In agricultural landscapes, arable plants are negatively affected by management intensification. These species can fulfill various ecosystem functions, such as biological pest control, by supporting predators. The ecosystem functions of common plant species are widely known. By contrast, the contribution of rare arable plants (RAPs) to biocontrol in cereal fields remains poorly understood. This study investigated the effect of RAPs on biocontrol potential. We compared cropped plots with and without sowing of rare and threatened arable plant species and investigated the effects on cereal aphids and their antagonistic predators, active hunting, and web-building spiders, as well as carnivorous/omnivorous carabids. We counted the total number of aphids on cereal shoots and trapped ground-dwelling arthropods on an experimental field and on 10 agricultural farms in the vicinity of Munich, Germany, in 2018 and 2019. The effects of the presence of RAPs were analyzed using linear mixed-effect models, whereas cover of RAPs was analyzed using structural equation models. Linear models revealed that the presence of RAPs did not significantly affect the aphid density and the activity densities of spiders and carabids. Structural equation models revealed direct negative effects of RAP cover on aphid density. However, no indirect effects via the predators of aphids were detected. Direct negative effects of active hunting spiders on aphids were determined, but not of the other potential predators. Our results suggest that RAPs may impact aphid infestation, however, the activity density of spiders and carabids were unsuitable indicators for such interactions.