Fungicide Non‐Target Effects Cause Reduced Sawfly Herbivory in Treated and Neighbouring Strawberry Plants

ABSTRACT Fungicides are intended to control fungal diseases in agricultural production systems in a target‐specific manner. However, in an open‐field experiment in garden strawberry ( Fragaria × ananassa ), in which the fungicide Switch 62.5 WG (cyprodinil and fludioxonil) was applied for the control of grey mould ( Botrytis cinerea ), we found that fungicide application was associated with a strong reduction in herbivory damage by sawflies ( Cladius spp. Hymenoptera: Symphyta). Three years of field data showed a consistent reduction in leaf damage in fungicide‐treated plants compared with the control, with up to a 94% reduction in leaf damage, along with improved fruit quality and increased fruit weight. To further investigate how fungicide treatment of individual plants affects the plant community, fungicide‐treated and non‐treated control plants were grown in close proximity in an alternating pattern. We observed that fungicide non‐target effects could spill over from fungicide‐treated plants and reduce herbivory damage in their non‐treated neighbours by 46%. This finding broadens the concept of associational resistance, which has previously been reported for mixtures of resistant and susceptible crop cultivars, but not for heterogeneous pesticide treatments. Our study provides new field‐based evidence for non‐target effects of a synthetic fungicide from the anilinopyrimidine and phenylpyrrole class on leaf‐dwelling insect pests and opens possibilities for novel pest management strategies via heterogeneous pesticide application.