Ornamental crops: Environmental fate considerations for pesticide registration in Great Britain and Northern Ireland

When you are applying for pesticide registration in Great Britain and Northern Ireland for products intended for use on ornamental plants, you must make it clear which group(s) of plants are included in your definition of ’ornamentals‘.

Ornamental plants are extremely variable covering a wide range of plant situations and morphologies. FOCUS scenarios for ornamentals in surface water and groundwater models are not available. This makes the evaluation complicated. For this reason HSE proposes the following grouping of crops when evaluating ornamental plants. Each ornamental group has a defined surrogate crop for use in FOCUS modelling as well as defined crop interception values for different growth stages. Ornamental groupings are detailed below.

It may also be possible to ‘risk envelope’ the use on ornamentals to another crop within the same product, see Risk envelope suitability for pesticide registration in Great Britain and Northern Ireland.

If your ornamentals are to be grown in permanent protection with full enclosure refer to Protected uses: Environmental fate pesticide registration in Great Britain and Northern Ireland

If you require further guidance please contact HSE.

Ornamental plant groupings

Ornamental plants have been categorised into four groups to simplify the exposure assessment.

Groupings:

  1. Pot and bedding plants grown in containers < 10 cm
    Pot plants are grown in pots of various sizes (but generally around 1 litre in capacity). Bedding plants can be grown in packs (of various types) and pots, especially towards the end of the season when ‘instant plants’ are offered. Most plant material is less than 30 cm in height. Crop cycles vary from a couple of weeks to 6 months. Production is primarily under protection (glass or polythene) for all crops, with some outside production of bedding plants.  Production can occur on the floor or on benching. Most pesticide applications are undertaken via hand-held devices from powered trollies, though gantry spray applications are becoming more common, especially in recently built structures. Integrated pest management (IPM) is common. The assessment for this group depends on the size of pots used; pot plants in pots with diameter greater than 10 cm are assessed in group 2.
  2. Pot and bedding plants grown in containers > 10 cm (including hardy nursery stock (HNS))
    Production occurs in a wider range of pot sizes (generally focused between 1-3 litres), with production occurring on outdoor beds, under polythene structures and sometimes under glass. There are some exceptions when production occurs on benching/mobile benching. A range of plant heights are common, reflecting the very wide number of plants in production.  Crop cycles are longer than in group 1, around 6 months to a year or longer depending upon pot size/plant species in question. Spray application can be from powered trollies (or knapsacks for smaller areas) or from tractor-mounted equipment for larger bed sizes. 
  3. Field grown HNS and non-bulb cut flowers
    Field grown HNS encompasses young plant production from seed or cuttings in beds on an annual cycle, up to the production of long-term semi-mature trees which are lifted and root-balled for use in landscape projects.  Non-bulb cut flower (and foliage) production from plants, shrubs encompasses intensive production under glass and more extensive production under polythene and outdoors. For outdoor applications tractors and towed equipment are common for cultural and spray application tasks.
  4. Bulb cut flowers
    This group include cut flower production from bulbs, tubers, corms or rhizomes, which can occur on a one to three year plus basis. It is divided between intensive production under glass, and more extensive production under polythene and outdoors.  The key crops are tulips, lilies, stocks (all generally under protection) and daffodils. Most are grown in the soil, but key exceptions include tulips and lilies. Spray application is by hand or tractor depending on how the crop is grown.

Use these crop groupings in your application.

PECsoil: Crop interception and surrogate crops

A value of 0% crop interception is appropriate in the following situations:

Use the following guide for crop interception values and suitable surrogate crops for each of the crop groupings.

Surrogate crop and corresponding crop interception values for the ornamental crop groupings for PECsoil

Ornamental group Surrogate crop Crop interception (%)

Bare soil/emergence

Leaf development

BBCH

0-09

10-19

  • Pot and bedding plants grown in containers < 10 cm(a)

Tomato

0

50

  • Pot and bedding plant grown in containers(b) > 10 cm(a)

Pea

0

35

  • Field grown HNS and non-bulb cut flowers

Potato

0

15

  • Bulb cut flowers

Onion

0

10

(a) Size corresponds to the top diameter of the pot
(b) includes Hardy Nursery Stock

Tiered approach for soil loading calculation

For ornamental applications for use at BBCH 0-9 – Use 0% crop interception.

