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How to Manage Pests

Interactive Tools and Models:
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.

Powdery mildew risk for stations in counties:
| Fresno | Madera | San Joaquin |
Choose year

RAIs are based on actual weather data for stations that take appropriate readings.

County Active weather stations
(Click on station for year-to-date graph/daily data)		 RAI*
for
09/29/2011		 Disease pressure Pathogen status
Fresno
(map)		 Based on bud break, March 17, in Thompson Seedless,
you may need to adjust for other cultivars that emerge earlier than the indicated date.
CARUTHERS-01.P, CAR 70 high reproduces every 5 days
Del_Rey/Fowler-01.P, DELF 30 intermediate reproduces every 15 days
EASTON-01.P, EAS 30 intermediate reproduces every 15 days
KERMAN-01.P, KER 20 low is present
KINGSBURG-01.P, KNG 50 intermediate reproduces every 15 days
Kearney_Ag_Ctr-01.P, KAC 30 intermediate reproduces every 15 days
Laton_North-01.P, LATN 70 (S1) high reproduces every 5 days
Madera
(map)		 Based on bud break, March 16, in Thompson Seedless,
you may need to adjust for other cultivars that emerge earlier than the indicated date.
FIREBAUGH/ALISO-01.P, FRBA 30 intermediate reproduces every 15 days
Madera_North-01.P, MADN 20 low is present
Madera_South-01.P, MADS 30 (S2) intermediate reproduces every 15 days
San Joaquin
(map) 		Based on bud break, March 17, in Chardonnay,
you may need to adjust for other cultivars that emerge earlier than the indicated date.
FARMINGTON-01.P, FGN 10 low is present
LIVE_OAK-01.P, LIV 10 low is present
LOCKEFORD-01.P, LOC 10 (S3) low is present
LODI-01.P, LOD 30 intermediate reproduces every 15 days
PETERS-01.P, PET 50 intermediate reproduces every 15 days

*   Bud break based on farm advisor countywide vineyard surveys:

  • Fresno: March 17 in Thompson Seedless
  • Madera: March 16 in Thompson Seedless
  • San Joaquin: March 17 in Chardonnay

S1 = missing data substituted with values from CARUTHERS-01.P
S2 = missing data substituted with values from FIREBAUGH/ALISO-01.P
S3 = missing data substituted with values from FARMINGTON-01.P

Because estimated data are 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.

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Statewide IPM Program, Agriculture and Natural Resources, University of California
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For noncommercial purposes only, any Web site may link directly to this page. FOR ALL OTHER USES or more information, read Legal Notices. Unfortunately, we cannot provide individual solutions to specific pest problems. See our Home page, or in the U.S., contact your local Cooperative Extension office for assistance. web template revised: February 12, 2012 Contact webmaster.