Die Broschüre fasst die Ergebnisse einer Untersuchung zur wirksamen Bekämpfung von Maiszünslerlarven auf dauerhaft konservierend bestellten Ackerflächen zusammen. Der alleinige Einsatz von Pflug und Grubber zeigte keine ausreichende Wirkung, weil der Anteil intakter und für die Überwinterung der Larven geeigneter Maisstoppeln zu groß ist. Der Einsatz des Pfluges erhöhte die Erosionsgefährdung des Bodens. Lediglich die Scheibenegge zeigte als Sologerät eine hinreichende Zerkleinerungswirkung bei der flachen Einarbeitung der Erntereste. In Kombination mit dem Mulcher werden bei allen untersuchten Bodenbearbeitungsvarianten ausreichend Maisstoppeln beschädigt. Es kann empfohlen werden, Maisstoppeln mit einer Kombination aus Mulcher und Scheibenegge bzw. Grubber zu bearbeiten. So kann bei hinreichendem Erosionsschutz der Maiszünslervermehrung vorgebeugt werden. Gleichzeitig wird damit die Gefahr einer Fusarieninfektion im nachgebauten Getreide reduziert.

O Papaya ringspot virus - type W (PRSV-W) e o Zucchini yellow mosaic virus (ZYMV) são as duas espécies de potyvírus que mais causam danos em cucurbitáceas no estado de São Paulo e no Brasil. Uma boa alternativa de controle para as doenças causadas por esses vírus é o emprego da premunização. O principal objetivo desse trabalho foi estudar a competição por sítios de replicação como possível mecanismo de proteção entre a estirpe fraca PRSV-W-1 e a estirpe severa PRSV-W-C em plantas de abobrinha-de-moita. Além disso, procurou-se também conhecer o período mínimo necessário para a proteção de plantas de abobrinha-de-moita premunizadas com a estirpe fraca ZYMV-M, só e em dupla premunização com a estirpe fraca PRSV-W-1, para fornecer subsídios para o uso em condições de campo. O estudo da competição por sítios de replicação como mecanismo de proteção foi feito inoculando-se plantas de abobrinha-de-moita ‘Caserta‘ com a estirpe fraca PRSV-W-1 e desafiando-as com a estipe severa PRSV-W-C. As inoculações de proteção foram feitas nas folhas cotiledonares e as de desafio na folha nova verdadeira, e vice-versa, aos 3, 6 e 9 dias após a primeira inoculação. Plantas infectadas com a estirpe fraca e não desafiadas e plantas infectadas com a estirpe severa foram usadas como controles. As avaliações foram feitas com base na manifestação dos sintomas 30 dias após o desafio. Também foi feito teste de recuperação da estirpe desafiante e detecção desta por RT-PCR, com primers específicos, aos 8 dias após o desafio. Os resultados sugerem que, independente do local onde foi realizada a inoculação de proteção (folha cotiledonar ou folha nova expandida), de uma maneira geral parece haver alguns sítios livres para a superinfecção com a estirpe severa. Quando esta foi inoculada aos três dias após a proteção, ela se estabeleceu em algumas plantas, moveu-se sistemicamente e sobrepôs a estirpe fraca, uma vez que as plantas exibiram sintomas severos. Com o passar do tempo (seis e nove dias após a proteção), todas as plantas ficaram protegidas contra a expressão dos sintomas severos da estirpe desafiante, porém esta foi capaz de se estabelecer nas folhas inoculadas e até mesmo mover sistemicamente em algumas plantas. No caso da proteção com a estirpe fraca ZYMV-M, só ou em mistura com a estirpe fraca PRSV-W-1, contatou-se que plantas de abobrinha-de-moita premunizadas e desafiadas sete dias depois ficaram protegidas contra a infecção e/ou manifestação dos sintomas das respectivas estirpes severas usadas no desafio. / Papaya ringspot virus - type W (PRSV-W) and Zucchini yellow mosaic virus (ZYMV) are two potyviruses associated with severe yield losses on cucurbit crops in the State of São Paulo and other parts of the Brazilian territory. Preimmunization with mild strains has proved to be a good alternative for the control of both viruses in susceptible cultivars. The main purpose of this work was to evaluate the competition for infectable sites as a possible mechanism of cross protection between the mild strain PRSV-W-1 and the severe strain PRSV-W-C in zucchini squash (Cucurbita pepo cv. Caserta). Protective inoculation with the mild strain was done at the cotyledon and the challenge inoculation with the severe strain was applied on the first true expanded leaf, and viceversa. Different plants were challenged at three, six and nine days, respectively. No challenge protected plants and healthy plants infected with