In den letzten 20 Jahren hat sich der Maiszünsler (<i>Ostrinia nubilalis HÜBNER</i>), aus der Schmetterlingsfamilie der Pyralidae oder Zünsler, zum bedeutendsten tierischen Schädling des Maises (<i>Zea mays</i>) entwickelt. Eine Möglichkeit den Befall des Maiszünslers abzuwenden, bietet der Anbau von <i>Bacillus thuringiensis</i>-Mais (Bt-Mais). Mit Hilfe der Gentechnik wurden Gene des Bakteriums <i>Bacillus thuringiensis</i> übertragen, die einen für Fraßinsekten giftigen Wirkstoff bilden, wodurch die Pflanzen während der kompletten Vegetation vor den Larven des Maiszünslers geschützt sind.<br><br> Ziel des vorliegenden Projektes war es, in einer 3-jährigen Studie die Auswirkungen des großflächigen Anbaus von Bt-Mais auf die ökologische Situation und den Handlungsrahmen des integrierten Pflanzenschutzes komplex zu untersuchen. Dazu wurden in Betrieben im Oderbruch, das als permanentes Befallsgebiet des Maiszünslers gilt, in den Jahren 2002 bis 2004 jährlich zwei Felder mit jeweils einer Bt-Sorte und einer konventionellen Sorte angelegt. Zusätzlich wurden biologische und chemische Maiszünsler-Bekämpfungsvarianten geprüft.<br><br> Durch verschiedene Methoden wie Bonituren, Ganzpflanzenernten, Bodenfallenfänge und Beobachtungen des Wahlverhaltens von (Flug-)insekten konnten Aussagen zum Vorkommen von Insekten und Spinnentieren getroffen werden, wobei hierfür Daten aus Untersuchungen der Jahre 2000 und 2001 im Oderbruch ergänzend herangezogen werden konnten. Durch Ertragsmessungen, Energie- und Qualitätsermittlungen, sowie Fusarium- und Mykotoxinanalysen konnte der Anbau von Bt-Mais als neue Alternative zur Bekämpfung des Maiszünslers bewertet werden.<br><br> Bezüglich des Auftretens von Insekten und Spinnentieren wurden im Mittel der fünfjährigen Datenerhebung beim Vergleich der Bt-Sorte zur konventionellen Sorte, mit Ausnahme der fast 100 %igen Bekämpfung des Maiszünslers, keine signifikanten Unterschiede festgestellt. Hierfür wurde ein besonderes Augenmerk auf Thripse, Wanzen, Blattläuse und deren Fraßfeinde, sowie mittels Bodenfallenfängen auf Laufkäfer und Spinnen gerichtet.<br><br> Die erwarteten ökonomischen Vorteile wie etwa Ertragsplus oder bessere Nährstoff- und Energiegehalte durch geringeren Schaden beim Anbau von Bt-Mais als Silomais blieben in den Untersuchungsjahren aus. Allerdings zeigten Fusarium- und Mykotoxinanalysen eine geringere Belastung des Bt-Maises, was möglicherweise auf den geringeren Schaden zurückzuführen ist, da beschädigte Pflanzen für Fusarium und Mykotoxine anfälliger sind.<br><br> Desweiteren konnten erste methodische Ansätze für ein auf EU-Ebene gefordertes, den Anbau von Bt-Mais begleitendes Monitoring, erarbeitet werden. So konnten Vorschläge für geeignete Methoden, deren Umfang sowie des Zeitpunktes der Durchführungen gemacht werden. / In the last 20 years the European corn borer (<i>Ostrinia nubilalis</i>, <i>Pyralidae</i>) has become the most important pest in maize (<i>Zea mays</i>). One of a couple of possibilities to reduce the infestation by the European corn borer is the cultivation of <i>Bacillus thuringiensis</i> maize (Bt maize). Genetic engineering transmitted genes from <i>Bacillus thuringiensis</i>, which produce a substance that is toxic to feeding insects and thus protect plants against the larvae of the European corn borer during the whole vegetation.<br><br> The present project is a 3-year study to identify the effects of Bt maize growing on the ecological situation and the possibilities of integrated plant protection. From 2002 to 2004, two fields in the Oderbruch region, where Ostrinia nubilalis occurs, were each planted with Bt maize and a conventional maize variety every year. Furthermore, a biological and a chemical strategy against the European corn borer were verified.<br><br> Different methods like counts, harvest of whole plants, pitfall traps and observation the landing behaviour of flying insects were used to determine the abundance of insects and spiders. Furthermore, we could use additional data from studies obtained in the Oderbruch region in 2000 and 2001. The determination of yield, quality and energy content of the crops as well as of the degree of Fusarium infection and contamination by mycotoxins led to the conclusion that the cultivation of Bt maize is a new alternative strategy to control the European corn borer.<br><br> The average occurrence of insects and spiders did not differ significantly between Bt maize and the conventional variety in the 5 years of data recording. The only exception is the almost total control of the European corn borer. Attention was especially paid to thrips, bugs, aphids and their feeding enemies and using ground traps to ground beetles and spiders.<br><br> The expected economic benefits like increased yield or nutrient and energy content of the crop as a result of a minimized damage to silage Bt maize were not achieved in the years under investigation. However, the analysis of Fusarium and mycotoxins indicated a lower exposure of Bt maize, which may result from a lower damage caused by Ostrinia nubilalis, and damaged plants are more susceptible to Fusarium and mycotoxins.<br><br> Furthermore, we developed a first methodological approach for the monitoring procedure of Bt maize growing required by the EU. We have made proposals on appropriate methods, their extent as well as the optimum time of their application.

