Assessing the Accuracy of Brown Ring Patch Severity Using Digital Image Analysis.

Many techniques have been developed to estimate turf disease severity. Visual estimates are used most often because it is easy and it provides a rapid measurement. Visual estimates may be accurate on diseases that have spot or patch symptoms because it evaluates disease coverage. However, to visually estimate diseases like brown ring patch (BRP) is challenging because of the ring shaped symptom. The symptoms of brown ring patch include yellow rings that may turn brown over time, and the rings may enlarge and merge with each other, forming irregular yellow patterns. In this study we evaluated brown ring patch on mixed annual bluegrass and creeping bentgrass greens by visual estimation and digital image analysis (DIA). Plots were affected by BRP, or a combination of BRP and other diseases. Comparison of the same plot evaluated with Sigma Scan at 0-45 and 0-50 hue angle ranges showed that 0-50 (r^2=0.69, p<0.0001) had lower correlation with visually estimates than 0-45(r^2=0.65, p<0.05). However, the area marked by 0-45 hue angle ranges setting seemed more true to real diseased area as compared to images marked with different hue angle ranges. This reflects the software only measuring actual area of the yellow symptomatic rings while visually estimating appears to measure the area contained within yellow rings. DIA of images taken with three different cameras were not significantly different. DIA was more closely related to visually estimating disease severity in a plot colonized by BRP in this study than by multiple diseases. This study showed that digital image analysis provided an accurate method to measure brown ring patch severity when only one disease appears.