the severe strain were used as controls. Evaluations were based on the expression of the symptoms at 30 days after challenge inoculation. Attempts to recover the challenge strain from challenge inoculated and new developed leaves were also done at eight days after challenge inoculation. RT-PCR with specific pairs of primers was also used to detect both stains in some of these samples. Regardless the leaf on which the protective strain was applied (cotyledon or first true expanded leaf) there appear to be some infectable sites available for superinfection with the severe strain. When the challenge inoculation was done at three days after preimmunization, the severe strain was able to superinfect some plants, move systemically and overcome the mild strain, since these plants expressed severe symptoms. All plants become protected against the expression of the symptoms induced by the severe strain when the challenge inoculation was done at six and nine days after preimmunization. However, the severe strain was still detected in the inoculated and upper leaves of few test-plants, eight days after challenge inoculation. In addition to this, it was also determined the period of time necessary to protect zucchini squash plants with a mild strain of ZYMV, named ZYMV-M, alone and in mixture with mild strain PRSV-W-1. The results indicated that single and double preimmunized plants were protected against infection and/or expression of the homologous severe strain seven days after protective inoculation.

This study investigated methods to reduce herbicide application through improved targeting of weeds, thereby also reducing damage to pastures. The focus was to evaluate and improve wiper and spot-spraying application techniques for pasture herbicides as they reduce chemical use by treating just the weed. Wiper application of herbicides was shown to be a useful technique for controlling Californian thistles. In one trial, a stem reduction of over 90% when assessed 10 months post application was achieved with a double pass of clopyralid, metsulfuron and glyphosate when the plants were treated at the post-flowering stage and were vigorously growing. A double pass was superior to a single pass for glyphosate and triclopyr/picloram, but not for clopyralid and metsulfuron. Subsequent trials produced poor results possibly because of the stressed condition of the thistles and their growth stage as well as lack of consistency in wiper output and operator differences. Despite wiper applicators usually being selective, some damage to pastures was observed in the field, and from a series of experiments it was concluded that rain falling soon after wiper application was the likely cause of pasture damage. An innovative and highly sensitive technique using a spectrophotometer was developed to measure herbicide output from wiper applicators. A spectrophotometer could accurately measure clopyralid concentrations as low as 0.02 g active ingredient in a litre of water. The Eliminator and Rotowiper outputs were found to be highly variable while the Weedswiper was more consistent although it applied less herbicide than the other two wipers. Spot spraying experiments confirmed that glyphosate and metsulfuron create bare patches by damaging both grass and clover while clopyralid and triclopyr/picloram only eliminate clover. However, metsulfuron patches stayed bare for much longer while glyphosate ones quickly filled up with weeds and clover. Ingress of clover stolons appeared to be more important than re-establishment from seed in the recovery of patches. The bigger the damaged patch, the higher the likelihood of recolonisation by opportunistic weeds. Bioassay studies found that over-application of clopyralid and triclopyr/picloram provided residual activity up to 18 and 30 weeks, respectively, thereby potentially preventing re-establishment of white clover. The negative effects on clover seedlings from metsulfuron ranged from 3 to 6 weeks for standard and high rates, respectively, with a stimulatory effect on seedlings thereafter for up to 18 weeks. Dose-response curves for the application of metsulfuron and triclopyr/picloram into the centre 5% versus full plant coverage of Scotch thistle and ragwort rosettes showed that application of herbicide to the centre 5% was as effective at the same concentration and greatly reduced the risk of damage to pasture.

