Development of strategies for fire blight control in organic fruit growing

Abstract: Fire blight (Erwinia amylovora) is the most serious bacterial disease in pome fruit.Effective control strategies are needed to prevent blossom infections by E. amylovora. InGermany, many potential control agents have been considered and 64 different preparations weretested in laboratory trials to select the products with highest efficacy. In thirteen field trialsconducted since 2004 Blossom ProtectTM and Myco-Sin® had the highest efficiencies.Blossom Protect contains blastospores of the yeast Aureobasidium pullulans. Theblastospores are sensitive to fungicides that are used for apple scab control and, in some cases A.pullulans enhanced fruit russet when applied during bloom. The increase in fruit russettingdepends on the number of applications and on the variety treated. Therefore spray strategies areneeded controlling both, fire blight and apple scab, without increasing fruit russetting. Fire blightand apple scab control could be achieved using tank mixtures of Blossom Protect + wettablesulphur. With a strategy to alternate Blossom Protect applications with sprays of a mixture ofwettable sulphur + Myco-Sin fire blight and apple scab was controlled significantly. In addition,this strategy reduced the number of Blossom Protect applications to two, and by this, reduced therisk for fruit russetting.