This rapid PRA shows that Ca. Phytoplasma fraxini is a damaging pest of Fraxinus (ash) and Syringa (lilac) in North America, and an emerging problem on a range of tree species in Columbia. Since no insect vector has been identified, the assessment of potential impacts in the UK is subject to considerable levels of uncertainty. Relevant sections of this PRA (establishment outdoors, spread and potential impacts in the UK) have been rated for two scenarios: the absence of an efficient vector in UK, and the presence of an efficient and polyphagous vector.