Hot water treatment for grape vines

December 2007
Corbans Viticulture is one of the largest dedicated viticulture nurseries in the country, supplying grafted grapevines to the wine industry. The company has a long track record in the industry with more than 40 years of experience in the industry.

The company has recently launched Total Vineyard Solutions, an integrated approach to vineyard consultancy encompassing the skills, knowledge, and technology of viticulture and Geographical Information Systems (GIS).

Furthermore the company has invested a significant amount of time and money on R & I (Research and Innovation) and the results of the latest projects are just coming to fruition this year.

In 2003 Dr Anna Graham began trials at Whenuapai, in west Auckland, to adapt the overseas practice of Hot Water Treatment (HWT) specifically to cool climate conditions as experienced here in New Zealand.

Standard HWT in warmer countries involves immersing dormant cuttings in water at 50 degrees Celsius for 30 minutes as a means of eliminating fungal, viral and bacterial pathogens (disease-causing organisms), but in New Zealand this resulted in unacceptably high losses about six weeks after grafting and planting. In the first trial undertaken at Corbans Viticulture cuttings were taken from various wine growing regions in NZ, and what resulted was a significant 80% loss rate. NZ vines are not as heat tolerant as those HWT treated overseas. Vines in hotter climates survive HWT at 50 degrees because of the accumulation of heat shock proteins which protect them.

The trials were supported by a Technology to Business Growth grant from the Foundation for Research, Science and Technology and it is the first time that HWT had been studied under NZ conditions.


Tissue samples are taken from the HWT trial vines after some months of growing in the field to gauge the effectiveness of the modified HWT protocols. The actual temperatures and times vary between grape varieties and growing regions in New Zealand and this information remains confidential to Corbans Viticulture.

Eight months after modified HWT, pathogen levels remained significantly lower in the treated grafted vines than in the untreated vines and these vines were repopulated with harmless and potentially beneficial fungal endophytes.

Dr Graham said vines grafted with modified hot water treated cuttings grew at least as well as untreated vines during the first year of growth. Further assessment parameters include graft strength, stem diameter and root mass of the treated vines. Two further vineyard trials have been set up in 2006 and 2007 to monitor long-term effects of HWT.

During the course of the research grafted vines losses have declined to less than 10% after modified treatment, compared with of up to 95 per cent following standard HWT.

The most critical time for disease control is prior to grafting, as it is effective against disease pathogens (fungi and bacteria) inside the wood. HWT at less than 50 degrees for 30 minutes is effective in cleaning up the cuttings before grafting and hothouse propagation. Otherwise cuttings may be infected with disease which will subsequently spread in the warm, moist hothouse during propagation. These vines may survive in the nursery and appear healthy until exposed to stress in the vineyard.

Research conducted both internationally and in New Zealand shows this treatment is effective against Crown gall, black goo, Phomopsis and Cylindrocarpon blackfoot diseases.

The basket and HWT tank bathing technique has been refined in the Corbans Viticulture facility at Whenuapai. Hot water circulation is required to kill any pathogens that may be present in the vine cuttings. The ratio of water to vine mass is also important to ensure that temperature doesnt drop when the basket is immersed.

The water temperature is computer controlled and it doesnt vary by more than plus or minus half of a degree Celsius.

Commercial application

So far Corbans Viticulture at Whenuapai hasnt HWT treated cuttings for grape growers of other companies, but it has shared the modified technique at industry conferences like Bragato and international conferences in California and Adelaide. It has the capability to do cuttings for clients.

This year it is HWT treating a significant quantity of proven rootstocks from the former two years of trials, plus a wider range of varieties to establish the optimum treatments.

The HWT cuttings are grafted and now commercially available to grape growing clients of Corbans Viticulture.