Separate field studies were started in fall 2005, which continued through fall 2007, to investigate the effect of different levels of European corn borer tunneling on yield in corn grown for grain and to predict spring infestation levels of early season soil insects, specifically white grubs (Coleoptera: Scarabaeidae) and wireworms (Coleoptera: Elateridae) in cornfields. In the first study, model variables included corn growth stage and larvae per plant. In both years of this study, larvae per plant had a significant effect on grain yield. Grain yield was reduced by 13.1 and 3.65% in plants infested with four larvae per plant in 2006 and 2007, respectively. For 2006, linear regression models provided average percent yield loss per larva per plant at 4.1, 6.8, and 1.8% during late vegetative (V12), early silking (R1), and blister (R2) growth stages, respectively. Economic injury levels (EILs) were calculated based on average percent yield reductions across each growth stage and year. In the second study, no significant differences were detected in both fall and spring between two sampling methods after correcting for differences in sampling volume. Strong correlations were observed between fall and spring grub densities in both years. In 2006, fields with grub densities above the spring nominal threshold had significantly greater stand and yield in the Poncho 1250 (1.25 mg clothianidin / kernel) treatment when compared to the Poncho 250 (0.25 mg clothianidin / kernel) and untreated plots. This information was used to develop fall EILs and economic thresholds for white grubs. / Master of Science in Life Sciences

Call number: LD2668 .T4 1985 M444 / Master of Science

Double-cropping of corn (Zea mays L.) for grain following the harvest of a small grain crop has been under evaluation in Virginia as an alternative cropping strategy (Brann and Pitman, 1997). To assess the potential constraints on late planted corn imposed by insects and diseases, double-cropped corn was evaluated in field experiments in Montgomery County, Virginia from 1998 to 2000. Factors included two near-isoline hybrids (NK4640 and NK4640Bt), insecticides at planting (tefluthrin in all years, 1998-2000; and imidacloprid in 1999 and 2000), and fungicide treatments (azoxystrobin or propiconazole). Response variables included yield, moisture at harvest, grain test weight, damage by European corn borer (Ostrinia nubilalis), damage by corn earworm (Heliothis zea), disease progress curves for gray leaf spot Cercospora zeae-maydis), and number of plants exhibiting virus symptoms. The Bt hybrid performed significantly better than the non-Bt hybrid for yield and test weight in double-cropped corn in 1998 and 2000, but not in 1999. A spatially referenced site suitability analysis was performed for full season and double-cropped corn in Virginia using weighted abiotic factors and constraints. Thornthwaite potential evapotranspiration (PET) and PET minus precipitation were used to identify areas of the state having a lower average moisture deficit during the silking months for double-cropped corn compared to full-season corn. It is concluded that double-cropped corn production is a viable option in Virginia where abiotic factors are not constraining, particularly growing season length and moisture availability during the sensitive stages of development. / Master of Science

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