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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    High-performance inhoudsstoffen vinden hun weg naar de markt
    Meer, I.M. van der; Vollebregt, M. - \ 2015
    Kennis & Innovatie (2015)3. - p. 2 - 4.
    biobased economy - materialen uit biologische grondstoffen - chemicaliën uit biologische grondstoffen - plantextracten - rubber - reststromen - kleurstoffen (dyes) - plantaardige pesticiden - innovaties - biobased economy - biobased materials - biobased chemicals - plant extracts - rubber - residual streams - dyes - botanical pesticides - innovations
    High-performance inhoudsstoffen uit biomassa ontstijgen de onderzoekslaboratoria en duiken op in proefprojecten met bedrijven en concrete toepassingen in eindproducten. Het tempo waarmee dit gebeurt en de onderliggende markt drivers verschillen per productgebied, zo blijkt uit een rondje langs biobased projecten op het gebied van kleurstoffen, farmaceutische producten/functional foods, gewasbescherming en natuurrubber.
    Natural products for malaria vector control: flora, fish and fungi
    Howard, A.F.V. - \ 2010
    Wageningen University. Promotor(en): Willem Takken; Marcel Dicke, co-promotor(en): J.J. Githure. - [S.l. : S.n. - ISBN 9789085857204 - 267
    malaria - ziekten overgebracht door muskieten - vectorbestrijding - natuurlijke producten - biologische bestrijding - plantaardige pesticiden - biopesticiden - vis - malaria - mosquito-borne diseases - vector control - natural products - biological control - botanical pesticides - microbial pesticides - fish
    Despite international organisations providing much focus over the past 10 years, malaria is still killing vast numbers of Africans, especially children. It is agreed that malaria can only be successfully controlled by using different control tools simultaneously in the spirit of integrated vector management (IVM), and that African communities will need to become more directly involved in mosquito control (Chapter 2). Using mosquito control tools in a way that requires almost no technical equipment or knowledge will open them up to the rural communities that are best placed to deploy them. In addition, widespread insecticide resistance is reducing the ability of insecticide-based tools to control mosquitoes. For these reasons, biological control and other natural mosquito control methods are being researched by many institutions. Several potential natural control tools are readily available in sub-Saharan Africa. If these tools prove effective and become operational, then it is possible that they will be sustainable because communities can intentionally produce the biological agents themselves, bringing a source of money to rural communities. This would be especially important in areas where infrastructure is poorly developed, and repeat applications of chemical control tools are not easily made. This thesis was designed to test the feasibility and effectiveness of a variety of natural products against both larval and adult malaria vector mosquitoes using low-tech methods in laboratory and field trials.

    Part I: Flora
    Azadirachta indica A. Juss (Meliaceae) (the neem tree) was chosen due to the already proved mosquitocidal properties, and its ready availability in Africa. We wanted to use neem in a way that could easily be deployed in resource-poor rural areas. Laboratory studies were conducted to examine the larvicidal and pupicidal properties of a crude aqueous extract of neem wood against the principle African malaria vector, Anopheles gambiae Giles s.s. (Diptera: Culicidae) (Chapter 3) [1]. The results indicate that even a relatively low dose of 0.15 grams of dried neem wood in 1 litre of water was able to inhibit the emergence of 90% of mosquito adults when larvae were exposed during their first three larval instars. Even for the fourth (last) larval instar, just 0.6 g/l was required to prevent 90% emergence. Furthermore, neem-exposed larvae exhibited significantly increased development times when compared to the controls. Pupae were also killed by the aqueous neem extracts, and were subject to neem-induced emergence abnormalities, but the concentrations required to kill pupae were much higher than for larvae and not likely to be used operationally. High performance liquid chromatography (HPLC) analysis identified several polar constituents in the aqueous neem extracts including nimbin and salannin. However, azadirachtin was not present in significant amounts. The effect of this extract on the oviposition behaviour of adult female An. gambiae s.s. mosquitoes was then monitored (Chapter 4) [2]. The oviposition results show that when using 0.1 g/l of the crude aqueous neem extract, significantly more mosquitoes laid their eggs when compared to mosquitoes exposed to the control treatment. For the doses 10x and 100x higher, the same proportion of mosquitoes laid their eggs as in the control, indicating that even at much higher doses than required for successful larval control, female oviposition will not be detrimentally affected.