Pharmaka werden nach ihrer Einnahme bzw. Verabreichung über verschiedene Pfade in die Umwelt eingetragen. Obwohl Arzneimittel zu den toxikologisch best-untersuchten und -charakterisierten Stoffen gehören, ist ihre Wirkung auf die Umwelt und die darin lebenden Organismen weit weniger gut untersucht. Wenn in der Literatur Daten zur Ökotoxizität vorhanden sind, so beziehen sich diese meist nur auf die Wirkung von Einzelstoffen. In der Umwelt sind die Organismen jedoch gegenüber Mischungen exponiert. Aufgrund der geschilderten Problematik wurden eine Reihe von Arzneimitteln unterschiedlicher Indikationsgruppen einzeln und in Kombination mit dem Embryotest mit dem Zebrabärbling (Danio rerio, DarT) untersucht. Dieses Testsystem wurde durch Schulte & Nagel (1994) als Alternativmethode zum akuten Fischtest nach OECD 203 entwickelt und bietet den Vorteil neben letalen auch eine Reihe von subletalen Endpunkten erfassen zu können. Es handelt sich zudem nach dem deutschen Tierschutzgesetz nicht um einen Tierversuch. Die generelle Vergleichbarkeit der ermittelten Werte mit Daten aus akuten Fischtests nach OECD 203 sowie die Anwendbarkeit für verschiedenste Fragestellungen konnten in einer Reihe von Studien gezeigt werden (Nagel, 2002). Für die hier vorgestellten Untersuchungen wurden zunächst 32 Pharmaka und drei Pflanzenschutzmittel als Einzelstoffe mit dem DarT untersucht. Basierend auf den Ergebnissen der Einzelstofftests wurden Mischungen sowohl aus Substanzen mit ähnlichen als auch unähnlichen Wirkmechanismen getestet. Es zeigte sich, dass unabhängig vom Wirkmechanismus die Mischungstoxizität durch das Konzept der Konzentrationsadditivität gut vorhergesagt wurde, während das Konzept der Unabhängigen Wirkung die Mischungstoxizität unterschätzte. Ebenfalls konnte gezeigt werden, dass die Kombination der Stoffe auf Basis der NOEC, die im DarT anhand der Herzschlagfrequenz nach 48 Stunden ermittelt wird, zu deutlichen Mischungseffekten führt.

Der Bericht informiert über die Ergebnisse des Projektes »Bekämpfung des Echten Mehltaus am Apfel mit dem Wirkstoff Penconazol im Raum Sachsen«. Die Untersuchung erfolgte im Zeitraum von 2010 bis 2012 in Labor- und Feldversuchen. Für eine optimale Bekämpfung des Erregers Podosphaera leucotricha ist die Erziehung des Baumes zu einer schlanken Krone unumgänglich. Der Primärbefallsdruck in einer Anlage und der angrenzenden Flächen darf 5 % nicht überschreiten. Untersuchungen der Wirkstoffverteilung mit wassersensitivem Papier und Rückstandsanalysen in Blättern sind für die Beurteilung der Feldleistung von Penconazol notwendig. Diese ermöglichen den Bezug zu im Biotest erhobenen Sensitivitätswerten. Ein »shifting« der Schaderregerpopulation in der Peconazolsensitivität ist zu erkennen, jedoch keine Resistenz.

The diploma thesis deals with the design of the structural optimalization of the chassis stabilization of the self-propelled agricultural spraying machine and the causes of instability. The introductory part describes the normative conditions for plant care by spraying. The history of the spraying technician and the use of this self-propelled machinery are also detailed. A substantial part of the work is devoted to the construction parts of the self-propelled spraying machine and their proper function. Important emphasis is placed on the chassis parts, whose features are key to rocking the machine. Part of the thesis is the design of construction solutions aimed at increasing the stability of the machine chassis, including the evaluation of the optimal variant. The conclusion of the thesis contains a balance sheet on the applicability of the proposed design solution, in terms of improved stability of the road and thus also the functionality of the whole sprayer.

