April 29, 1996

1995 Phylloxera Survey Results

The results of the 1995 Phylloxera and Planting Surveys of Napa and Sonoma Counties are reported below. Napa and Sonoma counties each have about 35,000 acres of grapes. Over 530 surveys were returned accounting for over 31,000 acres in each county. This high response rate increases our confidence in the accuracy of this report.

After adjusting the figures slightly upward to account for unreported acreage, the phylloxera survey results indicate that in Napa County, approximately 1,700 acres were removed in 1995 due to phylloxera, and another 380 acres were removed for other reasons. To date, over 9,100 acres of Napa County vineyards have been removed specifically due to type B phylloxera. An additional 5,800 acres are thought to be currently, with 1,350 of those scheduled for removal in 1996. In Sonoma County, over 2,850 acres have been removed to date with 4,500 additional acres infested. Of these, 650 acres are scheduled for removal in 1996.

The progression of vineyard removals due to Type B phylloxera can be estimated as follows:

Acres Removed Due To Type B Phylloxera

County1987-9019911992199319941995Total to Date1996*

* Anticipated

Removals in Napa County have remained relatively steady for the past four years. I previously estimated that at the beginning of the phylloxera crisis, there were approximately 22,000 acres of AXR#1 planted in Napa County. To date, I estimate that approximately 11,000 of these acres have been replanted (primarily due to phylloxera) or converted (interplanted or inarch grafted). Napa County appears to be half-way through the replanting cycle of AXR. Most of the remaining 11,000 acres will likely be replanted over the next 5 years. Responding growers indicated there were only 9,037 acres of AXR still left in Napa County (not all of Napa's acreage was accounted for in the survey) so it is possable that we are even a little past half way.

Below are the total responses to the 1995 survey from NAPA COUNTY.

A.What is your total vineyard acreage?32,402.9
B.How many of these acres are planted with AXR#1 rootstock?9,036.9
1How many acres planted on AXR#1 rootstook were removed due to phylloxera damage during 19951,669.5
2Of your existing AXR#1 vineyards, how many acres do you think are currently infested with Type B phylloxera5,711.3
3.How many of these infested acres planted on AXR#1 do you plan to remove in 1996 because of phylloxera?1,330.3
4.How many additional acres, on any rootstock, were removed in 1995 for reasons other than phylloxera367.7

The distribution of the acreage removed during 1995 in NAPA COUNTY was as follows

Carneros362.1Western Hills76.5
Napa to Yountville551.6Eastern Hills65.3
Yountville to Rutherford258.8Pope/Chiles/Wooden Valleys87.4
Rutherford to St. Helena185.0Other0.0
St. Helena to Calistoga82.8Total Napa County1669.5

Below are the total responses to the Phylloxera Survey from SONOMA COUNTY.

C. What is your total vineyard acreage?31,225.9
D. How many of these acres are planted on AXR#1 rootstock?12,370.5
5. How many acres planted on AXR#1 rootstock were removed due to phylloxera damage during 1995.729.1
6. Of your existing AXR#1 vineyards, how many acres do you think are currently infested with Type B phylloxera?4,466.2
7. How many of these infested acres planted on AXR#1 do you plan to remove in 1996 because of phylloxera?639.8
8. How many additional acres, on any rootstock, were removed in 1995 for reasons other than phylloxera?394.5

The distribution of the acreage removed in SONOMA COUNTY was as follows:

Carneros103.9Dry Creek Valley86.5
Sonoma Valley57.6Russion River Valley except Chalk Hill58.0
Knights Valley14.0Chalk Hill65.0
Alexander Valley: south of Geyserville295.6Other8.5
Alexander Valley: Geyserville and north40.0Total Sonoma County729.1

1995 Planting Survey Results

The results of the 1995 planting Survey are shown below. No attempt was made to account for the unreported acreage; only the actual responses are shown.

How many acres were planted in 1995?


2. What acreage of rootstocks was planted in 1995?

3309268.4188.2St. George62.371.3

3. What acreage of scion varieties was planted in 1995?

Cab. Sauvignon373.0266.5Chardonnay417.3360.8
Merlot579.7422.7Sauv. Blanc99.238.5
Cab. Franc23.44.0Chenin Blanc0.00.0
Pinot Noir127.461.1Viognier14.65.0
Sangiovase10.014.0Pinot Gris40.82.5
Not Yet Budded115.8120.2

4. How many acres of AXR#1 vineyards were interplanted or inarch grafted in 1995?

Inarch Grafted28.9150.0

Cabernet Sauvignon, Merlot and Chardonnay continue to be the principal varieties planted, accounting for 72.1% of the 1995 plantings in Napa County and 74.5% in Sonoma County.