    Part II: Fish
    Larvivorous fish have previously been shown to effectively control mosquito numbers. Therefore, a census was carried out to examine the current status of fish farming in western Kenya (Chapter 5) [3]. Working with the Kenyan Fisheries Department we found that while fish farming is a favoured activity, 30% of the 261 ponds found did not contain fish. These “abandoned” ponds had significantly more An. gambiae s.l., Anopheles funestus Giles and culicine mosquitoes when compared to the ponds that still contained fish. Furthermore, An. gambiae s.l. was proportionally more abundant in the abandoned ponds when compared to the other mosquito types. Surprisingly, vegetation did not significantly affect mosquito distribution. Following our study, demand for fish to restock abandoned ponds increased by 67% when compared to the previous year. The overwhelming majority of fish being farmed in our census area were fish of the tilapiine subfamily. Given this finding, we set up a small-scale field experiment to study the larvivorous potential of the tilapiine fish Oreochromis niloticus L. (Perciformes: Cichlidae) (Chapter 6) [4]. Taking daily measurements of mosquito numbers, we found that immediately after fish introduction, the density of mosquitoes in the treated ponds dropped in comparison to the increase in the control pond. After 15 weeks, anopheline numbers had decreased by >94% in the ponds containing the fish, and we found that fish were able to sustainably control mosquitoes for at least 6 months, when our study finished. It is concluded that this type of fish could be an effective and sustainable way to control mosquito numbers in rural western Kenya. Furthermore, this fish provides a source of much needed income and protein to rural African communities.

    Part III: Fungi
    For the control of mosquito adults using natural products, entomopathogenic fungi hold the most promise. In this thesis the entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae were separately suspended in mineral oil and applied to polyester netting. A laboratory experiment was then conducted to investigate the fungal susceptibility of insecticide-susceptible and insecticide-resistant strains of An. gambiae s.s.. In addition, fungal conidial viability was tested at various time points after application onto polyester netting (Chapter 7) [5]. Whilst both mosquito strains were susceptible to both species of fungal infection, the pyrethroid-resistant An. gambiae s.s. VKPER strain was significantly more susceptible than the insecticide-susceptible SKK strain, dying more quickly. Conidial viability was significantly lower for both species after application onto the polyester netting when compared to the viability in suspension. However, the ability of the treated netting to infect and kill mosquitoes was not significantly diminished over the one week trial period. Given the finding that fungal-treated polyester netting could infect and kill mosquitoes, an experimental hut field trial was conducted in Benin, West Africa, to investigate the effect of fungal treatment on blood feeding behaviour and survival of wild insecticide-resistant mosquitoes. Benin was chosen due to the presence of multi-insecticide-resistant mosquito populations that are threatening the effectiveness of current vector control. We used fungal-treated netting to infect mosquitoes entering the hut windows, and either an untreated or insecticide-treated bednet was placed into each hut to examine how the entomopathogenic fungi would work with current control tools (Chapter 8) [6]. Only enough Culex quinquefasciatus Say (Diptera: Culicidae) mosquitoes were collected from the huts for accurate analysis. Our study was the first to monitor the effect of entomopathogenic fungi on blood feeding of wild mosquitoes. We found that the B. bassiana treatments caused significant and instantaneous reductions in blood feeding. No significant effect of the fungi on mosquito mortality was found. Conidial viability of B. bassiana and M. anisopliae was found to decrease rapidly under field conditions [7].

    This thesis used several different experimental techniques to examine the potential of three natural products to control mosquitoes. For the flora, it was found that even a small amount of neem wood in water would control mosquitoes (Chapter 3), and at this and higher doses, the oviposition behaviour was not adversely affected (Chapter 4). Neem trees are readily available in many areas of Africa, and promising field trials indicate that the use of this tree species should be incorporated into malaria control trials.
    This thesis reports that edible native African fish can be effective at controlling mosquitoes (Chapter 6), but if fish farming is abandoned and the ponds not filled in, then they can allow large numbers of the most effective malaria vectors to breed (Chapter 5). Fish have been successfully used for malaria vector control in many countries and this could be rolled out across appropriate areas of Africa, as long as it is accompanied with adequate education about the dangers of abandoned ponds.
