Fungicidal control of Blumeria graminis f. sp. hordei occurring in barley late in the growing season was examined in field experiments over 2 years. A single application of triazole fungicides at late booting (GS49) reduced powdery mildew severity and increased yield by 5–13%, depending on the season. Grain protein was slightly increased with fungicide treatment in one experiment whereas grain density and percentage screenings were not affected. Estimated profits from disease control with triazoles were $20–46/ha for malting grade barley in one experiment and $60–75/ha for feed grade barley in a second experiment. A strobilurin fungicide (azoxystrobin) had similar activity to that of triadimefon applied at the same rate. The results demonstrate economic control of powdery mildew in barley with the application of triazole fungicides when mildew is first detected around the booting stage of crop development in a disease prone environment.