California Vineyard Seasonal Spray Calendar

By VitiScribe Editorial·June 17, 2025·Updated September 6, 2025

California spray calendars must account for huge climate variation from Napa to Paso Robles -- the same month looks very different in Sonoma's fog-influenced Russian River Valley versus the Central Valley heat of Fresno County. VitiScribe's weather integration adjusts the seasonal calendar to your specific vineyard location in California, rather than presenting a one-size approach that will underperform in any region that isn't exactly the baseline.

This calendar organizes California's vineyard IPM season month by month. Regional notes throughout reflect the major climate differences that shape pest pressure timing across the state.

TL;DR

Bloom in June is the single most critical spray window of the California season -- 7-day powdery mildew intervals are non-negotiable during flowering, and a skipped bloom-window application in a high-pressure year creates established cluster infections that summer sprays cannot correct
Dormant applications in January-February still require DPR pesticide use records -- monthly non-RUP filings are due by the 10th of the following month (February 10 for January applications)
Regional timing variation is substantial: Coachella Valley and San Joaquin budbreak occurs in early March, while Sierra Foothills budbreak can be late April -- a calendar built for one California region will be 4-6 weeks off for another
QoI (FRAC Group 11) resistance is confirmed in multiple California counties, requiring systematic FRAC rotation with Group 11 used at 2-applications-per-season maximum
PHI planning should begin 30 days before anticipated harvest date -- September harvest pressure should never cause you to miss the 24-hour DPR filing deadline for applications made during harvest
Spider mite miticide PHIs (Agri-Mek at 28 days) can limit late-season use; review PHI against anticipated harvest before any July application of long-PHI materials

January - February: Dormant Season Planning and Applications

Primary activities:

Trunk disease assessment: Scout during pruning for Eutypa dieback, Botryosphaeria, and Esca symptoms. Characteristic wedge-shaped wood discoloration in cross-section, dead arms that fail to break dormancy, external galls (crown gall). Mark affected vines for removal or cordon remediation decisions.

Pruning wound protection: Apply thiophanate-methyl (Topsin-M), myclobutanil (Rally), or biological wound protectants (Trichoderma-based) within 24 hours of pruning cuts. In California's North Coast, the dormant season coincides with primary Eutypa lata spore release periods -- protection is essential, not optional.

Dormant copper: Apply copper-based materials during late dormant period to suppress overwintering powdery mildew flag shoot development and reduce downy mildew oospore loads in coastal regions. Apply at silver tip to early budbreak at 3-5 lbs copper hydroxide equivalent per acre.

Dormant oil: Narrow-range horticultural oil (98%+) applied during dormant season controls European red mite eggs, San Jose scale, and overwintering grape leafhopper eggs. Apply before budbreak at labeled rate. Effective only on dormant, non-green tissue.

DPR compliance note: All dormant applications require pesticide use records. January and February applications are included in your monthly non-RUP filing (due February 10 for January applications). RUP dormant applications (some fumigants) require expedited filing.

March - April: Budbreak and Early Season

Regional timing variation:

Coachella Valley and San Joaquin Valley: early March budbreak
Napa/Sonoma valleys: late March to mid-April
Coastal regions (Monterey, Santa Barbara): mid-April
Sierra Foothills: late April

Primary activities:

Powdery mildew program start: Begin at 1-2 inch shoot growth in high-risk blocks (prior pressure history, dense canopy varieties). In coastal areas with fog influence (Russian River Valley, Petaluma Gap), start at 1-inch shoot growth. Open with sulfur (3-4 lbs/acre) or a DMI fungicide (Rally, Elite) if eradicant activity is needed for early infections. Interval: 10-14 days at this stage.

Phomopsis management (coastal and wet-spring regions): High-pressure regions -- particularly Mendocino Coast, Sonoma Coast, and other wet areas -- should apply captan, mancozeb (RUP), or ziram at budbreak. Apply at first 1-inch shoot growth in blocks with prior Phomopsis history. The 24-48 hour post-rain window is the critical application timing.

Mealybug monitoring: Deploy sticky tape traps on vine trunks at 6-inch height in blocks with prior mealybug history. Begin checking weekly for first-generation crawlers.

Pheromone trap deployment: Set GBM pheromone traps (Central Valley, Sierra Foothills) at tight cluster for biofix monitoring.

Pierce's disease monitoring: Deploy yellow sticky cards at vineyard margins adjacent to riparian corridors for sharpshooter monitoring in areas with Pierce's disease risk (Napa County, Central Valley, Southern California).

DPR compliance note: Expedited RUP filing begins. If applying mancozeb, phosmet, or other RUPs, 24-hour filing applies in most major wine counties.

