GovWire

Purpose

This guidance applies to suppliers of large oak trees of any species (girth at 1.2m above the root collar of >8cm) that are based in the oak processionary moth (OPM) buffer zone in England and want to move these trees within this buffer zone. No large oak trees may be moved within 10km of the edge of the buffer zone.

It provides details on the application of phytosanitary treatments required to move large oak trees under The Plant Health (Oak Processionary Moth) (England) Regulations 2023. This applies to the application of Plant Protection Products to large oak trees at sites of ornamental plant production. The treatments are being recommended as a means of reducing the risk of trees infested with OPM being moved to non-infested areas.

This guidance is for the preventative treatment of trees, trees which are known to be infested must not be chemically sprayed in order to be moved. Local Plant Health inspectors should be notified of any large oak trees known to be infested.

Application of Plant Protection Products

Registration is required for professional users of Plant Protection Products (PPPs) under the Official Control (Plant Protection Products) Regulations: Register as a PPP user.

All chemical treatments should be applied in line with the Code of Practice for using Plant Protection Products, product labels, and relevant Extensions of Authorisation for Minor Use.

All products must be approved for the intended use and situation. Records of all plant protection treatments must be kept.

There are 2 options for phytosanitary treatments, products containing either Bacillus thuringiensis var kurstaki (preferred) or products containing deltamethrin. Professional pesticide products can only be applied by people holding the relevant City & Guilds pesticide application certificates.

Products containing Bacillius thuringiensis var kurstaki are the preferred method of treatment due to reduced risk of non-target impacts.

Application of products containing Bacillus thuringiensis var kurstaki

Examples: Dipel DF

Effective growth stage: young caterpillars, indicative L1 to L3 instar.See guidance on instars and growth stages of OPM in the Forest Research OPM Manual.

Application:

• a good level of coverage must be achieved, including the very top of the tree canopy
• first treatment must be applied as soon as possible following leaf unfurling, at this stage the leaves will appear like the picture of the first leaf stage at the top of Natures calendar
• 2 applications are required with a 7 to 10 day gap between first and second application

Application of products containing deltamethrin

Examples: Decis forte

Effective growth stage: young to older caterpillars (L1 to L6) and ideal for later instar growth phases.

Application:

• a good level of coverage must be achieved, including the very top of the tree canopy
• treatment must be applied as soon as possible following leaf unfurling, at this stage the leaves will appear like the picture of the first leaf stage at the top of Natures calendar
• no follow up spray required

Indicative timeline of growth stages and application

March to mid-April

OPM egg hatch.

Mid-March to end of April

Larval instars L1 to L2.

Mid-March to mid-May

Bacillus thuringiensis var. kurstaki window of effectiveness.

Mid-March to end of May

Deltamethrin window of effectiveness.

April

Quercus budburst.

Mid-April to end of June

Larval instars L4 to L6.

July

OPM first flight.

July and August

Pupae stage and adult moths.

Further information

Read more about managing oak processionary moth in England.