampling methods for the detection of patchy infestations of potato cyst nematodes ( Globodera rostochiensis and G. pallida ) with known accuracy in all potato cropping areas of The Netherlands. Patchy infestations in cropping areas of the provinces of Zeeland, Friesland, Groningen and Drente were sampled to validate a model based on data from cropping areas in Flevoland and to determine whether one detection method could meet the requirements of all cropping areas in The Netherlands. The results are presented in Chapter 7 . Eighty two fields were presampled to locate patchy infestations using a coarse sampling grid (8 · 3 m). Parts of thirty seven fields, containing one or more foci, were sampled intensively by extracting at least 1.5 kg of soil per square metre (1.33 · 0.75 m). Forty foci were analysed for spatial distribution characteristics of cysts using Generalized Linear Models (GLM's) and classical Multiple Linear Regression Analysis, differing in assumptions about the distribution of the input variable (number of cysts per kg of soil).

    The results showed that the data from all investigated cropping areas fit well to an exponential model with two parameters, the length and width gradient parameters. Significant differences in these parameter values between cropping areas could not be demonstrated. As both parameters follow a normal distribution, the probability of any combination of these parameters can be described by a bivariate normal distribution. Gradient parameters were correlated but significant correlations between these parameters and certain variables, such as the nematode species involved ( G. pallida or G. rostochiensis ), the time interval between sampling and the last potato crop, soil type, cropping frequency and cyst density in the focus centre could not be demonstrated. It can be concluded that one detection method for small infestation foci suffices for all investigated cropping areas. Its expected accuracy is independent of soil type, potato cyst nematode species, cropping frequency or time interval between sampling and last potato crop.

    In Chapter 8 the model for infestation foci developed in the previous chapter was applied for practical usage. A computer program called SAMPLE was developed to evaluate existing and create new sampling methods for the detection of patchy infestations or 'foci' of the potato cyst nematode ( Globodera spp.). By combining a model for the medium scale distribution of cysts, which provides the expected population densities at each position within the focus, and a model for the small scale distribution within square metres (negative binomial distribution) SAMPLE allows to simulate sampling procedures.

    The importance of the parameters of the two distribution models - the length and width gradient parameters for the medium scale distribution and the aggregation factor k of the negative binomial distribution for the small scale distribution - was investigated by sensitivity analyses. The aggregation factor k proved to be less important when calculating the average detection probability of a focus than the length and width gradient parameters. Several existing versions of the statutory sampling method used in The Netherlands were tested for their performance on a standard infestation focus with a central population density of 50 cysts/kg soil.

    The standard focus is small enough to use resistant potato varieties as a control measure without noticeable yield reductions in a 1:3 potato crop rotation. As the statutory soil sampling methods did not perform with the desired average detection probability, set at 90%, the program was used to develop several new sampling methods for focus detection and to investigate their performance. SAMPLE is a tool to develop sampling methods on demand for every possible combination of characteristics required for use by seed and ware potato growers (recommendations for optimum control measures leading to maximum returns, Integrated Pest Management) and by governments (legislation, quarantine and export protection).

    For advisory purposes a model is required describing the relation between the number of potato cyst nematodes and tuber yield. A stochastic model with biologically relevant parameters was available. In Chapter 9 the direct relation between the number of potato cyst nematodes and plant growth is described and used to deduce the relation between nematode density and yield reduction of total plant weight and tuber yield. The relation between small and medium initial population densities and the relative total plant weight was derived as cross sections at right angles to the time axis of a growth model with three dimensions: time after planting t , relative total plant weight Y and relative growth rate r p /r 0 . The relative growth rate is the (constant) ratio between the growth rate r p of plants of a certain weight at a nematode density P and the growth rate r 0 of (younger) plants of the same weight without nematodes. Therefore, the ratio between the time after planting that plants need to reach a certain weight in the absence of nematodes and at nematode density P, t 0 /t p equals the ratio r p /r o (2).

    The relative growth rate r p /r o = k + (1 -k )0.95 P/T -1for P > T and = 1 for P ≤T (3). Formally, k is the minimum relative growth rate as P →∞. As a result the arbitrary equation y = m + (1- m )0.95 P/T- 1for P > T and = 1 for PT (6) also applies to the relation between small and medium initial population densities and relative total plant weight. T is the tolerance limit, below which growth and yield are not reduced by nematodes; m is the relative minimum yield.

