Turkey is the biggest producer of hazelnut (Corylus avellana L.) in the world, with a total cultivation area of more than 600,000 hectares, a total annual yield over 800,000 tonnes, and an average yield of around 1.2 tonnes ha in 2008 (FAO, 2008). Several bio-constraints negatively affect hazelnut production, such as pests, diseases and weeds (Anonymous, 1995). Among them Pestalotiopsis guepini...