    We found that insecticide-resistant mosquitoes were more susceptible to fungal infection than the insecticide-susceptible strain. Under field conditions fungi were able to prevent blood feeding but did not cause significant mortality in the wild-caught mosquitoes. Although entomopathogenic fungi produce high levels of mortality in laboratory settings, (Chapter 7), their use under field conditions still has a long way to go and is not yet at the operational stage. Although the results found in this thesis are encouraging for the use of fungi in African situations (Chapter 8), further work should be carried out to maximise fungal persistence under field conditions.
    The current emphasis is on IVM for malaria control (Chapter 2), and focus is turning to biological control tools that can help manage insecticide-resistant populations. With this in mind, the natural products investigated in this thesis have produced encouraging results that show they have the potential to be integrated into malaria control strategies. Furthermore, flora and fish are readily available in the areas where they are most required, and could be used almost immediately to help reduce mosquito numbers and correspondingly, malaria disease transmission.

    Ethnobotanicals for management of the brown ear tick Rhipicephalus appendiculatus in western Kenya
    Wanzala, W.W. - \ 2009
    Wageningen University. Promotor(en): Joop van Lenteren, co-promotor(en): Willem Takken; A. Hassanali. - [S.l.] : S.n. - ISBN 9789085853176 - 231
    rhipicephalus appendiculatus - metastigmata - vectoren, ziekten - etnobotanie - acariciden - plantaardige pesticiden - vectorbestrijding - rhipicephalus appendiculatus - metastigmata - disease vectors - ethnobotany - acaricides - botanical pesticides - vector control
    This thesis describes the results of a study to assess the effect of ethnobotanical products on the behaviour of the brown ear tick Rhipicephalus appendiculatus, the main vector of East Coast fever in sub-Saharan Africa. Ethnoknowledge of the Bukusu people in western Kenya on tick control and management was evaluated to identify plants that affect livestock ticks, using participatory action research approaches. More than 150 plant species spread over 110 genera and 51 families were identified and documented. From these, eight plants were selected and their essential oils extracted and used for screening in the laboratory on their behavioural effects on ticks. From these, the plants Tagetes minuta and Tithonia diversifolia were chosen for further studies. The essential oils of these two plants were further extracted and used in laboratory and field bioassays.
    From the laboratory assay, using a dual-choice apparatus, it was found that essential oils of both T. minuta and T. diversifolia affect tick climbing behaviour, representing a repellent response. Dose response effects were observed. On steers, differential effects to the essential oils were observed with R. appendiculatus, which prefer to feed mainly inside the ears of the host animal. It was found that treatment of the ear region with the essential oils of both T. minuta and T. diversifolia significantly deterred ticks from reaching the ear. The essential oils of T. minuta and T. diversifolia were evaluated in the field and significantly shown to affect R. appendiculatus and other ticks naturally attached to the host animals. The essential oil of T. minuta affects R. appendiculatus and other ticks more than the essential oil of T. diversifolia.
    The results suggest the potential for essential oils to be incorporated in the on-host “push” and “push-pull” strategy for the control and management of R. appendiculatus, other affected livestock ticks and associated tick-borne diseases among the resource-limited livestock farming community in tropical Africa.
    Effectiveness and safety of botanical pesticides applied in black pepper (Piper nigrum) plantations
    Wiratno, - \ 2008
    Wageningen University. Promotor(en): Ivonne Rietjens; Tinka Murk, co-promotor(en): D. Taniwiryono. - [S.l.] : S.n. - ISBN 9789085049838 - 126
    piper nigrum - zwarte peper - insectenplagen - plantenparasitaire nematoden - plantaardige pesticiden - veiligheid - veiligheid op het werk - geïntegreerde plagenbestrijding - piper nigrum - black pepper - insect pests - plant parasitic nematodes - botanical pesticides - safety - safety at work - integrated pest management
    Black pepper (Piper nigrum L) is an important commodity of Indonesia, which has been cultivated since the 6th century. The plant plays an important role in local economies since 95% of the plantations are cultivated by smallholder farmers. Because of this important economic value, proper plant production is highly valued. One of the central factors to maintain plant production is how to control key pests of the plant such as the root-knot nematode, Meloidogyne incognita, the stem borer, Lophobaris piperis, the tinged bug, Dasynus piperis, and the bug, Diconocoris hewetti (Chapter 1). Currently, farmers habitually use synthetic pesticides to control these pests. However, this habit poses not only a serious health risk to local workers and the people living near the treated areas, but also threatens non-target species (Chapter 2). Therefore, it has become an important issue to find relatively easy alternative control strategies, which are comparable effective as the synthetic pesticides, but safer to the farmers, consumers, and the environment and available at low price. One of the possible alternatives would be the use of botanical pesticides. Indonesia seems to be in a good position to develop and utilize this pesticide since the country has a rich biodiversity of plant species. Nowadays, the increased consumer request in developed countries for organic products stimulates the interest in the use of botanical pesticides.
