Improving hot water treatment in grapevine nurseries by adding fungicides to prevent fungal infections

PROJECT TITLE: Improving hot water treatment in grapevine nurseries by adding fungicides to prevent fungal infections

Project leader: Dr Francois Halleen (ARC)

Duration: 1 April 2021 – 31 March 2024

Project Summary:

The effect of Hot Water Treatment (HWT; 50°C for 45 min) on the occurrence of fungal pathogens associated with grapevine propagation material and nursery vines have recently been investigated in a different project. Results showed that pathogens associated with Black foot disease, Botryosphaeria canker and dieback and Phomopsis dieback were effectively inhibited by this treatment, but that Petri disease pathogens Phaeomoniella chlamydospora (51°C), Ca. luteo-olivacea (52°C), Phaeoacremonium parasiticum, Pm. minimum (53°C) and Pleurostoma richardsiae (more than 60°C) were not inhibited by this treatment and required substantial higher temperatures to be controlled.

HWT (50°C for 45 min) is effective in eliminating Aster Yellows and many fungal pathogens, but it is less effective in eliminating Petri disease pathogens, which, unfortunately is the biggest problem associated with young vine decline in South Africa. HWT (temperatures up to 56°C) combined with fungicides is successfully used in the fruit industries. The fungicides used include strobilurin, DMI, benzimidazole fungicides, etc. which have all shown efficacy to one or more of the GTD pathogen groups, but has not been evaluated in grapevine nurseries.
The aim of the current project is therefore to improve HWT (50°C for 45 min) in grapevine nurseries by adding fungicides to the hot water bath to prevent fungal infections, especially heat tolerant Petri disease pathogens.

The specific objectives will be:
1) To identify fungicides that are effective against Petri disease pathogens.
2) To confirm the efficacy of fungicides and fungicide combinations subjected to 50°C (in
vitro).
3) To test the efficacy of fungicide+HWT in detached rootstock assays (lab trials).
4) To test the efficacy of fungicide+HWT in commercial grapevine nurseries with grafting
material.