WIDESPREAD TRUNCATION OF PLANT DISEASE GRADIENTS LEADS TO UNDER-PREDICTIONS OF DISEASE DISPERSAL AND SEVERITY

Epidemiological models are important for understanding both the underpinnings of disease spread and projecting epidemic magnitude. Disease gradients are difficult to accurately measure in the field – particularly the distance disease should be tracked from a source to sufficiently represent the shape of the dispersal gradient and accurately reflect the expanse to which disease is dispersed. Truncated dispersal gradients could severely underestimate the extent and magnitude of epidemics, leading to deceptive projections and misinformed management recommendations. I reviewed dispersal gradient figures in journal articles published from 1950–2020 and found that truncated gradients were common (71.2% of studies) and occurred across all surveyed dispersal vector categories. Wheat stripe rust disease spread simulations confirmed that dispersal kernel truncation generates substantially misleading projections of disease when host plants are continuous (agricultural fields) or patchily distributed (natural ecosystems). Future studies of plant disease spread should attempt to more accurately represent the dispersal gradient.