Percent of Reported Acreage
Cabernet Sauvignon28.517.119.613.917.718.9
The "Big Three"73.668.672.170.973.774.5

Other varieties planted in Napa County include Malbec (12.9 acres), Petit Verdot (6.1 acres), and lesser amounts of White Riesling, Pinot blanc, Petite Sirah, Nebbiolo, Sauvignon musque, Napa Gamay and Gewurztraminer. Additional varieties in Sonoma County included Primitivo, Petite Sirah, Petit Verdot, Barbera, Marsanne and Sauvignon musque.

The rootstock 101-14 lept to the forefront of the plantings in Napa County accounting for 28.4% of the reported acreage. 5C, 3309 and 110R together accounted for 42.2% in Napa. 1103P was also widely used accounting for 9.6%. In Sonoma County, 5C, 3309, 110R and 101-14 accounted for 76.5% of the reported acreage. Both counties reported considerable acreage that had been interplanted, but Sonoma continues to greatly exceed Napa in inarch-grafted vineyards.

Thank You Harold Coffer

After 18 years of providing fruit frost and agricultural harvest weather forecasts for Napa and Sonoma county grape growers, Harold Coffer gave his final forecast on April 19. Despite pleas from agricultural organizations, the National Weather Service (NWS) was forced to discontinue this service as a result of congressional mandates. Harold will continue on with the NWS and we wish him the best of luck. The Napa Valley Grape Growers Association, the Sonoma County Grape Growes Association, Sonoma County Farm Advisor Rhonda Smith and myself have arranged for the continuation of frost and harvest weather forecasts for 1996 through a private vendor, Fox Weather, based in Ventura County. If you have any comments about the new service, please let us know.

Powdery Mildew Risk Assessment Network

Applying fungicides for control of powdery mildew based on the likelihood of disease development should allow for effective disease control with a possible reduction in fungicide use. Towards this goal, a powdery mildew disease risk assessment network for Napa Valley was established in 1995 utilizing 23 Adcon Telemetry weather stations located in vineyards throughout the region. There are currently 34 weather stations in the network. Each station collects temperature, relative humidity, precipitation and leaf wetness data which are transmitted at 15-minute intervals via radio telemetry to a base-station receiver and computer located at my office in Napa.

Software analyzes the weather data for each location using a disease risk model recently developed at UC Davis by Dr. Doug Gubler. Weather station owners have modem access to the base station and can download weather data and disease indices for their own location or any others on the network. The model predicts ascospore releases based on leaf wetness and temperature data. Daily risk assessments for conidial spore development are generated based on temperature. Risk levels rise or fall on a 0-100 scale. During low risk periods (0-30), spray/dust intervals can be extended due to low disease pressure; during high risk periods (60-100), spray/dust intervals should be shortened. Risk indices in 1995 varied geographically in Napa Valley due to differing weather patterns. Carneros showed the greatest disease pressure. Upvalley growers utilizing the risk assessment network were able to eliminate 1-3 fungicide applications during the growing season with no increase in powdery mildew.

Plant Pathology BBS Now Online for Access to Mildew Risk Assessments

A computer bulletin board system (BBS) focusing on California plant pathology developed by UC Davis Plant Pathology Specialist Doug Gubler is now accessible by modem. Contents include general agricultural information about grapes and other crops. Information from IPM manuals, Pest and Disease Control Guidelines and agricultural journals will be accessible.

Disease forecasts and risk assessments for grapevine powdery mildew as described above are currently available from weather networks in Napa, Sonoma and Kern counties, with Madera, Monterey and Santa Barbara likely to be available soon. Botrytis forecasts will likely be available in 1997.

Access to the BBS is free for examination until July 1, 1996. Afterwards, there will be an annual fee of $200 for subscribers using only the encyclopedic information. The annual fee will be $400 per year fee for those also using the risk assessment models. The BBS can be accessed from both PC and Macintosh platforms. The client software is free. For further information and a software package, please contact:

Matt Rademacher
Department of Plant Pathology
University of California
Davis, CA 95616
(916) 752-4982

1996 Napa Valley Viticultural Fair - November 13

Mark your calanders now for the third Napa Valley Viticultural Fair which promises to be the largest and best ever. Vendors, interested in exhibiting at the Fair, should contact Claudia Glade at the Napa Valley Grape Growers Association (707) 944-8311.

New Pierce's Disease Publication Available

A new publication reviewing Pierce's Disease was recently written by UC Cooperative Extension North Coast IPM Advisor Lucia Varela. Pierce's Disease in the North Coast reviews the biology and epidemiology of PD, describes the insect vectors and discusses management strategies. Copies are available through my office.

This page transcribed by Ben Henry. Benjamin Henry Viticultural Services.

E-mail: bhenry@bhvs.com
E-mail: Ed Weber

Last Updated: June 1, 1996