Cette thèse porte sur la régulation des innovations en Europe. Elle examine en particulier l'impact économique des procédures d'Autorisation de Mise sur le Marché (AMM) sur les comportements des acteurs économiques à savoir les firmes innovantes. Il s'agit d'un travail appliqué au secteur de la santé des plantes dans lequel l'AMM joue un rôle central. En effet, dans ce secteur, la mise sur le marché des pesticides est subordonnée à une autorisation officielle. Les procédures d'autorisation de mise sur le marché (AMM) des nouveaux produits consistent à vérifier qu'ils n'ont pas d'effets toxiques inacceptables sur la santé et l'environnement et à définir des conditions d'utilisation dans lesquelles ces produits sont réputés efficaces. En Europe, ces procédures sont instruites par des autorités européennes ou nationales. Dans le cas des pesticides, les matières actives sont autorisées à l'échelle européenne, les spécialités commerciales le sont à l'échelle nationale, par reconnaissance mutuelle au sein d'une zone géographique. Au cours des dernières décennies, les exigences dans le domaine des risques sanitaires ont conduit à un renforcement des contraintes imposées pour la mise en marché des produits phytosanitaires. Ces exigences renforcées ont conduit à une réduction du nombre de molécules autorisées en rapport au nombre de molécules potentiellement efficaces. Par exemple, le nombre de molécules pesticides autorisées a été réduit de moitié (de 800 à 400) au cours des dix dernières années. C'est pourquoi, l'objet principal de cette recherche est d'étudier les effets des procédures d'AMM sur le comportement des firmes agrochimiques. Cette recherche s'articule autour de trois chapitres. Le premier chapitre est théorique. Il analyse les interactions stratégiques entre les agences de régulation des pesticides dans un contexte d'autorisation de mise sur le marché par reconnaissance mutuelle. Le chapitre 2 est à la fois théorique et empirique et porte sur les délais de mise sur le marché des substances actives phytosanitaires. Dans le chapitre 3, nous examinons, à l'aide d'un modèle théorique, l'impact de la régulation des pesticides sur les incitations des firmes agrochimiques à investir en R&D. / This thesis focuses on the regulation of innovations in Europe. In particular, it analyses the economic impact of the market approval procedures on the behavior of economic actors such as innovative firms. This is an applied work in the health sector of plants in which the market approval procedures play a central role. Indeed, in this area, the introduction on the market of pesticides is subject to an official approval. The market approval procedures for new products are to ensure that they do not have unacceptable toxic effects on human health and the environment and to define the conditions of use in which these products were efficient. In Europe, these procedures are investigated by European or national authorities. In the case of pesticides, the active substances are approved at EU level and the pesticides formulation at the national level through mutual recognition within a geographic area. In recent decades, the requirements in the field of health risks have led to a strengthening of the constraints imposed on the approval of pesticides. These stringent requirements have led to a reduction in the number of approved molecules relative to the number of molecules potentially efficient. For example, the number of approved actives substances was reduced by half (800 to 400) over the last ten years. Therefore, the main purpose of this research is to study the effects of market approval procedures on the behavior of agrochemical companies. This research is based on three chapters. The first chapter is theoretical. It analyses the strategic interactions between pesticide regulatory agencies in the context of market approval through the mutual recognition system. The chapter 2 is both a theoretical and an empirical work. It examines the examination delays of plant protection active substances. In Chapter 3, we examine, using a theoretical model, the impact of the regulation of pesticides on the incentives of agrochemical companies to invest in R & D.

