Bacterial blossom blight infections on young pear trees: Pseudomonas syringae or Erwinia amylovora?

Blossom blight is an increasing problem on young pear trees in Belgium. Most of the blossom blight infections are due to an infection of Pseudomonas syringae pv. syringae. Some infections are due to a primary blossom infection of fire blight caused by Erwinia amylovora. In an early stage of blossom blight, the typical symptoms of both bacterial diseases are very similar and can only be distinguished by isolation in the lab. Infections of Pseudomonas syringae pv. syringae are considered to indicate a weakness factor over the whole orchard. Different possible weakness factors are discussed. Fire blight infections are more local in appearance and are often more related with earlier Erwinia infections during the previous years. Some control measures for both bacterial problems are discussed.