Sequential use of pre-flowering chemical fungicides and post-flowering natural products effectively controls strawberry powdery mildew while resulting in low residues in fruit

Consumer concern about pesticide residues in food has increased markedly, and strawberries are among the most criticized crops, due to frequent pesticide applications resulting in multiple residues of synthetic active ingredients at harvest. Strawberry powdery mildew (caused by Podosphaera aphanis ) is one of the major drivers of frequent chemical treatments, applied according to calendar-based schedules. To date, natural fungicides have not yet proven capable of fully replacing synthetic chemicals, underscoring the need for integrated well-designed strategies that ensure disease control while reducing residues on fruit. This study assessed a residue-reduction strategy in everbearing high-tunnel production, in which synthetic chemical fungicides were limited to the pre-flowering stage and replaced by natural fungicides (lupin seed extract, potassium bicarbonate, or sulfur) post-flowering. This integrated approach was compared with a standard calendar-based chemical strategy, and with two controls: synthetic fungicides up to pre-flowering followed by water, and an untreated water control. Residue analyses were conducted from the beginning of harvest. Results show that limiting synthetic fungicides to pre-flowering and applying natural products thereafter reduced up to 57% residue number and provided control comparable to the standard strategy, particularly with potassium bicarbonate or sulfur with up to 63% fruit incidence reduction. Lupin seed extract was slightly less effective under high disease pressure (15% higher fruit incidence) but still contributed to disease suppression. These findings demonstrate the feasibility of low-residue strawberry production and support the integration of natural fungicides into well-designed management strategies. • Consumer concern is rising over pesticide residues in strawberries • Strawberry powdery mildew causes frequent pesticide residues on fruit • Need for effective low-residue strategies in strawberry production • Using naturals post-flowering instead of synthetic fungicides cut residues 57% • Potassium bicarbonate and sulfur were as effective as synthetic fungicides • Lupin seed extract was slightly less effective at high disease pressure