Made available in DSpace on 2016-12-08T16:44:33Z (GMT). No. of bitstreams: 1 PGPV10MA034.pdf: 1439904 bytes, checksum: 4db5cc7ffec224395655a5207d466072 (MD5) Previous issue date: 2010-12-08 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Tomato plants (Solanum lycopersicum L.) cultivated under conventional production systems are frequently disturbed by insects and diseases. Synthetic organic pesticides that are used to manage tomato crops have been harmful to human being and environment as well. Fruits of tomato are very sensitive to handling and its quality is highly influenced by the crop system and post-harvest practices. The objective of this research was to evaluate the effect of high dilution preparations to manage pest and disease, and post-harvest conservation of tomatoes under organic production systems. Experiments were conducted as follow: a) Two experiments under field conditions; b) one experiment in greenhouse; c) one bio-assay concerning post-harvesting; d) twelve bio-assays in vitro conditions. The experiments were conducted in the Lages Experimental Station area of EPAGRI and at Centro Agroveterinario of University of Santa Catarina State, SC. Treatments consisted of high dilutions of Staphysagria, Arsenicum album, Sulphur at 12CH (centesimal hahnemaniana dilution), and Arnica montana, Sulphur, tomato, and jua (Solanum aculeatissimum), nosodes at 12 and 24DH. Bourdoux mixture at 0.3%, Cupric formulation EEC at 50 ppm, and Bacillus thuringiensis were included as standard treatments. Data were from field experiments consisted of septoriosis incidence (Septoria lycopersici), insect occurrence, damage caused by Agathomerus sellatus, yields, and fruit quality attributes. Data analysis was performed throughout statistical package. Results showed that Staphysagria 12CH and Arnica Montana 12DH could increase tomato fruit weigh. Damage caused by tomato caterpillars were reduced by spraying Sulphur 12CH and Bacillus thuringiensis. B. thuringiensis reduced also the incidence of septoriosis. High dilution preparation interfered to insect occurrence and reduced the damage of Agathomerus sellatus in the stages of larvae and adults. Tomato plants treated by jua nosodes at 12 and 24CH increased the SST (° Brix) contents, which gives better qualities of processing and palatability, as well. In the greenhouse experiment, it was evaluated the treatments of Arnica montana, Sulphur, tomato and jua nosodes, all at 12 and 24DH dinamization. Bourdoux mixture at 0.3% and cupric formulation EEC at 50 ppm were considered as standard treatments. It was observed that tomato nosodes at 12DH and 24DH supressed the septorioris incidence. In the post-harvest bio-assay, fruits were treated with Calcarea carbonica at 6, 12, 24CH dinamizations. The evaluation was concerning chemical contents and physical attributes. Calcarea carbonica post-harvest treatment did not affected the acidity, SST (° Brix), hardness or the weight losses of tomato fruits. However, Calcarea carbonica 24CH delayed the fruit maturation in such way that the kind sauce fruit was reduced. In the laboratory bio-assays the follow high dilution preparations were studied: Staphysagria, Arsenicum album, and Nitricum acidum at 6, 12, 25, 30, 50, 60, 80, and 100CH 11 dinamizations. All preparations were tested in two media combined by two application methods into Petry dishes with colonies of the fungus Alternaria solani. Bioassay was studied by measuring the diameter of the colonies. The measurements were made from 24h until the 10th day after install the assays. It was observed that the media with basic composition were more suitable to screening high dilution preparations against A. solani before to test in the field. The application method of high dilution preparations over the fungus colony was better than incorporated one. The use of high dilution preparations has the potential effect to replace pesticide used on tomato crops and it would be a suitable management strategy to fill legal requirements for organic production systems. / O tomateiro (Solanum lycopersicum L.) sob sistema de produção convencional está constantemente sujeito à pragas e doenças. Pesticidas orgânicos sintéticos usados para seu manejo podem causar graves pertubações ao meio ambiente e a saúde humana. Frutos de tomateiro também são sensíveis ao manuseio