Our research group addresses the question if viruses can be implemented into fungal pest control on crop plants and forest trees. It is a fact that viruses not only infect human beings but also plants and fungi. Similar to phytopathogenic fungi, viruses are capable to cause major yield losses in agriculture, horticulture and mushroom farms. However, by date, a few viruses are known which can reduce the infectiveness of phytopathogenic fungi or even prevent fungal infection completely. Worldwide, research groups are engaged in the search of viruses, which can be used as biological pest control. For instance, the chestnut blight which is caused by the fungus Cryphonectria parasitica is already successful controlled by the virus Cryphonectria parasitica Hypovirus 1 (doi: 10.3188/szf.2007.0342).