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Will we be making wine from 100 year old grafted vines?
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The alleged shorter economic life of grafted vines (rootstocks) compared with that of own roots has often been cited as a reason for not using rootstocks.
After reading in Kym Ludvigsen’s article on the economics of vineyard replacement in the February issue of Grapegrower and Winemaker that ‘Planting grafted vines … reduces the life of a vineyard”, ‘the life of a grafted vine appears to be 30–40 years with production reducing thereafter to uneconomical levels’ and also ‘vines planted as rootstocks will require earlier replacement than own rooted vines’ I thought it was time to have a closer look at this issue.
It is certainly true that vineyards in Europe are replaced more frequently than in Australia and these vineyards are planted almost exclusively on rootstocks. But is it the rootstock or more specifically the decline of the rootstock/scion graft union that is causing the economic decline of a vineyard or are there other factors having an influence?
On my study tour of Europe last year I investigated this issue and discovered that vineyard decline was not a result of the decline of the rootstock/scion graft union but was generally a result of high virus loads in the initial planting material and or the introduction of Grape Fan Leaf Virus (GFL) and other nepoviruses by nematode vectors.
The high incidence of trunk disease such as Esca (Phaeoacremonium chlamydosporum) also contributed to the higher frequency of replanting. So, given the relatively low virus status of Australian planting material compared with Europe and the absence of Grape Fan Leaf virus and its nematode vector (apart from limited areas around Rutherglen), will grafted vines in Australia have an economic life comparable with that of own roots?
Some further investigations using the Phylloxera and Grape Industry Board of South Australia’s planting register uncovered only three grafted winegrape blocks planted prior to 1970. One block of Shiraz on Ramsey situated in the Riverland planted in 1969 is still producing yields in the order of 18–20 tonnes/ha. Another block of Shiraz on Ramsey planted in 1969 in McLaren Vale is producing what the grower describes as ‘viable yields’ of 6–7 tonnes/ha and finally a dry-grown block of Riesling on Ramsey in the Barossa Valley planted in 1969 produced 16t/ha in vintage 2006, which according to the grower is its ‘biggest crop ever’.
There is no experimental evidence, to my knowledge, that supports the proposition that grafted vines have a shorter economic life than vines on own roots and while it is dangerous to draw conclusions from only three blocks this evidence suggests that 37-year-old grafted vines are able to produce ‘viable’ yields similar to that of own rooted vines.
Since 2000, approximately 30% of plantings have been on rootstock in South Australia so the true test of whether rootstocks will require earlier replacement than own rooted vines will only be known in 30 years. But given the good work of the vine improvement associations across Australia in ensuring that the material they supply is free of known viruses, there is a very good chance that rootstocks will be matching the performance of own-rooted vines well into their old age. Nick Dry reports.