e sua qualidade é afetada pelo sistema de cultivo e pelas práticas de conservação pós-colheita. O objetivo deste trabalho foi avaliar o efeito de preparados em altas diluições no manejo fitossanitário e pós-colheita da cultura do tomateiro sob sistema orgânico de produção. Foram conduzidos (a) dois experimentos em condições de campo, (b) um experimento em casa de vegetação, (c) um ensaio de conservação pós-colheita em laboratório e (d) doze bioensaios in vitro. Os experimentos foram conduzidos na Estação Experimental da EPAGRI de Lages e, no Centro de Ciências Agroveterinárias da UDESC. Os tratamentos avaliados nos experimentos a campo foram os preparados em altas diluições de Staphysagria, Arsenicum album, Sulphur na dinamização 12CH (centesimal hahnemaniana); Arnica montana, Sulphur, nosódios de tomateiro e de juá (Solanum aculeatissimum), nas dinamizações 12 e 24DH (decimal hahnemaniana). Calda bordalesa 0,3%, Calda cúprica EEC a 50 ppm e Bacillus thuringiensis foram incluídos em doses ponderais e considerados tratamentos padrões. Nos experimentos a campo avaliou-se a incidência de septoriose (Septoria lycopersici), ocorrência e danos por insetos, produtividade e atributos químicos de qualidade dos frutos. A análise dos dados mostrou que os preparados Staphysagria 12CH e Arnica montana 12DH proporcionaram a maior peso de frutos. Danos causados por brocas foram reduzidos com a aplicação de Sulphur 12CH igualando a Bacillus thuringiensis. B. thuringiensis também reduziu a incidência de septoriose. Observou-se que os preparados em altas diluições interferiram na ocorrência de insetos em plantas de tomateiro e reduziram os danos causados por Agathomerus sellatus, tanto na fase larval quanto na fase adulta. Tomateiros tratados com nosódio de juá 12 e 24DH tiveram incremento no teor de SST (° Brix) dos frutos, atributo que melhora a palatabilidade e a qualidade para a industrialização. No experimento em casa de vegetação, avaliou-se Arnica montana, Sulphur, nosódios de tomateiro e de juá, nas dinamizações 12 e 24DH. Calda bordalesa 0,3% e calda cúprica EEC a 50 ppm também foram incluídas em doses ponderais e considerados tratamentos padrões. Observou-se que o nosódio de tomateiro na 12DH e 24DH suprimiram a incidência de septoriose nas plantas tratadas. No ensaio em laboratório de conservação pós-colheita, frutos foram tratados com Calcarea carbonica nas dinamizações 6, 12, 24CH. Avaliou-se atributos químicos e físicos dos frutos. Calcarea carbonica em tratamento pós-colheita não interferiu na acidez, SST (° Brix), firmeza e perda de massa fresca dos frutos. Embora, Calcarea9 carbonica 24CH retardasse a formação de frutos do tipo molho. Nos estudos in vitro foram avaliados os preparados Staphysagria, Arsenicum album e Nitricum acidum nas dinamizações 6, 12, 25, 30, 50, 60, 80 e 100CH, em meios de cultivo básico e enriquecido e, em dois métodos de aplicação. Nos bioensaios foi avaliado o diâmetro das colônias do fungo Alternaria solani iniciando-se 24 horas após a instalação do ensaio e estenderam-se até o décimo dia. Observou que meios de cultivo com composição básica foram mais adequados para o screening de preparados em altas diluições e suas dinamizações, em estudos in vitro com A. solani. A aplicação dos preparados em altas diluições sobre a colônia do fungo foi o método mais adequado para estudos in vitro. Preparados em altas diluições tem potencial para serem eficazes na substituição de agrotóxicos que são utilizados na cultura do tomateiro, e poderiam ser adequados para preencherem requisito legal em sistemas orgânicos de produção

Diploma work is based on constructing of electronic informative system about greenhouse growns damaging pests - growtheal vegetables, concretely forced on forwarding cucumbers and tomatoes. The aim of diploma work is to make out the given information system with division of pests according to kind of the growth, place of damage and integrated locator of pests based on their Czech or Latin title, eventually based on information about pests and bioagens. The system contains detailed information about individual pests, their bionomii, enlargement and protection, including the biological protection. A part of this informative system is a large number of photographs of individual pests, biological preparations or injured plants with apparent symptoms.

