Candidates for substitution: pesticides active substances

An active substance is a ‘candidate for substitution’ if it has certain properties. These properties usually indicate a substance is more hazardous, so a candidate for substitution can only be approved for a maximum of 7 years before it needs to renewed.

HSE identifies candidates for substitution as part of the active substance approval process.

Candidates for substitution are identified in the GB approvals register.

You can still use a candidate for substitution in a plant protection product (PPP), but you might be asked to provide a comparative assessment.

Comparative assessment

Comparative assessment is how HSE compares the risks and benefits of a PPP containing an active substance that is a candidate for substitution. The assessment compares your product against other control or prevention methods for the same use.

Several factors decide if a comparative assessment is needed including:

  • that the PPP contains a candidate for substitution
  • the PPP is for use on a major crop
  • the PPP presents a new risk
  • whether there is an alternative option available
  • that substitution does not cause adverse consequences on crop protection - this includes authorised minor uses
  • that the PPP is only available for professional use
  • there are enough modes of action available to stop resistance build up

Where you need to get experience of using a product in practice, you can ask for an authorisation without a comparative assessment. This type of authorisation is only available once and lasts for a maximum of 5 years.

If the comparative assessment shows there are suitable alternatives available, it may result in substitution.


Substitution of a PPP can only happen when it contains a candidate for substitution.

After a comparative assessment, HSE may refuse, restrict or withdraw your application in favour of another control or prevention method.

HSE may refuse your application if:

  • the alternative control or prevention method shows significantly lower risk
  • substitution does not cause adverse consequences on crop protection

Northern Ireland

Active substances that are candidates for substitution in Northern Ireland (NI) may differ to those in Great Britain due to the Protocol on Ireland/Northern Ireland in the EU withdrawal.

You can find the NI list of candidates for substitution in the EU active substances database (Europa website).


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Updated 2023-10-03