What to Do About Red Blotch

Winemakers and growers offer practical advice regarding virus

by Paul Franson
Lise Asimont, director of grower relations at Francis Ford Coppola Presents (photo source), says half of the company’s grape contracts have been affected by red blotch, which causes a decline in tannins and anthocyanins.
Sacramento, Calif.—Among many useful sessions at the Unified Wine & Grape Symposium, one of the most valuable was the workshop on red blotch virus for winemakers organized by Alison Crowe of Garnet Vineyards, part of the Silverado Premium Properties family.

Crowe was joined by Peter Opatz of Silverado Winegrowers, Chik Brenneman of the University of California, Davis, Lise Asimont of Francis Ford Coppola Presents in Geyserville and Charles Thomas, winemaker for Huneeus Vintners including Quintessa Vineyards.

Opatz began by describing a “nightmare” in a 40-acre vineyard he manages in Alexander Valley: “It was a great site, and it wasn’t until the third leaf that we found a problem with red blotch. The symptoms we noted could almost be attributed to deficiencies with phosphorus or potassium at first.”

The vines had many red and pink leaves, and the grapes stopped accumulating sugar at 19º Brix. Commercial labs couldn’t identify the problem at the time, so Opatz turned to Jim Wolpert at U.C. Davis, who confirmed the virus. “About 75% of the vines in the vineyard were infected,” Opatz said.

Fortunately, a winery bought the grapes anyway, and the grower paid for Mega Purple and concentrate to make them usable.

Another infected vineyard Opatz managed contained Ruby Cabernet—and in this case, they could only sell the grapes for distilling. Opatz said the red blotch problem became so serious that Silverado stopped planting last year, though it has started again after much testing of vines.

Little research has been done into the wine made from infected grapes, but Brenneman at UC Davis has made some wine from test plots with mixed results. “It raised more questions than answers,” he admitted, and has proposals out for more research.

Asimont at Coppola reported widespread problems, with all but two vineyard sources she uses in 10 counties showing signs of red blotch (they don’t source grapes from Napa). “Half of our contracts have been affected. Many plans for planting have been tabled or delayed.” She added, “We’re looking intensely at future sources.”

Asimont said that visual identification of red blotch is possible. “The red starts in the fruiting zone and gradually spreads through the canopy. Fruit maturity is delayed, as is sugar accumulation.” Coppola also tests phenolics and finds a 5% to 30 % decline in tannins and anthocyanins in grapes from vines identified with red blotch.

Asimont also noted what she calls yellow or white blotch for the past eight vintages. The problems are especially prevalent on old-vine Zinfandel. “All the vines have some viruses,” she stated. The only variety not affected seems to be Sauvignon Blanc.

Coppola tries to be flexible but recommends that growers drop fruit to compensate two weeks before véraison. She encouraged growers and winemakers to talk it over. She asked winemakers, “Can you tolerate lower Brix?” suggesting that is a practical approach. She also outlined new contract provisions to deal with the problem.

Practical steps
After horror stories and suggestions from the other speakers, Huneeus Vintners’ Thomas offered some practical suggestions for dealing with vines infected with red blotch virus.

He started with steps to take in vineyards:

• Prune to lower bud count.

• Preserve photosynthate and carbo-load at each growth point.

• Sucker early.

• Pull leaves at berry set.

• Adjust fruit level early, drop affected fruit and adjust crop load at 70% véraison.

• Feed higher levels of potassium, phosphorus and micronutrients

Thomas also warns that winemakers might have to be realistic at harvest. “Maybe you need to redefine what 'ripe' is.” Selective picking may be needed. He noted that infected vines ripen one to three weeks late with a typical cap at 22º Brix and up to 30% lower tannins and anthocyanins.

Thomas hasn’t noted a consistent difference in acid levels, though malic acid can sometimes be higher than 30% of the total.

Once red blotch is identified in a vineyard, how do you prevent spread? The viticulture community is not sure about vectors but knows red blotch spreads by propagating vines. A grower can identify specific infected vines and remove them but may eventually have to replant the whole vineyard. In this case, it’s vital to find clean plant material with which to start.

Some vineydards are turning to using their own scion material, or sourcing it from others after testing, or using nursery material after they have tested it and they’re confident.

Above all, Thomas warns winemakers to partner with growers and not get into an adversarial relationship.

He offered some suggestions to compensate for deficiencies in affected grapes, including additions of concentrate, tannins and pigment. Other possible approaches are co-fermentation, adding skins from other grapes, flash detente, oak fermentation and blending.

All of these steps add additional costs, and unfortunately those additions can’t mitigate the effect of “unripe” tannins. “They leave a mid-palate ‘hole,’ a lack of textural sweetness,” he said.

Finally, Thomas graphically illustrated the financial impact red blotch can have on a top vineyard. Instead of returning as much as $90,000 per acre for a $100 wine, it might just generate wine sold as bulk at $24 per gallon—and that’s not the worse-case scenario.

Price Per Bottle FOB Case Price    Tons/Acre Revenue/Acre
Napa Cabernet Sauvignon — Wine Revenue Scenarios
$25 $150 5.0 $39,000
$50 $300 4.0 $62,400
$100 $600 3.0 $90,000
Red blotch vines Bulk at $24/gallon 3.0 $10,800

Not surprisingly, Thomas thinks beating the virus will take collaboration among vineyards as it did to whip the European grapevine moth. He thinks red blotch testing should be part of a nationwide certification campaign. He also called for increased spending on the problem. “We need to research epidemiology, vectors and more. It’s time to ante up!”

Posted on 02.08.2014 - 17:10:56 PST
Perhaps Foundation Plant Materials can solve the problems.
Bruce Coulthard

Posted on 02.10.2014 - 09:18:17 PST
Is there any correlation with planting density?
Jim Bullis

Posted on 04.09.2014 - 15:29:37 PST
There is NO correlation with planting density.
Also FPS is working on the problem. New planting materials take a long time to disseminate down through the nurseries to the end users though. The 2010 protocol materials have all tested clean of Red Blotch. Now we just need to have those vines blown up to usable quantities, with clean rootstocks to graft them too. That will take the next few years. Meanwhile vineyards are still being planted. Some people are being very careful about what is going into their vineyards, others are not.

Derek Cronk