The grape powdery mildew risk assessment index (RAI) is useful for determining disease pressure and how often you need to spray to protect the vines. For information on how to use the RAI, see the pest management guideline. RAIs are based on actual weather data for stations that take appropriate readings.
County | Active Weather stations | RAI* for 10-31-2024 |
Disease pressure | Pathogen status |
Amador
Based on bud break, April 17, in Zinfandel, may need to adjust for other cultivars that emerge earlier than the indicated date. |
---|---|---|---|---|
Amador Screaming Eagle | 50 | moderate | reproduces every 15 days | |
Rombauer Sierra Foothills | M | N/A | N/A |
Calaveras
Based on bud break, April 17, in Cabernet Franc, may need to adjust for other cultivars that emerge earlier than the indicated date. |
Ironstone (IST) | 50 | moderate | reproduces every 15 days | |
West Point | 50 | moderate | reproduces every 15 days |
El Dorado
Based on bud break, March 28, in Sangiovese, may need to adjust for other cultivars that emerge earlier than the indicated date. |
Fair Play | 50 | moderate | reproduces every 15 days | |
Gold Hill (SRL) | 60 | high | reproduces every 5 days | |
Lava Cap (LAV) | 50 | moderate | reproduces every 15 days |
Fresno
Based on bud break, March 11, in Thompson Seedless, may need to adjust for other cultivars that emerge earlier than the indicated date. |
Caruthers | 0 | low | present | |
Del Rey | 60 | high | reproduces every 5 days | |
Easton | 0 ( P ) | low | present | |
Kearney Ag Center | 50 | moderate | reproduces every 15 days | |
Kerman | 50 | moderate | reproduces every 15 days | |
Kingsburg | 50 | moderate | reproduces every 15 days | |
Sand Ranch | 60 | high | reproduces every 5 days |
Lake
Based on bud break, April 8, in Sauvignon Blanc , may need to adjust for other cultivars that emerge earlier than the indicated date. |
Kelseyville (KEL) | 0 | low | present | |
Middletown (MID) | 50 | moderate | reproduces every 15 days | |
Scotts Valley (SVL) | 50 | moderate | reproduces every 15 days | |
Upper Lake (UPL) | 0 | low | present |
Madera
Based on bud break, March 13, in Thompson Seedless, may need to adjust for other cultivars that emerge earlier than the indicated date. |
Firebaugh | 60 | high | reproduces every 5 days |
Mendocino
Based on bud break, April 17, in Chardonnay, may need to adjust for other cultivars that emerge earlier than the indicated date. |
Ukiah-Ruddick (RUD) | 0 | low | present |
San Joaquin
Based on bud break, March 15, in Chardonnay, may need to adjust for other cultivars that emerge earlier than the indicated date. |
Collegeville (COL) | 60 | high | reproduces every 5 days | |
Escalon (ESL) | 60 | high | reproduces every 5 days | |
Linden (LIN) | 0 | low | present | |
Lockeford (LOC) | 70 | high | reproduces every 5 days | |
Lodi (LangeTwins) | 0 | low | present |
* Bud break based on farm advisor countywide vineyard surveys
- Amador: Apr 17 in Zinfandel
- Calaveras: Apr 17 in Cabernet Franc
- El Dorado: Mar 28 in Sangiovese
- Fresno: Mar 11 in Thompson Seedless
- Lake: Apr 8 in Sauvignon Blanc
- Madera: Mar 13 in Thompson Seedless
- Mendocino: Apr 17 in Chardonnay
- San Joaquin: Mar 15 in Chardonnay
M = missing data - no substitution values were available
P = missing data substituted with values from previous day
Because estimated data is included in the index, use reported RAI with caution. Interpret RAI using field surveys and your knowledge of the particular vineyard, along with additional weather data if you have it.