Agronomic and economic effects of host resistance vs. fungicide control of barley powdery mildew in southern Sweden

Agronomic and economic effects of powdery mildew host resistance and a fungicide treatment were investigated in nine ‘Pallas' near-isogenic barley lines. Four years of field trials and virulence surveys detected virulence against all fourteen mildew resistance genes present in the lines. In the field trials, with the exception of gene Mlra, the resistance genes were found to significantly reduce disease severity by 38e99%. The gene mlo5 had a significant negative effect on agronomic characters, while the other resistance genes were neutral. Fungicide treatment reduced powdery mildew by 50e97% and increased grain yield 11e17%, thousand grain weight 6e10%, grain volume weight 2e3% and water content 8e13%, while there was no significant effect on straw strength. From an agronomic perspective, the benefit of the fungicide treatment was greater than that of the selected host resistance. Profitability was directly related to the grain price and cost of fungicide. Net return was negative when using fungicides in years with the lowest grain price, while a higher grain price resulted in a positive net return. It thus seems unprofitable to use fungicides in years with low grain prices, especially when cultivars with effective host resistance are available.