    The relations between small and medium initial population densities of potato cyst nematodes and relative tuber weight of potatoes can be derived from the growth model in an analogous way. However, there is one complication: tuber initiation does not start at the same haulm weight in plants with and without nematodes, but at the smaller haulm weight the larger the nematode density. As a consequence, tuber weights of plants with a certain total weight at nematode density P are not equal to those of plants with the same total weight without nematodes, but r p Δ t units of weight larger,Δ t being the difference between the actual time of tuber initiation and the time total plant weight becomes the same as that of plants without nematodes at the initiation of tuber formation.

    Relative total and tuber weights of plants with 'early senescence' and at large nematode densities are smaller than estimated by the model and equation (2). This indicates that at large initial population densities growth reducing mechanism(s) become active that were not operating at smaller densities.

    In Chapter 10 an advisory system is presented for the management of potato cyst nematodes ( Globodera pallida) . It emphasizes the use of partially resistant potato cultivars, which provide the possibility of keeping population densities of potato cyst nematodes at a low level in short fixed rotations. Using stochastic models based on the population dynamics of potato cyst nematodes and the relation between pre-plant nematode densities and relative yield it is possible to calculate the probabilities of population development and the reductions in yield caused by these population densities. A simulation model is developed which integrates both models, using the frequency distributions of some of the most variable parameters relevant to a particular combination of potato cultivar and nematode population. Also, the natural decline in population density when non-hosts are grown is incorporated in the model.

    The model makes it possible to calculate the probability of a certain yield reduction, given a certain potato cultivar, nematode population and rotation. Therefore, it becomes feasible for a farmer to evaluate risks and the costs of different control measures in fixed rotations. The application of this model in the starch potato growing areas could lead to significant improvements in financial returns and a major reduction of the use of nematicides.

    In Chapter 11 we describe the 'Seinhorst research program' initiated by Dr J.W. Seinhorst, former head of the Nematology Department of the IPO-DLO. It consists of an empiric philosophy, the scientific methods applied, and the models developed at the IPO-DLO during the last 45 years of nematological research, including the 13 years in which the research described in this thesis was carried out. All theories of the Seinhorst research program are developed by searching for recurring regularities (patterns) in a collection of observations, named 'the empirical base'. To prevent " ghost theories from sloppy data " all assumptions underlying the empirical base are carefully described in theories with respect to methodology and technology, including statistics.

    The patterns to be recognized are summarized by mathematical equations, which must be connected with biological processes to bridge the gap between 'normal' language and mathematical language for the description of biological theories. Often, the patterns result from more than one biological process. If so, the basic patterns are disentangled from one another using a method of pattern analysis. The procedure is best carried out when only a limited number of more or less congruent patterns are involved. Therefore, attention must be given to the choice of the hierarchic level and the complexity of the investigated system. Investigations proceed from simple experimental systems to complex natural systems at a hierarchic level that is neither so high that manifesting processes are very dissimilar nor so low that one runs the risk of describing processes irrelevant for the purpose of the investigation.

    In the 'Seinhorst Research Program' this purpose is finding methods for improvement of financial returns of host crops attacked by plant-parasitic nematodes through calculating risks of nematode population development and subsequent yield reduction. Pattern analysis yields theories about causes of phenomena observed at the investigated hierarchic level and about properties of processes at the nearest lower hierarchic level. Predictions at the next higher hierarchic level are made by synthesizing several patterns in (stochastic) simulation models. Synthesis is also applied to compound patterns of processes in simple experimental systems, with the objective to explain complicated patterns in complex systems.

    In the Conclusions ( Chapter 12 ) an overview is presented of the practical results and aspects of the research effort described in this thesis. Some comments are made on the present state of affairs concerning potato cyst nematode control in the Dutch seed- and ware potato growing areas.

