As they treated pruning cuts with fungicide, sawed off cordons, or ignored it, grape growers throughout California long have known eutypa dieback was costly, but little was known about how costly.
An agricultural economist at the University of California, Berkeley recently says eutypa could have robbed the state's wine industry of more than $260 million in 1999. That's nearly 16 percent of the $1.672 billion in gross returns from that crush.
Jerome B. Siebert, in reporting on his study funded by the American Vineyard Foundation, said eutypa is the primary grape vine disease in the state and impacts growers on several counts.
Those include: loss of yield; increased costs of preventive maintenance through chemical treatments; increased costs for pruning, top-working, and replants; and decreased vineyard life.
The disease, spread as its spores are driven by rain into fresh pruning wounds, strikes virtually all varieties, wine, raisin, and table.
Siebert pointed out that his estimates of eutypa-related losses represent the worst case. "The explicit assumption made in these estimates is that the infection of eutypa is uniform throughout varieties and districts. However, the actual infection rate of eutypa will vary by variety and location.
"In addition, eutypa is more prevalent in the later years of a vineyard's life than it earlier years. For example, most of the vines in Napa are relatively young due to a massive replanting of vineyards because of phylloxera."
Eutypa (Eutypa lata) has common symptoms and is often confused with another fungal disease, grape bot canker (Botryodiplodia theobromae), but for purposes of the study they are considered the same.
Siebert noted the earlier research by G.P. Munkvold and others that linked yield loss to disease severity. "This formula," Siebert said, "demonstrates the destructive potential of eutypa as some vineyards over 20 years old exhibited an 83 percent decline in yield compared with their peak years."
Barbera rarely affected That study also noted the Barbera variety is rarely affected by the disease. Characteristically, eutypa goes unnoticed until vines are about 10 years old, and then its symptoms and probability increase.
In Chenin Blanc, for example, between 12 and 20 years of age, the disease increases each year until all vines are infected at 20 years.
In a table illustrating yield with vineyard age, yields in the third year for infected and non-infected vines are 2 to 4 tons to the acre. At about five years, yields of infected and non-infected vines reach eight tons.
From then until 11 years, the infected vines might surpass slightly yields of the non-infected. But after that point, eutypa-free vines level off at about nine tons for the next decade, while yields of infected vines arc downward on the chart, reaching the four-ton level at about age 20 years.
Discussing the costs associated with management of the disease, Siebert said the preventive steps of daubing or spraying fungicide on pruning wounds is very labor intensive and costly, and since treatments last no more than a week, five or six may be required.
Expensive too is removal of infected wood and retraining of vines.
"A third alternative," he said, "is to allow the disease to take its course and plan on replanting the vineyard every 20 years or less."
However, the economist added, "A shortened vineyard life will only add increased costs to the grower and decrease net profits as well as build-up of equity."
In reaching an estimate for costs of statewide pruning wound treatments alone, Siebert said he made four assumptions. 1) It takes three hours per acre for a backpack sprayer treatment. 2) Benlate fungicide at 3.2 ounces per gallon is applied with 3.5 gallons of water per acre. 3) A labor wage of $6.50 (higher in premium wind districts) is used. 4) The cost of Benlate is $18 per pound.
"These assumptions yield a per-acre cost of $32.10, which corresponds to estimated costs resulting from interviews with vineyard managers.
"If it was assumed that 490,789 acres of grapes used for wine are treated in the manner described, total cost to the industry would be $15.8 million each application. Depending on the amount of rain encountered during the spring, recurring applications may have to be made up to four times, resulting in a cost of $63 million."
More data is needed, he said, before cost estimates could be made for practices of late pruning and top-working. A refinement of his study would require a formal study of incidence of the disease by variety, vineyard age, pruning method, and location.