For ornamental applications for use at BBCH 10+ – use the following tiered approach:

PECsoil for containerised plants on soft surfaces

Treatment of ornamentals plants in round pots standing on soft surfaces will result in a portion of the product reaching the soft surface. As worst case, assume the whole area is exposed via an overall spray. You can refine this by assuming that the grower will arrange the pots as close together as possible, and only the area between the pots is exposed.  The area covered by a circular pot is 78.5 % of the area covered by a square pot of the same width/diameter, so the gaps between circular pots will be equal to 21.5 % of the area covered by the pots. Calculate PECsoil correcting for the application rate multiplied by 0.215. Use the PECsoil calculator given in Environmental Fate Models: Excel Calculators Tools.  Additional information on the deriving PECsoil is given in Soil assessment for pesticide registration in Great Britain and Northern Ireland.

It may also be possible to ‘risk envelope’ this route of exposure to another crop or use a pattern such as: treatment of field grown ornamentals, treatment of other crops or the planting out of treated plants. Further details are available in Risk envelope suitability for pesticide registration in Great Britain and Northern Ireland

PECsoil for containerised plants on hard surfaces

If this exposure is within the risk envelope of other assessments such as: treatment of field grown ornamentals, treatment of other crops or the planting out of treated plants, you can justify not needing to calculate PECsoil for this eventuality. Further details are available in Risk envelope suitability for pesticide registration in Great Britain and Northern Ireland.

If the exposure of soft surfaces around the hard standing is not covered by other exposure calculations, please contact HSE information services with details of your specific application scenario and a proposal for how this can be assessed.

PECsoil for dip applications

Calculate the soil loading for dip applications using the proposed highest planting density. You should justify the planting density you propose.

Example calculation for application via dip:

Use the PECsoil calculator given in Environmental Fate Models: Excel Calculators Tools.  Additional information on the deriving PECsoil is given in  Soil assessment for pesticide registration in Great Britain and Northern Ireland.

Planting out of treated pot grown ornamentals

Provide an exposure assessment assuming ornamentals are planted out immediately after treatment. Refinement is possible for individual uses. 

PECsoil value is based upon the soil density of 1.5 g/cm3.

To calculate the PECsoil value following planting out, the following information is used:

Pot volume Pot depth (cm*) Planting density

Plug plant 125 mL

5

25 plug plants /m2
(plug plant volume of 125 mL (5x5x5 cm)).

1 litre

10

four medium sized plants grown in 1 L pots/m2

4 litre

15

one large plant grown in a 4 L pot/m2

* Conservative value

Calculate the PECsoil value for the volume of soil in one hectare (1 ha = 10 000 m2) based upon the planting depths in relation to the volume of soil per pot and the number of pots over a hectare.

Pot size The volume of soil/ha (m3)
based upon planting depth
Volume of soil in each pot size (m3) The number of pots planted per hectare

Plug plant

5 cm = 500

0.000125

250 000

1 litre

10 cm = 1000

0.001

40 000

4 litre

15 cm = 1500

0.004

10 000

Example calculations for a 1 L pot are detailed below assuming an application rate of 200 g/ha:

If you need to refine the assessment, consider degradation of the active substance before planting out. The application rate (g/ha), DT50 and crop interception values can be put into the PECsoil calculator and the time interval set at

Note that for persistent actives there is no need to calculate a soil accumulation value when treatment is only to the plant grown in a container. The PECsoil after 1 year of application is appropriate.

If the proposed uses include subsequent field treatments, the PECsoil calculated from planting out should be added to the PECsoil initial value for the field treatment in the consideration of accumulation assessments.

The PECsoil calculator is found at Environmental fate models: Excel calculator tools.

Compost disposal

Disposal of waste compost may be an important exposure route for ornamental plants because some plants will be disposed, either due to oversupply or because not all plants survive.  The resulting waste compost may be disposed of by spreading on agricultural land.

The compost disposal route only needs to be considered for use restricted on pot plants (Group 1 and 2) under permanent protection with full enclosure. This route does not need to be considered if treatment of field grown ornamentals or plants in beds is also proposed.  When the compost disposal route is relevant, an exposure assessment for PECsoil, PECgroundwater and a PECsurface water drainflow should be provided.

As a simple worst case, it should be assumed that all the stored compost contains the residues in question distributed homogenously and that the compost is spread on agricultural land immediately, ie with no degradation of residues occurring before spreading.

For more details please refer to Disposal and transplanting of growing media: environmental fate considerations for pesticide registrations in Great Britain and Northern Ireland.

Groundwater assessment for ornamental plants

Identify a suitable risk envelope for groundwater assessment if possible. For more information see Risk envelope suitability for pesticide registration in Great Britain and Northern Ireland.

