Does timing of application influence the efficacy of Trichoderma in reducing wood fungal infections and in improving plant quality in grapevine nurseries?

Wood pathogens of grapevine are recognized to be already present in propagation material, even if once in the field infections through pruning wounds are another source of infection. In these last years, the availability of biological control products increased. Application timing of a product based on Trichoderma atroviride SC1 (Vintec®) was tested in a commercial nursery to establish the influence of application timing on the quality of the grafted vine and level of infection in the nursery. The formulation was applied at three stages: rehydration, callusing, basal callus formation followed by soil drenching. In addition, the effect of the combined applications was also tested. All treatments were compared with controls (another Trichoderma-based product, plants treated with synthetic fungicide and untreated plants). Surveys included assessment of plant quality and viability after callusing and after a growth season in the nursery soil, root development and quality by video image analysis. The final grafted vines, ready for sale, were used for isolating the mycoflora, thus showing a direct influence of application at different stages of the grafted cuttings production and the fungi and in particular fungal colonization by wood pathogens. The rehydration stage showed to be the better performing application in reducing fungal infections, whereas the applications at the basal callus followed by soil drenching produced plants with a better root quality, and a different increase of the certifiable plants depending on the rootstock tested. The use of biological control products requires a lot of care in detecting the most useful application timing