Xanthomonas arboricola pv. juglandis is the causal agent of walnut blight. This disease causes severe damages to leaves, twigs and fruits, and lead to an important loss of nut’s harvest : about 70%. This bacterium has also been reported to be responsible of an emerging disease on walnut : the vertical oozing canker that has been observed in France for a decade. Moreover, the development of copper resistant populations makes inefficient the authorized chemical treatment. In order to fight against this bacterium and to clean up the nurseries, a specific and sensitive detection method become necessary. That’s why we developped a Bio-PCR method to detect specifically X. a. pv. juglandis.