    Chapter 3 describes the nematicidal activity of 17 plant extracts against the root-knot nematode, M. incognita. Results demonstrate that shapes of the dead nematodes in laboratory experiments can clearly be distinguished differed in a characteristic way, and groups of pesticides and plant extracts. This phenomenon may be an indicator for the modes of action of the tested pesticides. The green house experiment indicates that raw material of clove bud is comparable effective as the recommended synthetic pesticide. Chapter 4 describes contact toxicity, oral toxicity and repellency of 17 plant extracts against the model insect species Tribolium castaneum. This study shows that the most promising candidates for consideration as botanical pesticides are extracts of pyrethrum, sweet flag, tobacco, clove, lemongrass, neem, vetiver, graviola, citrosa and black pepper.
    Formulation of three of 10 most potent extracts was developed and tested in the laboratory followed by field experiments. Laboratory experiments indicate that extracts from pyrethrum, sweet flag and clove show the highest toxicity and/or repellent effect toward L. piperis. Field experiments reveal that the formulation is able to control most pest species of the pepper plants in the meantime being less toxic towards the 11 monitored species of natural enemies for known pest organisms such as caterpillars, aphids, moths, beetles than that of the recommended synthetic pesticide, deltamethrin. Furthermore, the field experiments reveal that within 9 hours after application the treated plants are recolonized again by ants and spiders, indicating a short degradation period of the formulation.
    Altogether it is concluded that the newly defined botanical formulation provides an effective and environmentally friendly alternative for controlling several pests of black pepper (Chapter 5).
    The safety of five botanical pesticides i.e. pyrethrum, clove, sweet flag, and derris is evaluated for human oral exposure via consumption of treated products. Based on literature data from human and animal studies safe levels for daily oral exposure to the various botanical preparations and/or their active ingredients were derived and these outcomes were compared to the estimated maximal daily intake of residues of the botanical pesticides expected to be present on pepper berries treated with these preparations as pesticides. Results indicate that use of extracts of sweet flag containing beta-asarone would result in a MoE that would not indicate a high priority for risk management. However, because for beta-asarone restrictions in applications as food additive are indicated and since use as a pesticide implies an avoidable risk, it is concluded that the application of this botanical pesticide should not be encouraged. The use and use levels of the other three botanical pesticides evaluated are not of safety concern (Chapter 6). Finally, in chapter 7, the implications of the presented work are discussed, with emphasis on the potency, suitability and the safety of the botanical pesticides when used against pests associated with pepper plants. Overall, the results obtained confirm the hypothesis that botanical pesticides have the potency to be used to control pests of black pepper, providing a promising alternative for synthetic pesticide use, especially because they pose lower risks for the local environment.

