Chemical and biological protection of grapevine propagation material from trunk disease pathogens

Wound protection during all stages of grapevine propagation is of utmost importance to prevent infection of propagation material by decline and dieback pathogens. In semi-commercial nursery trials, grapevine rootstock and scion cuttings were soaked in water (control), chemical or biological sanitation products prior to cold storage, prior to grafting (machine- or hand-grafting) and prior to planting in field nurseries. Natural infection levels in basal ends and graft unions of uprooted nursery grapevines were evaluated 8 months after planting. Total pathogen incidences in the water-treated control plants ranged from 30% in basal ends to 13.5% in graft unions. Phaeomoniella chlamydospora was the most commonly isolated pathogen, followed by Phaeoacremonium, Cylindrocarpon + Campylocarpon, Botryosphaeria and Phomopsis spp. Machine-grafted unions generally had lower pathogen incidences compared with hand-grafted graft unions. In general, repeated soak-treatments of propagation material in the tested products resulted in reduced pathogen incidences in nursery grapevines. However, products containing T. harzianum (Tricho flow-T), hydrogen peroxide (Bio-sterilizer) and 8-hydroxyquinoline sulphate (Chinosol) gave inconsistent results, whereas Bronocide (a blend of halogenated alcohols and water) proved to be a good sterilising agent, but reduced certifiable plant yield significantly. Benomyl (at 100 g/100 l), Sporekill (a patented didecyldimethylammonium chloride formulation at 150 ml/100 l) and captan (at 1000 ml/100 l) were consistently the best treatments as growth parameters were not negatively influenced and pathogen incidences in basal ends and graft unions of uprooted plants were reduced.