May: Shoot Elongation and Pre-Bloom

Regional timing variation:

Central Valley and Coachella: bloom occurs in late May
Napa, Sonoma, Mendocino: bloom in early-to-mid June
Coastal (Monterey, Santa Barbara): bloom in mid-to-late June

Primary activities:

Powdery mildew -- critical period: Intervals tighten to 7-10 days as shoot growth accelerates. Begin FRAC group rotation systematically if not already done. First-leaf tissue through flowering clusters are highly susceptible. FRAC Group 3 (DMI), Group 7 (SDHI), Group 13 (Quintec), Group 11 (QoI -- limit to 2/season max given confirmed resistance) in rotation.

For the full FRAC group rotation framework for California conditions, see the powdery mildew resistance management guide.

Downy mildew (coastal regions): Primary infection events in coastal Mendocino, Sonoma, and Monterey. Apply copper protectants and/or systemic materials (Revus, Presidio) before forecast rain events meeting 10-10-24 criteria.

Botrytis preparation: Not a spray priority yet, but monitor canopy development for conditions that will drive late-season pressure. Dense canopy development in May predicts botrytis risk at harvest.

Mealybug: First-generation crawler emergence monitoring. Apply Movento (Group 23) or Admire Pro (Group 4A soil drench) when monitoring shows peak crawler activity.

GBM (Central Valley, Foothills): Set biofix when consistent adult captures begin. Begin DD50 accumulation tracking.

June: Bloom

The most critical spray window for powdery mildew in California vineyards.

Primary activities:

Powdery mildew at bloom: 7-day intervals, without exception. This is non-negotiable for susceptible varieties (Chardonnay, Muscat, Grenache) and important for moderately susceptible ones (Cabernet Sauvignon, Merlot, Pinot Noir). Flower tissue and developing berry tissue are at peak susceptibility. Skip a bloom-window application in a high-pressure year and you'll be managing established cluster infections through harvest.

Apply high-efficacy systemics at bloom: Quintec (Group 13), SDHI products (Group 7), or Luna products. Don't rely solely on sulfur during bloom -- systemic materials with eradicant activity provide better protection during the rapid cell development of bloom.

Insecticide restriction: Avoid systemic insecticide applications during bloom. Neonicotinoids in plant tissue during bloom present bee exposure risk from residues in nectar and pollen. Wait until petal fall.

Botrytis first application (susceptible varieties): Apply first botrytis fungicide at 50% capfall in tight-cluster varieties with prior botrytis history. Elevate (Group 17), Switch (Groups 9+12), or Miravis Prime (Groups 7+12) are appropriate at this stage.

Leafhoppers: First-generation leafhopper nymph monitoring. Count nymphs per leaf at 5-10 representative locations per block. Compare to UC IPM threshold (15-20 nymphs/leaf for first generation).

GBM first generation: Apply at 100-150 DD50 from biofix. Altacor (Group 28), Delegate (Group 5), or Intrepid (Group 15).

Downy mildew: Continue program in coastal regions through bunch closure.

July - August: Berry Development and Veraison

Regional timing variation:

Central Valley: veraison begins late July
Napa/Sonoma: veraison in late July to mid-August
Coastal (Monterey, Santa Barbara): veraison mid-to-late August

Primary activities:

Powdery mildew: Extend to 10-14 day intervals if early-season pressure was well-controlled. Continue FRAC rotation. In years with high early-season inoculum loads or in heat-moderated years with extended infection windows, maintain 10-day intervals through veraison. Don't assume that because conditions look hot and dry that infection risk has passed -- moderate days (75-90°F) on either side of heat spikes are high-risk windows.

Spider mites: Scout leaf undersides for mite populations in July. Check predator-to-pest ratios. If pest mites substantially outnumber predators and the ratio is worsening, apply selective miticide (Agri-Mek, Kanemite, Envidor) rather than broad-spectrum knockdown that would disrupt predator populations. Note that some miticide PHIs (Agri-Mek: 28 days) limit late-season use.

Leafhoppers second generation: Monitor at 4-5 weeks post-bloom for second-generation nymph buildup. Higher damage risk at second generation than first.

GBM second generation: Target at 750-850 DD50 from biofix. Rotate IRAC group from first-generation application.

Botrytis: Maintain program through veraison in susceptible varieties. Bunch zone leaf removal is your most powerful botrytis intervention at this stage -- removing 2-3 leaves on the east side of the canopy in the bunch zone opens cluster environment to airflow and sunlight.

PHI planning begins: 30 days before your target harvest date, review every potential spray application against PHI. Identify which products you can still use and when the window closes for each.

September - Harvest

PHI compliance is the primary compliance concern. Every spray application during this period must be evaluated against harvest timing before application.

