In the field of plant health, and in particular for unculturable pathogens or pathogens difficult to grow, there is a lack of availability of reference materials, here defined as wellcharacterized material suitable to be used as reference positive test control. Reference materials differ in their commutability and complexity, as well as the effort required for their preparation and characterization. Here the preparation of two types of reference materials based on synthetic DNA and well characterized DNA of naturally contaminated plant material of grapevine on an example of “stolbur” phytoplasma associated with “bois noir” disease of grapevine is described. The materials are suitable as controls for quantitative PCR with the specific target of the 16SrXII group and for a wide variety of molecular tests. They provide comparability among tests, laboratories and over time, and are a useful reference in validation studies, test performance studies and proficiency tests.