Seed treatments: HSE requirements to address specialist assessments


Authorisations for seed treatments express the dose or applied rate in terms of volume or weight of product per unit of seed. The unit may be defined differently depending on crop, for example, 1 unit = 100,000 seeds for sugar beet.

Where expressed as a weight, depending on the individual seed type/variety, this may result in differences in numbers of seeds treated.

However, the amount of the seed treatment applied per hectare, a parameter required for risk assessment purposes, is determined by the volume or weight of product per unit of seed and the seed sowing rate.

There will be a wide range in actual seed sowing rates to achieve the optimum plant density, reflecting factors including crop type/variety, timing, row width, and local growing conditions each season.

Risk assessments are normally conducted on the basis of the assumed ‘worst case’ maximum sowing rate, to ensure assessment of the maximum possible amount of applied active substance in the soil. However, this maximum may represent scenarios which are not always typical each season and might not allow for an acceptable and viable use of the seed treatment.

Following a review, HSE may now include restrictions on the Notice of Authorisation which are considered applicable and necessary as part of the risk assessment, for example, the seed sowing rate, the dose per hectare or timing restrictions on planting. Such restrictions will reflect the parameters and conclusions of both the risk assessment and underpinning efficacy trials.

This will allow a more detailed GAP (Good Agricultural Practice, or the conditions of use) for seed treatment applications which can then be included in the authorisation (much in the same way it is currently done for other plant protection product (PPP) authorisations) and will be included on the product label and also on the seed bags.

This will give applicants more options for risk mitigation. For example, rather than using the worst-case maximum seed sowing rate (which fails one or more risk assessments), the applicant may state a lower rate in the application, more typical of most commercial situations, thereby reducing the amount of active substance per hectare. In cases where the proposed rate is less than the maximum, a restriction to a specific sowing rate would be included on an authorisation. The situation of the crop might also be specified; for example, if it is to be grown under cover, this might mitigate some aspects of the environmental risk.

It is important for applicants to note that this is not in any way a guarantee that authorisation for a proposed use can be given; the submitted, refined GAP with all the necessary information may still result in the refusal of the authorisation. It should also be noted that further specific restrictions may be applied to demonstrate an acceptable risk.

The requirements for Residues/Consumer Exposure, Environmental Fate, Ecotoxicology and Efficacy assessments are listed below and are based on retained Regulation (EC) No 284/2013 which sets out the data requirements for PPPs.

The requirements define the elements of the GAP that are needed in order to carry out the risk assessment, including a brief explanation for why they are required. Where applicable, the preferred units are stated.
Many of the requirements overlap, and they are collated in the seed treatment information requirements form which can be submitted as supplementary information with the product application.

Chemistry requirements

Physical chemical properties data are required to address the adherence and distribution of the product to treated seeds. This data requirement is usually addressed via a combination of data on seed loading, distribution to seeds and adherence to seeds, which are evaluated considering the GAP submitted for authorisation. This information is required under retained Regulation (EC) 284/2013 Annex point 2.10. However, it is also required to support other areas of the risk assessment such as ecotoxicology, residues/consumer exposure and efficacy.

If additional uses are requested, the appropriateness of any existing physical and chemical data to address adherence and distribution to seeds will need to be considered and cases or additional data may be required to address any extrapolations from one seed type to another. Extrapolations may be accepted from one seed type to another on the basis of comparable seed size, shape and surface morphology. Information must be presented by the applicant detailing these attributes of the seed for each crop and a justification for comparability.

Residues requirements

The available residues trials data must support the proposed GAP in relation to both the active substance per seed and the active substance per ha (taking account of the proposed sowing rate). The parameters specified (except for multiple crop sowing) in the environmental fate table below (for both the GAP specified and any new residues data submitted) are, therefore, required.

Where accumulation of parent or metabolites could be expected, information from the environmental fate assessment confirming the appropriate total soil loading would be used to evaluate if the available residues data to address both the nature and magnitude of residues in following crops are sufficient.

For possible residues extrapolations and tolerance rules, the appropriate guidance on residues trials and extrapolations should be consulted.

Non-dietary human exposure requirements

The following information is required under retained Regulation (EC) 284/2013 Annex point 7.2.

  • amount of active substance per seed unit (this could be the amount per 100,000 seeds or the weight of the seeds)
  • seed weight (mg or thousand seed weight in grams)
  • seed sowing rate
  • whether the seed is pelleted
  • application dilution rate if relevant
  • container sizes

Environmental fate requirements

The following information is required under retained Regulation (EC) 284/2013 Annex point 9.
For environmental fate and behaviour assessments, the amount of active substance per ha of land per year must be calculated. For this to be determined the following information must be provided:

