Powdery Mildew Control in
Southern California Wine Grapes
A practical IPM / Sustainable Pest Management workshop for small wine growers
Balanced comparison: conventional chemistry + biological/regenerative approaches
Educational only. Always follow labels, REIs/PHIs, organic certifier rules, county restrictions, and PCA guidance.
Temecula / Southern California vineyard context
What growers should leave with
Twenty-minute workshop objectives
Small Wine Growers Association | Temecula / Southern California
Educational only. Follow labels, local regulations, and PCA guidance.
2
Identify pressure
Use scouting, weather, cultivar susceptibility, and canopy microclimate - not calendar-only spraying.
Understand tools
Know the main chemical, mineral, soft-chemistry, and biological categories used against powdery mildew.
Rotate intelligently
Use FRAC groups to reduce resistance risk and protect limited single-site chemistries.
Build a program
Compare a balanced chemical-biological rotation with a biological-forward program and its constraints.
Frame: IPM and SPM are decision systems; products are only one part of the system.
Why powdery mildew is the disease we build around
In Southern California, powdery mildew control usually drives the fungicide program.
Small Wine Growers Association | Temecula / Southern California
UC IPM grape powdery mildew
3
Quality risk
Infected clusters can reduce marketability and wine quality; late-season visible control is often too late.
Timing risk
Control is largely preventative. Missing early infection windows can force more aggressive rescue decisions.
Resistance risk
Calendar repetition of single-site fungicides selects for reduced sensitivity in the pathogen population.
Coverage risk
Biologicals, contact products, and sulfur all require thorough coverage of leaves and clusters.
UC IPM describes early infection, repeated conidial cycles, and the importance of season-long preventative control.
Visual target: white powdery growth on leaves and clusters means you are already behind the pathogen.
Temecula / Southern California disease context
Dry climates still produce powdery mildew problems because canopy microclimate matters.
Small Wine Growers Association | Temecula / Southern California
Regional interpretation from UC IPM biology
4
LOCAL PRESSURE PATTERN
Warm days and cool nights can create favorable canopy windows.
Spring moisture, dew, fog, irrigation wetting, and shaded canopies increase early risk.
High heat can slow the pathogen, but it does not replace scouting or coverage.
Small blocks vary: cultivar, vigor, shade, slope, and irrigation patterns can change risk within a vineyard.
Practical implication
Treat the vineyard as zones, not as a single average.
UC IPM: ideal growth generally occurs at 70-85°F; temperatures above 95°F slow growth, but monitoring remains required.
From IPM to Sustainable Pest Management
SPM is the policy and systems-level evolution of IPM.
Small Wine Growers Association | Temecula / Southern California
CalEPA / DPR / CDFA SPM Roadmap
5
Least-risk, effective intervention
Product choice + FRAC rotation
Monitoring, thresholds, risk index
Prevention: canopy, sanitation, plant health
IPM core logic
Prevent -> monitor -> decide -> intervene with the least disruptive effective tool.
SPM adds three accountability pillars
Human health + social equity
Worker, neighbor, and community risk are part of the pest-management decision.
Environmental protection
Reduce unintended impacts while maintaining effective crop protection.
Economic vitality
Adoption must pencil out for growers and maintain crop value.
CalEPA states SPM builds on IPM by incorporating human health/social equity, environmental protection, and economic vitality.
Integrated management starts before the spray tank
Every intervention should target one side of the disease triangle.
Small Wine Growers Association | Temecula / Southern California
Educational only. Follow labels, local regulations, and PCA guidance.
6
HOST
PATHOGEN
ENVIRONMENT
Disease occurs when all three sides align
Host levers
Choose less susceptible varieties when possible; reduce excess vigor; protect young, susceptible tissue.
Pathogen levers
Reduce early inoculum; scout basal leaves; avoid letting colonies become spore factories.
Environment levers
Open canopies; improve air flow; manage irrigation and shade; improve spray penetration.
Product levers
Use labels, coverage, timing, and FRAC rotation to avoid product failure.