    GNO's tegen Pythium in komkommer
    Paternotte, S.J. ; Flier, W.G. ; Förch, M.G. ; Stevens, L.H. ; Verstappen, F.W.A. ; Bouwmeester, H.J. - \ 2008
    gewasbescherming - komkommers - cucumis sativus - plantenziekteverwekkende schimmels - pythium aphanidermatum - wortelrot - plantenziektebestrijding - biopesticiden - plantaardige pesticiden - teelt onder bescherming - kasproeven - glastuinbouw - plant protection - cucumbers - cucumis sativus - plant pathogenic fungi - pythium aphanidermatum - root rots - plant disease control - microbial pesticides - botanical pesticides - protected cultivation - greenhouse experiments - greenhouse horticulture
    Tegen Pythium aphanidermatum, het belangrijkste wortelpathogeen in de teelt van komkommer, worden relatief veel chemische gewasbeschermingsmiddelen gebruikt. Onderzocht wordt of GNO’s (Gewasbeschermingsmiddelen van Natuurlijke Oorsprong) een alternatief kunnen bieden
    GNO's tegen Botrytis in bolgewassen
    Werd, H.A.E. de; Boer, M. de; Stevens, L.H. ; Flier, W.G. ; Bouwmeester, H.J. - \ 2008
    gewasbescherming - bloembollen - plantenziekteverwekkende schimmels - vuur (plantenziektekundig) - botrytis - fungiciden - plantaardige pesticiden - lelies - veldproeven - plant protection - ornamental bulbs - plant pathogenic fungi - blight - botrytis - fungicides - botanical pesticides - lilies - field tests
    Voor vuurbestrijding (Botrytis) in bolgewassen worden relatief veel fungiciden gebruikt. Om de afhankelijkheid hiervan te verminderen werd onderzocht of GNO’s (Gewasbeschermingsmiddelen van Natuurlijke Oorsprong) een alternatief kunnen bieden
    Toedieningswijze en formulering cruciaal voor effectiviteit van GNO's
    Zande, J.C. van de; Stevens, L.H. ; Spits, H.G. - \ 2006
    gewasbescherming - pesticiden - plantaardige pesticiden - biopesticiden - toedieningswijzen - doseringseffecten - formuleringen - bladbespuiting - aardappelen - lelies - appels - toelating van bestrijdingsmiddelen - plant protection - pesticides - botanical pesticides - microbial pesticides - application methods - dosage effects - formulations - foliar spraying - potatoes - lilies - apples - authorisation of pesticides
    Succesvolle introductie van GNO’s in de praktijk is in hoge mate afhankelijk van een juiste toedieningswijze en daarmee samenhangende formulering. Verbetering van de effectiviteit verlaagt de benodigde hoeveelheid GNO’s, waardoor de kans op introductie wordt verhoogd. Onderzoek naar toediening en formulering is daarom een integraal onderdeel van de ontwikkeling van GNO-produkten voor de praktijk
    Inventory of possible emerging hazards to food safety and an analysis of critical factors
    Kleter, G.A. ; Poelman, M. ; Groot, M.J. ; Marvin, H.J.P. - \ 2006
    Wageningen : RIKILT (Rapport / RIKILT 2006.010) - 41
    voedselveiligheid - gevaren - risicoschatting - antibiotica - antibioticumresiduen - garnalen - garnalenteelt - plantaardige pesticiden - food safety - hazards - risk assessment - antibiotics - antibiotic residues - shrimps - shrimp culture - botanical pesticides
    Various recent incidents around food safety issues have led to the establishment of the European Food Safety Authority and its national counterparts in the member states of the European Union. Besides these measures, it is desirable to identify food risks while they are still emerging, i.e. when they still are hazards.
    BioSupport: op weg naar registratie van GNO's
    Köhl, J. - \ 2005
    gewasbescherming - biologische bestrijding - plantaardige pesticiden - natuurlijke producten - biopesticiden - registratie - marketing - plant protection - biological control - botanical pesticides - natural products - microbial pesticides - registration - marketing
    PRI en PPO ontwikkelen biologische bestrijders en GNO’s tegen ziekten en plagen. Ondanks de hoge werkzaamheid zijn tot nu toe weinig nieuwe middelen beschikbaar gekomen voor de praktijk. De marktintroductie van deze gewasbeschermingsmiddelen van natuurlijke oorsprong (GNO’s) verloopt moeizaam. Een van de oorzaken zijn de zeer hoge kosten van registratie. BioSupport helpt bij de registratie van ‘marktrijpe’ GNO’s en biologische bestrijders
