Downy mildew control in vineyards: what to do and when to act?

Managing downy mildew in grapevines remains one of the most critical agronomic levers in viticulture. Under high disease pressure, this oomycete pathogen can rapidly reduce yields and significantly compromise fruit quality when the protection strategy is not properly adjusted.

With increasingly unstable weather patterns across Europe, the central question for growers is clear: how to intervene effectively, at the right moment, while complying with regulatory constraints?

For professionals, downy mildew management is no longer limited to curative action. It forms part of a holistic, vineyard-wide strategy combining anticipation, product selection and adaptation to field conditions. Between conventional fungicide programmes and innovative solutions such as OPSeed75, growers are progressively moving towards more efficient and sustainable control strategies.

Downy mildew management strategies

Effective control relies above all on sound agronomic reasoning, aligned with regulatory and environmental requirements. A robust strategy draws on several key factors to determine the right timing and type of intervention:

•  Weather conditions: rainfall, humidity and temperature favouring pathogen development,
•  Growth stage of the vine: susceptible young shoots, leaves and clusters,
• Field history: previous years’ downy mildew pressure and inoculum levels.

This approach helps growers:

• Optimise spray timing,
• Secure the efficacy of applications,
• Reduce yield losses and preserve grape quality.

A well‑timed intervention is often far more effective than multiple poorly targeted applications.

Conventional chemical control of downy mildew

Synthetic fungicides and copper-based products

Conventional chemistry and copper formulations remain central tools against downy mildew. Systemic synthetic fungicides, although generally more effective, often come with less favourable toxicological profiles.

Their use requires rigorous management to:

•  Ensure consistent disease control,
• Limit soil accumulation,
• Preserve vineyard ecological balance,
• Reduce the development of fungicide resistance.

When a pathogen is repeatedly exposed to the same active substance, it can gradually adapt, thereby reducing the effectiveness of treatments. Alternating active ingredients and modes of action is essential to prevent and manage the development of resistance.

Towards more natural downy mildew control solutions?

Elicitors, biostimulants, biocontrol, basic substances, etc

These solutions complement synthetic and copper-based products and play an increasingly important role in integrated protection strategies. They rely on natural mechanisms such as:

• Competition or antagonism between micro-organisms,
• Activation of plant defence pathways,
• Modulation of abiotic stress responses.

Given their natural modes of action, these products help protect vineyards while reducing environmental and human health impacts. They integrate well into IPM (Integrated Pest Management) programmes, though their efficacy may remain variable depending on conditions.

OPSeed75 for controlling downy mildew in vineyards

OPSeed75 is a grape seed extract rich in polyphenols, containing more than 75% oligomeric proanthocyanidins (OPCs). Recognised as a basic substance* in the EU since 2025, grape seed extract is also listed by ITAB (French Technical Institute for Organic Agriculture).

OPSeed75 can be integrated into both conventional and organic programmes thanks to:

• Its direct, multi-site fungicidal action on the downy mildew pathogen,
• Its compatibility with other active substances.

This technical profile makes it a valuable tool within integrated strategies to:

•  Increase programme robustness,
• Diversify protection levers and modes of action,
• Limit resistance development,
• Reduce the overall Treatment Frequency Index (TFI).

Sustainable vineyard protection strategies

Downy mildew management today relies on a comprehensive approach that combines agronomic practices with plant protection solutions. It reflects a broader shift in the crop‑protection paradigm, moving away from a purely reactive model — focused on treatments targeting a specific pathogen — towards an integrated, systemic strategy that considers the vine within its wider agro‑ecosystem. The aim is to strengthen the plant’s intrinsic capacities, both against pests and pathogens and against abiotic stresses, in order to enhance its overall resilience to downy mildew.

Key agronomic levers include:

• Managing vine vigour to reduce humidity within the canopy and slow pathogen spread,
• Improving canopy aeration to promote faster drying,
• Managing plant residues to reduce primary inoculum sources.

Regular vineyard monitoring enables growers to:

• Anticipate risk periods,
• Refine spray timing,
• Optimise interventions.

This combined approach reduces reliance on inputs while maintaining a high level of vineyard protection. It aligns with agroecological principles and the « One Health »  paradigm.

Best practices for protecting vineyards from downy mildew

Intervention planning and the use of decision-support tools (DSTs)

Downy mildew management no longer relies on a fixed spray schedule. Instead, it requires dynamic intervention planning, adjusted to real vineyard conditions. Treatment decisions must be based on several key parameters:

• Vine growth stage,
• Weather conditions (rainfall, humidity, temperature),
• Disease pressure observed in the field.

In this context, decision‑support tools (DSTs) are becoming increasingly important. By combining meteorological data with downy mildew forecasting models, these tools help growers anticipate high‑risk periods with greater accuracy.

They support growers in:

• Applying treatments at the most effective timing,
• Avoiding unnecessary or automatic interventions,
• Optimising spray efficacy,
• Reducing yield losses and overall input use.

A strategy based on field observation and DST-guided decision‑making helps secure vineyard protection while aligning with a more sustainable approach.

Optimised dosage and application

To ensure reliable and long‑lasting protection, several principles must be respected:

• Spray quality: ensuring uniform coverage of all susceptible leaf and cluster surfaces so the product reaches vulnerable areas,
• Correct dosage: avoiding under‑dosing (ineffective) and over‑dosing (risk to the environment and to the vine),
• Post‑treatment monitoring: assessing the vineyard after application to detect any residual or new infections.

Applying these best practices helps:

• Guarantee the efficacy of interventions,
• Limit potential yield losses,
• Maintain continuous vineyard protection throughout the season within a sustainable and integrated framework,
• Secure the long‑term sanitary status of the parcels for subsequent years.

Effective downy mildew control relies on a combination of complementary levers. Conventional fungicides, biological vineyard solutions and basic substances such as OPSeed75 all contribute to building robust, field‑adapted and sustainable strategies tailored to real vineyard conditions.

*In accordance with Article 23 of Regulation (EC) No 1107/2009, a basic substance is not primarily intended for plant protection purposes but is nevertheless useful for plant protection; it has no immediate or delayed harmful effects on human or animal health, no unacceptable effects on the environment, and is not marketed as a plant protection product.