Key point: biological programs fail fastest when used as product substitutions without canopy and monitoring discipline.
Gubler-Thomas Powdery Mildew Index: the concept
A temperature-driven risk index to adjust spray timing.
Small Wine Growers Association | Temecula / Southern California
UC IPM Risk Index / Gubler-Thomas PMI
7
0
30
50
100
LOW
MODERATE
HIGH
0 = low disease potential 100 = high disease pressure
Temperature window
Ideal powdery mildew growth is generally associated with canopy temperatures around 70-85°F.
Index trigger
The epidemic phase begins after 3 consecutive days with 6+ continuous hours between 70-85°F.
Adjustment logic
Risk rises when favorable hours persist and falls when conditions are unfavorable or heat suppresses growth.
Use limitation
The index guides spray intervals; it does not replace scouting, coverage checks, or block-specific judgment.
UC IPM: after initial infection, the index uses canopy temperature to predict disease development and guide spray intervals.
How the index changes spray intervals
Use low/moderate/high pressure to adjust product choice and interval.
Small Wine Growers Association | Temecula / Southern California
UC IPM suggested spray intervals
8
Index
Pressure
Pathogen status
Biologicals/SARs
Sulfur
DMI / QoI / quinoline
0-30
Low
present
7-14 days
14-21 days
21 days or label
40-50
Moderate
reproduces ~15 days
7 days
10-17 days
21 days
60+
High
reproduces ~5 days
not recommended alone
7 days
10-14 / 14 days
Main workshop point
Biologicals are most useful before disease is established and while pressure is low to moderate.
High pressure reality
At 60+, switch from philosophy to control: protect the crop and avoid building inoculum.
UC IPM lists low, moderate, and high risk intervals; biologicals are not recommended as stand-alone tools under high pressure.
What is commonly used in California wine grapes?
Sulfur dominates wine-grape pesticide-use records by a wide margin.
Small Wine Growers Association | Temecula / Southern California
DPR 2023 Pesticide Use Report
9
Sulfur is the backbone
It is inexpensive, multi-site, widely available, and common in organic and conventional programs.
Oil is common but needs caution
Useful as protectant/eradicant contact material, but incompatible with sulfur timing.
Copper is common, but not the PM backbone
Copper is more relevant to downy mildew/Phomopsis-style risk; not primary PM control in SoCal.
Biologicals are underrepresented in top-use lists
They are used, but usually as part of softer programs or low-pressure rotations.
*Quinone outside Inhibitor, Succinate Dehydrogenase Inhibitor, interfere with fungal respiration
Powdery mildew material map
Classify by biology, chemistry, and resistance risk - not just by product name.
Small Wine Growers Association | Temecula / Southern California
UC IPM / FRAC principles
10
Mineral / contact
Sulfur
JMS Stylet Oil
Potassium bicarbonate
Fungicidal soaps
Generally lower resistance risk; coverage and compatibility drive success.
Synthetic single-site
DMI: Rally, Mettle
QoI: Flint, Sovran
SDHI/premix: Pristine, Luna
Quintec, Torino, Vivando
Powerful tools; rotate FRAC groups aggressively.
True biologicals
Serenade / Sonata
Double Nickel
Taegro
Other microbial biofungicides
Best as protectants under low/moderate pressure with excellent coverage.
Natural products / elicitors
Pinion
Regalia
Timorex / botanical oils
ProBlad-type products
Other soft chemistry
Can support biological-forward programs; not all are living biologicals.
Classification used here: living microbial products = biological; minerals, oils, salts, botanicals, and synthetics = chemical/non-living.
Two failure points: sulfur-oil conflict and resistance
Small growers can avoid a large share of problems with two simple rules.
Small Wine Growers Association | Temecula / Southern California
UC IPM label/compatibility guidance
11
!
Rule 1 - Keep sulfur and oil apart
Do not mix oil and sulfur. UC IPM cautions against applying one within 2 weeks of the other; labels may impose additional constraints.
