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February (No. 493)

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Shot in the arm for eutypa

Jo Jalfon , New Zealand correspondent

Most grapegrowers and viticulturists would acknowledge that Eutypa dieback – or dead arm as it is commonly called – is a costly disease. Vine removal, replanting or regrafting and delays in productivity of new vines all add up. But what about yield losses?

Five years ago an American agricultural economist at the University of California, Berkeley, stated eutypa had robbed the State’s wine industry of more than US$260,000 (Siebert). A more recent study reported that the losses where in the order of US$1 billion (Munkvold).

Closer to home, yield reductions in South Australian vineyards due to Eutypa are now reported to be similar to those in California – between 30-82%. A survey in the Eden Valley in South Australia showed there was a ‘significant relationship’ between the severity of Eutypa symptoms and yield loss (Creaser and Wicks).

Vineyards with infection levels of 50% are not uncommon and at 24% infection, yield loss is estimated to be 570kg or A$1150 per hectare. At 47% infection, loss is around 1500kg or A$3040 per hectare. Don’t forget these costs don’t include losses in wine quality, inefficient use of irrigation, fertiliser and pesticides and the costs of reworking vines.

Dr Adrian Spiers has been actively researching control measures for Eutypa, is warning of a “growing storm on the horizon” for Australasian grape growers with ageing vineyards.

“Eutypa is also alive and active in Australasia and I have seen 12-15-year-old plantings of Cabernet Franc, Sauvignon Blanc and Cabernet Sauvignon in the Hawkes Bay rendered uneconomic by severe Eutypa infection. Most vineyard owners and managers have no idea of the impact eutypa will have on the productivity and profitability of their vineyards 10 years down the track and this is compounded by the fact many New Zealand plantings are less than 10 years old.”

Spiers says all New Zealand vineyards – and many areas of Australia - will have high inoculum levels of Eutypa and few vines will escape infection.

“Eutypa tends to be more prevalent where annual rainfall exceeds 600mm and is unlikely to occur where rainfall is below 250mm,” he said. “Symptoms will appear when the fungus has invaded vessels feeding affected foliage and toxins produced by the fungus have damaged pre-emergent bud tissues.
“In the early stages of the disease if the plant manages to contain the fungus within the previous year’s wood and pre-emergent buds are not exposed to the toxins then tissues will be largely unaffected. Moderately and heavily infected vines generally continue to decline and death of the arms is inevitable. Inoculum enters pruning wounds during winter pruning when fungal spores are prevalent. The fungus then grows down the single main stem and eventually kills the vine.”
Spiers believes it is worthwhile for winemakers to rejuvenate declining vines as much as possible, especially given most acknowledge that fruit picked from old vines makes the best wine.

The good news is that while Eutypa can’t be eradicated, it can be managed provided the infection has not penetrated the main stem extensively.
Spiers, who after more than 30 years as a scientist, presently with Primaxa Limited in Auckland, has spent more than 20 years researching the control of stem-invading fungi, initially Silverleaf (Chondrostereum purpureum) and presently Eutypa. The end result is the development of an international-first in terms of Eutypa management.

Primaxa's new ‘tool’ is StemShot GN-I, a proprietary blend of nutrients which is injected through to the centre of a vine by hydraulic pressure.
Spiers says a hole (8mm diameter) is drilled centrally through the main stem to within 10mm of the opposite side.
“A fitting is screwed into the hole and 50mls of a formulated nutrient solution is injected under pressure (100-1500psi) with our newly-developed StemGun. After application, the StemGun head is unscrewed and a plastic plug inserted to seal the hole. The operation takes less than two minutes per vine and a single treatment is usually sufficient to help the vine to make some recovery.”

Spiers said infected vines are best identified by foliar symptoms exhibited in early spring and should be marked for treatment in autumn following harvest. As always, early identification and treatment is advised.
“Treatment can continue throughout autumn and winter but should be completed prior to sap flow and bud break,” he said. “If vines are to be reworked by removing both arms then the main stem should be injected prior to removal. This enables a good distribution of the injected material which otherwise would escape through the cut surface. Alternatively, decapitated vines could be treated after Christmas the following season.”

Primaxa conducted extensive trials on Stemshot GN-1 on a plot of land it leases in Hawkes Bay before launching it onto the market several months ago.
“We leased a large block of land in the Bay that was going to be pulled out due to Eutypa,” Spiers said. “This enables us to conduct research in a commercial environment. This will enable the evolution of further products for Eutypa Control.”
Primaxa is currently rolling out Stemshot GN-1 internationally as well as working on a range of pruning wound protectants which they hope to unveil in early 2005.

For more information email iand@primaxa.co.nz or murrayb@coonawarra.limestonecoast.net

References


J.B. Siebert, (2001) Wines & Vines.
Munkvold, G.P, J.A. Duthie and J.J. Marois (1994) Reductions in yield and vegetative growth of grapevines due to Eutypa dieback. Phytopathology. 84:186-192.
M. Creaser and T. Wicks (2001) Yearly variation in Eutypa dieback symptoms and the relationship to grapevine yield. The Australian Grapegrower & Winemaker. 452:50-52.



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