Evaluation of Conventional, Biological, and Natural Fungicides for Strawberry Powdery Mildew Management Under Greenhouse Conditions in San Luis Obispo, California, Spring 2026

Podosphaera aphanis , the causal agent of strawberry powdery mildew, is a foliar pathogen that infects all above-ground plant parts. Signs of the pathogen typically seen in field are white powdery patches, on both sides of leaves. If left untreated, the disease can lead to declining plant health and productivity, resulting in yield losses. In this trial, the efficacy of five conventional, four biological and one natural fungicide product was evaluated as weekly foliar sprays for the control of powdery mildew. The trial was conducted under greenhouse conditions in San Luis Obispo, California during May and June 2026 using Monterey, a susceptible cultivar. To assess fungicide performance, weekly assessments of disease incidence and severity were taken and area under the disease progress curve was calculated for both. The results of this study will help inform strawberry growers in the development of effective fungicide programs for managing powdery mildew.