    Schade wordt slechts minimaal beperkt : granulaten op licht mariene zavelgronden leveren niets op tegen Trichodorus
    Koot, P.A.C. ; Molendijk, L.P.G. - \ 1997
    PAV-bulletin. Vollegrondsgroenteteelt / Praktijkonderzoek voor de Akkerbouw en de Vollegrondsgroenteteelt 1997 (1997)1. - ISSN 1385-5298 - p. 20 - 23.
    allium cepa - beta vulgaris - schuld - ondernemingen - verliezen - nematiciden - nematoda - uien - gewasbescherming - aardappelen - rentabiliteit - winsten - bodem - solanum tuberosum - suikerbieten - oogsttoename - oogstverliezen - opbrengsten - paratrichodorus teres - allium cepa - beta vulgaris - debt - enterprises - losses - nematicides - nematoda - onions - plant protection - potatoes - profitability - profits - soil - solanum tuberosum - sugarbeet - yield increases - yield losses - yields - paratrichodorus teres
    Development and duration of accelerated degradation of nematicides in different soils
    Smelt, J.H. ; Peppel-Groen, A.E. van de; Pas, L.J.T. van der; Dijksterhuis, A. - \ 1996
    Soil Biology and Biochemistry 28 (1996)12. - ISSN 0038-0717 - p. 1757 - 1765.
    microbiële afbraak - nematiciden - persistentie - pesticidenresiduen - pesticiden - fysicochemische eigenschappen - gewasbescherming - bodemchemie - bodemeigenschappen - microbial degradation - nematicides - persistence - pesticide residues - pesticides - physicochemical properties - plant protection - soil chemistry - soil properties
    The development and duration of accelerated degradation of nematicides were studied in incubation experiments with soils from three experimental fields that had been treated annually for three to ten years with aldicarb, oxamyl, ethoprophos, fenamiphos or 1,3-dichloropropene. Highly accelerated degradation rates were measured for aldicarb, oxamyl and ethoprophos in a sandy soil (pH 7.3) treated three times. After five years without further treatments, these high rates were still found for aldicarb and oxamyl, but not for ethoprophos. In another field (sandy soil, pH 5.6) little or no increase in the degradation rates was measured in plots that had been treated ten times.
    Emission of fumigants from soil and dispersion in air
    Berg, F. van den - \ 1992
    Agricultural University. Promotor(en): L. Wartena, co-promotor(en): E.H. Adema; M. Leistra. - S.l. : Van den Berg - 223
    grondsterilisatie - bodemfumigatie - desinfecteren - bodem - gewasbescherming - pesticiden - pesticidenresiduen - persistentie - organische verbindingen - bodemchemie - nematiciden - luchtverontreiniging - milieu - schade - milieueffect - fumigatie - neerslag - chemische eigenschappen - zuurgraad - zure regen - milieuhygiëne - soil sterilization - soil fumigation - disinfestation - soil - plant protection - pesticides - pesticide residues - persistence - organic compounds - soil chemistry - nematicides - air pollution - environment - damage - environmental impact - fumigation - precipitation - chemical properties - acidity - acid rain - environmental hygiene

    In the Netherlands, soil fumigants are used on a large scale for nematode control in arable farming. After injecting the fumigant into the soil, a fraction of the dosage of 1,3-dichloropropene and methyl isothiocyanate (formed from metham-sodium) diffuses up to the soil surface and escapes into the air.

    The processes involved in fumigant behaviour in soil are described and the factors affecting these processes are discussed. A standard model including the most important processes is described and used to simulate the fumigation of fields injected with 1,3-dichloropropene or metham-sodium. It was computed that up to a few tens of percent of the dosage of the fumigant can be emitted into the air during the first three weeks after injection.

    The impact of several simplifications in the standard model on the rate and extent of emission of fumigant into the air was evaluated. The effect of a fumigant content- dependent rate coefficient for the transformation of fumigant in soil and that of changes in soil moisture content on the rate and extent of emission into the air was computed to be substantial. Although a diurnally changing soil temperature was computed to affect the rate of emission of fumigant into the air substantially, its effect on the cumulative emission in time, compared with a soil system at the average temperature, was computed to be negligible.

    Measurements on the one-hour concentrations of methyl isothiocyanate and 1,3-dichloropropene in air were done around two fields injected with metham-sodium and around two other fields injected with 1,3-dichloropropene. Concentrations measured in air were compared with those computed using a gaussian plume model. The comparatively large differences between the computed and measured concentrations in the air during the first few days after injection could be ascribed to an underestimation of the source strength of the emission. Improving the description of the pattern of concentrations of fumigant in air would require more detailed measurements on input parameters for the dispersion model.

    In two consecutive years, 6-hour concentrations of 1,3-dichloropropene and methyl isothiocyanate were measured at two locations in a region with intensive use of soil fumigants. For some weeks with many fumigations in this region, the concentration of fumigant in air at a receptor site, with representative fumigated fields at different upwind distances, was computed using a gaussian plume model. The computed and measured concentrations were of the same order of magnitude.

