Perennial fallow strips support biological pest control in spring cereal in Northern Europe

Abstract

Fallow strips are promoted through agri-climate-environment schemes to enhance farmland biodiversity, but their effects on biodiversity-mediated ecosystem services remain poorly studied in different cropping systems. The effects of fallow strips on biological control of bird cherry-oat aphids in spring barley were examined in a field experiment in Finland in 2014–2016. Two types of sown perennial fallow strips – grass strip and wildflower strip – were compared. The relative efficiency of biological pest control was tested by monitoring the number of experimentally added aphids in the fallow strips and in the adjacent barley fields at different distances from the strips. Data were also collected on the densities of naturally occurring aphids and ground-dwelling natural enemies. The effects of the fallow strips differed between years. When aphid pressure was high, the proximity of the strips slowed the growth of aphid population. In the year of low aphid abundance, the fallow strips sustained more aphids than the adjacent barley fields, but did not constitute a risk for pest control. In the second and third years, especially wildflower strips supported high activity density of ground-dwelling predators. The activity densities were particularly high in the both fallow strip types in early summer, highlighting the role of the perennial strips as refuges for natural enemies. The results suggest that perennial fallow strips, and especially those sown with diverse wildflower mixtures, can promote pest control in spring cereals, thus contributing to ecological intensification in agriculture.