Sanitation's Impact on Fungicide Use in Hop Growers

Interference occurs when a treatment on one individual or unit impacts connected, untreated ones due to physical or social links. This study applies novel causal inference methods to quantify this phenomenon in hop growing.

The research specifically examines how sanitation methods that reduce initial disease inoculum, such as thorough spring pruning, influence fungicide use and associated costs for hop growers. A key aspect is accounting for interference between different hop yards.

Utilizing four years of data on hop powdery mildew outbreaks, the authors constructed an epidemiological network. This network's edge weights were determined by factors like transmission source strength, distance between yards, and wind-driven spread from the previous month. Causal exposure–response relationships were then derived for thorough spring pruning, adjusting for interactions with other pruned yards. A joint propensity score was used to capture treatment states across both treated and connected outcome units, given various covariates.

The study's results indicate that thorough spring pruning led to reduced fungicide use and lower costs in the treated hop yards. Importantly, the research also found additive neighborhood effects, meaning that connected, untreated yards also benefited from the sanitation practices implemented in nearby treated yards.