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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 | 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
03/20/2019
Disease pressure Pathogen status
Fresno
(map)
Based on bud break, March 12, in Thompson Seedless,
you may need to adjust for other cultivars that emerge earlier than the indicated date.
CARUTHERS-01.P, CAR 80 (P) high reproduces every 5 days
Del_Rey/Fowler-01.P, DELF 50 intermediate reproduces every 15 days
EASTON-01.P, EAS 50 intermediate reproduces every 15 days
KERMAN-01.P, KER 50 (S1) intermediate reproduces every 15 days
KINGSBURG-01.P, KNG 50 intermediate reproduces every 15 days
Kearney_Ag_Ctr-01.P, KAC 50 (S1) intermediate reproduces every 15 days
SAND_RANCH-01.P, SR1 0 n/a no infection
San Joaquin
(map)
Based on bud break, March 19, in Chardonnay,
you may need to adjust for other cultivars that emerge earlier than the indicated date.
Collegeville-02.P, COL2 0 n/a no infection
Escalon-02.P, ESL 0 (S2) n/a no infection
LOCKEFORD-01.P, LOC 0 n/a no infection
LODI-01.P, LOD 0 (S2) n/a no infection

*   Bud break based on farm advisor countywide vineyard surveys:

  • Fresno: March 12 in Thompson Seedless
  • San Joaquin: March 19 in Chardonnay

P = missing data substituted with values from previous day
S1 = missing data substituted with values from Del_Rey/Fowler-01.P
S2 = missing data substituted with values from LOCKEFORD-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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