Biology and Control of Entyloma eryngii (Cda.) de By., the Cause of a Leaf Spot Disease on the Blue Thistle ( Eryngium alpinum L.)

The blue thistle ( Eryngium alpinum L.), an indigenous perennial flower of the alps, is grown in mountainous regions of south‐eastern Switzerland. The commercial value of the fresh cut flowers can be seriously reduced due to a leaf spot disease caused by the smut fungus Entyloma eryngii (Cda.) de By. The fungus produces thick walled chlamydospores and two types of conidia. The disease appears to be favoured by cool‐rainy weather and a dense foilage resulting in long periods of leaf wetness. Control of the disease can be achieved with the protective fungicide mancozeb or even more efficiently with the systemic ergosterol‐biosynthesis‐inhibiting fungicides cyproconazole and difenoconazole.