Colletotrichum: new pathogen in walnut orchards - characterization of the fungus and research on control methods

Since 2011, walnut trees orchards from southeastern France are attacked by a new pathogen: Colletotrichum. This fungus causes darkening of fruits, which can fall earlier. Harvest losses can reach 70% some years. A regular follow-up has been set up in order to understand better the fungal epidemiology. A fungal flora analysis in dormant buds highlighted the presence of Colletotrichum each year on several orchards. These analyses will also allow identifying the specific species involved. Improving knowledge about the pathogen is part of the work carried out, besides research of efficient means of control. Today, there is no plant-protection product known to be efficient against Colletotrichum. Several fungicides were tested in vitro and on detached fruits. Field trials are also conducted to study their efficacy and develop prophylactic methods.