  • the maximum amount of active substance per designated number of seeds (for example, 2g active substance/100,000 seeds)
    Note that it would be acceptable to provide details of the amount of product per designated number of seeds, since the active substance content of the product will also be specified within the submission. Also, it would be acceptable to provide information on the amount of product per weight of seed (for example, 1.2g active substance/kg seed if the thousand seed weight (TSW) for that crop is provided as this will be needed for the conversion)
  • the maximum seed sowing rate per ha for every crop requested
    This would ideally be provided as the number of seeds per ha. However, it is also possible to accept this information as the weight of seed per ha if the TSW is also provided which will allow the conversion to be made. For an example of a supplementary information source for sowing rates, please see OEPP/EPPO Bulletin (2016), 46 (3), 618-624
  • possibility of multiple crop sowing
    The environmental fate assessment is based on the g active substance/ha/year. Therefore, if any of the following are possible, they need to be taken into consideration along with details of such multiple cropping:
    • multiple sowing of the same crop on the same land within a given year
    • sowing of different crops which have been treated with the same product, on the same land in a given year
  • depth of seed sowing
    This mixing depth parameter may influence the groundwater assessment and possibly also predicted environmental concentration in soil (PECsoil).  Applicants should consider sowing depth and provide justification for their choice, including references to supporting information. However, for crops that are planted at or less than 5cm HSE propose that a 5cm depth is assumed for first tier soil and groundwater exposure assessments. If a crop is drilled much deeper than 5cm it may be more appropriate to use a 20cm depth, potentially leading to a reduction in the PECsoil value; this would be assessed on a case-by-case basis.
  • timings applicable to the crop
    The time of year that a treated crop is sown will directly influence the surface water drain flow consideration and the ground water consideration

Example table for data:

Crop type Seed sowing rate
Application rate to seeds
(g active substance/100,000 seeds)
Soil load
(g active substance/ha)
Number of crops per year** Total soil load (g active substance /ha/year)
Crop A 200,000 3g active substance/100,000 seeds 6g active substance/ha 1 6g active substance/ha
Crop B 350,000 2g active substance /100,000 seeds 7g active substance/ha 3 21g active substance/ha

*   If provided as a weight of seed per hectare, you must also provide the TSW. For example, Crop A has a TSW of 2.5g, application rate in weight of 0.5kg seed/ha = 200,000 seeds/ha.
** Additional information where combinations of crops may occur should be provided separately.

Note that for seed treatments an assessment of surface water exposure via drainflow must always be provided. Find information on first tier drainflow calculation.

Ecotoxicology requirements

As outlined in retained Regulation (EC) 284/2013 Annex point 10.1.1., the following information regarding the GAP is required:

  • concentration on seeds (mg active substance/seed and g active substance per 100,000 seeds and mg active substance/kg of seed)
  • seed weight (mg or thousand seed weight in grams)
  • number of seeds required to achieve the LD50 (based on the concentration per seed)

In addition, the following information should also be supplied:

  • amount of active substance per kg seed (this could be from the amount per 100,000 seeds and the weight of the seeds)
  • amount of active substance per hectare (this could be from the amount per 100,000 seeds and the seed sowing rate)
  • are the seeds sown under protection and if so what kind of protection? If the protection is removed or the plants are transplanted outside, at what growth stage does this happen?
  • is precision drilling relevant for the crop (if so, what is the incorporation efficiency)?
  • is the seed pelleted?

It should be noted that for pelleted seeds no consideration of risks to birds and mammals via the intentional consumption of treated seed as a food item is required. However, an assessment of the risk to birds from consumption of pelleted seeds with/as grit is needed. Additionally, for both pelleted and non-pelleted seeds, it is necessary to consider risks to birds and mammals via consumption of crop seedlings. Further guidance on how to assess risks to birds and mammals from seed treatment products can be found in chapter 5.2 of EFSA (2009).

In order to reduce risks to non-target organisms HSE will stipulate as standard that treated seed should not be broadcast. If such a stipulation would impact the proposed use of your seed treatment, then it will be necessary to provide an assessment demonstrating that broadcasting treated seed will not result in unacceptable impacts to non-target organisms, with appropriate supporting information.

Where broadcasting of treated seed is required, unless an acceptable risk to aquatic organisms can be demonstrated as a result of broadcasting treated seed, the following warning is required on the label: “Where treated seed is broadcast, treated seed should not fall within 6m of a watercourse or ditch. To achieve this, users should determine the spread width of the applicator with the treated seed prior to any application (to the rear as well as the side of the applicator). Calibrate your applicator before use.” This wording can be included on the product label by default rather than conducting an exposure and risk assessment for the aquatic environment.

Efficacy requirements

In addition to the requirements outlined above, collated in the seed treatment information requirements form and required under retained Regulation (EC) 284/2013 Annex point 6, a general overview of background crop agronomy must be provided. This may be particularly helpful for minor crops, including overall range of commercial sowing rates and factors which influence selection of sowing rate by the grower (for example, details of target optimal established plant density or information on the most common commercial varieties). Based on this information, a justification must be provided for the relevance and selection of the proposed maximum sowing rate. For an example of a supplementary information source for sowing rates, please see OEPP/EPPO Bulletin (2016), 46 (3), 618-624  which provides a link to sowing rates considered to be representative for several UK crops.

Differences in sowing rate, and the amount of available active substance in soil profile based on this, can have a significant impact on the level of effectiveness under field conditions. The proposed maximum sowing rate must, therefore, be reflected in the efficacy trials to ensure it is effective.

The information required in the seed treatment information requirements form should be provided for each efficacy trial, along with crop variety and sowing date, and any other information on assessments described in the relevant EPPO standard.

It is also critical to ensure the sowing rates used in each trial are appropriately described in the Biological Assessment Dossier (BAD) and accompanying draft Registration Report (dRR). Where there are differences in levels of control across sites, sowing density may be one of those influencing factors and an appropriate assessment of poor control should include possible differences in sowing density.

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Updated 2023-07-19