Plant Protection: 3-Dimentional Crops and Leaf Wall Area (LWA)

The terms “3-Dimensional crops”, “high growing crops” or “vertical crops” are used for crops such as grapes, pome fruit or tomato for which aerial spraying (upward or sideward directed spray application) has to be used.

Due to the height and the special growing conditions of these crops, the area to be treated with a plant protection product per hectare can be much higher (or for special situations even lower, e.g. bunch zone application) and much more variable compared to low growing crops such as cereals or potato. Considering the variable total plant height, the treated canopy height, the number of rows and the row spacing, the resulting huge variability of plant area treated per hectare can impact product performance in many ways. Site-specific growing conditions which lead to comparatively low plant surfaces to be treated per hectare increase the risk of phytotoxic effects or overdosing of the plant protection product and thus unnecessary risks for humans, animals or the environment. For fields with a high plant surface area per hectare, control values may be reduced or the risk of the development of resistance may increase. Therefore, for a more precise dosing of plant protection products, the relation of the dosage not to the ground area (hectare) but to the actually treated crop or leaf wall area per hectare is used.

Starting January 1st, 2020 application dossiers for new products intended to be used for the vertical crops grapevine, pome fruits and high growing vegetables in the EU Central Zone are only accepted when the efficacy trials are conducted based on the so-called Leaf Wall Area (LWA) concept. Consequently, efficacy trials for these crops carried out after 1 January 2018 are only accepted if they have been conducted on basis of the LWA dose expression. Furthermore, the dose rate per hectare of LWA has to be included in the GAP table, restricted by the maximum rate per hectare ground surface and the range of possible concentrations.

Often, parameters to calculate LWA are included also in old study reports, allowing for re-calculation and the use of such trials for authorisation even under the new requirements.

The requirement for the use of the LWA dose expression is currently only mandatory in the Central Zone. In the Southern Zone using a concentration for dose expression is quite common, which is why a transition to the LWA concept is not yet agreed.

Furthermore, the LWA concept is restricted to pome fruit only. This is due to the fact that the training systems for pome fruit are straight and close-banded, resulting in a more-or-less closed leaf wall. Stone fruit, citrus or olive trees on the other hand are trained as globular trees, for which the leaf-wall area concept does not fit. Efforts are made for a more sophisticated concept for globular trees, but until then the “per hectare” application rate applies.

Opinions from national authorities suggest that the data needed for calculation of LWA should also be recorded for residue trials, as the concept of LWA might also apply in future for residue calculations, and therefore the possibility for conversion of dose expression used in the residue trials should be granted.