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 04-02-2025 |
Disease pressure | Pathogen status |
Amador
Based on bud break, February 1, in Zinfandel, may need to adjust for other cultivars that emerge earlier than the indicated date. |
|---|---|---|---|---|
| Rombauer Sierra Foothills | 0 | N/A | Not Present |
Calaveras
Based on bud break, February 1, in Cabernet Franc, may need to adjust for other cultivars that emerge earlier than the indicated date. |
| Ironstone (IST) | 0 | low | present | |
| West Point | 0 | N/A | Not Present |
El Dorado
Based on bud break, February 1, in Sangiovese, may need to adjust for other cultivars that emerge earlier than the indicated date. |
| Fair Play | 0 | N/A | Not Present | |
| Gold Hill (SRL) | 0 | N/A | Not Present | |
| Lava Cap (LAV) | 0 | N/A | Not Present |
Fresno
Based on bud break, March 16, 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 | |
| Easton | 0 | N/A | Not Present | |
| Kerman | 0 | N/A | Not Present | |
| Kingsburg | 0 | N/A | Not Present | |
| Sand Ranch | 0 | N/A | Not Present |
Lake
Based on bud break, March 20, in Sauvignon Blanc, may need to adjust for other cultivars that emerge earlier than the indicated date. |
| Kelseyville (KEL) | 0 | N/A | Not Present | |
| Middletown (MID) | 0 | low | present | |
| Scotts Valley (SVL) | 0 | N/A | Not Present | |
| Upper Lake (UPL) | 0 | N/A | Not Present |
Madera
Based on bud break, March 16, in Thompson Seedless, may need to adjust for other cultivars that emerge earlier than the indicated date. |
| Firebaugh | 0 | N/A | Not Present |
Mendocino
Based on bud break, March 27, in Chardonnay, may need to adjust for other cultivars that emerge earlier than the indicated date. |
| Ukiah-Ruddick (RUD) | 0 | N/A | Not Present |
San Joaquin
Based on bud break, March 17, in Chardonnay, may need to adjust for other cultivars that emerge earlier than the indicated date. |
| Collegeville (COL) | 0 | N/A | Not Present | |
| Escalon (ESL) | 0 | N/A | Not Present | |
| Linden (LIN) | 0 | N/A | Not Present | |
| Lockeford (LOC) | 0 | N/A | Not Present | |
| Lodi (LangeTwins) | 0 | N/A | Not Present |