Detection of Benomyl-Tolerant Strains of Elsinoë fawcetti in Florida Citrus Groves and Nurseries. J. O. Whiteside, Plant Pathologist, University of Florida, Agricultural Research and Education Center, Lake Alfred, FL 33850. Plant Dis. 64:871-872. Copyright 1980 American Phytopathological Society. DOI: 10.1094/PD-64-871.

Elsinoë fawcetti is difficult to isolate from citrus scab pustules produced in the field because of contamination problems. Therefore, direct monitoring for tolerance to benomyl by transferring conidia or pieces of the stroma to benomyl-amended agar was impracticable. Instead, conidia were dispersed from scab pustules on fruit and leaves into water, and the resulting inoculum was applied to the apices of emerging shoots on greenhouse-grown rough lemon trap seedlings. Tolerance in the surviving population of E. fawcetti was based on the number of active pustules that developed on benomyl-soil-drenched plants relative to untreated plants. The fungus was readily isolated from young pustules produced in the greenhouse, and tolerance was confirmed by growing the isolates on benomyl-amended potato-dextrose agar. Estimates of tolerance in the surviving populations of E. fawcetti in seven ‘Temple’ orange groves and two citrus nurseries, in which scab was poorly controlled despite timely spraying with benomyl, varied from 27% to about 100%.