Reduzierter Blattlausbefall durch Strohmulch in ökologisch angebauten Kartoffeln

Blattläuse gelten in vielen landwirtschaftlichen Kulturen als bedeutende Schädlinge. In Kartoffeln (Solanum tuberosum) spielen sie vor allem wegen ihrer Fähigkeit zur Virusübertragung eine wichtige Rolle (RADCLIFFE & RAGSDALE 2002). Aus zahlreichen Untersuchungen ist die blattlausreduzierende Wirkung von Strohmulch bekannt, z.B. in Raps (HEIMBACH et al. 2002), Weizen (SCHMIDT et al. 2004), oder Leguminosen (EGGERS & HEIMBACH 2001). Über die Wirkung von Strohmulch in Kartoffeln auf Blattlausbefall und Befall mit dem Kartoffelvirus Y (PVY) in Kleinparzellenversuchen wurde bereits an anderer Stelle berichtet (SAUCKE & DÖRING 2004). In diesem Beitrag werden weitere Ergebnisse aus Praxisversuchen auf ökologisch wirtschaftenden Höfen präsentiert. Ein Schwerpunkt liegt dabei auf der Fragestellung, wie sich die Relation zwischen Dosis (d.h. Mulchmenge) und Wirkung (auf Blattlausbesatz und Virusbefall) gestaltet. Aphids are important pests in potatoes, mainly due to their ability to transmit virus diseases. 17 field experiments were conducted over 4 years at 4 sites on organically managed farms to investigate the effect of straw mulch, applied at various amounts (2–8 t ha-1) shortly after crop emergence, on aphid infestation of potato leaves. The percentage of leaves infested with aphids was repeatedly determined during the growing period in 10 experiments. It was significantly reduced in the mulched treatments at the time around 2 weeks after mulching in 4 experiments, and later, at peak infestation, in 8 experiments. The aphid population size was regularly determined in 11 experiments and was significantly reduced by mulching in 4 of them. In a small scale experiment, the response of aphids landing in green water traps to varied amounts of straw (0–800 g m-2) was investigated. Straw applied as a mulch patch of 60 × 83 cm under green water traps resulted in a general reduction of aphids landing in the traps compared to traps placed on bare soil. This effect was significant at application rates of 200 g m-2, 400 g m-2, or more, with differences among rates between 200 and 800 g m-2 not being significant. One of the possible mechanisms for straw mulch effects on aphids is seen in the interference with host finding behaviour.