Relative Efficacy of Fungicide Modes of Action for Hop Downy Mildew: An Individual Participant Data Meta-Analysis

Hop downy mildew, caused by Pseudoperonospora humuli, is routinely managed using fungicides. Plot-level data from fungicide efficacy trials (n = 46) in Oregon and Washington between 1997 to 2024 were analyzed in a one-stage, contrast-based, multi-treatment individual participant data (IPD) meta-analysis. Data was aggregated by fungicide mode of action (MOA) inferred from the Fungicide Resistance Action Committee group and analyzed when a given MOA appeared ≥ 5 times. In Oregon, fungicide MOA was resolved into four overlapping groups, with the most effective group being FRAC 49 + 4, providing estimated disease control of 87.4%. In Washington, the four MOA analyzed were more effective than the nontreated but had similar efficacy, with estimated disease control 67.4% to 74.8%. Trial-level disease severity had an additive and multiplicative interaction with MOA on estimated disease control in trials in Oregon or combined over both states. After controlling trial-level disease severity, state had a non-significant additive effect on estimated disease control (95% confidence interval -130.7% to 70.7%). Analysis of design inconsistency indicated relative efficacy was stable across study designs in Washington. However, design inconsistency was detected in trials in Oregon and over both states, indicating estimated efficacy varied depending on the specific combinations of MOA evaluated. Design inconsistency was related tohigh variance in certain trials including FRAC 49 + 40. These analyses provide a foundation for designing fungicide programs that are effective and consistent with resistance management principles. The study also illustrates the value of one-stage, multi-treatment IPD meta-analytic approaches and assessing design inconsistency.