In order to prevent or reduce infection in grapevine nurseries, greenhouse and nursery trials were carried out to evaluate the effects of Trichoderma harzianum (Rootshield®) on the morpho-physiological characteristics of grapevine and on Phaeomoniella chlamydospora artificially inoculated on potted cuttings. The long-distance activity of Trichoderma against Botrytis cinerea was also examined. The study was performed in a commercial nursery where plants were grown organically. Results greatly depended on the vine-growth stage at which Trichoderma was applied. Treatment at rooting was the most effective, whilst callusing-box application or treatments at both rooting and callusing gave inconsistent but generally negative results. Treatment at rooting further improved the quantitative and qualitative characteristics of the root system, and increased the percentage of certifiable vines produced. Moreover, Trichoderma application also reduced the necrotic area caused by B. cinerea inoculated on the leaves collected from Trichoderma-treated plants and the extent of necrosis of P. chlamydospora-inoculated cuttings. This reduction in necrosis was significantly higher 15 months after inoculation. On the other hand, Trichoderma increased vine mortality at the end of the growing season compared with untreated plants. On the whole, only when it was applied at rooting did Trichoderma produce positive effects on the morpho-phisiological characteristics of grapevine and increased its tolerance to stress–related diseases, such as forms of esca found in the nursery.