Woody perennial plants like grapevine and fruit trees can be infected by several viruses even as multiple infections. Since they are propagated vegetatively, the phytosanitary status of the propagation material (both the rootstock and the variety) can have a profound effect on the lifetime and health of the new plantations. The fast evolution of sequencing techniques provides a new opportunity for metagenomics-based viral diagnostics. Viral derived small RNAs produced by the host immune system during viral infection can be sequenced by next-generation techniques and analyzed for the presence of viruses, revealing the presence of all known viral pathogens in the sample. This method is based on Illumina sequencing of short RNAs and bioinformatics analysis of virus-derived small RNAs in the host. Here we describe a protocol for this challenging technique step by step with notes, in order to ensure success for every user.