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
09-28-2022
Disease pressure Pathogen status
Amador

Based on bud break, March 13, in Chardonnay, may need to adjust for other cultivars that emerge earlier than the indicated date.

Amador Screaming Eagle 70 high reproduces every 5 days
Rombauer Sierra Foothills 20 low present
Calaveras

Based on bud break, March 13, in Chardonnay, may need to adjust for other cultivars that emerge earlier than the indicated date.

Ironstone (IST) 30 moderate reproduces every 15 days
West Point 20 low present
El Dorado

Based on bud break, March 13, in Chardonnay, 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) 20 low present
Lava Cap (LAV) 50 moderate reproduces every 15 days
Fresno

Based on bud break, March 15, in Thompson Seedless, may need to adjust for other cultivars that emerge earlier than the indicated date.

Caruthers 40 moderate reproduces every 15 days
Del Rey 30 moderate reproduces every 15 days
Easton 40 moderate reproduces every 15 days
Kearney Ag Center 40 moderate reproduces every 15 days
Kerman 40 moderate reproduces every 15 days
Kingsburg 40 moderate reproduces every 15 days
Sand Ranch 40 moderate reproduces every 15 days
Lake

Based on bud break, March 18, 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) 20 low present
Scotts Valley (SVL) 20 low present
Upper Lake (UPL) 60 high reproduces every 5 days
Madera

Based on bud break, March 15, in Thompson Seedless, may need to adjust for other cultivars that emerge earlier than the indicated date.

Firebaugh 40 moderate reproduces every 15 days
Mendocino

Based on bud break, March 24, in Chardonnay, may need to adjust for other cultivars that emerge earlier than the indicated date.

Ukiah-Ruddick (RUD) 40 moderate reproduces every 15 days
San Joaquin

Based on bud break, March 31, in Sauvignon Blanc, may need to adjust for other cultivars that emerge earlier than the indicated date.

Collegeville (COL) 40 moderate reproduces every 15 days
Escalon (ESL) 40 moderate reproduces every 15 days
Linden (LIN) 40 moderate reproduces every 15 days
Lockeford (LOC) 40 moderate reproduces every 15 days
Lodi (LangeTwins) 40 moderate reproduces every 15 days

* Bud break based on farm advisor countywide vineyard surveys

  • Amador: Mar 13 in Chardonnay
  • Calaveras: Mar 13 in Chardonnay
  • El Dorado: Mar 13 in Chardonnay
  • Fresno: Mar 15 in Thompson Seedless
  • Lake: Mar 18 in Sauvignon Blanc
  • Madera: Mar 15 in Thompson Seedless
  • Mendocino: Mar 24 in Chardonnay
  • San Joaquin: Mar 31 in Sauvignon Blanc