Effects of organic mulching on arthropod pests and predators in potato cultivation

Conventional, insecticide-based control strategies against Colorado potato beetles, aphids, and potato viruses are often inadequate, while effective preventive measures remain difficult to implement. Organic mulching—covering the soil with plant materials such as straw, triticale/vetch, or grass/clover—offers an agroecological alternative. As previous research has largely been limited to small-scale straw mulch trials, this study addresses existing research gaps by applying alternative mulch materials in both small- and large-scale field trials (49 to 500 m²) in the regions of Witzenhausen and Göttingen. The study investigated the effects on Colorado potato beetles, aphids, potato virus Y (PVY), and potato leafroll virus (PLRV). Furthermore, predator communities (lady beetles, carabid beetles, and spiders) were analysed in detail. Methods included yellow water traps, visual assessments, antibody-based virus testing, and pitfall traps, with data analysed using state-of-the-art statistical methods. The results demonstrate that various organic mulches significantly reduce the abundance of Colorado potato beetle larvae and delays their development. This reduction is most pronounced in the most damaging instars (L3 and L4), substantially decreasing defoliation during critical plant growth stages. Consequently, mulched plots produced comparable or higher yields. Alongside straw, the alternative mulch materials also significantly reduced aphid landings by 30–75%, decreased general aphid colonization, and in most cases markedly lowered PVY incidence. For PLRV, only tendencies toward reduction were observed due to a generally low baseline infection pressure. The abundance of plant-dwelling predators, such as lady beetles, primarily correlated with aphid availability. However, mulching—particularly with triticale/vetch—significantly increased the abundance of ground-dwelling carabid beetles and spiders (e.g., Poecilus cupreus, Bembidion lampros, Linyphiidae). Furthermore, the species composition of both taxa shifted considerably. This enhances biological pest control, although the effects did not persist beyond the respective growing season. This thesis thus demonstrates the efficacy of alternative mulch materials on a practical field scale. It expands the current state of knowledge by encompassing additional pests and providing a detailed analysis of predator communities. Ultimately, organic mulching proves to be an effective tool for agroecological crop protection in potato cultivation.