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 03-11-2026 |
Disease pressure | Pathogen status |
Amador
Based on bud break, March 10, in Grenache, may need to adjust for other cultivars that emerge earlier than the indicated date. |
|---|---|---|---|---|---|
| Rombauer Sierra Foothills | 20 | N/A | Not Present |
Fresno
Based on bud break, March 9, in Thompson Seedless, may need to adjust for other cultivars that emerge earlier than the indicated date. |
|
| Caruthers | 0 | N/A | Not Present | ||
| Del Rey | 0 | N/A | Not Present | ||
| Kerman | 0 | N/A | Not Present | ||
| Kingsburg | 60 | high | reproduces every 5 days |
Lake
Based on bud break, January 1, in Sauvignon Blanc, may need to adjust for other cultivars that emerge earlier than the indicated date. |
|
| Kelseyville (KEL) |
No data yet available for this station. |
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| Middletown (MID) |
No data yet available for this station. |
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| Scotts Valley (SVL) |
No data yet available for this station. |
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| Upper Lake (UPL) |
No data yet available for this station. |
Madera
Based on bud break, March 9, in Thompson Seedless, may need to adjust for other cultivars that emerge earlier than the indicated date. |
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| Firebaugh | 0 | N/A | Not Present |
San Joaquin
Based on bud break, January 1, in Chardonnay, may need to adjust for other cultivars that emerge earlier than the indicated date. |
|
| Collegeville (COL) |
No data yet available for this station. |
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| Escalon (ESL) |
No data yet available for this station. |
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| Linden (LIN) |
No data yet available for this station. |
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| Lockeford (LOC) |
No data yet available for this station. |
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| Lodi (LangeTwins) |
No data yet available for this station. |
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