Fungicide insensitivity in cereal brown rust fungi

Abstract

This project was aimed at monitoring a range of barley brown rust (Puccinia hordei) and wheat brown rust (Puccinia recondita f.sp. tritici) isolates for insensitivity to different fungicides applicable to cereal rust control and to relate the responses of isolates to their source, history and virulence characteristics. Brown rust isolates collected mainly from southern England during 1987-1989 whose virulence characteristics had been determined at Aberystwyth were screened against fenpropimorph, fenpropidin, propiconazole, triadimenol, flutriafol and tridimefon using leaf segments on benzimidazole agar. EC50 values or ratios of fungal growth on sprayed leaf segments to that on controls were determined. Both barley and wheat brown rust isolates varied in their sensitivity to the fungicides with greater variation being shown by wheat brown rust. There was a greater risk of insensitivity to triazoles, particularly triadimenol than to morpholines especially with barley brown rust. No pattern was found in relationships between virulence characteristics, source and insensitivity.