Rule 2 - Rotate FRAC groups
Do not make repeated applications of the same single-site mode of action. Rotate by FRAC code, not by brand name.
Rule 3 - Coverage beats cleverness
Poor coverage makes every product look weak. Biologicals and contacts fail especially fast when coverage is poor.
FRAC
rotation
UC IPM: oil and sulfur timing restrictions; fungicides with different FRAC numbers are suitable to alternate in resistance management.
Conventional chemical approach: strengths and limits
Reliable disease control when pressure is high - but requires disciplined rotation.
Small Wine Growers Association | Temecula / Southern California
UC IPM conventional fungicide principles
12
Strengths
• Strong efficacy under moderate/high pressure
• Longer intervals than biological-only programs
• More options during critical periods
• Easier rescue when infection is detected early
Limits / risks
• Resistance if FRAC groups are repeated
• Worker, environmental, residue, and certification constraints
• Can mask weak scouting or poor canopy management
• Product costs can rise quickly
Examples
DMI: Rally / Mettle
QoI: Flint / Sovran
SDHI/premix: Pristine / Luna
Quinoline: Quintec
U6: Torino
FRAC 50: Vivando
Best use case
Use synthetic chemistry as a precision tool for pressure, timing, resistance management, and crop protection - not as an automatic calendar reflex.
UC IPM emphasizes multi-site starts, FRAC rotation, label rates, and limiting total seasonal applications to manage resistance.
Chemistry depends on coverage.
Biological / regenerative approach: benefits and challenges
Best viewed as an integrated system, not a one-for-one product swap.
Small Wine Growers Association | Temecula / Southern California
UC IPM biological guidance
13
Potential benefits
• Lower residue and softer ecological profile
• Better fit with organic/regenerative positioning
• Lower resistance pressure when using multi-mechanism tools
• Can support beneficial microbiology and grower storytelling
• Useful as a preventative base in low/moderate pressure
Practical challenges
• Requires earlier starts and tighter intervals
• More dependent on coverage and canopy openness
• Weaker rescue performance once disease is established
• Weather/risk index must be watched closely
• Cost per effective control day can be higher
Operational rule
Biological-forward programs work best when the grower is willing to scout more, spray more precisely, manage canopy early, and switch tactics when pressure crosses a clear threshold.
UC IPM comments: Bacillus products should begin before disease onset or when pressure is low and be repeated at 7-10 day intervals until pressure increases.
Biological programs lean on the whole system.
Balanced comparison for small growers
Select the program style that matches your risk tolerance, equipment, and scouting discipline.
Small Wine Growers Association | Temecula / Southern California
Educational only. Follow labels, local regulations, and PCA guidance.
14
Question
Chemical-forward
Integrated chemical + biological
Biological-forward
Best fit
High-value crop; history of PM; limited spray windows
Most small growers: control + reduced load
Low pressure; excellent coverage; high monitoring
Main benefit
Reliability under pressure
Balance: control, resistance, sustainability
Residue reduction and regenerative story
Main weakness
Resistance and higher pesticide reliance
Needs planning and records
Failure risk if pressure rises
Trigger to adjust
Repeated FRAC use or residue concerns
Index rises / colonies detected
PMI 60+, visible colonies, poor coverage
Program examples are educational templates. Local labels, cultivar susceptibility, disease pressure, and PCA advice should control final decisions.
Why canopy management matters
Canopy architecture influences disease pressure, spray coverage, fruit quality, and scouting speed.
Airflow & drying — Open canopies reduce humidity and help leaves and clusters dry faster.
Scouting — Better visibility helps find powdery mildew early.
Coverage — Good canopy structure improves spray penetration and deposition.
Fruit quality — Balanced light exposure supports ripening and reduces disease risk.
Field rule: canopy management is a disease-management tool, not just a viticulture detail. It becomes even more important in biological/regenerative programs.
Examples include shoot positioning, leaf removal, lateral control, and hedging when needed.
Small Wine Growers Association | Temecula / Southern California
Educational only. Follow labels, local regulations, and PCA guidance.