    Bestrijding wortelknobbelaaltjes in chrysant: Effectiviteit van Chitosan*, Chitine* en 'ruwe Chitine*'
    Stapel, L.H.M. ; Amsing, J.J. ; Jongh, M.A. de; Jong-Lanser, C.J. de; Hazendonk, D.A. - \ 2004
    Aalsmeer : Praktijkonderzoek Plant & Omgeving B.V. (Rapporten PPO ) - 30
    chrysanten - snijbloemen - nematoda - meloidogyne javanica - gewasbescherming - teelt onder bescherming - plantaardige pesticiden - nederland - chrysanthemum - glastuinbouw - chrysanthemums - cut flowers - nematoda - meloidogyne javanica - plant protection - protected cultivation - botanical pesticides - netherlands - chrysanthemum - greenhouse horticulture
    Bestrijding wortelknobbelaaltjes in chrysant: effectiviteit van Lignosulfonaat* en Carvacrol*
    Stapel, L.H.M. ; Amsing, J.J. ; Jongh, M.A. de; Jong-Lanser, C.J. de - \ 2004
    Aalsmeer : Praktijkonderzoek Plant & Omgeving B.V. (Rapporten PPO ) - 27
    chrysanten - snijbloemen - nematoda - meloidogyne javanica - gewasbescherming - teelt onder bescherming - plantaardige pesticiden - nederland - chrysanthemum - glastuinbouw - chrysanthemums - cut flowers - nematoda - meloidogyne javanica - plant protection - protected cultivation - botanical pesticides - netherlands - chrysanthemum - greenhouse horticulture
    Appelluis vlucht voor stank : olie en feromoon als bestrijdingsmiddel
    Tol, R.W.H.M. van; Helsen, H.H.M. - \ 2004
    Oogst : weekblad voor de agrarische ondernemer. Landbouw 17 (2004)7. - ISSN 1566-2616 - p. 34 - 35.
    dysaphis plantaginea - aphididae - malus - appels - plantenplagen - insectenplagen - plagenbestrijding - gewasbescherming - plantaardige pesticiden - plantaardige insecticiden - plantaardige oliën - insectenafweermiddelen - insectenbestrijding - feromonen - geurstoffen - apples - plant pests - insect pests - pest control - plant protection - botanical pesticides - botanical insecticides - plant oils - insect repellents - insect control - pheromones - odours
    Stand van zaken bij het onderzoek van PPO Randwijk en PRI naar de werkzaamheid van plantaardige oliën en feromonen voor de bestrijding van de roze appelluis in appel. De werking is gebaseerd op geurstoffen die het paringsgedrag van mannelijke en vrouwelijke bladluizen beïnvloeden
    Gladiolentripsen verjagen met signaalstoffen
    Conijn, C.G.M. ; Breedeveld, M.E. ; Kogel, W.J. de - \ 2003
    BloembollenVisie 22 (2003). - ISSN 1571-5558 - p. 24 - 24.
    bloembollen - gladiolus - insecten - thrips - plantaardige pesticiden - gewasbescherming - ornamental bulbs - gladiolus - insects - thrips - botanical pesticides - plant protection
    Gladiolentrips is een plaag in gladiolen op het veld, in de kas en de bewaring. Om minder afhankelijk te zijn van chemische middelen onderzoekt PPO of Gewasbeschermingsmiddelen van natuurlijke oorsprong in staat zijn gladiolenknollen tijdens de bewaring vrij te houden van trips. Plant Research International vond enkele stoffen uit planten die gladiolentripsen bestrijden. De eerste proeven met besmette gladiolenknollen gaven hoopvolle resultaten
    Visie biologische boeren op inzet van biologische en natuurlijke middelen
    Meekes, E.T. ; Belder, E. den - \ 2003
    Wageningen : Plant Research International (Rapport / Plant Research International 62) - 28
    biologische landbouw - groenteteelt - gewasbescherming - biologische bestrijding - plantaardige pesticiden - nederland - organic farming - vegetable growing - plant protection - biological control - botanical pesticides - netherlands
    Effect van Citrex op Phytophthora infestans in een ecologisch teeltsysteem; verslag van veldexperimenten in 1999-2001 op de Lovinkhoeve te Marknesse
    Smid, H.G. ; Scheepens, P.C. - \ 2002
    Wageningen : Plant Research International - 18
    phytophthora infestans - solanum tuberosum - aardappelen - biologische landbouw - bestrijdingsmethoden - plantaardige pesticiden - plantenziekteverwekkende schimmels - Citrex - phytophthora infestans - plant pathogenic fungi - solanum tuberosum - potatoes - organic farming - control methods - botanical pesticides - Citrex
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