    Transformation rate of methyl isothiocyanate and 1,3-dichloropropene in water-saturated sandy subsoils.
    Boesten, J.J.T.I. ; Pas, L.J.T. van der; Smelt, J.H. ; Leistra, M. - \ 1991
    Netherlands Journal of Agricultural Science 39 (1991)3. - ISSN 0028-2928 - p. 179 - 190.
    groundwater pollution - leaching - nematicides - persistence - pesticide residues - pesticides - plant protection - pollution control - protection - sandy soils - soil - water quality
    Onderzoek naar het effect van systemische nematiciden bij koolgewassen
    Moel, C.P. de; Kramer, C.F.G. - \ 1990
    Lelystad : PAGV (Verslag / Proefstation voor de Akkerbouw en de Groenteteelt in de Vollegrond nr. 114) - 30
    koolsoorten - nematiciden - gewasbescherming - systemische werking - cabbages - nematicides - plant protection - systemic action
    Populatie - ontwikkeling van het bietecysteaaltje (Heterodera schachtii) en de optredende schade bij continueteelt van suikerbieten in combinatie met grondontsmetting
    Lamers, J.G. ; Moel, C.P. de - \ 1990
    Lelystad : PAGV (PAGV verslag 113) - 35
    suikerbieten - beta vulgaris - plantenparasitaire nematoden - heterodera schachtii - populatiedynamica - grondbehandeling - nematiciden - nederland - grondsterilisatie - sugarbeet - beta vulgaris - plant parasitic nematodes - heterodera schachtii - population dynamics - soil treatment - nematicides - netherlands - soil sterilization
    Effect of crop rotation, cultivar and nematicide on growth and yield of potato (Solanum tuberosum L.) in short rotations on a marine clay soil
    Scholte, K. ; Jacob, J.J. 's - \ 1990
    Potato Research 33 (1990)2. - ISSN 0014-3065 - p. 191 - 200.
    zware kleigronden - gewassen - cultivars - groei - nematiciden - gewasbescherming - aardappelen - rassen (taxonomisch) - rotaties - solanum tuberosum - rassen (planten) - oogsttoename - oogstverliezen - opbrengsten - clay soils - crops - cultivars - growth - nematicides - plant protection - potatoes - races - rotations - solanum tuberosum - varieties - yield increases - yield losses - yields
    The effects of cropping frequency on the yield of potato and on the development of soil-borne diseases was studied from 1979 to 1985 in a crop rotation experiment on a marine clay soil. Tuber yield decreased markedly with increasing cropping frequency. The yield of cv. Hertha was reduced by 27% in continuous cropping and by 15% in a wheat/potato or sugar beet/potato rotation, when compared with the rotation wheat/sugar beet/oats/potato. However, a pot experiment showed that yield depression in continuous cropping depended on the cultivar used.

    Crop growth declined in the second part of the growing season, and senescence accelerated as the cropping frequency increased.Verticillium dahliae was the most important yield-reducing factor. Root infection by this fungus was stimulated by the root-lesion nematodePratylenchus neglectus.
    Accelerated transformation of 1,3-dichloropropene in loamy soils.
    Smelt, J.H. ; Teunissen, W. ; Crum, S.J.H. ; Leistra, M. - \ 1989
    Netherlands Journal of Agricultural Science 37 (1989)3. - ISSN 0028-2928 - p. 173 - 183.
    boulder clay soils - carbohydrates - cellulose - chlorinated hydrocarbons - ddt - decomposition - disinfestation - loam soils - nematicides - organochlorine compounds - persistence - pesticide residues - pesticides - plant protection - soil - soil fumigation - soil sterilization
    Neveneffecten van grondontsmetting op de totale bouwplanopbrengst op kleigrond
    Hoekstra, O. - \ 1989
    In: Jaarboek 1987-1992 : verslagen van in 1987-1992 afgesloten onderzoekprojecten op Regionale Onderzoek Centra en het PAGV Lelystad : Proefstation voor de Akkerbouw en de Groenteteelt in de Vollegrond (Publikatie / Proefstation voor de Akkerbouw en de Groenteteelt in de Vollegrond, Regionale Onderzoekcentra no. 38-64) - p. 10 - 18.
    grondsterilisatie - bodemfumigatie - desinfecteren - bodem - gewasbescherming - nematiciden - pesticiden - nadelige gevolgen - selectiviteit - toxiciteit - onbedoelde effecten - niet-doelorganismen - oogsttoename - oogstverliezen - opbrengsten - soil sterilization - soil fumigation - disinfestation - soil - plant protection - nematicides - pesticides - adverse effects - selectivity - toxicity - nontarget effects - nontarget organisms - yield increases - yield losses - yields
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