Pesticides e-bulletin: Transitional phase for adopting leaf wall area (LWA) in the Central Zone for the conduct of Efficacy trials in grapevine, pome fruit and high growing vegetables

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Transitional phase for adopting leaf wall area (LWA) in the Central Zone for the conduct of Efficacy trials in grapevine, pome fruit and high growing vegetables


This is a reminder that for the Central Zone the units of dose expression for efficacy trials data will be leaf wall area (LWA) for high growing crops (pome fruit, grapevine and high growing vegetables). Specifically, efficacy trials must be carried out on the basis of Leaf Wall Area from 1st January 2018.  Applications for new products (or new uses on relevant crops) to the central zone (under Article 33), from 1st January 2020 must be supported by trials carried out based on LWA as the efficacy unit of dose expression. 



The use of different, individual National dose expressions in high growing (3D) crops has caused great difficulty in supporting uses across multiple Member States.  In order to allow better exchange of data between countries and to avoid unnecessary repetition of trials, a harmonized dose expression for high growing crops (pome fruit, grapes and high growing vegetables) in trials and in zonal efficacy evaluations is essential. 


The EPPO standard PP 1/239 “Dose expression for plant protection products” was amended in 2012 to reflect the need to harmonise and recognised that dose expression ‘per treated leaf wall area (LWA) unit’ is becoming a common dose expression method in high growing crops. This method is suitable for trials work and to enable the harmonized evaluation of the efficacy data for high growing crops.  The revised standard provided common methods for converting between terms, but in the intervening years it has become clear that LWA was not widely understood.


Further, the presentation of trials data in draft Registration Reports, where often trials with a range various dose expressions, has caused significant confusion for applicants and evaluators.  Different approaches have been taken to ‘mixed data sets’, and Member States have responded in different ways to the acceptability of the data.  In response, there was an EPPO Workshop in Vienna in 2016 which explored these issues (

 and concluded that LWA was an appropriate unit of dose expressions for efficacy for pome fruit, grapevine and high growing vegetables.  Further amendment to EPPO PP 1/239(2) is planned to provide further guidance and clarity.


Transition Phase to adopt LWA

In response to the Vienna workshop in 2016 the European Efficacy Evaluators discussed this issue and proposed that the following procedure be adopted and this was agreed by the CZSC (Central Zone Steering Committee).  The following was agreed for the efficacy dose expression for new products (or new relevant uses) for Article 33 applications made in the Central Zone:


  • The leaf wall area (LWA) concept needs to be used in the conduct, presentation and evaluation of efficacy trials for grapevine, pome fruit and high growing vegetables
  • From 1st January 2018 trials on these crops must be planned and carried out based on LWA
  • From 1st January 2020 efficacy dossiers for new products and new uses for these crops (under Article 33) will only be accepted when trials were planned and carried out based on LWA
  • The LWA dose rate shall be included in the GAP table.


It is important to note that the rate per unit of ground area will always still need to be given as this is required for other specialist areas to complete their risk assessments.  This conclusion also does not affect National dose expression terms on product labels.


This was announced on CIRCABC on 12 December 2017 (see ‘2017-11 Bullet points on transition phase for adopting LWA).


What may Good Agricultural Practice (for the efficacy dose expression) in the zonal authorisation look like? 

An example of what the efficacy dose expression may look like is given below for a fungicide for use against powdery mildew on apples for a zonal application.  It should be noted that the national addenda e.g. for the UK should still be expressed in a rate per unit ground area.  This is also required for other specialist areas of the risk assessment. In terms of UK product labels, UK growers are also familiar with the use of a rate per hectare and this will continue at present.  If applicants wish to discuss the dose expression for their product with HSE's Chemicals Regulation Division (CRD) then they can contact us. 


It is important to note that the rate per unit ground area will always need to be specified (as this is needed for the risk assessment by other specialist areas).  So the rate per hectare ground area must always be clearly specified. 

This example is based on the efficacy data being from trials where the trees had a canopy height of 3 m and a row spacing of 3.5 m and where the Leaf Wall Area was 17143 m2 LWA/ha (ground area).  See EPPO PP1/239(2) for further details. 

It should be noted that for the UK doses should still be expressed in terms of a rate per hectare.  However, it will be necessary to clearly explain how the rates have been converted from the LWA dose expression to the rate per hectare.  As currently required, the data need to clearly support the efficacy rates proposed.  Details of conversions are explained in EPPO PP1/239(2) for apple crops.  All new data should clearly have the parameters measured recorded as detailed in EPPO PP1/239(2) so that it is clear how the efficacy data have been collected and how the trials were conducted. 

What crops does this apply to?

As detailed above LWA will be used as the efficacy unit of dose expression for pome fruit (apple and pear), grapes and high growing vegetables.  High growing vegetables are considered to be crops such as tomatoes and cucumbers which are grown on high wires.  In the UK this is likely to be primarily in a protected environment such as glasshouses or poly-tunnels. 

Contact Details

If you have any questions relating to this Regulatory Update, please contact us.



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