If no risk envelope exists, an assessment for the relevant groupings can be provided by modelling the indicated crops below using the crop interception values for the surrogate crops as agreed for soil exposures.

Surrogate crop and corresponding crop interception values for the ornamental crop groupings for PECgw

Ornamental group

Modelled crop

Surrogate crop

Crop interception (%)

Bare soil/ emergence

Leaf development

BBCH

0-09

10-19

  • Pot and bedding plants grown in containers < 10 cm1)

Pea

Tomato*

0

50

  • Pot and bedding plant grown in containers(b) > 10 cm(a)

Pea

Pea

0

35

  • Field grown HNS and non-bulb cut flowers

Potato

Potato

0

15

  • Bulb cut flowers

Onion

Onion

0

10

(a) Size corresponds to the top diameter of the pot

(b) includes Hardy Nursery Stock

*Note that tomato is not parameterised in FOCUS groundwater models for the relevant UK scenarios therefore for Group 1, pot and bedding plants grown in containers < 10 cm, use the Tomato C.I. values to amend the application rate, but select Pea as the crop to be modelled.

Carefully consider the application dates based on the ornamental grouping used. Choose application dates to ensure they cover a representative worst case. It may be necessary to consider more than one application timing for each scenario in the modelling. 

For more information on groundwater modelling see Groundwater assessments for pesticide registration in Great Britain and Northern Ireland.

Surface water spray drift for ornamental plants

If you propose a risk envelope, ensure that the method of application is suitable. For more information see Risk envelope suitability for pesticide registration in Great Britain and Northern Ireland.

Identify the specific method of application. The most likely methods for each grouping are:

If considering field grown crops where a conventional sprayer or hand-held lance is used the ‘field crops’ spray data should be used (which is the same as the 'Vegetables < 50 cm' value).

If considering application to taller ornamentals crops where for example variable geometry boom sprayers are used, the higher drift values for 'Vegetables > 50 cm' (identical to the 'Late grapevine' values) should be used.

If considering application via air-assisted sprayers, the early application drift values for pome fruit should be used unless a case can be made to indicate that the late application drift values are appropriate for the given grouping/situation of use. See further advice at Spray drift surface water exposure assessments for pesticide registration.

Summary of approach for spray drift:

Type of application Rautmann Spray drift data to be used

Application by conventional sprayer, or lance to the base of the crop

standard field crops
(also ornamentals < 50 cm)

Application to ornamentals with non air assisted sprayers at >  50 cm

late stage vines drift values
(veg/ornamentals > 50 cm)

Application to ornamentals crops via air assisted sprayers at >  50 cm 

fruit crops drift values

Using the standard PECsw spray drift (multiple buffer zone) calculator from Environmental fate models: Excel calculator tools

For more information on spray drift see  Spray drift surface water exposure assessments for pesticide registrations in Great Britain and Northern Ireland.

Surface water drainflow for ornamental plants

You need to provide a drainflow assessment if the method of application includes anything other than hand-held or knapsack sprayers only.

Follow the standard approaches outlined in the First tier drainflow calculation for pesticide registration in Great Britain and Northern Ireland.

Surrogate crop and corresponding crop interception values for the ornamental crop groupings for PECsw drainflow

Ornamental group

Modelled crop

Surrogate crop

Crop interception (%)

Bare soil/ emergence

Leaf development

BBCH

0-09

10-19

  • Pot and bedding plants grown in containers < 10 cm1)

Pea (legume)

Tomato

0

50

  • Pot and bedding plant grown in containers(b) > 10 c m(a)

Pea (legume)

Pea

0

35

  • Field grown HNS and non-bulb cut flowers

Potato

Potato

0

15

  • Bulb cut flowers

Onion

Onion

0

10

a) Size corresponds to the top diameter of the pot

b) includes Hardy Nursery Stock

Tier 1: Apply surrogate crop C.I. value in line with Table above.

Tier 2: Higher tier drainflow (HTDF):

Waste treatment solution

Any dilute pesticide waste that requires disposal must be disposed of in line with the advice detailed in the Code of Practice for Using Plant Protection Products   (Section 5: Disposing of Pesticide Waste).  The following text should be specified on the label so that users are aware of the requirement to adhere to this code:

’The use of this product in recirculating water systems in a glasshouse may result in dilute pesticide waste that requires disposal. All dilute pesticide waste must be disposed of safely and legally to protect humans, wildlife and the environment, especially groundwater and surface water.  Pesticide disposal advice is detailed in the ‘Code of Practice for Using Plant Protection Products (Section 5: Disposing of Pesticide Waste’).’

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Updated 2021-04-09