Open Access

Helmut Saucke, Monique Juergens, Thomas Felix Döring, Susanne Fittje, Dietrich-Eckhard Lesemann, Heinrich-Josef Vetten

• Fababohnen (Vicia faba L.) nehmen in der Ökologischen Landwirtschaft als Protein- und N-Quelle eine wichtige Stellung in der Fruchtfolge ein (Lampkin 1994; Müller & von Fragstein und Niemsdorff 2006). Als ertragslimitierende Faktoren spielen neben Wasserknappheit auch Schaderreger wie Insekten, Pilze und verschiedene Viruserkrankungen (Cockbain 1983) eine wichtige Rolle. Virusbedingte Ertragseinbußen wurden von Schmidt (1984) in konventionellen Fababohnen Ostdeutschlands auf jährlich ca. 8% geschätzt. Unter den nicht-chemischen Verfahren zur Minderung von vektorvermittelten Viruserkrankungen in Ackerkulturen, mit zugleich potentieller Eignung für ökologische Anbauverhältnisse, gehört neben der Frühsaat (Heathcote & Gibbs 1962) auch die Anwendung von Strohmulch. Mulchen erzielte insbesondere bei nicht-persistenterÜbertragung durch Blattläuse virusreduzierende Effekte in Lupinen. (Jones 1994), Kartoffeln (Heimbach & al. 1998; Saucke & Döring 2004) und Raps (& al. 2002). Ziele der vorliegenden Arbeit bildeten die Anwendung von Strohmulch in Kombination mit Früh- und Spätsaat in einem faktoriellen Parzellenversuch im Ökologischen Anbau von Fababohnen hinsichtlich der Auswirkungen auf Blattlausbesiedelung, Virusinfektionen, Pflanzenentwicklung und Ertrag.
• We investigated the combined effects of straw mulch and sowing date on aphid infestation and virus incidence in faba beans in organically managed small scale field experiments. Straw mulch was applied in early and late sown treatments shortly before commencing vector activity in May. Aphids were monitored by yellow water traps. In addition, crop colonisation over time was assessed for the main vectors Acyrthosiphon pisum and Megoura viciae. PEMV (pea enation mosaic virus) and BYMV (bean yellow mosaic virus) were most abundant in three consecutive years, constituting 22-54% and 9-69% of the detected virus total, respectively. However, relationships between Acyrthosiphon pisum activity and virus loads were less consistent within years. Significantly decreased A. pisum colonisation over time by mulching was prevalent but restricted to one or few dates within the entire colonisation period. Factorial analysis of resulting virus loads revealed significant reduction by early sowing but not by mulching and interaction within these factors was not significant or poor. It is suggested that relatively weak mulching effects towards visually guided aphids were assigned to rapid canopy closure in combination with the tall crop stature. In late sowings however, the ratio of soil background to vegetative cover was more permissive to interfere with vector alighting. Irrespective from mulch application, exposure of young plants lead to significantly enhanced virus loads. Straw mulching in late spring had a neutral effect on yield and did therefore not compensate for yield depression in late sown treatments. Thus, the perspectives of a mulching approach to control virus diseases in faba beans are apparently lower than anticipated.