Reduzierter Blattlausbefall durch Strohmulch in ökologisch angebauten Kartoffeln

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 treatrnents 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 x 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.