Fungicide Resistance in , Cause of Pecan Scab: Current Status and Practical Implications.

Pecan scab, caused by , is the most economically damaging disease of pecan in the southeastern United States, and annual epidemics are most effectively managed through multiple fungicide applications. The fungicide applications can be the single greatest operating cost for commercial growers and the return on that investment is impacted by fungicide resistance. produces multiple generations of conidia per season, exhibits substantial genetic diversity, overwinters as stromata in the tree, and is under immense selection from the applied fungicides, all of which lead to a high risk for developing fungicide resistance. Since the mid-1970s, resistance or reduced sensitivity has been observed in isolates of to the methyl benzimidazole carbamates, demethylation inhibitors, quinone outside inhibitors, organotin compounds, and the guanidines. Over the last 10 years, several studies have been conducted that have improved both scab management and fungicide resistance management in . The aim of this review is to summarize recent developments in our understanding of fungicide resistance in in the context of scab management in southeastern pecan orchards. The history, modes of action, general use of the labeled fungicides, and mechanisms and stability of fungicide resistance in are discussed; conclusions and future research priorities are also presented.