Landscape heterogeneity and disease spread: experimental approaches with a plant pathogen.

Understanding landscape effects on disease spread can contribute to the prediction and control of epidemic invasions. We conducted large-scale field experiments with wheat stripe rust, which is caused by a wind-dispersed rust fungus. Three landscape heterogeneity variables were altered: host frequency (mixtures of susceptible and resistant plants), host patch size (different plot sizes), and size of initial disease focus (attained by artificial inoculation). Assessments of disease prevalence at different distances from the disease foci were used to quantify effects of landscape variables. We expected that a low frequency of susceptible hosts, small host patch sizes, and small initial disease foci would reduce secondary inoculum levels and thus suppress disease spread. Low host frequency and small initial disease foci greatly reduced epidemic spread. We did not detect an effect of host patch size on disease spread, though artificial inoculations did not allow us to measure the potential for small patches to escape infection under conditions of random deposition of initial inoculum. Our results suggest that, for diseases epidemiologically similar to wheat stripe rust, epidemic invasions may be suppressed by decreasing host frequency, limiting the size of initial outbreak foci, and applying control measures soon after epidemic establishment.