O Papaya ringspot virus - type W (PRSV-W) e o Zucchini yellow mosaic virus (ZYMV) são as duas espécies de potyvírus que mais causam danos em cucurbitáceas no estado de São Paulo e no Brasil. Uma boa alternativa de controle para as doenças causadas por esses vírus é o emprego da premunização. O principal objetivo desse trabalho foi estudar a competição por sítios de replicação como possível mecanismo de proteção entre a estirpe fraca PRSV-W-1 e a estirpe severa PRSV-W-C em plantas de abobrinha-de-moita. Além disso, procurou-se também conhecer o período mínimo necessário para a proteção de plantas de abobrinha-de-moita premunizadas com a estirpe fraca ZYMV-M, só e em dupla premunização com a estirpe fraca PRSV-W-1, para fornecer subsídios para o uso em condições de campo. O estudo da competição por sítios de replicação como mecanismo de proteção foi feito inoculando-se plantas de abobrinha-de-moita ‘Caserta‘ com a estirpe fraca PRSV-W-1 e desafiando-as com a estipe severa PRSV-W-C. As inoculações de proteção foram feitas nas folhas cotiledonares e as de desafio na folha nova verdadeira, e vice-versa, aos 3, 6 e 9 dias após a primeira inoculação. Plantas infectadas com a estirpe fraca e não desafiadas e plantas infectadas com a estirpe severa foram usadas como controles. As avaliações foram feitas com base na manifestação dos sintomas 30 dias após o desafio. Também foi feito teste de recuperação da estirpe desafiante e detecção desta por RT-PCR, com primers específicos, aos 8 dias após o desafio. Os resultados sugerem que, independente do local onde foi realizada a inoculação de proteção (folha cotiledonar ou folha nova expandida), de uma maneira geral parece haver alguns sítios livres para a superinfecção com a estirpe severa. Quando esta foi inoculada aos três dias após a proteção, ela se estabeleceu em algumas plantas, moveu-se sistemicamente e sobrepôs a estirpe fraca, uma vez que as plantas exibiram sintomas severos. Com o passar do tempo (seis e nove dias após a proteção), todas as plantas ficaram protegidas contra a expressão dos sintomas severos da estirpe desafiante, porém esta foi capaz de se estabelecer nas folhas inoculadas e até mesmo mover sistemicamente em algumas plantas. No caso da proteção com a estirpe fraca ZYMV-M, só ou em mistura com a estirpe fraca PRSV-W-1, contatou-se que plantas de abobrinha-de-moita premunizadas e desafiadas sete dias depois ficaram protegidas contra a infecção e/ou manifestação dos sintomas das respectivas estirpes severas usadas no desafio. / Papaya ringspot virus - type W (PRSV-W) and Zucchini yellow mosaic virus (ZYMV) are two potyviruses associated with severe yield losses on cucurbit crops in the State of São Paulo and other parts of the Brazilian territory. Preimmunization with mild strains has proved to be a good alternative for the control of both viruses in susceptible cultivars. The main purpose of this work was to evaluate the competition for infectable sites as a possible mechanism of cross protection between the mild strain PRSV-W-1 and the severe strain PRSV-W-C in zucchini squash (Cucurbita pepo cv. Caserta). Protective inoculation with the mild strain was done at the cotyledon and the challenge inoculation with the severe strain was applied on the first true expanded leaf, and viceversa. Different plants were challenged at three, six and nine days, respectively. No challenge protected plants and healthy plants infected with the severe strain were used as controls. Evaluations were based on the expression of the symptoms at 30 days after challenge inoculation. Attempts to recover the challenge strain from challenge inoculated and new developed leaves were also done at eight days after challenge inoculation. RT-PCR with specific pairs of primers was also used to detect both stains in some of these samples. Regardless the leaf on which the protective strain was applied (cotyledon or first true expanded leaf) there appear to be some infectable sites available for superinfection with the severe strain. When the challenge inoculation was done at three days after preimmunization, the severe strain was able to superinfect some plants, move systemically and overcome the mild strain, since these plants expressed severe symptoms. All plants become protected against the expression of the symptoms induced by the severe strain when the challenge inoculation was done at six and nine days after preimmunization. However, the severe strain was still detected in the inoculated and upper leaves of few test-plants, eight days after challenge inoculation. In addition to this, it was also determined the period of time necessary to protect zucchini squash plants with a mild strain of ZYMV, named ZYMV-M, alone and in mixture with mild strain PRSV-W-1. The results indicated that single and double preimmunized plants were protected against infection and/or expression of the homologous severe strain seven days after protective inoculation.