Vine fungus most serious threat since phylloxera
During my recent visit to Sienna to attend a joint birthday party of Waiheke wine pioneers Kim and Jeanette Goldwater, I caught up with fellow guest and old friend, Dr Richard Smart. Richard is one of the world’s most distinguished viticulturists. An Aussie by birth and now living in the UK, he was New Zealand’s Ruakura and Te Kauwhata-based Government viticulturist for a decade from 1980.
“If you’ve got a minute, I’d like to show you something interesting in a local vineyard.” Richard said.
We drove down the road until I could park in a relatively young and apparently healthy vineyard. Armed with pruning shears, Richard strode purposefully along the row of vines until he came to a rather sickly specimen sporting an arm with little leaf growth. Richard snipped a cross-section of the sickly vine arm and showed me dark concentric rings within.
“This vine is dying”, he explained. “It has a trunk disease, a now-common fungal disease which is slowly killing it.”
As we walked further down the row he pointed to more sickly vines. Soon I could spot them myself.
There are three common types of fungal diseases, Richard explained. Esca, which creates black goo and a measle-like pattern; Eutypa and Botryosphaeria, which shows no foliar symptoms. A recent French study revealed that 15% of vines in that country have one or more of the three fungal diseases and the incidence is increasing. In the Barossa Valley, the yield of shiraz grapes has fallen to about 4-5 tonnes/hectare while a healthy vineyard should produce twice that amount of grapes. Vine fungal diseases is a crisis that has the potential to be as devastating as the phylloxera epidemic of the 1860s, according to Richard.
Vine fungal diseases are spread around the world by planting infected young vines, grafted onto phylloxera tolerant rootstocks. Another spread in vineyards is by infection of pruning wounds.
The solution to these devastating diseases is relatively straightforward.
- We need to improve the health of grafted vines in vine nurseries (that is underway but is likely to take 5-10 years)
- Pruning wounds need to be protected against airborne fungi spores, using fungicide paint.
- Infected vines can be rejuvenated if treated early by simply removing the main trunk and training a new trunk in its place. It is possible to rejuvenate a vineyard without significant loss of production.
If the three vine fungal diseases are allowed to develop unchecked the price of grapes and vine must increase, while the concept of “old vine” wine will cease to exist as vines will have a maximum reduced life of 20 years.
All three fungal diseases are present in New Zealand and sauvignon blanc, which accounts for 75% of this country’s production, is one of the most susceptible grape varieties. Local research means, however, that growers are shown how to control the diseases. If they follow the guidelines production should not be affected.