From Ground Area to Leaf Wall: The Evolution of Pesticide Dosing in 3D Crops

by Stefano Ravagli | Mar 30, 2026 | Regulatory Update, Science & Assessment | 0 comments

Introduction

The management of 3D crops, such as deciduous fruits, grapes, and olives, represents a significant portion of European agriculture, with nearly 12 million hectares under cultivation. Unlike flat field crops, these “vertical” structures present a unique challenge for plant protection: how to apply the Minimum Effective Dose (MED) while minimizing environmental impact. For decades, the industry relied on the “per hectare of ground” model, but as regulatory requirements under Regulation (EC) No 1107/2009 become more stringent, a shift towards harmonised dose expression is no longer optional—it is a technical necessity.

The Historical Context: The Ground Area Fallacy

Historically, pesticide doses were expressed in kg/ha of ground area or as a concentration (%). This logic, inherited from herbaceous crops, assumes that the target is a flat surface. However, in orchards and vineyards, the “target” is a three-dimensional volume of foliage that varies dramatically based on growth stage, training system, and row spacing.

Research has consistently shown that applying a constant dose per unit of ground area results in foliar deposits that are inversely proportional to the Leaf Area Index (LAI) of the crop. In simpler terms, as the canopy grows denser, the actual concentration of the product on the leaves decreases, potentially leading to reduced biological efficacy or, conversely, excessive residues and wastage in younger or sparser canopies.

The Evolution of Dosing Models

To address these discrepancies, several models were developed across Europe, reflecting local agricultural traditions:

Tree Row Volume (TRV): This model assumes that the canopy width is a relevant parameter for determining volume rates and optimal doses. While technically thorough, it is often more difficult to implement as it requires measuring height, width, and row distance.
Canopy Height (CH): This model focuses on the vertical dimension but often ignores the density and width of the foliage.
Leaf Wall Area (LWA): Initially proposed as a common model by the chemical industry and later adopted by EPPO (Standard PP 1/239), the LWA model treats the crop as a vertical plane. Studies have shown a strong positive linear correlation (r²=0.953) between dose per unit of LWA and the actual deposit on the target.

The Regulatory Imperative for Harmonisation

The lack of a unified dosing language has long hampered the mutual recognition of plant protection products (PPPs) across EU Member States. Under the current zonal registration system, a single Zonal Rapporteur Member State (zRMS) must evaluate efficacy for an entire zone.

The EPPO Workshop in Vienna (2016) marked a turning point, emphasizing that harmonised dose expression is primarily a tool for regulators to ensure consistent risk and efficacy assessments. This has led to the current EPPO Standard PP 1/239 (3), which provides clear definitions for terms like treated Leaf Wall Area (tLWA) and treated Tree Row Volume (tTRV).

Towards Precision Agriculture: Dose Adjustment

It is crucial to distinguish between dose expression (the unit on the label) and dose adjustment (how the farmer adapts that dose to a specific field). Modern Decision Support Systems (DSS), such as DOSA3D, OPTIDOSE, and PACE, now allow growers to input canopy parameters to calculate the precise amount of product needed.

Furthermore, the integration of LiDAR technology and electronic sensors on “smart” sprayers allows for real-time adjustments. These systems can detect gaps in the canopy or variations in foliage density, reducing drift and ensuring that pesticides are only applied where they are needed.

Case Study: The EU Renewal of Captan – A Paradigm Shift

The recent renewal of the active substance captan provides a landmark example of how these dosing and precision principles are being implemented in law. Under Commission Implementing Regulation (EU) 2024/2186, captan has been renewed for 15 years (until 31 October 2039).

Captan is an essential multi-site fungicide for orchard growers, but its renewal came with stringent new conditions to mitigate “Critical Areas of Concern” identified by EFSA, including high risks to birds, wild mammals, bees, and aquatic life.

Precision Agriculture as a Legal Requirement

For the first time, an approval renewal is tied directly to precision agriculture practices. The regulation mandates that outdoor applications in orchards must only be performed using equipment that enhances precision (e.g., shielded, sensor-controlled, or tunnel sprayers). This equipment must achieve:

An average reduction of at least 61% in applied product per hectare.
A minimum of 20% reduction in loss to the ground.

This requirement effectively shifts the focus from ground-based application to target-specific delivery, aligning with the principles of the LWA model to ensure the product remains within the canopy.

Technical Implementation: Transforming tLWA to Ground Area

To bridge the gap between precision efficacy and ground-based risk assessment, practitioners must use conversion formulae. According to EPPO guidelines, the transformation is calculated as follows:

Dose per ha (ground area)=Dose per tLWA * tLWA per ha/10.000}

Where the tLWA per hectare is determined by: tLWA per ha=2 * Spray Band Height×10,000/Row Spacing

This conversion is essential for generating the GAP (Good Agricultural Practice) tables required for the dRR (Draft Registration Report), ensuring that the realistically relevant high rate per hectare of ground is used for endpoint calculation and risk characterisation

Conclusion: Strategic Recommendations for Stakeholders

Harmonising LWA methodology with ecotoxicological risk assessment triggers is essential for the future of sustainable viticulture and pomology. The reliance on 2D ground-area units for 3D safety evaluations is technically obsolete and creates unnecessary regulatory hurdles for low-risk products.

Industry Mandates for Practitioners

Sprayer Calibration: Full adoption of sprayer inspection and calibration is a prerequisite for LWA dosing to ensure intended foliar deposits.
LWA Adoption: Standardise LWA for all espalier-trained crops to minimise deposit variability and chemical waste.
Dose-Response Priority: Prioritise dose-response data over simple limit tests to allow for more accurate Hazard Quotient assessments and refined risk evaluations.