18
Example rotation A: balanced chemical + biological
Purpose: protect the crop while reducing unnecessary single-site fungicide pressure.
Small Wine Growers Association | Temecula / Southern California
Educational template - verify labels
15
Balanced program by growth stage
1
2-6" shoots
Sulfur OR oil start
+ scout basal leaves
2
Pre-bloom
Biological or sulfur
if index low/moderate
3
Bloom
FRAC 3 or U6
when pressure rises
4
Fruit set
FRAC 7/11 or 50
rotate mode of action
5
Bunch close
Sulfur/contact or bio
if pressure allows
6
Veraison+
Bicarbonate / bio / sulfur
subject to label + heat
Built-in discipline
No back-to-back single-site FRAC groups unless label and PCA reasoning support it.
Biological role
Use biologicals as preventative gap-fillers and resistance-management partners, not as late rescue tools.
Do not use this as a label. It is a planning example; local pressure, cultivar, REI/PHI, and product labels control.
Example rotation B: biological-forward / soft program
Purpose: reduce synthetic chemistry, but accept higher monitoring and failure-trigger discipline.
Small Wine Growers Association | Temecula / Southern California
Educational template - verify labels
16
Biological-forward program by growth stage
1
2-6" shoots
Microbial biofungicide
+ canopy scouting
2
Rapid growth
Sulfur or oil?*
choose one path
3
Pre-bloom
Bacillus rotation
+ botanical/elicitor
4
Bloom
Bio + bicarbonate/contact
short interval
5
Fruit set
Bio rotation
coverage audit
6
Trigger point
If PMI 60+ or colonies:
switch to stronger tool
Define “biological-forward” carefully
This example includes true microbial biologicals plus organic-compatible soft chemistry. Strict microbe-only is usually too risky in commercial wine grapes.
Non-negotiable trigger
Do not keep repeating weak tools after colonies appear or pressure turns high. Protect the crop.
*Sulfur, oils, bicarbonates, soaps, and botanicals are not living biologicals even when organic-compatible.
A simple decision framework for each spray window
Use the same logic every week rather than defaulting to a calendar.
Small Wine Growers Association | Temecula / Southern California
Educational only. Follow labels, local regulations, and PCA guidance.
17
1. Scout
Basal leaves, clusters, shady zones, known hotspots
2. Check risk
Gubler index, forecast, canopy temperature, moisture events
3. Assess coverage
Can your sprayer reach leaves and clusters? Is canopy too dense?
4. Select tool
Pressure + FRAC history + certification + label restrictions
5. Record result
Date, material, FRAC, interval, weather, observed control
Field rule for biological/regenerative programs
The more you reduce conventional rescue chemistry, the more you must increase prevention, scouting, canopy management, coverage quality, and speed of response.
Grower action: keep a one-page PM log with stage, index, product, FRAC group, interval, observations, and next decision date.
Key takeaways and core sources
Use biology, weather, and records to make better decisions.
Small Wine Growers Association | Temecula / Southern California
Educational only. Follow labels, local regulations, and PCA guidance.
19
Five grower takeaways
1. Sulfur is the dominant backbone, but not the whole program.
2. The Gubler Index helps adjust intervals; it does not replace scouting.
3. Biologicals are most useful early and under low/moderate pressure.
4. Sulfur and oil conflicts are a common preventable mistake.
5. SPM asks growers to keep efficacy, health, environment, and economics in the same decision.
Core source list
UC IPM: Grape Powdery Mildew Pest Management Guideline
https://ipm.ucanr.edu/agriculture/grape/powdery-mildew/#gsc.tab=0
UC IPM: Fungicide Efficacy and Treatment Timing for Grapes
https://ipm.ucanr.edu/agriculture/grape/2017-fungicide-efficacy-and-treatment-timing/#gsc.tab=0
Closing thought
Biological approaches canreduce dependence on conventional chemistry, but only when supported by better timing, better coverage, and better records.
Full URLs are included in the speaker notes / source notes for this deck.
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