Chemical control of loose smut (Ustilago segetum var. tritici) of barley and the effects of cultivar and environment on disease incidence

Abstract

The reasons for an increase in barley loose smut in high rainfall areas of Western Australia were investigated in field trials from 1986 to 1988 by examining the effects of environment, cultivar and adequacy of chemical control. Disease was 4-18 times greater in 2 seed lines produced in very high rainfall areas (>750 mm/year) compared with that produced in high (450-750 mm/year) or low (<325 mm/year) rainfall areas. The effectiveness of 5 fungicide seed treatments was assessed. No fungicide seed treatment controlled disease completely. Triadimenol at 225 mg a.i./kg and carboxin at 940 mg a.i./kg were most effective, providing 93-96% disease control. Treatments were significantly (P<0.01) less effective in high rainfall areas of Western Australia. Barley cultivars released recently in Western Australia were found to be susceptible to loose smut; we suggest that the replacement of the moderately resistant Dampier with these cultivars has contributed to an increased incidence of disease.