Management of Chestnut Blight in Greece Using Hypovirulence and Silvicultural Interventions

Abstract

Sweet chestnut (Castanea sativa Mill.) is an important tree for Greece. The invasive fungus Cryphonectria parasitica, which causes chestnut blight, was first found in Central Greece in 1963. It has since spread all over the country, significantly reducing the national annual nut production. The increasing decline of forests and orchards due to the disease led to a project in 1995, which aimed at studying the feasibility of applying biological control. A prerequisite study of the existing vegetative compatibility types of the pathogen showed only four, and their distribution was mapped. A pilot project (1998–2000) that consisted of clear cutting heavily infected coppice stands and introducing hypovirulence to the remainder was implemented on Mt. Athos on a 7000 ha sweet chestnut forest. Two evaluations (in 2003 and 2011) revealed that hypovirulence was established in the sweet chestnut forests and spread more or less homogeneously. A nationwide project introducing hypovirulence to 29 counties was implemented in two, 3-yr-periods 2007–2009 (17 counties) and 2014–2016 (12 counties). The new evaluations showed that hypovirulence spread profoundly and forests and orchards started recovering. The appearance of natural hypovirulence cannot be predicted. Introduced hypovirulence and silvicultural interventions can be used to manage the disease. It is the responsibility of the forest/orchard manager to decide whether to wait for appearance of natural hypovirulence, or to introduce it for a faster decline in disease.