Primary activities:

Powdery mildew late-season: Use 0-day PHI materials: sulfur, potassium bicarbonate, Pristine (0-day PHI), Flint Extra (0-day PHI), Vivando (0-day PHI). Continue through veraison in blocks with active canopy disease.

Botrytis at harvest: Oregon-level attention to botrytis is less often needed in California's drier harvest climate, but wet September and October years demand active management. 0-day PHI options: Elevate (0-day PHI), Miravis Prime (0-day PHI), Serenade Optimum (biological, 0-day PHI), Botector (biological, 0-day PHI).

Leafhoppers third generation: Adults are difficult to control. Assess whether treatment is warranted based on honeydew deposit levels on fruit and potential quality impact.

PHI harvest clearance documentation: Export block-level PHI clearance reports from VitiScribe before any harvest decision. Have documentation available for winery buyer audit requests.

DPR filing catches up: September applications -- particularly any RUP applications -- must be filed within 24 hours. Don't let harvest season distract from compliance filing deadlines.

Post-Harvest (October - December)

Primary activities:

Post-harvest fungicide: Some growers apply copper or other materials at leaf fall to reduce overwintering inoculum for powdery mildew and downy mildew. Evidence for benefit varies by region.

Annual record review: Export and archive your season's spray records. Review block-level spray frequency, product costs, FRAC rotation history, and pest pressure trends. Identify blocks that consistently require intensive programs and blocks where the program can be reduced next season.

Certification preparation: If you're pursuing or maintaining SIP Certified, Lodi Rules, or other sustainable certification, this is when you prepare your annual pest management documentation for the upcoming audit.

Frequently Asked Questions

What are the most critical spray windows in a California vineyard season?

The three most critical spray windows in a California vineyard season are: (1) early budbreak through first 6-inch shoot growth, when primary inoculum is being released and new tissue is most susceptible; (2) bloom, when flower and developing cluster tissue are at peak powdery mildew susceptibility and 7-day intervals are non-negotiable; and (3) veraison through harvest, when PHI management becomes critical and late-season botrytis and powdery mildew require continued management with short-PHI materials.

How does my spray calendar change from a cool coastal to warm inland California vineyard?

Cool coastal vineyards (Russian River Valley, Petaluma Gap, Santa Cruz Mountains) face earlier powdery mildew pressure due to marine fog driving nighttime humidity, more frequent downy mildew infection events in wet springs, and more concentrated botrytis risk at harvest in wet autumns. Programs start earlier and maintain tighter intervals through summer. Warm inland vineyards (Napa Valley, Paso Robles, Central Valley) have higher summer heat events that slow pathogen activity but create extended powdery mildew pressure as conditions moderate. Spider mite management is more often necessary in heat-stressed inland conditions. Downy mildew is rarely the major concern it is in coastal regions.

How does VitiScribe automatically adjust spray timing recommendations by my CA region?

VitiScribe connects to local weather station data for your specific vineyard location in California. The spray window alerts are calibrated to your local temperature, humidity, and precipitation data rather than regional averages. Degree day calculations for GBM biofix accumulation use your local station, not a regional model. Disease pressure alerts (downy mildew infection events, humidity-driven powdery mildew risk windows) are triggered by your vineyard's actual conditions, not a generalized California calendar. The result is spray recommendations timed to what's actually happening at your location, not what a textbook says should be happening in your region.

How should a California vineyard manager document a spray calendar deviation -- when the anticipated June bloom window shifts earlier or later by two weeks due to unusual spring temperatures?

The spray record for each application captures the phenological stage at time of application alongside the date. When bloom occurs 2 weeks earlier than the calendar average -- as happens in warm-spring years -- the records should show applications keyed to "50% capfall" or "10-20% bloom" rather than a calendar date, demonstrating that the spray decision was made on actual vine development, not a fixed schedule. For a sustainable winegrowing certification audit (Lodi Rules, SIP Certified), phenological staging notation in the spray record converts calendar-spray records into IPM-decision records. VitiScribe's bloom-stage notation at application entry captures the phenological reference alongside date, so multi-year records show whether programs are consistently phenology-based or calendar-based.

How should a North Coast California vineyard manager document the PHI clearance decision for a late-season botrytis application when harvest date is uncertain within a 5-7 day window?

When harvest date is uncertain, PHI clearance should be calculated against the earliest date in the anticipated pick window. If harvest could occur any day between September 15-22, a botryticide with a 7-day PHI must be applied no later than September 8 to clear the earliest possible pick date. The spray record should note the anticipated harvest window used for PHI calculation ("PHI calculated against earliest anticipated harvest September 15"). If harvest actually occurs September 20, the PHI clearance is even more comfortable, but the documentation should reflect the conservative calculation made at time of application. VitiScribe's PHI alert system calculates clearance against a block's entered anticipated harvest date and sends warnings when any pending application would fall within the PHI window.