Organic Botrytis Control for Vineyards

By VitiScribe Editorial·March 3, 2025·Updated May 26, 2025

Bacillus subtilis products are the most consistent organic botrytis tools at harvest -- that's the honest assessment from research and from experienced organic growers who've worked through multiple seasons testing alternatives. Botrytis management in certified organic vineyards is genuinely difficult, and pretending otherwise doesn't help you design a program that works.

TL;DR

Bacillus subtilis (Serenade Optimum, Serenade ASO) is the best-studied biological botrytis control, with a 0-day PHI that makes it applicable right up to harvest -- but it provides 50-70% efficacy in moderate-pressure years, not the 85-95% of high-efficacy synthetics
Cultural management -- fruit zone leaf removal timed to berry set -- is more powerful than any single organic botrytis application and is the essential first layer of every organic program
Cumulative copper inputs are tracked by most organic certification programs and should be monitored across the season before making late-season botrytis applications that could push annual rate limits
Kaolin clay can provide measurable botrytis suppression and has a 0-day PHI, but late-season deposits may require communication with your winery buyer about residue expectations
CCOF auditors require documented application rationale for every botrytis input -- scouting records showing the disease pressure that triggered the application are mandatory
In severe late-season rain events near harvest, adjusting pick date is sometimes a better decision than trying to manage an established botrytis outbreak with organic tools alone

Organic botrytis programs require careful timing. You can't rely on the same high-efficacy synthetics that conventional growers use in late-season botrytis crises, which means your organic program needs to be more preventive and more culturally intensive than a conventional one. VitiScribe tracks OMRI-listed inputs for CCOF certification, so your organic records stay clean without extra administrative work.

The Core Challenge with Organic Botrytis

Botrytis cinerea sporulates heavily in wet, cool conditions and infects through wounds, petal debris trapped in cluster tissue, and directly through thin grape skin at high inoculum levels. The synthetic fungicides that work best for botrytis -- fenhexamid (Elevate), cyprodinil plus fludioxonil (Switch), and boscalid plus pyraclostrobin (Pristine) -- aren't available to organic growers. The tools you do have are less systemic, have shorter residual activity, and rely more heavily on timing to work.

That's not a reason to avoid organic production. It's a reason to build your organic botrytis program around cultural management first and applied inputs second.

Cultural Management as Your First Layer

Canopy management is the most powerful botrytis tool available to organic growers, and it doesn't require an OMRI listing. A well-opened bunch zone -- adequate leaf removal, fruit exposure, airflow through the cluster zone -- reduces humidity at the cluster surface, speeds drying after rain and dew, and physically removes some of the debris that acts as a botrytis infection site.

Research at Cornell, UC Davis, and Oregon State consistently shows that bunch zone leaf removal timed to berry set reduces botrytis incidence more than any single fungicide application in high-pressure years. This is true for both conventional and organic programs, but it's especially important for organic growers who have fewer high-efficacy rescue materials.

Shoot positioning, hedging, and maintaining appropriate vine spacing all contribute to the airflow that makes botrytis less severe. These cultural records matter for your CCOF audit too -- documenting your canopy management program as an IPM strategy demonstrates that your organic program is genuinely IPM-based and not just input substitution.

Bacillus subtilis Products

Bacillus subtilis strain QST 713 (Serenade Optimum, Serenade ASO) is the best-studied biological botrytis control for vineyards. The bacterium produces iturin and fengycin lipopeptides that disrupt fungal cell membranes, providing both direct antagonism against Botrytis cinerea and some evidence of induced systemic resistance in host plant tissue.

Serenade Optimum is OMRI-listed and has a 0-day PHI on grapes, which makes it useful right up to harvest -- something that's critical during wet autumns when botrytis pressure continues until pick day.

For efficacy, B. subtilis works best when applied preventively on a 7-10 day interval starting at early bunch closure. Applications made to already-infected clusters are less effective -- this is not a rescue chemistry. The pathogen needs to be present at low levels for the biological antagonist to be competitive. In high-pressure years with visible bunch rot, Serenade can slow progression but won't stop an established infection.

Best practices for B. subtilis applications:

Apply in the morning when temperatures are moderate and foliage is dry
Avoid applying directly after a rain event when inoculum load is highest -- wait 12-24 hours
Maintain coverage intervals of 7-10 days through harvest
Tank mixing with copper or kaolin for some additional contact suppression is acceptable from an organic standpoint (check your certifier's requirements)

Copper-Based Materials

Copper is registered for botrytis suppression, though it's most commonly thought of as a downy mildew tool. At the right rate and timing, copper hydroxide, copper sulfate, and cupric octanoate products provide some contact suppression of botrytis sporulation.

The challenge with copper in late-season botrytis programs is the cumulative rate concern. Most organic certification programs now track cumulative copper inputs, and applying high copper rates at harvest to address botrytis can push you toward annual rate limits that may compromise your fall dormant copper application for downy mildew in the following season. VitiScribe tracks cumulative copper applications automatically, so you can see your season total across all blocks before making late-season decisions.

Copper also has a 0-day PHI for most formulations in grapes, but late-season copper deposits on berry skin can cause phytotoxicity and quality issues in some circumstances. Talk to your PCA or extension agent about appropriate rates and timing for your varieties and region.

Kaolin Clay

Surround WP (kaolin clay) is most commonly used as an insecticide barrier for glassy-winged sharpshooter and mealybug, but some research supports its use for botrytis suppression through physical barrier mechanisms. The white clay coating creates an inhospitable surface for spore germination and may reduce moisture retention in the bunch zone.

