Weather, models & degree-days

Grape Powdery Mildew Risk Assessment Index

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
06-22-2024
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 60 high reproduces every 5 days
Rombauer Sierra Foothills 80 high reproduces every 5 days
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) 70 high reproduces every 5 days
West Point 70 high reproduces every 5 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 80 high reproduces every 5 days
Gold Hill (SRL) 80 high reproduces every 5 days
Lava Cap (LAV) 80 high reproduces every 5 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 ( P ) low present
Del Rey 0 low present
Easton 0 low present
Kearney Ag Center 0 low present
Kerman 0 low present
Kingsburg 0 low present
Sand Ranch 0 low present
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) 40 moderate reproduces every 15 days
Middletown (MID) 80 high reproduces every 5 days
Scotts Valley (SVL) 60 high reproduces every 5 days
Upper Lake (UPL) 60 high reproduces every 5 days
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 0 low present
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) 60 high reproduces every 5 days
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) 0 low present
Escalon (ESL) 0 low present
Linden (LIN) 0 low present
Lockeford (LOC) 0 low present
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

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.