Further extending the functional capacity of classic DPL programs, we developed “dfoliatR”, an R package based on the program OUTBREAK developed by Richard Holmes and Thomas Swetnam in the 1980s. dfoliatR uses dplR to access standardized tree-ring series from insect defoliator host species and chronologies from non-host species. It infers defoliation events with an indexing procedure that removes the climatic signal (represented in a non-host chronology) from individual host-tree series. Site-level analyses identify outbreak events that synchronously affect a user-defined number or proportion of the host trees. dfoliatR provides summary statistics and graphics of tree- and site-level series. Running in the R computing environment empowers dendroecologists to simplify and strengthen workflows compared to OUTBREAK, provides customizable tools for analyses and publication-quality graphics, and enables a suite of analyses including sensitivity tests and batch processing. Our presentation will cover basic usage of the package and provide examples of how we’re applying dfoliatR to a synthesis of western spruce budworm outbreak reconstructions across western North America.