Improved resolution of disease epidemics will provide statistical evidence that at one point in time the spatial pattern of disease can be represented by a specific scale-dependent spatial heterogeneity.
impact statement issue
Spatial analysis of epidemics is notoriously difficult and laborious and underestimates and oversimplifies the disease pattern. Improved analysis of disease epidemics is important for predicting crop loss and improving plant disease management
impact statement response
A desktop application was developed to fully utilize the benefits of simply taking a photograph of a plant disease epidemic and using that information directly for spatial analysis of patterns.
impact statement summary
We developed a desktop application called ‘Cluster’ to spatially analyse pixelated data in digital photographs. The user isolates target entities (clusters) by designating up to 24 pixel colours as non-targets and applying a threshold slider to visualise the targets. The app calculates the percent area occupied by targeted pixels and identifies the centroid and compass angle of orientation for each cluster. Anomalous clusters can be interactively deselected and excluded from analysis. Up to 1,000 stochastic simulations randomly place cluster centroids in ranked order according to size (largest to smallest) within each simulated matrix while preserving the angles of cluster orientation. A two-tailed probability t-test compares the observed versus randomly generated values for mean inter-cluster distance. The app transfers the quantitative attributes of clusters (pixel number, length, width, compass orientation, and length/width ratio) to a downloadable spreadsheet. Each simulated map image may be saved and inspected. In this manuscript we used Cluster to analyse the spatial distribution of lesions on a leaf, a foliar disease epidemic viewed by aerial photography, satellite images of a weedy tree infestation in an abandoned pineapple field, and the distribution of lakes in Minnesota. Cluster is available as a free download for Apple computers at iTunes.