A Visual Rating Scale for Quantifying the Severity of Greasy Spot Disease on Grapefruit Leaves

Abstract

Accurate quantitative assessment of greasy spot of grapefruit, caused by Mycosphaerella citri Whiteside, is crucial for designing appropriate disease management strategies and estimating yield losses. A visual rating scale was developed by measuring the total leaf area of 143 'Rio Red' grapefruit leaf samples, and calculating the percent diseased area. The mean severity of the entire sample was 23.1%, but many leaves on the orchard floor exhibited symptoms on more than 50.0% of the leaf area. This rating scale should be highly useful to growers and researchers for field assessments of greasy spot severity. © 2013 Copyright Taylor and Francis Group, LLC.