Kaolin is OMRI-listed and has a 0-day PHI. At high application rates (typically 25-50 lbs/acre), it can provide measurable botrytis suppression in moderate-pressure years, though it's generally not as effective as Bacillus subtilis in high-pressure conditions.

The practical concern with kaolin is residue visibility on fruit at harvest. Wineries purchasing organic grapes often have protocols for kaolin residue, and you should communicate your kaolin program timing to your winery buyer before applying late in the season.

Timing Your Organic Botrytis Program

An effective organic botrytis spray calendar:

Bloom through bunch closure: Focus on cultural management -- leaf removal at berry set, shoot positioning, hedging if needed. If you apply fungicides at this stage for botrytis, Serenade or copper at moderate rates can provide some early protection, but the bigger priority is opening the canopy.

Bunch closure through veraison: Begin regular Bacillus subtilis applications on a 10-day interval. This is when petal debris trapped in cluster tissue starts to decay and create botrytis infection sites. B. subtilis applied at this stage competes with botrytis for those infection sites before the pathogen can establish.

Veraison through harvest: Tighten intervals to 7 days. After rain events, apply B. subtilis within 24-48 hours before the next dry period. Monitor clusters closely for early symptoms -- gray spore masses on berry skin, berry shriveling, brown lesions at the pedicel. If you're seeing more than 5% cluster incidence, you're already in a high-pressure situation where cultural and biological tools need to be supplemented with tighter intervals and maximum coverage.

Rain events near harvest: This is the hardest situation for organic botrytis management. If you get 2+ inches of rain within 2 weeks of your target harvest date, consider adjusting your pick date rather than trying to spray your way through a late-season infection. Sometimes the best botrytis management decision is harvesting earlier with some green fruit rather than losing 20-30% of your crop to bunch rot.

Recording Organic Inputs for CCOF Certification

CCOF auditors examine your spray records for three things: that every input is OMRI-listed or has documented certifier approval, that you documented why you applied each input (pest pressure observation, not just calendar), and that your records are complete with no gaps.

Your VitiScribe spray records for organic inputs should include:

Product name and OMRI listing status
Application date and weather conditions
Rate applied and total product used
The IPM observation or threshold that triggered the application
Block and acreage treated

VitiScribe's organic input tracking flags OMRI-listed products in your product library and records their certification status automatically. See how VitiScribe handles organic certification records in detail.

When your CCOF auditor asks for your botrytis management records, you can export a full spray history filtered to botrytis-targeted applications across all organic blocks, complete with OMRI status notation for each product.

Frequently Asked Questions

What organic materials are approved for botrytis control in certified organic vineyards?

OMRI-listed materials with efficacy against botrytis include Bacillus subtilis (Serenade Optimum, Serenade ASO), Bacillus amyloliquefaciens (Double Nickel, Stargus), Trichoderma-based products (RootShield, Trichodex -- check current OMRI status), copper-based fungicides (copper hydroxide, copper sulfate, cupric octanoate), potassium bicarbonate (Kaligreen, MilStop, Armicarb), and kaolin clay (Surround). Always verify current OMRI listing status before purchase -- products can lose OMRI status. For CCOF certification, your certifier may also approve materials not on the OMRI list through an individual input review process.

How effective are biological controls for organic botrytis management?

Bacillus subtilis products in university trials typically show 50-70% disease reduction compared to untreated controls in moderate-pressure years. That's meaningful protection but considerably lower than the 85-95% control offered by high-efficacy synthetic fungicides like Switch or Elevate. In high-pressure years -- wet autumns, tight cluster varieties, high inoculum -- biological controls alone often aren't sufficient without aggressive cultural management and possibly harvest timing adjustments. The most successful organic botrytis programs combine canopy management as the primary tool with biological inputs as a secondary layer, rather than relying on biologicals alone to carry the program.

How do I record organic botrytis inputs in VitiScribe for CCOF certification?

In VitiScribe, organic inputs are flagged by their OMRI listing status in the product library. When you log a spray application, selecting an OMRI-listed product automatically adds the certification notation to the record. Your spray entry should also include the scouting observation or disease risk trigger that justified the application -- a note like "applied following 48-hour high-humidity period with botrytis clusters visible at 3% incidence in block 4" satisfies CCOF's requirement for documented application rationale. At audit time, you can export organic-only spray records with OMRI status notations in CCOF-compatible format for your auditor's review.

How do organic transition vineyards manage botrytis in years 2 and 3 when they can no longer use synthetic fungicides?

The three-year transition period is often the hardest for botrytis management because the cultural program may not yet be optimized and you no longer have synthetic tools for high-pressure situations. The practical approach is to accelerate your cultural program -- prioritizing canopy work over any other field activity -- and to build your Bacillus subtilis program from the first season of transition rather than waiting for certification. Document every canopy management activity and biological input during transition years so you can demonstrate to your certifier that your organic system plan was being followed before the certification was official.

Does potassium bicarbonate have meaningful efficacy against botrytis in vineyards?

Potassium bicarbonate (Kaligreen, Armicarb, MilStop) is most commonly used for powdery mildew management but also shows some efficacy against botrytis in trials. At high rates and good coverage, it can reduce botrytis sporulation through osmotic disruption of fungal cell membranes. Its efficacy against botrytis is generally considered lower than Bacillus subtilis and much lower than copper, but it has a 0-day PHI and is OMRI-listed, making it a usable late-season supplement. Some growers tank-mix it with B. subtilis for a broader-spectrum biological program.